Aplastic Anemia

Practice Essentials

Aplastic anemia is a syndrome of bone marrow failure characterized by peripheral pancytopenia and marrow hypoplasia (see the image below). Although the anemia is often normocytic, mild macrocytosis can also be observed in association with stress erythropoiesis and elevated fetal hemoglobin levels.

View Image

Low power, H and E showing a hypocellular bone marrow with increased adipose tissue and decreased hematopoietic cells in the marrow space.

Signs and symptoms

The clinical presentation of patients with aplastic anemia includes symptoms related to the decrease in bone marrow production of hematopoietic cells. The onset is insidious, and the initial symptom is frequently related to anemia or bleeding, although fever or infections may be noted at presentation.

Signs and symptoms of aplastic anemia may include the following:

• Pallor
• Headache
• Palpitations, dyspnea
• Fatigue
• Foot swelling
• Gingival bleeding, petechial rashes
• Overt and/or recurrent infections
• Oropharyngeal ulcerations

A subset of patients with aplastic anemia present with jaundice and evidence of clinical hepatitis.^{[1, 2]}

See Presentation for more detail.

Diagnosis

Testing

Laboratory testing for suspected aplastic anemia includes the following:

• Complete blood count
• Peripheral blood smears
• Hemoglobin electrophoresis and blood-group testing
• Biochemical profile
• Serology for hepatitis and other viral entities
• Autoimmune-disease evaluation for evidence of collagen-vascular disease
• Fluorescence-activated cell sorter profiling
• Fluorescent-labeled inactive toxin aerolysin testing
• Diepoxybutane incubation
• Histocompatibility testing
• Kidney function studies
• Liver function studies
• Transaminase, bilirubin, and lactate dehydrogenase levels

Procedures

Bone marrow biopsy is performed in addition to aspiration to assess cellularity qualitatively and quantitatively. Bone marrow culture may be useful in diagnosing mycobacterial and viral infections; however, the yield is generally low.

See Workup for more detail.

Management

Severe or very severe aplastic anemia is a hematologic emergency, and care should be instituted promptly. Clinicians must stress the need for patient compliance with therapy. The specific medications administered depend on the choice of therapy and whether it is supportive care only, immunosuppressive therapy, or hematopoietic cell transplantation.^[3]

Pharmacotherapy

The following medications are used in patients with aplastic anemia:

• Immunosuppressive agents (eg, cyclosporine, methylprednisolone, equine antithymocyte globulin, rabbit antithymocyte globulin, cyclophosphamide, alemtuzumab)
• Hematopoietic growth factors (eg, eltrombopag^[4] , sargramostim, filgrastim)
• Antimetabolite (purine) antineoplastic agents (eg, fludarabine)
• Chelating agents (eg, deferoxamine, deferasirox)

Nonpharmacotherapy

Nonpharmacologic management of aplastic anemia includes the following:

• Supportive care
• Blood transfusions with blood products that have undergone leukocyte reduction and irradiation
• Hematopoietic cell transplantation

Surgical option

Central venous catheter placement is required before the administration of hematopoietic cell transplantation.

See Treatment and Medication for more detail.

• References

Background

Paul Ehrlich introduced the concept of aplastic anemia in 1888 when he reported the case of a pregnant woman who died of bone marrow failure. However, it was not until 1904 that Anatole Chauffard named this disorder aplastic anemia. (See Etiology.)

The British Society for Standards in Haematology has issued guidelines on diagnosis and management of aplastic anemia in adults^[5]  and pediatric patients.^[6] The Pediatric Haemato-Oncology Italian Association has issued guidelines on diagnosis and management of acquired aplastic anemia in childhood.^[7]

For more information, see the following Medscape articles:

• Anemia
• Chronic Anemia
• Megaloblastic Anemia
• Myelophthisic Anemia
• Hemolytic Anemia
• Sideroblastic Anemias

• References

Etiology

The theoretical basis for marrow failure includes primary defects in or damage to the stem cell or the marrow microenvironment.^{[8, 9, 10, 11]}  The distinction between acquired and inherited disease may present a clinical challenge, but more than 80% of cases are acquired. Clinical and laboratory observations suggest that acquired aplastic anemia is an autoimmune disease.

On morphologic evaluation, the hematopoietic elements in the bone marrow are less than 25%, and they are largely replaced with fat cells. Flow cytometry shows that the CD34 cell population, which contains the stem cells and the early committed progenitors, is substantially reduced.^{[9, 12]} Data from in vitro colony-culture assays suggest profound functional loss of the hematopoietic progenitors, so much so that they are unresponsive even to high levels of hematopoietic growth factors.

Previously, it had been hypothesized that aplastic anemia may be due to a defect at various levels, such as an intrinsic defect of hematopoietic cells; external injury to hematopoietic cells; and defective stroma, which is critical for normal proliferation and functioning of hematopoietic cells. Theoretically, all of these mechanisms could be responsible for aplastic anemia. This theory was the basis of many in vitro stem cell culture experiments using a crossover design in which stem cells from patients with aplastic anemia were cultured with normal stroma and vice versa. The conclusions from these studies led to the understanding that stem cell defect is the central mechanism in the majority of patients with aplastic anemia.^{[13, 14]}

In patients with severe aplastic anemia, stromal cells have normal function, including growth factor production. Adequate stromal function is implicit in the success of hematopoietic cell transplantation (HCT) in aplastic anemia, because the stromal elements are almost entirely (frequently) of host origin.

The role of an immune dysfunction was suggested in 1970, when autologous recovery was documented in a patient with aplastic anemia who failed to engraft after HCT. Mathe proposed that the immunosuppressive regimen used for conditioning promoted the return of normal marrow function. Since then, numerous studies have shown that, in approximately 70% of patients with acquired aplastic anemia, immunosuppressive therapy improves marrow function.^{[10, 15, 16, 17, 18]}

Immunity is genetically regulated (by immune response genes), and it is also influenced by environment (eg, nutrition, aging, previous exposure).^{[19, 20]} Although the inciting antigens that breach immune tolerance with subsequent autoimmunity are unknown, human leukocyte antigen (HLA)-DR2 is overrepresented among European and United States patients with aplastic anemia, and its presence is predictive of a better response to cyclosporine.

Suppression of hematopoiesis is likely mediated by an expanded population of CD8+ HLA-DR+, cytotoxic T lymphocytes (CTLs) that are frequently detectable in the blood and bone marrow of patients with aplastic anemia. These cells produce inhibitory cytokines, such as gamma-interferon and tumor necrosis factor, which can suppress progenitor cell growth. Polymorphisms associated with an increased immune response are more prevalent in these cytokine genes in patients with aplastic anemia. These cytokines suppress hematopoiesis by affecting the mitotic cycle and cell killing by inducing Fas-mediated apoptosis.

In addition, such cytokines induce nitric oxide synthase and nitric oxide production by marrow cells, which contributes to immune-mediated cytotoxicity and the elimination of hematopoietic cells. Hirano et al reported that CD8+ cytotoxic T cells raised against kinectin-derived peptides suppress colony forming units (CFUs) in an HLA class I–restricted fashion, findings that suggest kinectin may be a candidate autoantigen in the pathophysiology of aplastic anemia.^[21]

Constitutive expression of Tbet, a transcriptional regulator that is critical to type 1 T helper cell (Th1) polarization, occurs in a majority of aplastic anemia patients.^[15] Perforin is a cytolytic protein expressed mainly in activated cytotoxic lymphocytes and natural-killer cells. Mutations in the perforin gene are responsible for some cases of familial hemophagocytosis^[22] ; mutations in SAP, a gene encoding for a small modulator protein that inhibits undefined-interferon production, underlie X-linked lymphoproliferation, a fatal illness associated with an aberrant immune response to herpesviruses and aplastic anemia. Perforin and SAP protein levels are markedly diminished in some cases of acquired aplastic anemia.

