Immunohistochemical differentiation of inflammatory myopathies.

BACKGROUND: Idiopathic inflammatory myopathies are a heterogeneous group of acquired muscle disorders with considerable overlap in the histological features, making histological diagnosis difficult at times. AIMS: To determine the immunohistochemical profile of clinically suspected cases of inflammatory myopathies, using monoclonal antibodies to HLA-1 and membrane attack complex (MAC), and to correlate the clinical, serological, and electromyographic profile and the histopathological picture, with the immunohistochemical profile. SETTINGS AND DESIGN: This was a retrospective study analyzing the clinical and histopathological features in muscle of clinically suspected cases of inflammatory myopathy and correlating it to their HLA-1 and MAC immunostaining profiles. MATERIAL AND METHODS: The study subjects included 33 cases with suspected inflammatory myopathy and 59 with non-inflammatory muscle disease, as controls. Clinical data, electromyographic findings, serological profile, and details of therapy were obtained from patient records. STATISTICAL ANALYSIS: Student 'T' test, Pearson's Chi square test, and Kappa statistics were used appropriately. RESULTS: Although HLA-1 and MAC immunostaining did not help to differentiate the individual subtypes of inflammatory myopathy, when either HLA-1 or MAC was positive, inflammatory myopathy could be ruled in with 86.5% certainty and when both HLA-1 and MAC were negative, it could be ruled out with 95% certainty. CONCLUSIONS: A combination of clinical presentation, serological profile, electromyographic and histopathological features, together with the immunoprofile for HLA-1 and MAC, contribute toward making a diagnosis of inflammatory myopathy.