Tropical Spastic Paraparesis/HTLV-1–Associated Myelopathy (TSP/HAM)
Tropical spastic paraparesis/HTLV-1–associated myelopathy (TSP/HAM) is a slowly progressive viral immune-mediated disorder of the spinal cord caused by the human T-lymphotropic virus 1 (HTLV-1). It causes spastic weakness of both legs. Diagnosis is by serologic and PCR tests of serum and CSF. Treatment includes supportive care and possibly immunosuppressive therapies.
(See also Overview of Spinal Cord Disorders.)
The HTLV-1 retrovirus is transmitted via sexual contact, IV drug use, or exposure to infected blood or from mother to child via breastfeeding. It is most common among prostitutes, IV drug users, hemodialysis patients, and people from endemic areas such as equatorial regions, southern Japan, and parts of South America.
TSP/HAM affects < 2% of HTLV-1 carriers. It is more common among women; this finding is consistent with the higher prevalence of HTLV-1 infection in women. HTLV-2 may cause a similar disorder.
The virus resides in T cells in blood and CSF. CD4+ memory T cells, CD8+ cytotoxic T cells, and macrophages infiltrate the perivascular areas and parenchyma of the spinal cord; astrocytosis occurs. For several years after onset of neurologic symptoms, inflammation of spinal gray and white matter progresses, causing preferential degeneration of the lateral and posterior columns. Myelin and axons in the anterior columns are also lost.
TSP/HAM is suggested by typical neurologic deficits that are otherwise unexplained, particularly in patients with risk factors.
Serum and CSF serologic tests, PCR tests, and spinal cord MRI are indicated. If CSF-to-serum ratio of HTLV-1 antibodies is > 1 or if PCR detects HTLV-1 antigen in CSF, the diagnosis is very likely. Protein and Ig levels in CSF may also be elevated, often with oligoclonal bands; lymphocytic pleocytosis occurs in up to 50% of patients. Spinal cord lesions often appear hyperintense on T2-weighted MRI.