Myofascia-dominant involvement on whole-body MRI as a risk factor for rapidly progressive interstitial lung disease in dermatomyositis

Objective. Rapidly progressive interstitial lung disease (RPILD) is a major cause of death in patients with DM. Although clinically amyopathic DM (CADM) represents risk for RPILD, the incidence rate of RPILD in patients with CADM varies widely. Whole-body (WB) MRI can reveal involvement of systemic muscle and myofascia. The objective of this study was to explore the risk factors for RPILD in patients with DM using WB-MRI. Methods. This retrospective study comprised 41 patients with DM who underwent WB-MRI before the initiation of treatment in our hospital. Muscular and myofascial signals were scored on 42 muscular groups. The myofascia/muscle ratio was calculated and used to define the relevance of myofascia-dominant involvement. RPILD was defined as worsening of dyspnoea, hypoxaemia and radiographic ILD/fibrosis within 3 months from the onset of respiratory symptoms. Results. Among the 41 patients, 17 had CADM and 30 had ILD, including 10 patients with RPILD. All patients including those with CADM showed abnormal signal intensity in both muscle and myofascia (median score: 15 and 23, respectively). Muscle signal scores positively correlated with the serum creatine kinase level (r=0.714; P< 0.001). Patients with RPILD showed a significantly higher myofascia/muscle ratio than those without RPILD (1.929 vs 1.200; P= 0.027). Logistic regression analysis identified higher myofascia/muscle ratio as independent risk factors for developing RPILD. Conclusion. Myofascia-dominant involvement was defined and appreciated in patients with DM using WB-MRI. This may be one of the risk factors for RPILD.