Fatty degeneration and atrophy in skeletal muscles in children with dermatomyositis and/or polymyositis

Background: Idiopathic inflammatory myopathies (IIMs) are chronic autoimmune connective tissue disorder which involve dermatomyositis (DM) and polymyositis (PM). Objectives: To study abnormal changes in affected muscles in dermatomyositis and polymyositis patients. Methods: The study sample comprised 27 patients (9 males, 18 females) ages 8–16 years who were diagnosed with PM or DM according to of Bohan and Peter criteria. In each case, age, sex, duration of the disease, clinical symptoms, cutaneous manifestations, clinical morphology, laboratory investigations, electromyographic findings, musculoskeletal ultrasound, histopathologic features in the skeletal muscle biopsy, treatment and response were recorded. Results: Musculoskeletal ultrasound and Doppler showed that 21 patients (77.8%) had hyperechoic muscle, fatty tissue infiltration, decrease of muscle thickness and hypervascular changes on power Doppler in active early disease and six patients (22.2%) showed decrease of muscle thickness only. Conclusion: Fat substitution and fibrosis can be developed in affected muscles, that is transformed into hyperechoic due to increased amount of muscle reflective surfaces. Alterations in muscle thickness throughout the affected muscles might also take place.