The transcription factors FOXP3 and NFAT1 have key roles in regulatory T-cell (Treg) development and function, and Tregs play a role in autoimmunity. Tregs are decreased at presentation in almost all patients with aplastic anemia; FOXP3 protein and mRNA levels also are significantly lower in patients with this condition, whereas NFAT1 protein levels are decreased or absent.^[23]

Variations in telomere length have been reported in severe aplastic anemia, but their clinical significance is unknown. However, although telomere length was unrelated to response, it was associated with the risk of relapse, clonal evolution, and overall survival in patients with severe aplastic anemia.^[24]

Congenital or inherited causes

Congenital or inherited causes of aplastic anemia are responsible for at least 25% of children with this condition and for perhaps up to 10% of adults.^[25] Patients may have dysmorphic features or physical stigmata, but marrow failure may be the initial presenting feature. Several loci have been identified that are associated not only with increased susceptibility to aplastic anemia but also with other physical findings.

Fanconi anemia

Fanconi anemia is characterized by the following:

• Multiple congenital anomalies (60-75%): Short stature, abnormal skin pigmentation, malformations of the thumbs with or without dysplastic or absent radii, as well as microphthalmos and malformations of the heart, kidneys, intestines, and ears
• Bone marrow failure: Thrombocytopenia, leukopenia, or aplastic anemia; most patients with Fanconi anemia have bone marrow failure by adulthood
• Cancer: Hematologic malignancies are common with Fanconi anemia and myelodysplasia, with acute myeloid leukemia (AML) being the most common; solid tumors such as those in squamous cell head and neck cancer, female genital tumors, and liver tumors are also seen; Fanconi anemia is associated with increased chromosomal breakage and abnormal sister chromatid exchange in the presence of agents such as diepoxybutane or mitomycin C
• Predominantly autosomal recessive inheritance pattern: Fifteen genes are now known to be causative for Fanconi anemia; only 1 of these— FANCB (X-lined recessive)—is not inherited in an autosomal recessive manner
• Association between bone marrow progression and a complex pattern of recurrent chromosomal abnormalities: Some chromosomal abnormalities are commonly found in non-Fanconi anemia myelodysplastic syndrome (MDS) and secondary acute myeloid leukemia (eg, -7/7q or RUNX1 abnormalities), whereas others are specific for Fanconi anemia (eg, 1q+ and 3q+)

Dyskeratosis congenita

Dyskeratosis congenita is characterized by the diagnostic physical triad of dysplastic nails, lacy reticular pigmentation of the upper torso, and oral leukoplakia. However, over the past decade, it has been increasingly recognized that patients may have dyskeratosis congenita without the triad. The following are also features of this condition:

• Some signs of premature aging, such as early graying of the hair
• Progressive bone marrow failure at any age, which can cause any combination of cytopenias, including aplastic anemia
• Malignancy: Common; frequently MDS or AML; solid tumors such as head and neck cancer or genital cancers can also be seen
• Pulmonary fibrosis
• Autosomal dominant, autosomal recessive, and X-linked inheritance patterns; 6 genes are known to cause this disorder

Familial aplastic anemia

This is an isolated aplastic anemia. Mutations have been found in the TERC and TERT genes and are thought to confer a susceptibility to aplastic anemia. These genes encode proteins that are part of the telomerase apparatus that restores repeated regions in the telomere.^[26]

Cartilage-hair hypoplasia

Cartilage-hair hypoplasia, which is caused by mutations in the RMRP gene, is inherited in an autosomal recessive manner. This condition is characterized by the following:

• Short stature with short and bowed limbs
• Sparse, lightly pigmented hair
• Variably severe immune deficiency
• Anemia during childhood
• Hematopoietic malignancies, as well as malignancies of the skin, eyes, and liver
• Gastrointestinal malformations and malabsorption

Pearson syndrome

Pearson syndrome causes sideroblastic anemia and exocrine pancreatic dysfunction. This condition results from mitochondrial deoxyribonucleic acid (DNA) deletions.

Thrombocytopenia-absent radius syndrome

Thrombocytopenia-absent radius (TAR) syndrome is characterized by deletions located at chromosome 1q21.1 (which are typically about 200kb in size). Patients have bilateral absence of the radii with presence of the thumbs, as well as thrombocytopenia. Other congenital anomalies can also occur (eg, cardiac disease, skeletal anomalies, urogenital anomalies).

Shwachman-Diamond syndrome

Shwachman-Diamond syndrome is caused by mutations in the SBDS gene and is inherited in an autosomal recessive manner. This disease is characterized by dysfunction of the exocrine pancreas with malabsorption and growth failure, as well as cytopenias of single or multiple lineage. Patients with Shwachman-Diamond syndrome also have an increased risk of MDS and AML.^[27]

Dubowitz syndrome

Dubowitz syndrome is caused by an as-yet unknown gene. This condition is characterized by intrauterine growth retardation, extremely short stature, and wizened facial appearance. Patients also have microcephaly and mild developmental delay. Dubowitz syndrome is also associated with eczema, immune deficiency, and aplastic anemia. Malignancy is more common with this disorder, particularly lymphoma and neuroblastoma.

Diamond-Blackfan anemia

Diamond-Blackfan anemia (DBA) is characterized by a normochromic macrocytic anemia that can be isolated, or it can be associated with growth retardation or congenital malformation in the upper limbs, heart, and genitourinary systems. In a small minority of patients, DBA can progress to aplastic anemia. Nine genes have been found to be causative for DBA, and they are inherited in an autosomal dominant manner.^[28] Approximately 50% of cases are inherited from a parent, and about 50% result from de novo mutations.

Acquired causes

Acquired causes of aplastic anemia (80%) include the following:

• Idiopathic factors
• Infectious causes, such as hepatitis viruses, Epstein-Barr virus (EBV), human immunodeficiency virus (HIV), parvovirus, and mycobacteria
• Exposure to ionizing radiation
• Exposure to toxic chemicals, such as benzene or pesticides^[29]
• Transfusional graft versus host disease (GVHD)
• Orthotopic liver transplantation for fulminant hepatitis
• Pregnancy
• Eosinophilic fasciitis
• Anorexia
• Severe nutritional deficiencies (B12, folate)
• Paroxysmal nocturnal hemoglobinuria (PNH)
• MDS
• Acute lymphoblastic leukemia (ALL)(rarely)

Drugs and elements (eg, chloramphenicol, phenylbutazone, gold) may cause aplasia of the marrow. The immune mechanism does not account for the marrow failure in idiosyncratic drug reactions. In such cases, direct toxicity may occur, perhaps due to genetically determined differences in metabolic detoxification pathways. For example, the null phenotype of certain glutathione transferases is overrepresented among patients with aplastic anemia.

PNH is caused by an acquired genetic defect affecting the PIGA gene and limited to the stem cell compartment. Mutations in the PIGA gene render cells of hematopoietic origin sensitive to increased complement lysis. Approximately one third of patients with aplastic anemia have evidence of PNH at presentation, as detected by means of flow cytometry.^[30] Furthermore, patients whose disease responds after immunosuppressive therapy may recover with clonal hematopoiesis and PNH.

• References

Epidemiology

United States statistics

No accurate prospective data are available regarding the incidence of aplastic anemia in the United States. Findings from several retrospective studies usually overlap those from Europe and suggest that the incidence is 0.6-6.1 cases per million population; this rate is largely based on data from retrospective reviews of death registries.

