Tropical Myeloneuropathies

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Background

Tropical myeloneuropathies were described initially in tropical countries and are classified into 2 clinical syndromes that can have overlapping features—tropical ataxic neuropathy (TAN) and tropical spastic paraparesis (TSP). TAN and TSP are 2 separate diseases that are grouped together because they both occur predominantly in tropical countries. TSP also has been described in temperate countries (eg, southern Japan) as HTLV-1–associated myelopathy (HAM). However, TAN and HAM/TSP have different etiologies and clinical presentations. TAN is predominantly a sensory neuropathy, whereas HAM/TSP affects predominantly the spinal cord, resulting in an upper motor neuron syndrome.

Pathophysiology

Tropical ataxic neuropathy (TAN) is predominantly a sensory neuropathy. This disorder is encountered frequently in malnourished populations. TAN is observed quite frequently in populations that use large quantities of cassava in their diets. The bitter varieties of cassava have a relatively high content of cyanide. However, the exact mechanism of cyanide neurotoxicity is unknown. Cassava is resistant to drought, but levels of cyanogenic glycoside increase in the dry season, even in sweet varieties. Preparation of cassava by using soaking and grating methods removes 90% of glycoside content, thereby reducing the incidence of TAN. However, no actual causal relation between cassave and TAN has been established.[1] B-group vitamin deficiency was thought to produce this disorder, but treatment trials with such vitamins were not successful. In prisoners of war during World War II and the Korean War, TAN was thought to be caused by vitamin deficiencies and/or tropical malabsorption. In most cases, the affected individuals were deficient in group B vitamins. Despite all these theories, the actual etiology remains unknown.[1]

HTLV-1–associated myelopathy/tropical spastic paraparesis (HAM/TSP) is an upper motor neuron syndrome affecting primarily the lower extremities. While seronegative TSP has been described, by definition patients with HAM are infected with HTLV-1. HTLV-1 is a type C retrovirus, related to other human and primate lymphotropic viruses and the bovine leukemia virus. Several studies indicate that HTLV-1 transmission occurs through sexual or other intimate contact—intrauterine, perinatal, breastfeeding, sharing of needles by drug users, or blood transfusion from infected persons. One study showed that transfusion of HTLV-1 antibody-positive blood causes seroconversion in 60% of recipients. Transfusion of plasma alone in humans did not result in seroconversion.

The pathogenesis of HAM/TSP is still a matter of debate in the literature.[2] Whereas only a small proportion of HTLV-1–infected individuals develop HAM/TSP (1–4%), the mechanisms responsible for the progression of a HTLV-1 carrier state to clinical disease are not clear. No specific sequence differences have been found between HTLV-1 recovered from patients with HAM, those with adult T-cell leukemia/lymphoma also caused by HTLV-1 (ATLL), and HTLV-1 carriers. According to one theory, supply of HTLV-1–infected CD4 cells via the blood to the CNS is essential for development of CNS lesions. Both anatomically determined hemodynamic conditions and adhesion molecule-mediated interactions might contribute to localization of the lesions. Several studies have found a correlation between a high proviral load in CSF and peripheral blood and symptom severity in HAM/TSP. Another small study found an association of vitamin D receptor gene ApaI polymorphism with susceptibility to HAM/TSP.[3]

Following stimulation by HTLV-1 antigens on the surface of infected T cells in the CNS compartment, expansion of immunocompetent T cells directed against viral proteins may result in CNS tissue damage, which may be mediated by cytokines such as tumor necrosis factor (TNF) alpha.[4]

Epidemiology

Frequency

United States

HAM/TSP: Sporadic cases have been reported in the United States, mostly in immigrants from countries where this disease is endemic. In the United States, the lifetime risk of an HTLV-1–infected person developing TSP/HAM has been calculated to be 1.7–7%, similar to that reported for United Kingdom, Africa, and the Caribbean.

International

TAN and HAM/TSP: The incidence is difficult to estimate because of the insidious nature of these diseases.

