Juvenile polymyositis or paediatric muscular dystrophy: a detailed re-analysis of 13 cases

Aims: There has been much debate about the existence of juvenile polymyositis (JPM) as an entity distinct from muscular dystrophy (MD). The aim of this study was to retrospectively analyse muscle biopsies and clinical features of 13 Australian children given an initial diagnosis of JPM, to determine their clinicopathological, immunohistochemical and molecular characteristics. Methods and results: The muscle biopsies on 13 cases were reviewed using detailed morphological and immunoperoxidase studies, with additional protein and molecular analyses, in conjunction with clinical review. Only one case had a true connective tissue disease inflammatory myopathy. Twelve (92.3%) cases with an initial diagnosis of JPM were found on clinical, pathological and molecular review to be MD. Conclusions: Inflammatory changes in apparently sporadic juvenile myopathies should prompt consideration of an early presentation of MD. Detailed analysis of muscle histopathology, specifically the detection of sub-sarcolemmal blebbing, isolated fibre degeneration occurring independent of inflammatory infiltrates, patchy clustered major histocompatibility complex-I expression and a CD68+/CD3+ perimysial infiltrate, assists in the diagnosis of early MD. Specific protein and gene analysis adds support to the pathological diagnosis of dystrophy. This series adds weight to suggestions that JPM may not represent a discrete clinical or pathological entity.