International statistics

The annual incidence of aplastic anemia in Europe, as detailed in large, formal epidemiologic studies, is 2 cases per million population.^[31] Aplastic anemia is thought to be more common in Asia than in the West. The incidence was accurately determined to be 4 cases per million population in Bangkok,^[32] but based on prospective studies, it may actually be closer to 6 cases per million population in the rural areas of Thailand. This increased incidence may be related to environmental factors, such as increased exposure to toxic chemicals, rather than to genetic factors, because this increase is not observed in people of Asian ancestry who are living in the United States.

Race-, sex-, and age-related demographics

Although no racial predisposition for aplastic anemia is reported in the United States, the prevalence is increased in the Far East. The male-to-female ratio for acquired aplastic anemia is approximately 1:1, although there are data to suggest that a male preponderance may be observed in the Far East.

Although aplastic anemia occurs in all age groups, a small peak in the incidence is observed in childhood because of the inclusion of inherited marrow-failure syndromes. A second peak is observed in people aged 20-25 years.

• References

Prognosis

The outcome of patients with aplastic anemia has substantially improved because of improved supportive care. The natural history of aplastic anemia suggests that a small number of patients may spontaneously recover with supportive care^[33] ; however, observational and/or supportive care therapy alone is rarely indicated.

The estimated 10-year survival rate for the typical patient receiving immunosuppression is 68%, compared with 73% for hematopoietic cell transplantation (HCT).^[34] However, there is a significantly improved outcome for HCT over time, for matched sibling and alternative donors, and with younger age.^[34] In cases of immunosuppression, relapse and late clonal disease are risks.

In a single-institution analysis of 183 patients who received immunosuppressive treatments for severe aplastic anemia, the telomere length of peripheral blood leukocytes was unrelated to treatment response.^[24] In a multivariate analysis, however, telomere length was associated with risk of relapse, clonal evolution, and overall survival.^[24] Additional studies are needed to validate these findings and to determine how this information might be incorporated into treatment algorithms.

Mortality/morbidity

The major causes of morbidity and mortality from aplastic anemia include infection and bleeding. Patients who undergo HCT have additional issues related to acute and chronic toxicity from the conditioning regimen and graft versus host disease (GVHD), as well as a potential for graft failure.^{[20, 35, 36, 37, 38, 39]} In approximately 25-30% of patients with aplastic anemia, the condition does not respond to immunosuppression. In cases with a treatment response, relapse and late-onset clonal disease, such as paroxysmal nocturnal hemoglobinuria (PNH), myelodysplastic syndrome (MDS), and leukemia, are risks—regardless of the treatment response or degree of response.^{[16, 40, 41, 42, 43]}

Kulasekararaj and colleagues reported that the presence of somatic mutations (including ASXL1, DNMT3A, and BCOR) in patients with aplastic anemia for more than 6 months was associated with 40% risk of transformation to MDS. Nearly a fifth of patients with aplastic anemia have mutations in genes typically seen in myeloid malignancies that predicted for later transformation to MDS.^[44]

In a Japanese study of 427 patients (16-72 years old) with aplastic anemia who underwent unrelated-donor bone marrow transplantation, outcome was significantly inferior in patients whose donors were 40 years of age or older than in those with younger donors. In the older donor group, overall survival was significantly inferior (adjusted hazard ratio, 1.64), the incidence of fatal infection was significantly higher (13.7% vs. 7.5%), and primary engraftment failure and acute GVHD occurred significantly more often (9.7% vs. 5.0% and 27.1% vs. 19.7%, respectively).^[45]

An Australian population-based cohort study of adults receiving allogeneic HCT reported an elevated secondary cancer risk in several patient groups, including those transplanted for severe aplastic anemia. Overall, in patients alive 2 years after transplantation (n=1463), the cumulative incidence of late mortality was 22.2% at 10 years and the risk of death relative to the matched general population was 13.8.^[46]

• References

History

The clinical presentation of patients with aplastic anemia includes symptoms related to the decrease in bone marrow production of hematopoietic cells. The onset is insidious, and the initial symptom is frequently related to anemia or bleeding, although fever or infections may be noted at presentation. Specific manifestations include the following:

• Anemia: May manifest as pallor, headache, palpitations, dyspnea, fatigue, or foot swelling
• Thrombocytopenia: May result in mucosal and gingival bleeding or petechial rashes
• Neutropenia: May manifest as overt infections, recurrent infections, or mouth and pharyngeal ulcerations

Most cases of aplastic anemia are idiopathic,^[5] and the search for an etiologic agent is often unproductive. Obtain an appropriately detailed work history, with emphasis on solvent exposure, as well as a family, environmental, and infectious disease history.

In the absence of obvious phenotypic features, the presentation of a patient with an inherited marrow-failure syndrome is subtle, and a thorough family history may first suggest the condition, as well as potentially identify rarer inherited marrow-failure syndromes.

With regard to environmental agents, the time course of aplastic anemia and exposure to the offending agent varies greatly, and only rarely is an environmental etiology identified.

• References

Physical Examination

Physical examination may show signs of anemia (eg, pallor, tachycardia) and of thrombocytopenia (eg, petechiae, purpura, ecchymoses). Overt signs of infection are usually not apparent at diagnosis. A subset of patients with aplastic anemia present with jaundice and evidence of clinical hepatitis.^{[1, 2]} Findings of adenopathy or organomegaly should suggest an alternative diagnosis (eg, hepatosplenomegaly and supraclavicular adenopathy are observed more frequently in cases of leukemia and lymphoma than in cases of aplastic anemia).

In any case of suspected aplastic anemia, look for physical stigmata of inherited marrow-failure syndromes, such as the following:

• Abnormal skin pigmentation
• Short stature
• Renal, cardiac, and gastrointestinal (GI) abnormalities
• Microcephaly
• Microphthalmos
• Hypogonadism
• Skeletal anomalies

The oral pharynx, hands, and nail beds should be carefully examined for clues of inherited bone marrow-failure syndromes. Oral leukoplakia in dyskeratosis congenita is shown in the image below.

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Oral leukoplakia in dyskeratosis congenita.

• References

Approach Considerations

Aplastic anemia is diagnosed with blood and bone marrow studies. This condition is defined by the finding of a hypoplastic bone marrow that has fatty replacement and that may have relatively increased nonhematopoietic elements, such as mast cells. Careful examination is necessary to exclude metastatic tumor foci on biopsy, as occasionally metastatic tumor deposits may cause pancytopenia. Carefully consider dysplasia to rule out myelodysplastic syndrome (MDS), although some degree of dysplasia may be present in aplastic anemia.

• References

Complete Blood Cell Count and Peripheral Smears

A paucity of platelets, red blood cells (RBCs), granulocytes, monocytes, and reticulocytes is found in patients with aplastic anemia. Mild macrocytosis is occasionally observed. The degree of cytopenia is useful in assessing the severity of aplastic anemia.

A peripheral blood smear may be helpful in distinguishing aplasia from infiltrative disease causes. Teardrop poikilocytes and leukoerythroblastic changes suggest an infiltrative process.

• References

Peripheral Blood Testing

Peripheral blood tests in patients with suspected aplastic anemia may include the following:

• Hemoglobin electrophoresis and blood-group testing
• Biochemical profile
• Serology
• Fluorescence-activated cell sorter (FACS) profiling
• Fluorescent-labeled inactive toxin aerolysin (FLAER) testing
• Diepoxybutane incubation
• Histocompatibility testing

Hemoglobin electrophoresis and blood-group testing may show elevated levels of fetal hemoglobin and red cell I antigen, suggesting stress erythropoiesis. These findings are observed in aplastic anemia and in other marrow-failure states and are often proportional to the macrocytosis. A positive Coombs test may point to autoimmune hemolytic anemia.