TAN: The prevalence in some areas in Africa ranges from 29–34 cases per 1000 inhabitants. In 1981 during a drought, several epidemic outbreaks of cassava-related TAN were described. A particularly severe outbreak, called "mantakassa," took place in Mozambique. More than a thousand cases of spastic paraparesis were reported, affecting women and children in particular.[5]

HAM/TSP is common in regions of endemic HTLV-1, such as the Caribbean, equatorial Africa, Seychelles, southern Japan, and South America. However, it also has been reported from non-endemic areas, such as Europe and the United States. The prevalence in southern Japan is in the range of 8.6–128 cases per 100,000 inhabitants. An estimated 10–20 million individuals worldwide are carriers of HTLV-1.

TSP has been reported in India as well and one case series identified 25 patients. Only one patient was found to be positive for HTLV-1.{ref53]

Interestingly, the lifetime risk of an HTLV-1–infected person from Japan developing HAM/TSP has been calculated at 0.25%, which is much lower than in other countries.

Mortality/Morbidity

Studies on mortality and morbidity of TAN are very scarce; however, one study conducted in Nigeria showed high mortality in TAN population compared to the rest of the community. Interestingly, the mortality was not related to greater exposure to cyanide from cassava foods.[6]

HAM/TSP: The incubation period from infection to onset of myelopathic symptoms is believed to range from months to decades. This period is usually shorter in cases in which HTLV-1 was acquired by blood transfusion.

Age of onset at 50 years or older and high HTLV-1 proviral load are associated with a more rapid progression to a severe disability.[7]

Patients may survive for 10-40 years. Those who die early are paraplegics, who develop repeated urinary infection or pulmonary emboli.

Demographics

TAN is prevalent in Africa and tends to affect people from lower socioeconomic classes.

In Africa and the Caribbean, most patients with HAM/TSP are from the lower socioeconomic class and usually of black or mixed origin.

TAN and HAM/TSP generally affect women more than men, with a female-to-male ratio of 3:1. One small case series of 25 patients from India found more male predominance with a ratio of 2:1.[8]

TAN and HAM/TSP may occur at any age, with a peak in the third or fourth decade.

History

Tropical ataxic neuropathy (TAN)

See the list below:

HTLV-1–associated myelopathy/tropical spastic paraparesis (HAM/TSP)

See the list below:

Physical

Tropical ataxic neuropathy (TAN)

See the list below:

HTLV-1–associated myelopathy/tropical spastic paraparesis (HAM/TSP)

See the list below:

Causes

Tropical ataxic neuropathy (TAN)

In many cases, TAN is associated with excessive consumption of cassava, also known as the mandioca or tapioca plant, which is one of the most important sources of calories in the tropical countries. About 300 million people depend on it for subsistence, especially in the tropical regions of the Americas and in Africa. Cassava contains cyanide in the form of a cyanogenic glycoside, linamarin, which releases cyanide by the enzymatic action of linamarinase or by hydrolysis. Chronic cyanide intoxication has been confirmed as the cause of the TAN described in Nigeria and Tanzania. In these patients, treatment with high-dose vitamins was not satisfactory, suggesting that the vitamin deficiencies are not important in the etiology of the disease in these cases. There are two neurological disorders associated with cassava consumption: tropical ataxic neuropathy (TAN) and epidemic spastic paraparesis (konzo). Konzo is a syndrome that mainly affects young women and children.[12]

Processing of the cassava flour removes almost all the cyanide, but during a drought, these procedures tend to be shortened or ignored. Many people, especially women and children, eat the cassava raw or merely sun dried. The cyanide content of cassava increases during a drought, which may lead to a relatively higher incidence of severe cyanide intoxication.

Vitamin deficiencies and tropical malabsorption were the causes of TAN in prisoners of war. In most of the cases, the affected individuals were deficient in group B vitamins. One literature review suggests that chronic thiamine deficiency has a strong correlation with TAN.[1]

HTLV-1–associated myelopathy/tropical spastic paraparesis (HAM/TSP)

TSP is caused by an infection with HTLV-1.

