Muscle pathology of antisynthetase syndrome according to antibody subtypes

Abstract

AbstractAntisynthetase syndrome is recently recognized as one of the major entities of autoimmune myositis. The prototype of antisynthetase syndrome is anti-Jo-1 antibody associated syndrome while the syndromes associated with non-Jo-1 antisynthetase antibodies are clinically and pathologically less recognized. Identifying a non-Jo-1 antisynthetase syndrome patient could be challenging because the full panel serology test may not be available at the time of diagnosis in addition to technical difficulty especially for anti-OJ antibody detection. This study aimed to characterize the muscle pathology and explore the utility of myofiber HLA-DR expression for the diagnosis of antisynthetase syndrome.We retrospectively compared 212 muscle biopsies from antisynthetase syndrome patients regarding four pathology domains and histology of interests using t test and Fisher’s exact test as appropriate. We further compared the myofiber HLA-DR expression pattern in antisynthetase syndrome with 602 muscle biopsies with other autoimmune myositis and 140 muscle biopsies with other myopathies potentially containing myositis-like pathology and calculated sensitivity, specificity, positive predictive value, and negative predictive value to identify the most diagnostic pattern for antisynthetase syndrome.The most common myopathological pattern in antisynthetase syndrome was necrotizing myopathy (46.2%). Perifascular necrosis was present in 28.3% of antisynthetase syndrome. Anti-OJ and anti-EJ antisynthetase syndrome were associated with high muscle fiber scores. Anti-OJ also showed high inflammatory domain score. If muscle biopsies suspicious for dermatomyositis by sarcoplasmic myxovirus resistance protein A immunohistochemical expression and those with inclusion body myositis clinicopathology were excluded, myofiber HLA-DR expression was the most diagnostic of antisynthetase syndrome with 95.4% specificity, 61.2% sensitivity, 85.9% positive predictive value, and 84.2% negative predictive value. HLA-DR expression in perifascicular fibers was highly specific to anti-Jo-1 antisynthetase syndrome.Anti-OJ antisynthetase syndrome has more prominent myopathology than the other antisynthetase syndrome subtypes. Presence of myofiber HLA-DR expression in a clinicopathologically approved non-dermatomyositis and non-inclusion body myositis muscle biopsy is highly indicative of antisynthetase syndrome. Presence of HLA-DR expression suggests the involvement of type II interferon in the pathogenesis in antisynthetase syndrome subpopulation although the detailed mechanism and the reason for preferential perifascicular localization are yet to be identified.