Although a biochemical profile has limited value in examination of the etiology and differential diagnosis of aplastic anemia, an analysis of kidney function, as well as measurement of transaminase, bilirubin, and lactate dehydrogenase (LDH) levels, can indicate relevant renal or hepatic diseases. Liver function test (LFT) results can indicate hemolysis.

Serologic testing for hepatitis and other viral entities, such as Epstein-Barr virus (EBV), cytomegalovirus (CMV), and human immunodeficiency virus (HIV), may be useful. An autoimmune-disease evaluation for evidence of collagen-vascular disease may be performed.

Aplastic anemia often occurs together with paroxysmal nocturnal hemoglobinuria (PNH).^[47] Although the Ham test, or the sucrose hemolysis test, was frequently performed in the past to diagnose PNH, it has been replaced by FACS profiling of phosphatidylinositol glycan class A (PIGA) anchor proteins, such as CD55 and CD59. This study is more accurate than the Ham test for excluding PNH.

FLAER is also a highly sensitive flow cytometry test for PNH that uses whole blood and binds specifically to glycophosphatidylinositol (GPI) anchor proteins in peripheral blood granulocytes.^{[48, 49]} In PNH, mutation of the PIGA anchor proteins results in a lack of the GPI anchors. Thus, the lack of FLAER binding to granulocytes is sufficient for the diagnosis of PNH.^{[48, 49]} The disadvantage of the test is in measuring binding in the absence of adequate granulocytes—such as in severe aplastic anemia when the number of circulating granulocytes is extremely low.

Diepoxybutane incubation is performed to assess chromosomal breakage in Fanconi anemia and is available only in reference laboratories. This test is required even in the absence of phenotypic features of Fanconi anemia, because up to 50% of patients may not have any clinical stigmata.

Histocompatibility testing should be conducted early to identify potential related donors, especially those for young patients. Because the extent of previous transfusion has been shown to significantly affect the outcomes of patients undergoing hematopoietic cell transplantation (HCT) for aplastic anemia, the rapidity with which these data are obtained is crucial.

Hosokawa et al identified three microRNAs that are dysregulated (>1.5-fold change) in acquired aplastic anemia, compared with healthy controls, and could be used in diagnosis: miR-150-5p, miR-146b-5p, and miR-1. Plasma levels of miR-150-5p and miR-146b-5p are elevated in aplastic anemia, whereas levels of miR-1 are decreased. Because miR-150-5p expression decreased significantly after successful immunosuppressive therapy, but did not change in non-responders, these authors propose that miR-150-5p could be used for disease monitoring.^[50]

In a study of pediatric patients with very severe aplastic anemia, Fang et al found that the percentage of CD20⁺ B cells in peripheral blood was higher than that in healthy children (P < 0.01), whereas the percentage of regulatory T cells (Tregs) was lower than that in healthy children (P < 0.001). After treatment, the percentage of CD20⁺ B cells was decreased, and the percentage of Tregs was significantly increased. The authors suggest CD20⁺ B cells and Tregs as potential markers for evaluating therapeutic efficacy and prognosis in these cases.^[51]

• References

Bone Marrow Aspiration and Biopsy

Bone marrow biopsy is performed in addition to aspiration to assess cellularity qualitatively and quantitatively. In aplastic anemia, the specimens are hypocellular. Aspiration samples alone may appear hypocellular because of technical reasons (eg, dilution with peripheral blood), or they may appear hypercellular because of areas of focal residual hematopoiesis.

By comparison, core biopsy better reveals cellularity. The specimen is considered hypocellular if it is less than 30% cellular in individuals younger than 60 years or if it is less than 20% cellular in those older than 60 years (see the following image). Some dyserythropoiesis with megaloblastosis may be observed in aplastic anemia.

View Image

Low power, H and E showing a hypocellular bone marrow with increased adipose tissue and decreased hematopoietic cells in the marrow space.

Bone marrow culture may be useful in diagnosing mycobacterial and viral infections. However, the yield is generally low. Currently, alternative studies include polymerase chain reaction (PCR) assay, but the value of this technique is unclear in this setting. Leukemia and metastatic cancers may also be diagnosed with bone marrow examination.

Myelodysplastic syndrome

Aplastic anemia must be differentiated from myelodysplastic syndrome (MDS) The bone marrow in patients with aplastic anemia may have hyperplastic pockets, which can sometimes be confused with MDS; moreover, hypoplasia of bone marrow may be present in some cases of MDS.^[52] However, in aplastic anemia,  CD34 evaluation always reveals a low count; further, ringed sideroblasts,  myeloblasts, and dysplastic megakaryocytes are never seen in aplastic anemia but are often seen in MDS.

Characteristic bone marrow abnormalities that are often found in MDS include the following:

• Dyserythropoietic red blood cells (RBCs)
• Neutrophils with hypogranulation, hypolobulation, or apoptotic nuclei reaching to the edges of the cytoplasm
• Increased or decreased cellularity

Myelodysplastic features are usually observed in hematopoietic precursors and progeny. Islands of immature cells or abnormal localization of immature progenitors (ALIP) indicate MDS. Patients with MDS may have megakaryocytic abnormalities (micromegakaryocytes, megakaryocytes with dyskaryorrhexis), greater than 5% ring sideroblasts (observed only on iron stains), and granulocytic abnormalities (pseudo–Pelger-Huët cells, hypogranulation, excess of blasts). On occasion, marrow fibrosis may be observed. Monocytes are similarly hypogranular, and their nuclei may contain nucleoli.

Chromosomal rearrangements are considered diagnostic of MDS, with trisomies of 8 and 21 and deletions of 5, 7, and 20 being the most common. However, the conventional karyotype technique reveals abnormalities in only about 50% of patients with MDS. Additionally, fluorescence in situ hybridization (FISH) may be used to visualize chromosomal abnormalities in interphase cells. Note that in hypoplastic marrows, obtaining sufficient sample for karyotyping is often difficult.

• References

Magnetic Resonance Imaging

Although aplastic anemia is characterized by hypocellularity of bone marrow, a small minority of patients have pockets of hypercellularity, and a bone marrow biopsy may give misleading results if the sample is taken from one of those hypercellular areas. Overall bone marrow cellularity may be assessed by evaluation of magnetic resonance imaging (MRI) scans of the marrow areas of the axial skeleton.

Matcuk et al reported that calculations of bone marrow cellularity based on T1 signal intensity measurements from MRI show statistically significant correlation with determinations of cellularity from bone marrow biopsy. Cellularity increased from T11 to S1 and decreased with patient age.^[53]

• References

Staging

Staging of aplastic anemia is based on the criteria of the International Aplastic Anemia Study Group (IAASG).

Severe aplastic anemia (SAA) is defined as marrow cellularity < 25% (or 25–50% with < 30% residual hematopoietic cells), plus at least two of the following peripheral blood findings:

• Neutrophils less than 0.5 × 10⁹/L
• Platelets less than 20 × 10⁹/L
• Reticulocytes less than 20 × 10⁹/L

Very severe aplastic anemia (VSAA) is defined as as marrow cellularity < 25% (or 25–50% with < 30% residual hematopoietic cells), plus at least two of the following peripheral blood findings:

• Neutrophils less than 0.2 × 10⁹/L
• Platelets less than 20 × 10⁹/L
• Reticulocytes less than 20 × 10⁹/L

• References

Approach Considerations

Therapy for aplastic anemia may consist of supportive care only, immunosuppressive therapy, or hematopoietic cell transplantation (HCT). Severe and very severe aplastic anemia (SAA and VSAA, respectively; see Workup) have a mortality rate of greater than 70% with supportive care alone^[54] and are therefore a hematologic emergency. Treatment should be instituted promptly for SAA or VSAA, and clinicians must stress the need for patient compliance with therapy.