Cases of TSP have been documented in which HTLV-1 was not detected.

Imaging Studies

HTLV-1–associated myelopathy/tropical spastic paraparesis (HAM/TSP)

Radiographs of the chest and myelogram are normal.

MRI of the spinal cord is indicated to rule out other causes of myelopathy and may show evidence of demyelination. Similar changes can occur in the periventricular white matter. Cord swelling or atrophy has been noted in a few cases.[13]

Other Tests

Tropical ataxic neuropathy (TAN)

Nerve conduction studies and electromyography (NCS/EMG) typically show reduction in sensory conduction velocities.

Motor nerve conduction study findings are usually normal.

Blood work including checking thiamine level, riboflavin level, albumin/total protein level, cholesterol, nicotinic acid, folate, pantothenic acid, and pyridoxine has been suggested, but there is no established diagnostic value in any of these.[14]

HTLV-1–associated myelopathy/tropical spastic paraparesis (HAM/TSP)

Electrophysiological abnormalities often are noted below the cervical spinal cord. The most common somatosensory evoked potential study (SEP) finding is abnormal central conduction time in the lower extremity. Electric brain stimulation (caution: not approved by the US Food and Drug Administration [FDA]) often reveals abnormal motor evoked potentials. Visual and auditory evoked potentials are occasionally abnormal.

NCS/EMG usually reveals slow conduction velocity and prolonged distal latency. These findings are suggestive of a demyelinating polyneuropathy. Needle EMG often shows increased insertional activity (fibrillations and positive sharp waves) in lower thoracic paraspinal muscles.

Between 25% and 60% of patients have a mild lymphocytic pleocytosis (< 50 cells/µL) in the cerebrospinal fluid (CSF). A higher percentage have mild protein elevation. Most patients have CSF oligoclonal bands.

Patients have high titers of HTLV-1 antibodies in serum and CSF. Enzyme-linked immunosorbent assay (ELISA) or the particle agglutination method is used to detect antibodies to core, envelope, and tax viral proteins. Western blot assay can confirm the diagnosis and distinguish HTLV-1 from HTLV-2. Polymerase chain reaction (PCR) for tax and pol also can be used on peripheral blood cells and CSF cells from infected individuals. PCR is able to distinguish HTLV-1 from HTLV-2. The HTLV-1 proviral load in peripheral blood mononuclear cells is 10- to 100-fold higher than that in CSF. Patients with high proviral load and no intrathecal synthesis antibodies to HTLV-1 have more rapid progression to serious clinical disease.[15]

Urodynamic examinations reveal mainly a detrusor external sphincter dyssynergia.

Sural nerve biopsy can reveal inflammatory infiltrates, axonal degeneration, and segmental demyelination.

Histologic Findings

Tropical ataxic neuropathy (TAN)

Autopsies in a group of ex-prisoners of war revealed posterior column demyelination, particularly of the fasciculus gracilis and the optic nerves (primarily the papillomacular fibers).

Nerve biopsies in a group of Nigerian patients showed nonspecific patchy demyelination with variable pericapillary cellular reaction and perineural fibrosis.

HTLV-1–associated myelopathy/tropical spastic paraparesis (HAM/TSP)

A histopathological study of 15 Jamaican patients revealed chronic inflammation with mononuclear cell infiltration of the meninges and the gray and white matter along with proliferation of the small parenchymal vessels and perivascular cuffing (primarily lymphocytes). Demyelination was most marked in the lateral columns but also was seen in nerve roots. In the areas of most severe demyelination, the axons were relatively well preserved. The gray matter was affected to a lesser degree, although changes were sometimes observed in anterior cells. The spinothalamic and spinocerebellar tracts usually showed less severe demyelination, but when damage was severe, focal spongiosis was seen.

A detailed Japanese study of 7 autopsies revealed the same pattern of inflammation. Immunohistochemistry demonstrated T-cell dominance. The numbers of CD4 and CD8 cells were equal in patients with shorter clinical courses. CD8 cells predominated over CD4 cells in patients with prolonged clinical courses. In situ PCR demonstrated HTLV-1–infected cells exclusively in the perivascular mononuclear infiltrates.

