DIAGNOSIS OF INFLAMMATORY MYOPATHY BY PERCUTANEOUS NEEDLE-BIOPSY WITHDEMONSTRATION OF THE FOCAL NATURE OF MYOSITIS

Inflammatory myopathies are a group of acquired disorders with histolo gic features of inflammation and nonspecific myopathic changes in the muscle fibers. Up to 25% of patients with clinical features of polymyo sitis reportedly have no inflammatory changes in their muscle biopsy s pecimens, but the absence of inflammatory infiltrates does not exclude an inflammatory myopathy. However, whether the lack of inflammation i s caused by sampling variation or by a total lack of demonstrable infl ammation in a particular patient has been unclear in the literature. T he authors diagnosed polymyositis in six patients who underwent percut aneous muscle biopsy using a Bergstrom needle. Through one skin incisi on, the needle was inserted into different areas within the muscle com partment, obtaining three or four concurrent specimens from each patie nt. In all cases of needle biopsy, adequate tissue was obtained for hi stochemical and electron microscopic examination. All patients tolerat ed the procedure well and resumed normal daily activities the morning after biopsy. Although we saw inflammatory changes in at least one bio psy specimen from each patient, one or more of the remaining specimens contained no evidence of inflammation. This illustrates that inflamma tory infiltrates can be focal in polymyositis. Because a specific diag nosis of inflammatory myopathy cannot be made in the absence of demons trable inflammation, the diagnostic yield of multiple percutaneous nee dle biopsy specimen is potentially higher than that of the traditional single biopsy specimen obtained with the open surgical method.