Thrombotic Thrombocytopenic Purpura

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Author

Deborrah Symonette, MD, MPH, Healthcare Consultant, DSKSD, Inc

Nothing to disclose.

Coauthor(s)

Deepak Sharma, Touro College of Osteopathic Medicine, New York

Nothing to disclose.

Priya S Abraham, Touro College of Osteopathic Medicine, New York

Nothing to disclose.

Vanessa Yoo, Touro College of Osteopathic Medicine, New York

Nothing to disclose.

Wafa Qamar, Touro College of Osteopathic Medicine, New York

Nothing to disclose.

Specialty Editor(s)

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine

eMedicine Salary Employment

Jeffrey L Arnold, MD, FACEP, Chairman, Department of Emergency Medicine, Santa Clara Valley Medical Center

Nothing to disclose.

John D Halamka, MD, MS, Associate Professor of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center; Chief Information Officer, CareGroup Healthcare System and Harvard Medical School; Attending Physician, Division of Emergency Medicine, Beth Israel Deaconess Medical Center

Nothing to disclose.

Miguel C Fernández, MD, FAAEM, FACEP, FACMT, FACCT, Associate Clinical Professor; Medical and Managing Director, South Texas Poison Center, Department of Surgery/Emergency Medicine and Toxicology, University of Texas Health Science Center at San Antonio

Nothing to disclose.

Chief Editor

Barry E Brenner, MD, PhD, FACEP, Professor of Emergency Medicine, Professor of Internal Medicine, Program Director, Emergency Medicine, University Hospitals, Case Medical Center

Nothing to disclose.

Background

Thrombotic thrombocytopenic purpura (TTP) is a rare life-threatening multisystem disorder that is considered a true medical hematological emergency. Moschcowitz first described TTP in 1924 when he observed that a 16-year-old girl had anemia, petechiae, and microscopic hematuria. She died of multiorgan failure, and, at autopsy, disseminated microvascular hyaline platelet thrombi were prevalent in terminal arterioles and capillaries of the heart and kidneys. These platelet-rich thrombi remain the hallmark of the pathologic diagnosis. Microangiopathic hemolytic anemia along with the aggregation of platelet thrombi are present in a setting of microvascular injury and high fluid shear stress.

Varying degrees of organ ischemia due to the vascular occlusion occur. In this life-threatening disease, recognizing the clinical presentation and initiating medical intervention early are critical. This is difficult at times because there is a range of overlapping signs and symptoms with other microangiopathic diseases, such as hemolytic uremic syndrome (HUS). Both TTP and HUS have thrombocytopenia and microangiopathic hemolytic anemia but different medical management pathways. The patient may not present with all of the signs and symptoms of TTP, and there can be a gray zone as to which microangiopathy truly exists. TTP is a medical emergency with diagnostic criteria for treatment that is not always definitive but, if TTP is suspected, then the first-line treatment of plasma exchange should be initiated to save the patient's life.

Prior efforts to identify this disease clinically lead to the development of a diagnostic criteria classifying thrombotic thrombocytopenic purpura as a syndrome in 1966 by Amorosi and Ultmann. They reviewed 255 patients previously reported and 16 other patients. They outlined a pentad of clinical features including microangiopathic hemolytic anemia, thrombocytopenia, neurologic abnormalities, fever, and renal dysfunction.[1] Later studies show this pentad is seen in 40% of cases. A triad of microangiopathic hemolytic anemia, thrombocytopenia, and neurologic abnormalities are seen in 74%.[2] Clinically, if a patient presents with thrombocytopenia (without coagulopathy), red cell fragmentation (schistocytes) noted on peripheral smear, decreased hemoglobin, marked elevation of the lactate dehydrogenase (LDH) level, normal coagulation studies and muscle and organ ischemia, consider TTP urgently in the differential diagnosis.[3]

Thrombotic microangiopathic diseases

Thrombotic thrombocytopenic purpura (TTP) is categorized into acquired (idiopathic) TTP and congenital (familial, hereditary) TTP. Acquired TTP is mainly idiopathic, but there are other nonidiopathic conditions and comorbidities. Congenital TTP is a rare autosomal recessive disease present often in childhood. Acquired and congenital TTP are both part of the larger spectrum of thrombotic microangiopathic diseases. These diseases have microvascular thrombosis and hemolysis with fragmented red blood cells.

