P.206 - Anti-HMGCR antibody positive myopathy shows bcl-2-positive lymphocyte follicles

Abstract

Idiopathic inflammatory myopathies (IIM) are classified in five categories including polymyositis (PM), dermatomyositis (DM), immune-mediated necrotizing myopathy (IMNM), inclusion body myositis (IBM), and non-specific myositis. Muscle pathologies are required elements for the classification of IIM. In addition to the pathological patterns, more than 15 autoantibodies specific for myositis are already recognized. Recently, Anti-HMG-CoA reductase (HMGCR) antibody is reported to be one of the myositis-specific autoantibodies. HMGCR affects survival of low grade lymphoma by regulating mevalonate pathway. In this study, we aimed to determine the association between anti-HMGCR antibody positive IMNM and a specific morphological phenotype. The muscle biopsy specimens of anti-HMGCR antibody positive IMNM (n = 10), other IMNM (n = 20), PM (n = 13), DM (n = 11), IBM (n = 15), and histologically normal control (n = 5) were examined. These specimens were subjected to routine histochemistry and immunohistochemistry. We also examined skin biopsy specimens from anti-HMGCR antibody positive IMNM (n = 4), other IMNM (n = 4), and DM (n = 8) cases with skin lesions. In anti-HMGCR antibody positive patients, perivascular bcl-2 positive lymphocyte infiltrations were frequently observed in muscle and skin. About 50% of all inflammatory cells were positive for bcl-2. In addition, extranodal lymphocytic follicles are scatterd in 40% of cases with anti-HMGCR antibody. In these follicles, lymophcytes were positive for bcl-2, CD3, CD4, CD8, and CD79a, but not for CD10, CD20. Abnormal lymphocytes were not observed. In IIM except for anti-HMGCR antibody positive IMNM, bcl-2 positive lymphocytes were less than 5% of all inflammatory cells. Perivascular bcl-2 positive lymphocyte infiltration and extranodal lymphocytic follicle might be characteristic findings of anti-HMGCR antibody positive IMNM.