See the images below.



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Light microscopy of thoracic spinal cord of 2 patients with HTLV-1–associated myelopathy (Klüver-Barrera staining). (Source: Aye et al, 2000, Fig. 1.)....



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Light microscopy of perivascular inflammatory infiltration in the spinal cord (A, C) and in the brain (B, D) (A, B H&E; C, D Elastica Van Gieson; A, C....



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Light microscopy of the middle thoracic spinal cord (A, C, E) and subcortical white matter of the brain (B, D, F). Fibrotic changes are seen even in t....



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Immunostaining of the infiltrating cells in the thoracic spinal cord (A, C, E) and subcortical white matter of the brain (B, D, F) (A, B UCHL-1 [antib....



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Immunostaining of the infiltrating cells in the thoracic spinal cord (A, C) and subcortical white matter of brain (B, D) (A, B UCHL-1[antibody to CD45....

Medical Care

The mainstay of treatment is symptomatic. No standard treatment is available for tropical ataxic neuropathy (TAN) or HTLV-1–associated myelopathy/tropical spastic paraparesis (HAM/TSP).

Diet

Tropical ataxic neuropathy (TAN)

Supplementation with multivitamins is recommended, but in most cases only minor improvement occurs. In areas where cassava flour is used, following standard cassava processing measures is imperative.

Prevention

An important component in care of patients with tropical spastic paraparesis (TSP) is prevention of infection with HTLV-1 virus. Several studies indicate that transmission of the HTLV-1 virus occurs through sexual or other intimate contact (intrauterine, neonatal contact, perinatal exposure via breast milk, sharing of needles by drug abusers, and blood transfusion from infected persons). One study showed that transfusion of HTLV-1 antibody-positive blood causes seroconversion in 60% of recipients. Transfusion of plasma alone in humans did not result in seroconversion. Breastfeeding is contraindicated for mothers who are carriers of HTLV-1.

Medication Summary

A multicenter, randomized, double-blind study in 48 patients indicated that treatment with subcutaneous interferon alfa (Roferon) 3 million U (MU) twice a week was effective in more than 66.7%.[18] In another study, 32 patients were treated with interferon alfa; 20 patients showed a fair-to-excellent response in motor function. The effect was sustained, however, for only 1-3 months after the last injection.[16]

An open-label study showed that pentoxifylline 300 mg PO once a day induced clinical improvement in 14 of 15 patients. The authors postulated that the effect probably was due to TNF-alpha suppression.[19] In one open-label trial, 12 patients with HAM/TSP were treated with doses of interferon beta-1a of up to 60 µg twice weekly. During the trial, the therapy reduced the HTLV-1 tax messenger RNA load, but the HTLV-1 proviral DNA load remained unchanged. Some measures of motor function were improved, and no significant clinical progression occurred during therapy.[20]

A cross-sectional study of 13 patients treated with triple therapy of peg interferon (INF) as an immunomodulator, sodium valproate as a deacetylase inhibitor, and methylprednisolone as an anti-inflammatory agent showed marked improvement in spasticity and disability after 6 months of treatment.[21]

Mogamulizumab is a humanized anti-CCR4 monoclonal antibody that targets infected cells in patients with HAM/TSP. It was evaluated in an uncontrolled phase 1 and phase 2a trial in Japan, results of which showed a decrease in the number of HTLV-1-infected cells and inflammatory markers. Studies are still needed to demonstrate clinical efficacy of this medication.[22]

Interferon beta-1a (Avonex, Rebif)

Clinical Context:  For treatment of relapsing remitting MS. Avonex has also gained approval for treating patients with a first MS attack if brain MRI shows abnormalities characteristic of MS. Believed to act via ability to counteract cell surface expression of proinflammatory or pro-adhesion molecules on immune cells, among other effects. More studies needed to fully understand mechanisms of action. Only differs from interferon beta-1b in that it has amino acid sequence identical to that of natural compound and is glycosylated. Presence of glycosylation may lead to structural stability and presumably to higher biological potency.

