AUTOIMMUNE & INFLAMMATORY NMD: EP.06 Granulomatous myositis, perimysial pathology and immune-mediated necrotizing myopathy in anti-PL7 antisynthetase syndrome

Abstract

A 72-year-old woman presented with a 6-month history of anorexia, weight loss (-14kg) and myalgia in upper limbs. Clinical examination showed moderate proximal muscle weakness in upper limbs and crepitation at lung auscultation, but no skin rash nor joint involvement. Biological assessment disclosed increased C-reactive protein (68µM) and creatine-kinase (3800 U/l) serum levels and anti-nuclear and -PL7 autoantibodies at immunological screening. Thoracic CT-scan showed abnormalities consistent with interstitial pneumonia. Search for cancer was negative. Deltoid muscle biopsy revealed an unusual myositis combining (i) randomly distributed myonecrosis with complement activation and membrane attack complex deposition at the surface of non-necrotic myofibers, (ii) perimysial inflammation with collagenolysis, and (iii) non-caseous granulomas. Immunohistochemical techniques revealed ubiquitous myofiber expression of major histocompatibility complex (MHC)-class I and multifocal MHC-II myofiber expression witnessing interferon-gamma signature. The peculiar histopathological features found in this patient was strikingly similar to that previously reported in anti-PL7 myositis, suggesting that anti-PL7 could be the marker of a specific subtype of overlap myositis.