Magnetic resonance imaging of skeletal muscles in idiopathic inflammatory myopathies of adults

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Abstract
The purpose of the study was to describe typical MRI findings in various types of idiopathic inflammatory myopathies in adulthood and to correlate the MRI with histopathological and electromyographic findings, and the serum creatine kinase (CK) activity. A third goal was to assess the diagnostic value of the use of gadolinium-DTPA (Gd-DTPA). Fifty-eight patients (35 women, 23 men), aged 21–83 years (median age 59 years), suffering from idiopathic myositides (13 with acute and 45 chronic diseases; 25 with polymyositis, 14 with dermatomyositis, 8 with granulomatous and 11 with inclusion body myositides) were examined with MRI. Seventeen of them received an intravenous infusion of Gd-DTPA. Histopathological and MRI findings of 21 muscles of 18 patients were compared. MRI of skeletal muscles showed abnormal signal intensities in 56 (96.6%) of the 58 patients. MRI abnormalities were found more often than elevated CK activity (P < 0.001). The hyperintensity of T2-weighted images was more conspicuous than on T1-weighted images in 26 (44.8%) patients, indicating oedema-like abnormalities. MRI of 50 (86.2%) patients showed fat replacement. In acute myositides, oedema-like abnormalities were more often visible and in muscle lipomatosis less often visible than in chronic diseases (P < 0.05 each). In dermatomyositis oedema-like abnormalities were more and lipomatosis less frequent than in the other types of myositis (P < 0.005) and correlated with the acuteness of the disease. In 3 of 17 patients in whom contrast-enhanced T1-weighted images were obtained in addition to plain T1- and T2-weighted images, T2-weighted images were more sensitive in the detection of oedema-like abnormalities than the contrast-enhanced T1-weighted images. In no patient was the opposite true. Thus, contrast-enhanced T1-weighted images did not provide more information than T2-weighted images. Nine patients with poly-, dermato- and inclusion body myositis showed clearly asymmetrical findings. Imaging of the thighs and legs was of similar sensitivity. The different types of myositides showed typical but not specific distributions of the mesenchymal abnormalities in MRI. The findings indicate that MRI of skeletal muscles in myositides can visualize the presence and distribution of oedema-like abnormalities and intramuscular lipomatosis and is suitable for the assessment of the chronicity and severity of the disease.