Various terms have been used for other thrombotic microangiopathies such as nonidiopathic TTP, TTP-like diseases, or secondary TTP. In addition, TTP may also be drug-induced.[4] It is not clear if the drug-induced TTP is immunomediated or due to direct dose-induced toxicity.[5] These thrombotic microangiopathies have varying causes and pathology but present with clinical manifestations that are TTP-like. These include drugs such as antiaggregating drugs (eg, ticlopidine, clopidogrel), chemotherapeutic drugs (eg, mitomycin-C, cisplatin, gemcitabine), and immunosuppressant (eg, cyclosporine); cancers; vasculitis; hematopoietic stem cell transplantation; quinine; infections such as human immunodeficiency virus infection; and pregnancy, especially in the third trimester.[4]

Distinguishing TTP from other thrombotic microangiopathies that have similar overlapping clinical presentations is very difficult. In addition, certain nonidiopathic TTP does not respond to the first-line treatment of plasmapheresis. The complexity of categorizing these other conditions or comorbidities has not been resolved, and further investigation is needed to better classify this group.[6]

TTP and hemolytic uremic syndrome (HUS) are the main thrombotic microangiopathies and were once thought to have a shared pathophysiological etiology. They are closely related. Hemolytic uremic syndrome is usually found in children, and renal involvement is significant. Hemolytic uremic syndrome is caused by Shiga -like toxin-producing E coli O157:H7 in 90% of the cases.[6] Hemolytic uremic syndrome is characterized by a triad of hemolytic anemia, thrombocytopenia, and acute renal failure. TTP is usually found in adults and characterized by hemolytic anemia, thrombocytopenia, and, to a lesser extent, neurological manifestations. Symptoms are similar for TTP and HUS based solely on their clinical presentation. Microthrombi in TTP are mainly platelets, but microthrombi in HUS have more fibrin deposition.

In 1977, a breakthrough in treatment was reported by Bukowski et al using whole-blood exchange transfusion, also known as plasmapheresis and fresh frozen plasma (FFP). Shortly after, Byrnes and colleagues used plasma infusion. During the plasma exchange, the entire plasma volume is replaced with normal human plasma and the large molecular inhibitory antibodies are removed and the plasma is replenished with the deficient protease. Delay in starting the plasma exchange is correlated with treatment failure. If a delay is unavoidable, begin plasma infusion until the plasma exchange is available. Intravenous (IV) plasma exchange is the present standard of treatment for thrombotic thrombocytopenic purpura. Fresh frozen plasma has become the standard replacement fluid with its plasma protein levels closely paralleling physiological levels.[3, 7]

Plasma infusion and plasma exchange have had a significant impact on the life expectancy of patients. With the introduction of plasma exchange, the survival rate has improved from approximately 3% prior to the 1960s to 82%. By 1991, a landmark clinical trial by Rock et al presented evidence of the efficacy of plasma exchange treatment.[8] Early recognition of the clinical features and intervention with plasma exchange can reduce the mortality rate associated with TTP from 90% to approximately 10-20%. Early recognition and management are essential for patient survival. Plasma infusion is a temporary measure, and its use is limited by volume overload. Plasma exchange is the treatment of choice for patients with acquired TTP. Congenital TTP responds to plasma infusion.

Pathophysiology

The TTP syndrome is characterized by microangiopathic hemolysis and platelet aggregation/hyaline thrombi whose formation is unrelated to coagulation system activity. Platelet microthrombi predominate; they form in the microcirculation (ie, arterioles, capillaries) throughout the body causing partial occlusion of vessels. Organ ischemia, thrombocytopenia, and erythrocyte fragmentation (ie, schistocytes) occur. The thrombi partially occlude the vascular lumina with overlying proliferative endothelial cells. The endothelia of the kidneys, brain, heart, pancreas, spleen, and adrenal glands are particularly vulnerable to TTP. The liver, lungs, gastrointestinal tract, gallbladder, skeletal muscles, retina, pituitary gland, ovaries, uterus, and testes are also affected to a lesser extent. No inflammatory changes occur. The occlusion of the microthrombi affects many organs, and a myriad of symptoms are presented.

Mechanism

von Willebrand factor (vWF) was observed in 1982 by Moake and his colleagues. This is a large, adhesive glycoprotein that mediates thrombus formation at sites of vascular injury. vWF is synthesized in the endothelium and megakaryocytes, and it circulates in the plasma. Various sizes of multimers were noted, and the large form, ultralarge von Willebrand factor (ULVWF) multimers were secreted from the endothelium.[9] These are the largest soluble protein found in human plasma and are considered the major pathogenic factor in TTP due to the platelet clumping in the microvasculature.

