HTLV-1 Associated Myelopathy

HTLV-1 associated myelopathy is a slowly progressive spastic paraparesis caused by chronic infection with human T lymphotropic virus type 1. It occurs in a small proportion (estimated at approximately one to two percent) of individuals infected with this retrovirus over their lifetime.

Endemic regions include Japan, the Caribbean, parts of South America, and sub Saharan Africa. The virus is transmitted through breastfeeding, sexual contact, and blood or blood product exposure.

The same viral infection carries a distinct, separate association with adult T cell leukaemia lymphoma. Confirmed HTLV-1 infection identified in the context of this myelopathy therefore carries broader implications, requiring corresponding surveillance and patient counselling beyond the neurological manifestation itself.

Pathophysiology

• The precise mechanism of myelopathy in the small proportion of chronically infected individuals who develop it remains incompletely understood. It is believed to reflect an immune mediated inflammatory process directed against HTLV-1 infected lymphocytes that have infiltrated the spinal cord, rather than direct viral cytopathic destruction of neural tissue.
• Chronic inflammation predominantly affects the thoracic spinal cord and produces progressive corticospinal tract demyelination and axonal loss.
• Risk of developing myelopathy is influenced by the route and timing of acquisition, proviral load, and host genetic and immunological factors. Transfusion acquired infection carries a higher subsequent myelopathy risk than perinatal or sexual transmission.
• The majority of chronically infected individuals never develop this or any other HTLV-1 associated complication.

• The typical presentation is slowly progressive, symmetrical or asymmetrical spastic weakness of the lower limbs, developing over months to years. It reflects the predominantly thoracic corticospinal tract localisation of the inflammatory process.
• Lower back pain, sensory disturbance (typically less prominent than the motor features) and bladder dysfunction accompany it. Bladder dysfunction is urinary urgency and frequency, progressing to more significant voiding dysfunction.
• Examination typically reveals spasticity, hyperreflexia and extensor plantar responses in the lower limbs.
• A sensory level, where present, is generally less sharply demarcated than that typically seen with a compressive structural spinal cord lesion. This is an important point supporting the distinction from more acute or structural causes of myelopathy.
• The upper limbs are generally relatively spared, or affected only mildly and late in the disease course, consistent with the predominantly thoracic localisation of the pathological process.
• Actively seek a relevant epidemiological history in any patient presenting with a compatible chronic progressive spastic paraparesis.
• This includes birth in or residence in an endemic region, and a history of breastfeeding as an infant (the dominant global transmission route).
• It also includes relevant sexual history, or history of blood transfusion (particularly in regions or time periods without established HTLV-1 blood donor screening).

• Serological testing for HTLV-1 antibody establishes the underlying viral infection, with confirmatory testing (Western blot or polymerase chain reaction based confirmation) where initial screening is positive.
• The absolute proportion of infected individuals who develop myelopathy is low. Positive serology alone in a patient with an alternative, unrelated cause of spastic paraparesis does not necessarily establish causation and requires careful clinical correlation.
• Cerebrospinal fluid examination typically shows a mild lymphocytic pleocytosis and elevated protein. Demonstration of HTLV-1 specific antibody within the cerebrospinal fluid provides further support for the diagnosis.
• Where measured, an elevated cerebrospinal fluid to serum antibody ratio supports intrathecal antibody production rather than simple passive transfer from serum.
• Magnetic resonance imaging of the spinal cord may show non specific signal change or mild atrophy, particularly affecting the thoracic cord. Imaging findings can be relatively unremarkable relative to the clinical severity.
• Imaging is also essential to exclude alternative structural or compressive causes of the spastic paraparesis before this diagnosis is accepted.
• The differential diagnosis for chronic progressive spastic paraparesis is broad. It includes multiple sclerosis, hereditary spastic paraparesis, spinal cord compression from a structural lesion, and vitamin B12 deficiency related subacute combined degeneration, among others.
• Full exclusion of these alternative causes through appropriate imaging and targeted laboratory testing is an essential component of the diagnostic evaluation alongside confirmation of HTLV-1 infection itself.

• There is no specific antiviral treatment with established, consistent efficacy for HTLV-1 associated myelopathy. Management is therefore predominantly symptomatic and rehabilitative, addressing the functional consequences of the progressive spastic paraparesis.
• Corticosteroids may provide modest symptomatic benefit in some patients, particularly during periods of more active disease progression. Sustained long term benefit is not well established, and use requires balancing against the cumulative risks of prolonged corticosteroid exposure.
• Interferon alfa has been used in some settings with reported modest benefit, and other immunomodulatory approaches have been explored.
• Robust evidence supporting a clearly effective disease modifying treatment remains limited, reflecting the relative rarity of this condition and the resulting paucity of large scale controlled treatment trials.
• Spasticity management follows standard principles applicable to spastic paraparesis from any cause. This includes baclofen or tizanidine for pharmacological spasticity control, together with regular physiotherapy to maintain mobility, prevent contracture and optimise functional capacity.
• Bladder dysfunction is managed according to the pattern identified on urological assessment. Options are anticholinergic medication for urgency symptoms and intermittent self catheterisation where voiding dysfunction is significant.
• Regular urological follow up is needed given the associated risk of recurrent urinary tract infection in this population.
• Confirmed HTLV-1 infection has broader implications beyond the myelopathy itself. Patients should receive counselling on transmission risk reduction: safe sexual practices, and avoidance of breastfeeding where infection is identified in a mother of childbearing age, given the risk of vertical transmission.
• They should also receive information on the distinct, separate association with adult T cell leukaemia lymphoma.
• Routine specific haematological surveillance for this malignancy in the absence of relevant symptoms is not generally recommended, given the relatively low absolute risk and lack of established benefit from active surveillance in asymptomatic carriers.
• Screening of relevant sexual partners and, where clinically relevant, family members is advised. Appropriate public health and specialist infectious disease or neurology involvement supports management of both the individual patient and the implications of the diagnosis for their close contacts.