Pattern of muscle involvement in dermatomyositis – A retrospective analysis using STIR MRI imaging

Abstract

All patients with suspected Idiopathic Inflammatory Myopathy, over a 4 year period - from August 2014 to August 2018, seen in the departments of Neurology and Rheumatology of Aster Medcity, Kochi, India, were included in the retrospective analysis. 28 patients with DM were selected, who fulfilled the EULAR/ACR classification criteria. Of the 28 patients, 17 patients who had undergone fat suppression sequence, short tau inversion recovery (STIR) MRI muscle imaging were selected. The MRI images were collated and analysed by a single examiner who has over 4 years of experience with muscle MRI. Of the 17 patients with STIR imaging, 12 underwent a whole-body MRI and 5 underwent thigh muscle MRI only. We found that 76% patients were women, with a mean age of 48 yrs. 13 were adult DM, 3 were amyopathic DM and 1 case was a juvenile DM (9 years). The mean disease duration was 10.8 months, and the mean time to MRI from diagnosis and initiation of treatment was 4.7 months except in 3 cases who presented very late (1-2 years after onset). Most muscle changes were patchy, involving muscles asymmetrically. 70% cases showed involvement of lower limb muscles. And 30% showed upper limb and trunk muscle involvement. Paraspinal muscles and shoulder girdles were involved in 50% patients in whom whole-body MRI was performed. Interestingly, the muscles involved the most were the thigh (anterior and posterior compartment muscles), calf muscles, the glutei and pelvic muscles. The pelvic muscles were frequently involved (47%), especially obturator internus and externus.