The ULVWF is the most active of the various-sized multimers and is found in platelets, endothelial cells, and subendothelium. They were seen in the plasma of 4 patients with relapsing TTP.[10, 11] The plasma of normal individuals has much smaller vWF. Moake suggested that there is a deficiency in an enzyme that reduces the large vWF to its normal size in plasma of patients with TTP. This large vWF appeared to have a greater ability to adhere with platelets mediating a thrombus formation. The large vWF combine with platelets consumed from the arterioles and capillaries of organs in a high-shearing stress environment and cause endothelial injury leading to ischemia. The red blood cells collide with the thrombi, and fragment leads to hemorrhage. As a result, the organ function is compromised.

The agitated endothelial cells are the main source of ULVWF multimer secretion into the bloodstream where they bind to specific surface platelet receptors. The ULVWF multimers adhere to the damaged endothelium or exposed subendothelium, with the platelet receptor binding to the ULVWF. The sheer stress of fluid and platelet thrombi in the microcirculation does not enhance proteolysis of ULVWF but rather thrombi formation. How the ULVWF multimers-platelets thrombus is able to adhere and oppose the high velocity blood flow is unclear, and research is ongoing.[12]

In 1996, the von Willebrand factor-cleaving protease was isolated by two independent laboratories. Furlan, Lammle, and colleagues[13] in Switzerland and Tsai[14] in New York isolated the von Willebrand factor-cleaving protease known as ADAMTS-13. ADAMTS-13 is a metalloprotease consisting of multiple structural and functional domains and is the major regulator of the size of vWF in plasma. These domains may participate in the recognition and binding of ADAMTS-13 to vWF. The ULVWF multimers are cleaved by ADAMTS-13 as they are secreted from endothelial cells.


View Image

Thrombotic thrombocytopenic purpura. Image courtesy of Deepak Sharma.

Acquired idiopathic and certain nonidiopathic TTP are associated with production of anti-ADAMTS13 antibodies inhibiting ADAMTS-13 activity. Congenital TTP is associated with mutations of the vWF-cleaving protease ADAMTS-13 gene encoding, and ADAMTS-13 is inactivated or decreased. ADAMTS-13 is severely deficient in patients with both congenital TTP or acquired TTP. Furlan et al found in their investigation, including retrospective analysis of plasma samples, that an autoimmune mechanism may be responsible in patients with acquired deficiency of ADAMTS-13.[13] Plasma exchange has been the first-line therapy for acquired TTP since 1991. Plasma infusion is used for congenital deficiency and can replace the deficiency and mutations in the ADAMTS-13 gene. Congenital TTP is a relapsing condition. For acquired TTP, more than 50% of patients with severe ADAMTS-13 deficiency relapse usually within the year.[15] For acquired TTP, the inhibitor of ADAMTS-13 is removed by plasma exchange by replacing the missing protease ADAMT-13 and removing the circulating autoantibody against ADAMT-13. It is more effective than plasma infusion. Nevertheless, relapsing cases do occur in those with severe ADAMTS-13 deficiency.[11] Low level ADAMTS-13 activity and elevated inhibitors are indicators for poor prognosis in acquired idiopathic TTP.[16]

Reasons for relapsing after plasma exchange in patients with severe ADAMTS-13 deficiency are unclear. An immune regulation defect may play a role in patients with recurrent ADAMTS-13 deficiency contributing to the presence of the inhibitor, but investigation is ongoing. The lifespan of ADAMTS-13 is 2-4 days, and, if a relapse occurs after plasma exchange, then repeat treatment with plasma exchange is recommended. Certain immunosuppressive drugs and splenectomy are treatments used for refractory cases of acquired TTP.

Relapsing and idiopathic TTP case reports refractory to plasmapheresis have shown some success with an immunomodulator rituximab.[17] This is a monoclonal antibody that is believed to destroy the CD20 protein that is the precursor of B cells that produce ADAMT-13 inhibitors. Rituximab does not destroy existing inhibitors but eliminates the next generation.[18] Positive outcomes have occurred when plasma exchange was slow to work or ineffective in cases including chemotherapy-induced TTP or systemic lupus erythematosus.

Future development in research

A greater focus on thrombotic thrombocytopenic purpura has emerged in recent years with advances in pathophysiology and diagnostic testing. Understanding the pathophysiology of thrombotic thrombocytopenic purpura is continuous and too early to have clearly defined evidence-based standards applicable to patient management and treatment.

Classification of thrombotic microangiopathies through better methods of assays measuring the ADAMTS-13 activity and detecting autoantibodies are important for treatment protocols.

