(18)F-FDG PET/CT in patients with polymyositis/dermatomyositis: correlation with serum muscle enzymes

BACKGROUND: Muscle enzymes are the major noninvasive diagnostic parameters useful in polymyositis/dermatomyositis (PM/DM). Few studies have yet correlated findings on (18)F-FDG PET with disease activity in patients with PM/DM. PURPOSE: We evaluated (18)F-FDG muscle uptake in patients with PM/DM compared with non-muscular diseases and correlated the results with serum muscle enzymes. METHODS: A total of 28 patients with untreated PM/DM and 28 control patients with non-muscular diseases were examined with (18)F-FDG PET/CT. (18)F-FDG uptake was evaluated in 9 proximal skeletal muscle regions bilaterally. The uptake was scored as follows: 0 = less than that of the mediastinal blood vessels, 1 = greater than or equal to that of the mediastinal blood vessels, and 2 = greater than or equal to that of the liver. A score 1 or 2 was considered positive. The mean and maximum standardized uptake values (SUV) were calculated in each muscle and were averaged for all muscle regions. PET findings were correlated with serum muscle enzymes. RESULTS: (18)F-FDG uptake was observed in 82% of patients with PM/DM and 7% of control patients. The number of positive regions, total score, mean SUVmean, and mean SUVmax in patients with PM/DM were significantly higher than those in the control patients (all P < 0.001). The total score of 2 was the best cut-off value that could discriminate patients with PM/DM from control patients. The total score, mean SUVmean, and mean SUVmax showed significant correlations with creatine kinase (P = 0.047, 0.002, 0.010, respectively) and aldolase (P = 0.036, 0.005, 0.038, respectively). CONCLUSION: (18)F-FDG PET/CT using visual and SUV methods demonstrated its usefulness by discriminating PM/DM from non-muscular diseases and correlating with serum muscle enzymes in patients with PM/DM.