The Utility of Magnetic Resonance Imaging in Inflammatory Myopathy

Objective. The idiopathic inflammatory myopathies (IIMs) are chronic systemic connective tissue diseases. The muscle biopsy is a definitive diagnostic tool but blind biopsy sometimes produces to negative results. Magnetic resonance imaging (MRI) as a tool for early diagnosis, guidance for biopsy, assessing extent of lesions and monitoring therapy in IIMs has been reported. The aim of this study is to assess the association of thigh inflammation through MRI and biopsy specimens with clinical findings. Methods. Sixty patients diagnosed with dermatomyositis (DM) or polymyositis (PM) from 2004 to 2011 in one center of rheumatology were enrolled. We reviewed clinical, laboratory, histopathologic and MRI of thigh data at initial diagnosis. The inflammation grades by MRI and histopathology of muscles were evaluated through 4-point scoring systems. Results. The laboratory findings for aldolase and CK differed significantly between DM patients (68.3%) and PM patients (31.7%). Fasciitis was detected by MRI in 43.3% of patients, of whom 88.5% had DM (p<0.05). The fasciitis was also associated with myalgia (p<0.05). Almost all MRI findings were symmetric except for two patients. The mean of total signal intensity was higher in patients with decreased muscle power. The signal intensity of affected muscle was slightly associated with muscle enzymes and histopathologic grading. Conclusion. Fasciitis was observed more in DM patients. MRI findings were associated with muscle enzymes and histopathologic grading. Signal intensity on MRI may be useful for measurement of disease activity in acute IIMs. The noninvasive nature and high sensitivity of muscle inflammation suggest that MRI images should be considered prior to muscle biopsy and treatment of IIMs.