Human T-Cell Leukaemia Virus Type 1-Associated Myelopathy in Patients with Rheumatoid Arthritis: A Case Series Highlighting Functional Disability and Diagnostic Challenges.

OBJECTIVES: Although rheumatoid arthritis (RA) and human T-cell leukaemia virus type 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) occasionally coexist, their clinical characteristics and impact on patient outcomes remain poorly elucidated. METHODS: We conducted a retrospective case series of five patients with RA complicated by HAM/TSP (HAM-RA) enrolled in the HTLV-1 Positive Rheumatoid Arthritis Miyazaki Registry. Data on clinical characteristics, disease course, functional status, quality of life and HTLV-1-associated parameters were reviewed. Age- and sex-matched patients with HTLV-1-positive RA and HTLV-1-negative RA served as comparison groups. RESULTS: All patients were women, (median age, 67 years). HAM/TSP preceded RA onset in two patients, whereas RA developed first in three. Neurological disability substantially differed, with Osame Motor Disability Scores of 2-11; three patients necessitated wheelchair use. Despite comparable RA disease activity, patients with HAM-RA demonstrated worse physical function and health-related quality of life than matched controls. Patients with HAM-RA tended to have higher HTLV-1 proviral loads (PVLs) than those with HTLV-1-positive RA without HAM/TSP. CONCLUSIONS: HAM/TSP may develop before or after RA onset and cause substantial functional disability despite satisfactory control of arthritis. Knowledge of HTLV-1 infection status may facilitate consideration of HAM/TSP and timely neurological evaluation. Considering the high PVL in patients with HAM-RA and its association with elevated adult T-cell leukaemia/lymphoma (ATL) risk, cautious long-term monitoring for ATL development may be warranted.