Inpatient care for patients with aplastic anemia may be needed during periods of infection and for specific therapies, such as antithymocyte globulin (ATG) or HCT. In addition, iron chelation may be required in chronically transfused patients who develop elevated serum ferritin levels above 1000 µg/L.^[5]

The British Committee for Standards in Haematology recommends treating infection or uncontrolled bleeding before administering immunosuppressive therapy, including in patients scheduled for HCT.^[5] In the presence of severe infection, however, it may be necessary to proceed directly to HCT to provide the patient with the best chance for early neutrophil recovery.^[5]  

Both the British Committee for Standards in Haematology and the Pediatric Haemato-Oncology Italian Association recommend HCT from a matched sibling donor for severe aplastic anemia. If a matched donor is not available, options include immunosuppressive therapy or unrelated donor HCT.^{[6, 7]}

Approximately one third of patients with aplastic anemia do not respond to immunosuppression. The thrombopoietin receptor agonist eltrombopag is approved for use in patients with severe aplastic anemia who fail to respond adequately to immunosuppressive therapy. Independent of response or degree of response, risks include relapse and late-onset clonal disease, such as paroxysmal nocturnal hemoglobinuria (PNH), myelodysplastic syndrome (MDS), or leukemia.^{[16, 40, 41, 42, 43]}

Pregnant women with aplastic anemia have a 33% risk of relapse.^[5] Provide supportive care in these patients, maintain the platelet count above 20 × 10⁹/L, if possible, and consider administering cyclosporine.^[5]

Note that monotherapy with hematopoietic growth factors (eg, recombinant human erythropoietin [rHuEPO], granulocyte colony-stimulating factor [G-CSF]) is not recommended for newly diagnosed patients.^[5]

Frequent outpatient follow-up for patients with aplastic anemia is needed to monitor blood counts and any adverse effects of various drugs. Transfusions of packed red blood cells (RBCs) and platelets are administered on an outpatient basis.

Transfer considerations

Patients with aplastic anemia should be treated by physicians who are experts in the care of immunocompromised patients and in consultation with a hematologist and/or an HCT physician.

• References

Blood Transfusion

Patients with aplastic anemia require transfusion support until the diagnosis is established and specific therapy can be instituted. The British Committee for Standards in Haematology recommends prophylactic transfusions in patients whose platelet counts fall below 10 × 10⁹/L (or < 20 × 10⁹/L in febrile patients).^[5] However, it is important that transfusions be guided by the patient’s clinical status and not by numbers alone. Avoiding transfusions from family members is important because of possible sensitization against non-HLA (human leukocyte antigen) tissue antigens of potential donors.

For patients in whom hematopoietic cell transplantation (HCT) may be attempted, transfusions should be used judiciously because minimally transfused subjects have achieved superior therapeutic outcomes.

If using blood-bank support, attempt to minimize the risk of cytomegalovirus (CMV) infection. The blood products should, if possible, undergo leukocyte reduction to prevent alloimmunization and CMV transmission and should be irradiated to prevent transfusion-associated graft versus host disease (GVHD) in HCT candidates.

The British Committee for Standards in Haematology also recommends irradiated blood products for all patients receiving antithymocyte globulin (ATG) therapy. In patients with life-threatening neutropenic sepsis, the committee suggests consideration of irradiated granulocyte transfusions.^[5]

Development of a transfusion plan in consultation with a physician who is experienced in the management of aplastic anemia is essential.

• References

Treatment of Infections

Infections are a major cause of mortality in patients with aplastic anemia.^{[55, 56]} Risk factors include prolonged neutropenia and the indwelling catheters used for specific therapy. Fungal infections, especially those due to Aspergillus species, pose a major risk. Patients should maintain hygiene to reduce infection risk.

The British Committee for Standards in Haematology recommends prophylactic antibiotic and antifungal agents for patients whose neutrophil counts are below 0.2 ×10⁹/L.^[5] Empirical antibiotic therapy should be broad based, with gram-negative and staphylococcal coverage based on local microbial sensitivities. Especially consider including antipseudomonal coverage at the start of treatment for patients with febrile neutropenia; also consider early introduction of antifungal agents for individuals with persistent fever.

However, the strategy of empiric antibiotic use has also resulted in the development of resistant organisms and thus is not favored by some clinicians.^[57]

Cytokine support with granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) may be considered in refractory infections, although this therapy should be weighed against its cost and efficacy.^{[9, 58, 59, 60]} Discontinue cytokine support after 1 week if the neutrophil count doesn’t rise.^[5]

• References

Hematopoietic Cell Transplantation

Central venous catheter placement is required prior to hematopoietic cell transplantation (HCT). Note that the following recommendations do not apply to patients with Fanconi anemia and other types of inherited marrow failure;^[5] these patients require special consideration.

HCT using an HLA-matched sibling donor

Human leukocyte antigen (HLA)-matched sibling-donor HCT is the treatment of choice for a young patient with severe or very severe aplastic anemia (SAA or VSAA, respectively), being generally accepted for patients younger than 50 years.^[5] Persons undergoing this procedure do not require irradiation-based conditioning regimens.^[5]

A study of 692 German patients with SAA who received transplants from HLA-matched siblings, noted that bone-marrow grafts were preferable to peripheral blood progenitor cell (PBPC) grafts in patients younger than 20 years.^[61] A multinational study of patients with SAA who received HCT from an HLA-matched sibling donor concluded that although bone marrow should definitely be the preferred graft source for these patients, PBPCs may be an acceptable alternative in countries with limited resources where patients present later in their disease course and risks of graft failure and infective complications are high.^[62]

Although evidence suggests that stem cells from bone marrow afford better outcomes compared with PBPCs, an additional consideration is the perspective of the donor, who must be informed of the difference between the methods of harvesting. Bone marrow harvesting is usually performed with the donor under general anesthesia, while with PBPC harvesting the donor is awake and connected via large-bore intravenous catheters to an apheresis machine, which separates out the stem cells (for descriptions of the two methods, see Bone Marrow Donor Procedure).

Along with the risks associated with anesthesia, bone marrow donors typically experience moderate pain for several days following the procedure. PBPC donors usually experience bone pain, which may be severe, from the filgrastim-induced bone marrow stimulation used to mobilize stem cells in advance of the procedure.

One of the major problems of HCT in aplastic anemia is the high rate of rejection (10%; range, 5-50%). This is positively correlated with the number of transfusions the patient received and the duration of his or her disease, prior to transplantation.

Previously, a higher stem cell dose, as well as the addition of total body irradiation to cyclophosphamide conditioning, was tried. Although it was associated with a reduced incidence of graft rejection, the benefit was negated by high transplant-related mortality (TRM) due to an increase in graft versus host disease (GVHD).