Interferons act through common receptor that activates Jak/Stat pathway of signal transduction molecules, which, in turn, lead to activation of interferon-responsive genes. Interferon beta may decrease expression of B7-1 (a proinflammatory molecule) on surface of immune cells and increase levels of TGF-beta (anti-inflammatory) in circulation of MS patients. Interferon beta-1a is most convenient ABC drug to administer due to weekly schedule.

Peginterferon alfa 2a (Pegasys)

Clinical Context:  PEG-IFN alfa-2a consists of IFN alfa-2a attached to a 40-kd branched PEG molecule. Clinical and immunological improvements reported with use. It is predominantly metabolized by the liver. Used in combination with sodium valproate and prednisolone. 

Class Summary

These agents are naturally produced proteins with antiviral, antitumor, and immunomodulatory actions.

Pentoxifylline (Trental)

Clinical Context:  May alter rheology of red blood cells, which, in turn, reduces blood viscosity

Class Summary

These agents decrease the viscosity of blood.

Prednisolone (Orapred, Millipred)

Clinical Context:  Prednisolone inhibits inflammatory reactions associated with the disease by suppressing key components of the immune system. Administered in combination with valproate sodium and peginterferon alfa 2a. 

Class Summary

Corticosteroids have anti-inflammatory properties and cause profound and varied metabolic effects. They modify the body’s immune response to diverse stimuli.

Valproic acid (Depakote, Depakote ER, Depakote Sprinkles

Clinical Context:  Sodium valproate, as a histone deacetylase inhibitor, has positive effects on the reduction of proviral load (PVL) and improves recognition of infected cells by the immune system. Administered in combination with peginterferon alfa 2a and prednisolone. 

Class Summary

Agents that are histone deacetylase inhibitors may improve clinical aspects of the disease. 

Mogamulizumab (Mogamulizumab-kpkc, Poteligeo)

Clinical Context:  This anti-CCR4 antibody selectively targets and therefore reduces the number of HTLV1 infected cells. It also decreases the inflammatory markers in CSF, which may be associated with the efficacy of this drug. Side effects include rash, leukopenia, and lymphopenia. This was a phase 1-2a trial. A longer-term safety trial is being performed to obtain additional data on the safety of the medication. Further trials will be needed to assess the clinical efficacy of the drug

Class Summary

Monoclonal antibodies in this class may cause target cell depletion by binding to CCR4 target cells. 

Author

Emad R Noor, MBChB, Assistant Professor of Neurology and Clinical Neurophysiology, Hackensack Meridian School of Medicine; Attending Neurologist/Clinical Neurophysiologist, Neuroscience Institute at JFK Medical Center

Disclosure: Nothing to disclose.

Coauthor(s)

Gayane Avagyan, MD, MPH, Resident Physician, Department of Neurology, JFK University Medical Center, Hackensack Meridian School of Medicine

Disclosure: Nothing to disclose.

Hasnain Arshad, MD, Resident Physician, Department of Neurology, JFK University Medical Center, Hackensack Meridian School of Medicine

Disclosure: Nothing to disclose.

Mahsa Mohajery, MD, Chief Resident Physician, Department of Neurology, JFK University Medical Center, Hackensack Meridian School of Medicine

Disclosure: Nothing to disclose.

Specialty Editors

Francisco Talavera, PharmD, PhD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Florian P Thomas, MD, PhD, MA, MS, Chair, Neuroscience Institute and Department of Neurology, Director, Hereditary Neuropathy Center, Co-Director, Center for Memory Loss and Brain Health, Co-Director, ALS Center, Hackensack University Medical Center; Associate Dean of Faculty, Founding Chair and Professor, Department of Neurology, Hackensack Meridian School of Medicine

Disclosure: Nothing to disclose.