There is continued research into replacement therapy with recombinant ADAMTS-13 instead of plasma[19] and refining standardized assays with rapid results to measure ADAMTS-13 levels of activity. Advances in our understanding of how ADAMTS-13 is regulated are improving.[8] One diagnostic laboratory recently announced a new ADAMTS-13 antibody assay, which measures the antibodies that inhibit ADAMTS-13 activity. Previously about 80% of the inhibiting antibodies were detected by their laboratory's inhibitor assay, but there is greater detection with the new assay.[20]

Breakthroughs will assist in diagnosis, leading to appropriate treatment plans. For example, differentiating TTP from HUS benefits the patient since plasma exchange is the treatment of choice for TTP not HUS, and plasma exchange is not a benign intervention. It is known that TTP has a severe deficiency in ADAMTS-13 not seen in HUS. Clinical trials using immunosuppressive treatments or alternative replacement fluids along with better prognostic measures for treatment are for the future considerations.

vWF plays a role in occlusive arterial thrombosis and the possibility of ADAMTS-13 as a therapeutic instrument to discover ways of treating and managing more common platelet-mediated illnesses such as myocardial infarction and ischemic stroke is a beneficial research challenge.

Epidemiology

Frequency

United States

More than 80 years ago, the occurrence rate of this uncommon disorder was 1 case per 1 million patients; however, the incidence rate is increasing, with the incidence rate a decade ago being 4-11 cases per 1 million patients. The incidence today is higher, with greater awareness of this disorder and increasing reports of thrombotic thrombocytopenic purpura (TTP) in patients with comorbidities, conditions, and drug therapy.[21]

Incidence today is 6.5 cases per million per year, with a predominance in women. Less than 5% of cases are congenital.

Mortality/Morbidity

The mortality rate associated with thrombotic thrombocytopenic purpura (TTP) approached 100% until the 1980s; the drop in mortality rate since that time is attributed to earlier diagnosis and improvement in therapy with plasma exchange.

Presently, the mortality rate is approximately 95% for untreated cases. The survival rate is 80-90% with early diagnosis and treatment with plasma infusion and plasma exchange.

Thirty percent of patients who survive the initial episode experience one or more relapses within 2 years.

Race

No significant racial difference exists.

Sex

Thrombotic thrombocytopenic purpura is more common in women than in men, with a female-to-male ratio of 2:1 to 3:1.[22]

Age

Thrombotic thrombocytopenic purpura is most common in adults, although it can occur in neonates to persons as old as 90 years. The peak occurs in the fourth decade of life, with a median age at diagnosis of 35 years.

History

Physical

Physical examination findings may be normal. Typical signs include the following:

Causes

Laboratory Studies

Thrombotic thrombocytopenic purpura (TTP) is a clinical diagnosis with no pathognomonic laboratory test findings.

Imaging Studies

CT scan of the head may be indicated to assess for intracranial bleeding and infarcts.

Other Tests

Bone marrow or gingival biopsy samples yield diagnostic lesions (hyaline thrombi) in 30-50% of cases. This is not a necessary test for diagnosis of TTP.

Emergency Department Care

Practice diagnostic criteria for initiating therapy are thrombocytopenia, schistocytosis, and significant elevations in serum LDH levels.

Plasma exchange

Initiate therapy within the first 24 hours of clinical presentation. Use a device with a wide-bore, 2-lumen catheter at the femoral site. Use blood-cell separators so that the patient's plasma is removed and replaced by standard replacement fluid, fresh frozen plasma (FFP), to eliminate ADAMTS-13 autoantibodies. Start with a single plasma volume and exchange FFP at a rate of 40 mL/kg of body mass. A plasma exchange twice a day may be necessary for resolution of thrombocytopenia and neurologic complications if the response to the initial daily exchange is poor. The procedure may be repeated for days to weeks for effect. The target platelet level is 150,000/mL, although this number is variable. A declining lactate dehydrogenase level, thrombocytopenia, and hemoglobin indicate a positive response to treatment. Complications include death, systemic infections, allergic reaction, catheter or venous thrombosis, serum sickness, fever, and hypocalcemia from citrate.[2]

Other treatments

Plasma infusion

Infusion of high-dose fresh-frozen plasma FFP (30 mL/kg) is used as a temporizing measure until the patient can be transferred to a facility where plasma exchange is available. Patients with congenital TTP undergo infusion therapy using 10-15 mL of FFP per kg of body weight every 2-3 weeks.[29] Infusion therapy has been effective in relapsing congenital TTP.

Cryosupernatant is the residual plasma fraction after the separation of cryoprecipitate that can be used in plasma exchange, but it has not been found to be better than FFP.