Currently, antithymocyte globulin (ATG) with cyclophosphamide is a commonly used conditioning regimen for transplantations in aplastic anemia. The addition of ATG to cyclophosphamide for conditioning has resulted in infrequent graft rejections, as well as improved overall survival.^{[18, 58, 59, 63]}

Fludarabine- and cyclophosphamide-based reduced-intensity conditioning (RIC) regimens with or without ATG reduced rejection and improved outcome in Indian patients undergoing allogeneic HCT for SAA.^[64] When compared with 26 patients previously transplanted using cyclophosphamide/antilymphocyte globulin, there was faster neutrophil engraftment (12 vs 16 days, respectively), with significantly lower rejection rates (2.9% vs 30.7%, respectively), and superior event-free (82.8% vs 38.4%, respectively) and overall (82.8% vs 46.1%, respectively) survival rates.^[64]

Standard conditioning regimens use a cyclophosphamide dose of 200 mg/kg, which is known to be associated with significant organ toxicity. In a multicenter phase 1-2 study of adult patients with SAA receiving bone marrow grafts from unrelated donors, Anderlini et al found that a regimen of cyclophosphamide in doses of 50 or 100 mg/kg, combined with TBI 2 Gy, fludarabine, and ATG, provided effective conditioning and few early deaths.^[65]

The occurrence of GVHD as a complication of HCT is positively correlated with increasing age of the patient. Grafts depleted of T cells reduce the risk of GVHD but increase the risk of graft failure. The addition of cyclosporine along with methotrexate is the standard GVHD approach for matched siblings.^[63] However, very few comparative data exist, and no data have reported an alternative approach to be superior to this regimen.

Although horse ATG is better than rabbit ATG as an immunosuppressive therapy, a multinational study that included 546 HLA-matched sibling HCT transplants for severe aplastic anemia, 3-year overall survival rates were not significantly different with rabbit versus horse ATG used as part of the conditioning regimen. However, the day-100 incidences of both acute and chronic GVHD were higher with horse than with rabbit ATG (acute GHVD, 17% versus 6%, respectively, p< 0.001; chronic GVHD, 20% versus 9%, p< 0.001). The authors concluded that these support the use of rabbit ATG for bone marrow conditioning.^[66]

Early referral to a transplantation center at diagnosis is recommended for all young patients, even if they lack a suitable related donor, because transplant planning needs to be done even if patients are receiving immunosuppressive therapy due to a significant number of failures.^[19]

Fertility

Patients receiving high-dose cyclophosphamide conditioning in allogeneic HCT from an HLA-identical sibling donor for aplastic anemia have relatively well-preserved fertility.^[5] Provide these patients with appropriate contraceptive advice to prevent unintended pregnancies.

Longer-term data are limited for patients with fludarabine-based regimens. Therefore, discussions related to potential fertility preservation, including cryopreservation of sperm and oocytes/embryos, is recommended.^[5] Cyclosporine is safe for use in pregnancy.

HCT using an unrelated donor

Unrelated-donor HCT is currently justified only if the donor is a full match and only if immunosuppressive therapy fails (failure of ≥1 course of ATG and CSA) or treatment as part of a clinical trial fails.^[5]

High-resolution allelic matching, however, has improved outcomes in unrelated-donor HCT, especially in younger patients. Maury et al found that results for young patients who are fully HLA matched at the allelic level with their donor are comparable to those observed after stem cell transplantation from a related donor.^[67]

GVHD

In the first cohorts transplanted, HCT using an unrelated donor was associated with very high mortality due to high rates of graft failure, infection, and GVHD. This poor outcome resulted primarily from the use of less stringent HLA matching in addition to the fact that these first patients had long-term disease, a history of infection, iron overload, transfusion resistance, and other related factors. However, more recent reports suggest a better outcome after unrelated transplants, an improvement that is due mainly to high-resolution HLA testing, optimization of the conditioning regimen, better supportive care, and better management of GVHD.

A retrospective study of comparative data from Japan indicated similar overall survival in children and young adults with aplastic anemia who received transplants from either a sibling or an unrelated donor, although rates of acute and chronic GVHD were significantly higher in the group receiving unrelated transplants.^[68]

Due to the rates of GVHD in unrelated donor transplantation, this procedure is not preferred over immunosuppressive therapy.^[36]

Partial T-cell depletion may decrease the risk of severe GVHD while still maintaining sufficient donor T lymphocytes to ensure engraftment.^[36]

In a multinational study that included 287 patients with severe aplastic anemia who received ATG as part of their conditioning regimen for unrelated-donor HCT, rabbit ATG resulted in a lower incidence of acute (but not chronic) GVHD and better survival (3-year overall survival, 83% for rabbit ATG versus 75% for horse ATG P=0.02). The authors concluded that these data support the use of rabbit ATG in this setting.^[66]

Graft failure

In a study that evaluated data for unrelated matched HCT versus mismatched transplants, the probability of graft failure at 100 days after using a 1-antigen mismatched, related donor was 21%, whereas the probability was 25% for a greater-than-1-antigen mismatched, related donor; 15% for a matched, unrelated donor; and 18% for a mismatched, unrelated donor.^[19]

Pharmacotherapeutic regimens in HCT

In unrelated-donor transplantation, radiation, along with cyclophosphamide, may be used to reduce graft rejection. Fludarabine-based conditioning regimens have been studied,^[37] along with ATG and cyclophosphamide.

It should be noted, however that early results from a cyclophosphamide deescalation study in a fludarabine-based conditioning regimen for unrelated donor HCT demonstrated life-threatening adverse events (excessive organ toxicity) at predefined cyclophosphamide dose levels.^[69] The investigators reported an association between such toxicity and cyclophosphamide 150 mg/kg plus total body irradiation at 2 Gy, fludarabine at 120 mg/m², and ATG.^[69]

Although the optimal regimen for unrelated-donor HCT remains unclear, the British Committee for Standards in Haematology indicates that a non–irradiation-based fludarabine regimen appears to be favored for younger patients.^[5]

According to a study by Samarasinghe et al, a conditioning regimen with fludarabine, cyclophosphamide, and alemtuzumab with matched unrelated-donor (MUD) HCT appears to be very well-suited in children with severe aplastic anemia and has excellent outcomes.^[70] The investigators suggested that MUD HCT may be a reasonable alternative when immunosuppressive therapy fails.^[70]

Hamad and colleagues reported on HCT using a conditioning regimen with intermediate-dose alemtuzumab (50 to 60 mg) and high-dose cyclophosphamide or fludarabine in 41 adult patients with aplastic anemia, and reported excellent survival with a favorable impact on GVHD and long-term health outcomes, but frequent viral complications. At 3 years, survival was 96% in patients younger than 40 years of age and 67% in those 40 years and older.^[71]

Haploidentical HCT

A pilot study by Clay and colleagues in the United Kingdom reported successful use of nonmyeloablative peripheral blood haploidentical stem cell transplantation as rescue therapy. The study included eight patients with refractory severe aplastic anemia who lacked a matched sibling or unrelated donor or who had failed unrelated-donor or umbilical cord blood transplant.^[72]

Six of the eight patients engrafted; graft failure occurred in patients with donor-directed HLA antibodies, although they had undergone intensive desensitization with plasma exchange and rituximab.The European Group for Blood and Marrow Transplantation Severe Aplastic Anaemia Working Party will be evaluating this protocol in a future observational study^[72]

• References

Umbilical Cord Blood Transplantation

Umbilical cord blood transplantation (CBT) is not yet recommended as first- or second-line therapy for aplastic anemia. This treatment should be used as experimental therapy for patients who do not have a human leukocyte antigen (HLA)–matched donor and who have 1-2 courses of failed immunosuppressive therapy, and it should be evaluated only through prospective clinical trials.^[73] Controlled trials are needed to better define the role and timing of CBT in aplastic anemia.^{[74, 75, 76]}

• References

Immunosuppressive Therapy

Immunosuppressive therapy using antithymocyte globulin (ATG) and cyclosporine is associated with an overall response rate of 60-80% and a 5-year survival rate of 75% in most reports, but event-free survival rates are in the range of 35-50%.

