Infectious and Hereditary Myelopathies

Human T-cell Lymphocytic Virus-1 (HTLV-1) Myelopathy. This disorder, also known as tropical spastic paraparesis/HTLV-1–associated myelopathy (TSP/HAM), may be acquired as a sexually transmitted disease, particularly in the Caribbean, eastern South America, equatorial Africa, and southern Japan, where HTLV-1 is endemic. Transmission is by semen, blood or its products, and breast milk. Only a small proportion of HTLV-1 carriers develop the myelopathy after a latent period that may be many years. The mid- to lower thoracic cord is most severely affected, especially the lateral columns and corticospinal tracts. Patients typically present in the midfourth to fifth decades with a slowly progressive spastic paraparesis and paraparesthesis. Bladder disturbances, impotence, and constipation also develop. Cerebral, cerebellar, and cranial and peripheral nerve dysfunction may occur, as may HTLV-1–associated systemic disorders.

MRI may show spinal atrophy and sometimes the presence of cerebral periventricular white matter lesions. The cerebrospinal fluid (CSF) may contain a mononuclear pleocytosis or elevated protein concentration, with oligoclonal bands. Anti–HTLV-1 antibodies are present in CSF, and polymerase chain reaction (PCR) is positive for the virus. There is no effective treatment for HTLV-1–related myelopathy other than symptomatic measures. Preventive measures to reduce transmission include screening blood products, sexual education, and use of formula rather than breast milk of infected mothers.

Schistosomal Myelopathy. Millions of persons worldwide are infected with schistosomes, parasitic blood flukes that are transmitted to humans in contact with fresh water. Neurologic involvement is relatively uncommon in schistosomiasis, but an inflammatory myeloradiculopathy may occur, especially with Schistosoma mansoni and S. haematobium infection (cerebral involvement is more common with S. japonicum infection). Schistosoma organisms are found in tropical areas such as the Nile and Amazon River basins, Lake Victoria in East-Central Africa, the Caribbean, and Middle East. Infective larvae (cercariae) are released into fresh water by infected snails (the intermediate host). After they penetrate the skin of humans, the parasite migrates to selected vascular beds, depending on species. After reproduction of adult male and female parasites, eggs are deposited in various tissues and eventually exit the body in urine or feces; in the right context, the eggs open to release free-swimming larvae (miracidia) that infect snails. Involvement of the human nervous system probably occurs by transport of eggs into the central nervous system (CNS) circulation by collateral veins or by aberrant migration of adult worms.

Spinal cord involvement, often at the level of the conus medullaris, often follows an initial radiculopathy and may progress acutely or subacutely. Patients may present with back or root pain, paraparesis, sensory abnormalities, and bladder dysfunction. Expanding granulomatous inflammation may lead to a progressive myelopathy; in some instances, an acute transverse myelitis leads to a catastrophic deficit.

The diagnosis should be suspected in any recent traveler to an endemic area. An eosinophilia in the blood, and sometimes the CSF, is suggestive but may not be present. Enlargement and gadolinium enhancement of the thoracolumbar spinal cord may be evident on magnetic resonance imaging (MRI). Serologic tests may reveal evidence of schistosomal exposure. Rapid diagnosis and early treatment with praziquantel and corticosteroids improves the ultimate prognosis.

Hereditary Spastic Paraplegia. This term refers to a group of clinically heterogeneous hereditary disorders in which a progressive spastic weakness affects the lower extremities. Patients differ according to the mode of inheritance and genetic locus (when known). Age at onset and the severity of symptoms also vary widely. Corticospinal tract and posterior column involvement occurs from a dying-back process affecting the distal ends of long axons, causing the motor and sensory deficits. The disorder occurs most often with autosomal dominant inheritance, but autosomal recessive and X-linked inheritance also occur. Many different genes and genetic loci have been identified.

Patients with the “pure” form of the disorder present with progressive spasticity, hyperreflexia, and weakness of the lower extremities. Vibratory sensation is sometimes mildly decreased. Occasional patients experience sphincter disturbances manifested by a spastic bladder with urgency and frequency. In the complicated form, other findings include cognitive impairment, aphasia, dysarthria, dysphagia, pale optic discs, nystagmus, cataracts, upper extremity weakness, motor neuronopathy, sphincter disturbances, and muscle wasting; neuroimaging may reveal cerebellar or cerebral atrophy, hydrocephalus, white matter changes, and a thin corpus callosum.

A positive family history is one of the most important diagnostic clues. Genetic screening may be supportive, but, in many cases, the genetic abnormality has yet to be identified. MRI helps to exclude other structural causes of the patient’s symptoms and sometimes reveals marked spinal atrophy. No specific therapy is available. Management is therefore supportive and treatment is symptomatic.

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