Spatial distribution of muscle necrosis in biopsies from patients with inflammatory muscle disorders

Muscle biopsies from 56 patients with polymyositis (PM), juvenile dermatomyositis (JDM) and adult dermatomyositis (ADM) were investigated using a range of quantitative histological techniques. The objective was to present data on the extent and distribution of muscle fibre degeneration in these patients and to determine whether these data were compatible with postulated mechanisms of fibre injury. Atrophy of one or more of the major fibre types was found in 45/56 biopsies but there was no evidence that particular patterns of type-specific atrophy were characteristic of any individual disease group. However, selective atrophy and/or necrosis of perifascicular fibres was much more common in JDM patients than in ADM or PM groups. In virtually all biopsies where abnormalities of the microvasculature were apparent (7/8 JDM biopsies, 4/13 ADM biopsies and 5/33 PM biopsies) the distribution of acute muscle necrosis was found to be non-random (clustered). However, a substantial proportion of biopsies in the PM group showed clustering of necrotic fibres in the absence of evidence of vascular involvement. This finding suggests that non-random targetting of muscle fibres by effector cells may occur.