Muscular ultrasound in idiopathic inflammatory myopathies of adults

To evaluate the value of myosonography in inflammatory myopathies ultrasound of skeletal muscles was performed in 70 patients, aged 21-82 years, suffering from histologically proven polymyositis (n = 30), dermatomyositis (n = 18), granulomatous myositis (n = 9), inclusion body myositis (n = 13), and in 102 control persons. The sensitivity of muscle ultrasound in detecting histopathologically proven disease (82.9%) was not significantly different from electromyography (92.4%) or serum creatine kinase activity (68.7%). The positive predictive value of ultrasound was 95.1%, the negative predictive value 89.2%, and the accuracy 91.3%. The different types of inflammatory myopathies presented with typical, but not specific ultrasound features. Polymyositis showed atrophy and increased echointensity predominantly of lower extremity muscles, whereas in dermatomyositis clear muscle atrophy was rare and echointensities were highest in forearm muscles. Echointensities were lower in dermatomyositis compared to poly- and granulomatous myositis. Granulomatous myositis was characterized by the highest echointensities and a tendency towards muscle hypertrophy. Severe muscle atrophy was the most impressive feature in the majority of patients with inclusion body myositis. Comparison of ultrasound and histopathological findings indicates that muscle lipomatosis has a much greater impact on muscular echointensity than does muscle fibrosis. Ultrasound of myositis improved clinical assessment of patients by supplying differential diagnostic clues based on precise muscle size measurements and identification of mesenchymal abnormalities, particularly muscle lipomatosis.