Mixed connective tissue disease with interstitial pneumonia in HTLV-1 carrier: case report and review of the literature.

We report on a carrier of human T-lymphotropic virus type 1 (HTLV-1) who developed mixed connective tissue disease (MCTD). This patient suddenly manifested clinical symptoms and interstitial pneumonia ascribable to MCTD following long-term infection with HTLV-1. After initiation of oral prednisolone all manifestations quickly improved in parallel with a decrease in inflammatory reactions. In this patient HTLV-1 infection might have played an important role in the pathogenesis of MCTD. Since HTLV-1 can cause adult T-cell leukemia and HTLV-1-associated myelopathy, and also collagen diseases including MCTD, careful observation is necessary even in a carrier, particularly when autoantibodies are detectable in serum.