Myopathological findings in interstitial myositis in type II polyendocrine autoimmune syndrome (Schmidt's syndrome)

We report on a patient with an interstitial myositis in type II polyendocrine autoimmune disease (Schmidt's syndrome) showing an immunohistochemical demonstrated perifascicular expression of Leu 19 indicating perifascicular denervation, which could not be detected with classical histological methods. In neurogenic muscular atrophy, idiopathic polymyositis and normal muscle we could not find such an exclusive perifascicular expression of the Leu 19 antigen. We conclude that perifascicular denervation is a characteristic feature in IM and thus might have diagnostic value. Furthermore the interstitial myositis is characterized by a complement-mediated angiopathy (vascular deposition of the membranolytic attack complex C5b-9). This pattern is comparable to well-known changes in dermatomyositis. Interstitial myositis and dermatomyositis are evidently pathogenetically similar according to myopathological criteria, but show phenotypic differences. Additional in interstitial myositis and idiopathic polymyositis inflammatory infiltrates surrounding Leu 19 expressing myocytes are regarded as the cause of disseminated intrafascicular muscle fibre denervation.