The value of direct immunofluorescence as a diagnostic aid in dermatomyositis - a study of 35 cases

Dermatomyositis (DM) is an inflammatory disorder of skeletal muscle and skin closely related to other connective tissue diseases; however, to date, no conclusive immunofluorescence (IMF) data are available for the disorder. The aim of this study was therefore to analyse retrospectively the clinical, histological and direct IMF findings for a group of 35 patients who had presented during an 8-year period. Clinically, 29 of the patients had the typical cutaneous features of DM, while 16 had evidence of myositis based on electromyographic or muscle biopsy findings; six developed malignant rumours during the study period, three of which proved fatal. Cutaneous histopathology findings were compatible with the diagnosis of DM in 18 cases, with evidence of a lupus band in six. Direct IMF showed a lupus band at the basement membrane zone in 19 (with IgM, IgG or C3), with colloid bodies in seven. Serologically, only nine were antinuclear antibody positive, one extractable nuclear antibody positive and all 35 anti-Jo-1 negative. Eight had other circulating autoantibodies, namely thyroid (three), gastric parietal cell (two), smooth muscle (two) and rheumatoid factor (one). Our findings suggest that direct IMF can be a useful adjunct in the investigation of patients with DM, and may prove helpful in diagnosis when both the histopathology and serology are inconclusive.