Histopathological differences between human T-lymphotropic virus type 1-positive and human T-lymphotropic virus type 1-negative polymyositis

Abstract

Objectives: Epidemiological studies show that human T-lymphotropic virus type 1 (HTLV-1) is closely associated with polymyositis (PM). However, the pathogenic roles of HTLV-1 in PM remain unknown. The present study aims to assess skeletal muscle morphology in the presence of HTLV-1 infection to compare the histopathological findings of HTLV-1-positive and HTLV-1-negative PM. Methods: Among the 68 patients with inflammatory myopathy diagnosed through muscle biopsy over the previous 10 years at Kagoshima University Hospital, we retrospectively selected 21 patients with PM not associated with any other disease; we evaluated HTLV-1 positivity through serology, confirmed it by nested polymerase chain reaction using DNA extracted from muscles, and then assessed the tissue viral load. Meticulous histopathological examination was carried out using routine histochemical and immunohistochemical staining, and specimens from selected cases were examined by electron microscopy. Results: The clinical and histopathological findings of muscle biopsy specimens of HTLV-1-positive (n = 11) and HTLV-1-negative PM cases (n = 10) were compared. Compared with HTLV-1-negative patients, HTLV-1-positive patients showed protracted clinical courses, prominent endomysial infiltrates, infrequent necrotic fibers and prominent regenerative activities. Furthermore, they showed frequent cytochrome c oxidase deficiency and ultrastructural abnormalities in mitochondria. Conclusions: These differences are significant, but not specific to HTLV-1-positive PM. Therefore, HTLV-1 might induce the clinical and histopathological modifications of PM observed in the present study. (Clin. Exp. Neuroimmunol. doi: 10.1111/j.1759-1961.2011.00017.x, January 2011)