Comparison of the polymerase chain reaction and serology for the diagnosis of HTLV-I infection.

Human T-lymphotropic virus type I (HTLV-I) is associated with tropical spastic paraparesis (TSP) and adult T-cell leukaemia/ lymphoma (ATL). HTLV-I seroconversion may not take place for many years after infection and some patients develop relatively low concentrations of antibodies that are difficult to detect by means of conventional assays. Some serologic tests also yield high rates of false-positive results. We therefore decided to determine whether the polymerase chain reaction (PCR) might be more sensitive than serology for the diagnosis of HTLV-I infection. Samples of serum and of peripheral blood mononuclear cells were obtained from 50 patients with spastic myelopathy and nine with T-cell neoplasia. The serum samples of serum were tested for the presence of HTLV-I antibodies by means of an enzyme-linked immunosorbent assay (ELISA). Positive results were confirmed by Western blot (WB) assay. DNA was extracted from the peripheral blood mononuclear cells and a PCR performed by use of two primer pairs from the env and pol regions of the proviral genome. Seven of the 50 patients with myelopathy and none of those with T-cell neoplasia had detectable antibodies to HTLV-I and all seven were PCR positive. One patient with an indeterminate WB result and one who was HTLV-I antibody-negative, both with myelopathy, were also PCR-positive. In this study, PCR was found to be more sensitive than serology for the diagnosis of HTLV-I infection. PCR should therefore be considered for selected HTLV-I antibody-negative patients with unexplained spastic myelopathy or T-cell neoplasia.