Platelet-depleted packed RBCs may be necessary for severe hemolytic anemia.

Splenectomy sequesters red blood cells, platelets, and B cells that produce antibodies to VWF-cleaving protease.[2] Splenectomy is performed occasionally to treat patients who do not respond to plasma exchange or who relapse chronically. Some patients benefit from splenectomy and others do not. The spleen is a major site of microvascular occlusive lesions in severe TTP.

Hemodialysis as supportive care for end-organ damage may be required.

Medication treatments

Contraindications

Platelet transfusion is contraindicated because it is associated with rapid deterioration. The platelet aggregation worsens with platelet transfusions. In some studies, extensive platelet aggregates were found throughout the CNS on postmortem examination.

Heparin and fibrinolytic agents are contraindicated due to their increase bleeding risk and ineffectiveness.[2]

Desmopressin (DDAVP) is contraindicated because it acts by releasing ULVWF from the endothelium into the circulating blood.

Consultations

Early consultation with a hematologist is beneficial because of the diagnostic and management complexity of TTP.

The differential diagnosis is extensive for thrombocytopenia, but early recognition of TTP is essential for the patient's survival.

Medication Summary

The goal of therapy is to reduce destruction of platelets.

Class Summary

These agents have immunosuppressant activity.

Prednisone (Sterapred)

Clinical Context:  Glucocorticoids inhibit phagocytosis of antibody-covered platelets. Treatment of hemolytic anemia during pregnancy is conservative unless disease is severe (use lowest dose of glucocorticoids). In neonates, if platelet count drops below 50-75 X 109/L, consider prednisone and exchange transfusions of immune globulin.

Class Summary

These agents inhibit key factors involved in immune reactions. In addition to the drugs listed below, treatment of refractory or relapsing TTP includes vincristine, a second-line therapy with an unknown mechanism of action. Vincristine is occasionally given to treat resistant cases, but it has no proven benefit. Dosing is 1 mg/m2, with a maximum dose of 2 mg, given weekly.

Rituximab (Rituxan)

Clinical Context:  Indicated to reduce signs and symptoms for moderately-to-severely active rheumatoid arthritis in combination with methotrexate. For use in adults who have experienced an inadequate response to one or more TNF antagonist therapies. Antibody genetically engineered. Chimeric murine/human monoclonal antibody directed against the CD20 antigen found on surface of B lymphocytes.

Cyclophosphamide (Cytoxan, Neosar)

Clinical Context:  Cyclic polypeptide that suppresses some humoral activity. Chemically related to nitrogen mustards. Activated in the liver to its active metabolite, 4-hydroxycyclophosphamide, which alkylates the target sites in susceptible cells in an all-or-none type reaction. As an alkylating agent, the mechanism of action of the active metabolites may involve cross-linking of DNA, which may interfere with growth of normal and neoplastic cells.

Biotransformed by cytochrome P-450 system to hydroxylated intermediates that break down to active phosphoramide mustard and acrolein. Interaction of phosphoramide mustard with DNA considered cytotoxic.

When used in autoimmune diseases, mechanism of action is thought to involve immunosuppression due to destruction of immune cells via DNA cross-linking.

In high doses, affects B cells by inhibiting clonal expansion and suppression of production of immunoglobulins. With long-term low-dose therapy, affects T-cell functions.

Cyclosporine (Neoral, Sandimmune)

Clinical Context:  An 11-amino acid cyclic peptide and natural product of fungi. Acts on T-cell replication and activity.

Specific modulator of T-cell function and an agent that depresses cell-mediated immune responses by inhibiting helper T-cell function. Preferential and reversible inhibition of T lymphocytes in G0 or G1 phase of cell cycle suggested.

Binds to cyclophilin, an intracellular protein, which, in turn, prevents formation of interleukin 2 and the subsequent recruitment of activated T cells.

Has about 30% bioavailability, but there is marked interindividual variability. Specifically inhibits T-lymphocyte function with minimal activity against B cells. Maximum suppression of T-lymphocyte proliferation requires that drug be present during first 24 h of antigenic exposure.

Suppresses some humoral immunity and, to a greater extent, cell-mediated immune reactions (eg, delayed hypersensitivity, allograft rejection, experimental allergic encephalomyelitis, and graft-vs-host disease) for a variety of organs.

Further Inpatient Care

Emergency medicine is acute care management to stabilize the patient with thrombotic thrombocytopenic purpura (TTP) for continued care. Follow-up is referred to internal medicine.

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Thrombotic thrombocytopenic purpura. Image courtesy of Deepak Sharma.