Chief Editor

Niranjan N Singh, MBBS, MD, DM, FAHS, FAANEM, Adjunct Associate Professor of Neurology, University of Missouri-Columbia School of Medicine; Medical Director of St Mary's Stroke Program, SSM Neurosciences Institute, SSM Health

Disclosure: Nothing to disclose.

Additional Contributors

Carmel Armon, MD, MSc, MHS, Chair, Department of Neurology, Assaf Harofeh Medical Center, Tel Aviv University Sackler Faculty of Medicine, Israel

Disclosure: Received research grant from: Neuronix Ltd, Yoqnea'm, Israel<br/>Received income in an amount equal to or greater than $250 from: JNS - Associate Editor. UpToDate - Author Royalties.

Friedhelm Sandbrink, MD, Assistant Professor of Neurology, Georgetown University School of Medicine; Assistant Clinical Professor of Neurology, George Washington University School of Medicine and Health Sciences; Director, EMG Laboratory and Chief, Chronic Pain Clinic, Department of Neurology, Washington Veterans Affairs Medical Center

Disclosure: Nothing to disclose.

Acknowledgements

Eliad Culcea, MD Consulting Staff, Department of Neurology, Benefis Medical Group

Eliad Culcea, MD is a member of the following medical societies: American Academy of Neurology and American Association of Neuromuscular and Electrodiagnostic Medicine

Disclosure: Nothing to disclose.

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Light microscopy of thoracic spinal cord of 2 patients with HTLV-1–associated myelopathy (Klüver-Barrera staining). (Source: Aye et al, 2000, Fig. 1.)

Light microscopy of perivascular inflammatory infiltration in the spinal cord (A, C) and in the brain (B, D) (A, B H&E; C, D Elastica Van Gieson; A, C x400; B, D x200). (Source: Aye et al, 2000, Fig. 2.)

Light microscopy of the middle thoracic spinal cord (A, C, E) and subcortical white matter of the brain (B, D, F). Fibrotic changes are seen even in the capillaries (arrows) (A, B, F H&E; C-E Elastica van Gieson; A, C, D, F x400; B x300; E x100). (Source: Aye et al, 2000, Fig. 3.)

Immunostaining of the infiltrating cells in the thoracic spinal cord (A, C, E) and subcortical white matter of the brain (B, D, F) (A, B UCHL-1 [antibody to CD45RO]; C, D CD8; E, F OPD-4; A-F x150). (Source: Aye et al, 2000, Fig. 4.)

Immunostaining of the infiltrating cells in the thoracic spinal cord (A, C) and subcortical white matter of brain (B, D) (A, B UCHL-1[antibody to CD45RO]; C, D CD8; A-D x160). (Source: Aye et al, 2000, Fig. 5.)

Light microscopy of thoracic spinal cord of 2 patients with HTLV-1–associated myelopathy (Klüver-Barrera staining). (Source: Aye et al, 2000, Fig. 1.)

Light microscopy of perivascular inflammatory infiltration in the spinal cord (A, C) and in the brain (B, D) (A, B H&E; C, D Elastica Van Gieson; A, C x400; B, D x200). (Source: Aye et al, 2000, Fig. 2.)

Light microscopy of the middle thoracic spinal cord (A, C, E) and subcortical white matter of the brain (B, D, F). Fibrotic changes are seen even in the capillaries (arrows) (A, B, F H&E; C-E Elastica van Gieson; A, C, D, F x400; B x300; E x100). (Source: Aye et al, 2000, Fig. 3.)

Immunostaining of the infiltrating cells in the thoracic spinal cord (A, C, E) and subcortical white matter of the brain (B, D, F) (A, B UCHL-1 [antibody to CD45RO]; C, D CD8; E, F OPD-4; A-F x150). (Source: Aye et al, 2000, Fig. 4.)

Immunostaining of the infiltrating cells in the thoracic spinal cord (A, C) and subcortical white matter of brain (B, D) (A, B UCHL-1[antibody to CD45RO]; C, D CD8; A-D x160). (Source: Aye et al, 2000, Fig. 5.)