Systemic sclerosis-associated myopathy

Skeletal muscle involvement is a common feature in systemic sclerosis (SSc) because muscle weakness is found in up to 90% SSc patients when systematically assessed. Muscle clinical, biological, and electromyographic features are similar to those of polymyositis or dermatomyositis, except for a higher proportion of mild symptoms. SSc-associated myopathy is more prevalent in diffuse SSc and is also associated with cardiomyopathy. The pathophysiological process leading to SSc-associated myopathy is likely to be complex, given the heterogeneity of pathological muscle findings, including stigma of microangiopathy, and also inflammatory infiltrate in about half of the cases and interstitial fibrosis. Conflicting results have been reported regarding the correlation between clinicobiological presentation and pathological muscle features, nevertheless there is a general agreement that histologically proven inflammatory myopathies usually regress under high-dose corticosteroid therapy, or even low dose in case of positive anti-PM/Scl antibody. In contrast, noninflammatory myopathies often result in milder clinical expression but do not respond to immunosuppressive treatment.