BackgroundHuman T-cell lymphotropic virus type 1 (HTLV-1) infection is associated not only with some severe manifestations, such as HTLV-1-associated myelopathy (HAM) and ATLL, but also with other, less severe conditions. Some studies have reported neurologic manifestations that did not meet all the criteria for the diagnosis of HAM in individuals infected with HTLV-1; these conditions may later progress to HAM or constitute an intermediate clinical form, between asymptomatic HTLV-1 carriers and those with full myelopathy. This study evaluated the prognostic value and looked for a possible association of those parameters with the intermediate syndrome (IS) status and HAM status.MethodsProviral load (PVL), spontaneous lymphoproliferation, interferon (IFN)-γ spontaneous production was quantified in samples of asymptomatic and HAM patients, as well as patients with IS.ResultsThe critical age range was 50–60 years for IS outcome and more of 60 years for HAM outcome, with an increased risk of 2.5-fold for IS and 6.8-fold for HAM. IFN-γ was increased in patients with IS compared with asymptomatic carriers (ACs) (p = 0.007) and in patients with HAM compared with ACs (p = 0.03). Lymphoproliferation was increased in patients with HAM vs ACs (p = 0.0001) and patients with IS (p = 0.0001). PVL was similar between groups.ConclusionIFN-γ has high specificity of prediction of subject remain asymptomatic compared with PVL and lymphoproliferation assay tests. IFN-γ has been shown to be a biomarker of progression to intermediate stage and to HAM. The association of other markers with manifestations associated with HTLV-1 infection that does not meet the HAM criteria should be verified.