Epidemiological studies have firmly established the association between HTLV-I infection and the development of this slowly progressive neurologic syndrome.
Sensory changes are less common.
The CSF of patients with HAM may demonstrate high protein and oligoclonal bands, indicative of intrathecal antibody synthesis. Patients with HAM will usually have a progressive course, leading to lower limb paralysis and, possibly, arm involvement. HAM is rarely fatal, however. Autopsy studies have revealed low levels of HTLV-I within the spinal cord of HAM patients, indicating that direct cytolysis by virus infection may not cause the myelopathy. Those patients infected with HTLV-I in whom this complication develops have a robust cytolytic T cell response to the viral protein tax.