Immunosuppressive therapy using ATG plus cyclosporine is being administered as first-line therapy^[77] for patients with severe or very severe aplastic anemia (SAA or VSAA, respectively) who are older than 50 years (35-50 years in presence of comorbidities) and as second-line therapy in younger patients with SAA or VSAA if a human leukocyte antigen (HLA)–matched sibling donor is not available. Immunosuppressive therapy is also recommended in patients with nonsevere aplastic anemia who are transfusion dependent.^[5]

Central venous catheter placement may be required before the administration of immunosuppressive therapy, and patients with these catheters should be treated as inpatients. Patients may require blood product support during ATG therapy, as well as close monitoring for allergic or anaphylactic signs and symptoms and for prophylaxis and treatment of fevers.^[5]

ATG and cyclosporine

Scheinberg et al reported that a large difference was observed in patients with aplastic anemia in the rate of hematologic response at 6 months in favor of horse ATG (68%), as compared with rabbit ATG (37%).^[78] Overall survival at 3 years also differed, with a survival rate of 96% in the horse-ATG group, compared with 76% in the rabbit-ATG group when data were censored at the time of stem-cell transplantation, and 94% versus 70% in the respective groups when stem-cell–transplantation events were not censored.^[78]

A review by Risitano also demonstrated that immunosuppression with rabbit ATG, as well as cyclophosphamide and alemtuzumab, in patients with aplastic anemia or immune-mediated bone marrow failure syndromes had an inferior outcome relative to horse ATG.^[79] Therefore, rabbit ATG, cyclophosphamide, and alemtuzumab are not recommended as first-line therapy in these patients.^[79]

In other studies of ATG, responses have been defined as complete responses (CRs) when all blood counts return to normal, and as partial responses (PRs) when there is an improvement in blood counts with transfusion independence. In these analyses, response to ATG is slow, usually taking 10-12 weeks for a response to occur; and the response may also continue to improve or occur later. If the patient has not responded to a first course of ATG, then a second course may be given, using either the same preparation or another one. Approximately 30-60% of patients may respond to a second course of ATG.^{[80, 81, 82, 83, 84, 85, 86]}

In one study, response rates to cyclosporine alone were 45% overall, 16% for VSSA, 47% for SAA, and 85% for moderate aplastic anemia.^[87] Therefore, the only predictor of response to cyclosporine was an absolute neutrophil count (ANC) of less than 200/mm³. Adding granulocyte colony-stimulating factor (G-CSF) to ATG and cyclosporine in patients with an ANC of over 200/mm³ does not provide any additional advantage in reducing the infection rate or in increasing survival or therapeutic responses.

A meta-analysis by Hayakawa et al of 13 studies comparing horse ATG with rabbit ATG for immunosuppressive therapy in severe aplastic anemia concluded that horse ATG results in a higher respnse rate (p=0.015); further, a sensitivity analysis showed that there was higher early mortality with rabbit ATG.^[88] Hence, horse ATG is the preferred choice in this setting.

Time to response and relapse

The treatment response in aplastic anemia, unlike in other autoimmune diseases, is slow. At least 4-12 weeks is usually needed to observe early improvement, and the patient may continue to improve slowly thereafter. About 50% of patients respond by 3 months after ATG administration, and about 75% respond by 6 months. Most patients improve and become transfusion independent, but many still have evidence of hypoproliferative bone marrow.

Although the initial response rate is good, durable responses with no relapse or clonal evolution are observed in 50% of the patients.^[89] To reduce the risk of relapse, continue cyclosporine for a minimum of 12 months after achieving maximal hematologic response, with a very slow tapering thereafter.^[5] Approximately one third of patients have a relapse, most of whom have a relapse at the time of cyclosporine taper. About one third of responders are cyclosporine dependent. Of patients without a response or who relapse, 40-50% respond to a second course of immunosuppressive therapy.

In rare cases, full hematologic recovery is observed, but most patients improve to a functional hematologic recovery that obviates further transfusion support. Furthermore, the risk of some form of clonal disease other than paroxysmal nocturnal hemoglobinuria (PNH) is 15-30% and may be due to the inability of these therapies to completely correct bone marrow function, a missed diagnosis of myelodysplastic syndrome (MDS), or the fact that the stem cells under proliferative stress may be more prone than other cells to mutation.

Investigational immunosuppressive therapy

At present, the use of high-dose cyclophosphamide should be limited to clinical trials.^[89] Preliminary data have suggested that high-dose cyclophosphamide may result in durable remissions in some patients with aplastic anemia. However, some of these patients develop PNH and cytogenetic abnormalities on follow-up. When investigators conducted a prospective, randomized study based on the above preliminary report by using cyclophosphamide versus ATG plus CSA, the study was terminated early because of very high mortality and fungal infections in the cyclophosphamide arm.^{[90, 91]}

Up to 50% of patients with aplastic anemia demonstrate small PNH clones in the absence of evidence of hemolysis.^[5] In patients with a history of PNH-associated thrombosis, use of ATG is not recommended. In addition, because abnormal cytogenetic clones can occur in up to 12% of patients with aplastic anemia, the presence of some clones in otherwise typical cases of aplastic anemia does not necessarily signify a diagnosis of myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML).^[5] However, an exception is when the monosomy 7 clone is present, in which case there is a high risk of transformation to MDS or AML.^[5]

Other promising investigational immunosuppressive therapies include alemtuzumab (monoclonal anti-CD52 antibody). However, daclizumab (monoclonal anti-CD25 antibody) was withdrawn from the market due to toxicity. Mycophenolate mofetil and sirolimus have also been used but did not result in treatment responses.

Except in the setting of prospective clinical trials, hematopoietic growth factors (eg, recombinant human erythropoietin [rHuEPO], granulocyte colony-stimulating factor [G-CSF]) is not recommended for routine long-term use following ATG and CSA therapy.^[5]

• References

Eltrombopag

In patients with aplastic anemia that is refractory to immunosuppressive therapy (IST), treatment with eltrombopag (Promacta) may be considered. Eltrombopag, a thrombopoietin receptor agonist, was approved in August 2014 for severe aplastic anemia in patients who fail to respond adequately to at least one prior IST regimen. Approval was supported by a phase II study in which 41% of patients experienced a hematologic response in at least one lineage (ie, platelets, red blood cells, neutrophils) after 12 weeks of treatment with eltrombopag.^{[92, 93]}

In the extension phase of the study, three patients achieved a multi-lineage response. Four of those patients subsequently tapered off treatment and maintained the response (median followup 8.1 months, range 7.2-10.6 months).^{[92, 93]}

Eltrombopag has also shown benefit as first-line therapy. Townsley et al combined standard immunosuppressive therapy with eltrombopag in previously untreated patients with severe aplastic anemia, using three different regimens. The best response was noted in patients receiving eltrombopag from day 1 to 6 months, along with horse ATG on days 1 to 4 and daily cyclosporine from day 1 to 6 months. In this cohort, at 6 months, complete responses were seen in 58% of patients and hematologic responses in 94%. This compared with 10% and 66% rates, respectively, observed in a historical cohort treated with IST alone. In addition, the improved blood counts were accompanied by increased marrow cellularity and hematopoietic progenitor numbers.^[94]

Geng et al reported on upfront use of eltrombopag in two pediatric patients with non-severe aplastic anemia. Both patients achieved hematologic response with eltrombopag monotherapy.^[95]

In November 2018, the FDA expanded approval for eltrombopag to include use as first-line therapy, in combination with standard IST, for adult and pediatric patients 2 years and older with severe aplastic anemia.^[96]

• References

Diet and Activity

The diet for the patient with aplastic anemia who has neutropenia or who is receiving immunosuppressive therapy should be tailored carefully to exclude raw meats, dairy products, or fruits and vegetables that are likely to be colonized by bacteria, fungus, or molds. Furthermore, a salt-limited diet is recommended during therapy with steroids or cyclosporin-A (CSA).

