Correlation between quantitative and semiquantitative magnetic resonance imaging and histopathology findings in dermatomyositis.

OBJECTIVES: The aim of this study was to compare muscle biopsy findings, as well as clinical and analytical features, with those of magnetic resonance imaging (MRI) studies of muscle in patients with dermatomyositis. METHODS: All patients from the Longitudinal Myopathy Cohort of the Hospital Clinic de Barcelona were prospectively included in the study from 2009 to 2016. MRI images of muscle and fascial oedema were compared with muscle pathology results using both quantitative and semi-quantitative scores. RESULTS: We found a statistically significant association between the inflammatory infiltrate and both muscle (r2=0.54, p=0.001) and fascial oedema (r2=0.54, p<0.001). In addition, muscle oedema was significantly associated with punched-out vacuoles (p=0.04) and muscle enzymes in serum (r2=0.34, p=<0.01 for CK and r2=0.22, p<0.05 for aldolase). The number of treatment drugs received at the time of MRI was inversely associated with the number of muscle inflammatory cells in the biopsy and with both muscle and fascial oedema (all p<0.05). CONCLUSIONS: Key MRI findings correlate with the main features of dermatomyositis muscle biopsy results, suggesting that MRI findings could be used as a surrogate marker of disease activity.