Whole-body MRI in adult inflammatory myopathies: Do we need imaging of the trunk?

Objective: To evaluate whether imaging of the trunk could be omitted in patients with inflammatory myopathies without losing diagnostic accuracy using a restricted whole-body magnetic resonance imaging (rWB-MRI) protocol. Methods: After approval by the institutional review board, this study was performed in 63 patients (male/female, 13/50; median age, 52years; range, 20-81years) with new-onset myopathic symptoms (group 1, n = 41) or previously diagnosed inflammatory myopathy (group 2, n = 22). After performing whole-body MRI (WB-MRI) at 3.0 Tesla, myositis and fatty atrophy were evaluated in different muscles by two independent radiologists. The intra-class correlation coefficient (ICC) was calculated to evaluate inter-observer reliability. Results: Acquisition time was 56:01minutes for WB-MRI and 37:37minutes (32.8% shorter) for rWB-MRI. In group 1, 14 patients were diagnosed with inflammatory myopathy based on muscle biopsy. rWB-MRI and WB-MRI showed equal sensitivity (42.9%) and specificity (100%) for myositis, and showed equal sensitivity (71.4%) and similar specificity (63.0% and 48.1%, respectively) for fatty atrophy. No myositis was found in the body trunk in any patient. Inter-observer reliability was between substantial and perfect (ICC, 0.77-1.00). Conclusions: rWB-MRI showed diagnostic accuracy similar to WB-MRI for inflammatory myopathy at markedly reduced overall acquisition time. Key Points : • Whole-body MRI (WB-MRI) is a time-consuming imaging modality. • A shortened MRI protocol was evaluated for inflammatory myopathies. • The proposed protocol showed diagnostic accuracy similar to WB-MRI