The patient should avoid any activity that increases the risk of trauma during periods of thrombocytopenia. Menstruating women are also advised to be on hormonal pills to avoid menstrual cycles that are likely to be heavy due to thrombocytopenia.

Inform patients of the increased risk of community-acquired infections during periods of neutropenia and lymphopenia. Patients should maintain hygiene to reduce the risks of infection.

• References

Medication Summary

The goals of pharmacotherapy in cases of aplastic anemia are to reduce morbidity and prevent complications.

Options in immunosuppressive treatment include combination therapy, including antithymocyte globulin (ATG), cyclosporine, and methylprednisolone, with or without cytokine support. ATG or cyclosporine alone may also produce a response in aplastic anemia, but the combination improves the likelihood of a response. Nevertheless, a prospective study from India concluded that for resource-poor patients, cyclosporine monotherapy, in a dosage of 5 mg/kg/day, is a relatively safe treatment option for aplastic anemia.^[97]

Hematopoietic support with eltrombopag, granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) may be considered in refractory infections, although cost and efficacy of this therapy should be weighed.^{[9, 58, 59, 60, 92, 93]}

• References

Cyclosporine (Sandimmune, Neoral)

• Dosing, Interactions, etc.

Clinical Context:  Cyclosporine is a cyclic polypeptide that suppresses some humoral immunity and, to a greater extent, cell-mediated immune reactions (eg, delayed hypersensitivity, allograft rejection, experimental allergic encephalomyelitis, graft versus host disease) for a variety of organs.

For children and adults, base the initial dosing on the ideal body weight and subsequently adjust for levels. Frequent monitoring of drug levels is needed. To convert to the oral dose, use an intravenous (IV)-to-oral correction factor of 1:4. The dosage and duration of therapy may vary with different protocols. When used without hematopoietic growth factor in children, ATG and cyclosporine-based immunosuppressive therapy has been shown to lead to an excellent response and survival rate with low incidence of clonal evolution.

• References

Methylprednisolone (Medrol, Solu-Medrol)

• Dosing, Interactions, etc.

Clinical Context:  Steroids ameliorate the delayed effects of anaphylactoid reactions and may limit biphasic anaphylaxis. In severe serum sickness (mediated by immune complexes), parenteral steroids may reduce the inflammatory effects. Hence, methylprednisolone is used with antithymocyte globulin (ATG) to decrease the adverse effects (eg, allergic reactions, serum sickness). Also, this agent has an additional immunosuppressive effect. High doses or long duration may be needed if serum sickness occurs with ATG. The doses and duration may vary with different protocols.

• References

Alemtuzumab (Campath, MabCampath)

• Dosing, Interactions, etc.

Clinical Context:  Alemtuzumab is a recombinant monoclonal antibody against CD52 (lymphocyte antigen). This agent promotes antibody-dependent lysis.

• References

Lymphocyte immune globulin, equine (Atgam)

• Dosing, Interactions, etc.

Clinical Context:  Lymphocyte immune globulin inhibits the cell-mediated immune response by altering T-cell function or by eliminating antigen-reactive cells. There is little prospective, randomized data to suggest a single schedule that is superior, but experience suggests that a 4- to 5-day infusion is associated with less toxicity than older 7- to 10-day schedules.

• References

Cyclophosphamide (Cytoxan)

• Dosing, Interactions, etc.

Clinical Context:  Cyclophosphamide is chemically related to nitrogen mustards. As an alkylating agent, the mechanism of action of the active metabolites may involve cross-linking of deoxyribonucleic acid (DNA), which may interfere with the growth of normal and neoplastic cells. Monitor carefully; used only on an investigational basis.

• References

Antithymocyte globulin, rabbit (Thymoglobulin)

• Dosing, Interactions, etc.

Clinical Context:  Antithymocyte globulin (ATG) may modify T-cell function. The dose and duration of therapy vary with the investigational protocols.

• References

Class Summary

The merits of additional immunosuppression versus the increased risk and cost should be considered. Data from a randomized, prospective study indicated that an increased proportion of patients responded to the addition of CSA to ATG but that this did not translate into a long-term survival advantage.^[98] That is, failure-free survival is better with CSA, but long-term overall survival was similar between CSA and ATG.

For patients who cannot tolerate equine-based products, use of the commercially available, rabbit-based ATG product (Thymoglobulin) may be considered. This product is currently approved in the United States and has been used for the treatment of aplastic anemia in Europe (although note the different dose schedule).

• References

Eltrombopag (Promacta)

• Dosing, Interactions, etc.

Clinical Context:  Eltrombopag is a thrombopoietin (TPO)-receptor agonist that interacts with human TPO receptor transmembrane domain of human TPO-receptor. It initiates signaling cascades that induce proliferation and differentiation of megakaryocytes from bone marrow progenitor cells. It is indicated for severe aplastic anemia in patients who fail to respond adequately to at least 1 prior immunosuppressive therapy.

• References

Sargramostim (Leukine)

• Dosing, Interactions, etc.

Clinical Context:  A recombinant human GM-CSF, sargramostim can stimulate production of neutrophils and activate mature granulocytes and macrophages. The dose and frequency of administration vary with the investigational protocol.

• References

Filgrastim (Neupogen)

• Dosing, Interactions, etc.

Clinical Context:  Filgrastim is a G-CSF that activates and stimulates the production, maturation, migration, and cytotoxicity of neutrophils.

• References

Class Summary

Eltrombopag has gained FDA approval for severe aplastic anemia and may be considered in patients who fail immunosuppressive therapy. Several preliminary studies have demonstrated that the addition of cytokines (eg, granulocyte colony-stimulating factor [G-CSF], granulocyte-macrophage colony-stimulating factor [GM-CSF]) may hasten the neutrophil recovery and that these agents may improve response rate and survival, although long-term use may increase the risk of clonal evolution.

• References

Fludarabine (Fludara)

• Dosing, Interactions, etc.

Clinical Context:  Fludarabine contains fludarabine phosphate, a fluorinated nucleotide analogue of the antiviral agent vidarabine, 9-b-D-arabinofuranosyladenine (ara-A) that enters the cell and is phosphorylated to form the active metabolite 2-fluoro-ara-adenosine triphosphate, which inhibits deoxyribonucleic acid (DNA) synthesis. Specifically, this agent inhibits DNA polymerase, DNA primase, DNA ligase, and ribonucleotide reductase, as well as ribonucleic acid (RNA) function, RNA processing, and mRNA translation. Fludarabine also activates apoptosis.

• References

Class Summary

Antimetabolites are antineoplastic agent that inhibit cell growth and proliferation.

• References

Deferoxamine (Desferal)

• Dosing, Interactions, etc.

Clinical Context:  Deferoxamine chelates iron by forming a stable complex that prevents the iron from entering into further chemical reactions; it also chelates iron readily from ferritin and hemosiderin but not readily from transferrin. Desferoxamine does not combine with the iron from cytochromes and hemoglobin. The chelate is readily soluble and is renally excreted.

• References

Deferasirox (Exjade)

• Dosing, Interactions, etc.

Clinical Context:  Deferasirox chelates trivalent iron. This agent is used to treat chronic iron overload due to blood transfusions. Monitor patients' renal and hepatic function.

• References

Class Summary

Chelating agents eliminate iron overload from transfusions.

• References