Synonyms of HTLV Type I and Type II
- acute T-cell leukemia
- acute T-cell lymphoma
- HTLV-I associated myelopathy
- tropical spastic paraparesis
HTLV-I was first isolated in 1980 from a patient originally thought to have a cutaneous lymphoma. It became clear that it was a distinct form of lymphoma, which was designated as acute T-cell leukemia/ lymphoma (ATL). Some years later, different groups in Martinique and Japan described an association between a chronic disease of the spinal cord and HTLV-I infection, which was later named HTLV-I associated myelopathy/tropical spastic paraparesis (HAM/TSP). Since then, several other conditions have been linked to HTLV infection.
It is estimated that between 10 and 20 million people are infected by HTLV-I in the world. Only 0.25-2% of the infected individuals will develop a progressive neurologic disease named HTLV-I associated myelopathy/tropical spastic paraparesis (HAM/TSP). Approximately 2-5% of HTLV-I carriers will develop ATL. More rarely, HTLV-I may lead to arthropathy, uveitis (inflammation of the eye), pneumonitis and thyroid problems. Areas of the world that are endemic to the HTLV-1 virus are the Caribbean, southern Japan, equatorial Africa, Middle East, South America, and Melanesia.
Signs & Symptoms
HAM/TSP usually has an insidious onset and chronic evolution. Initial symptoms are subtle and include gait problems, unexplained falls, low back pain, constipation, urinary urgency/incontinence and numbness or pain in the lower limbs. Over the years, progressive leg weakness ensues followed by the exacerbation of the urinary and sensory symptoms. The prognosis of the neurological disability is variable. While some patients are still ambulatory after one or two decades of disease, others may be confined to a wheelchair months after onset of disease.
HTLV-I-induced ATL has four different subtypes: acute, lymphomatous, chronic and smoldering. Each of them has a distinct clinical picture and evolution. A combination of skin and bone lesions, pulmonary infiltrates, elevation of serum calcium, enlargement of the liver, spleen and lymph nodes, and opportunistic infections may be present.
The transmission of HIV (the virus responsible for AIDS) and HTLV-Type I infection are similar. Infection can occur by sexual contact with an infected individual, through sharing of contaminated needles and syringes by intravenous drug users, or as the result of a transfusion of contaminated blood. Mother to child transmission may happen through perinatal exposure or most often through breast-feeding. The intrauterine transmission is very rare.
The cause of HAM/TSP has not been completely understood to date, since most infected individuals will never develop any symptoms or signs of disease. Theories include a direct effect of the virus on the central nervous system or an autoimmune process. In ATL, there is a disordered clonal expansion of blood cells called CD4+ T lymphocytes, which are infected by the virus.
The diagnosis of HTLV-I infection is usually made by detection of antibodies against the virus in the blood or cerebrospinal fluid. In some cases, techniques that detect HTLV-I genome in infected cells may be necessary.
Concerning HAM/TSP, many HTLV-I infected individuals remain asymptomatic throughout their lives, beyond the positive laboratory findings of HTLV-I infection. Thus, it is necessary to rule out the presence of typical symptoms and exclusion of other disorders than can present in the same way (other infections, vitamin deficiencies, genetic disorders and compression of the spinal cord).
ATL is diagnosed based on the clinical picture, evidence of HTLV-I integration into host cells, peripheral blood analysis and biopsy of affected sites. Atypical lymphocytes named flower cells may be present on examination of blood smears. Elevation of serum calcium (hypercalcemia) is common.