Clinical value of a [18F]-FDG PET-CT muscle-to-muscle SUV ratio for the diagnosis of active dermatomyositis.

Abstract

To study a muscle-to-muscle standardised uptake value (SUV) ratio with FDG-PET/CT (FDG-PET) as a marker for the detection of disease activity in dermatomyositis (DM). Patients with DM (n = 24) who met the European Neuro-Muscular Centre diagnostic criteria were retrospectively identified over a 3-year period through a national survey. Muscle biopsy was performed in all patients. Maximum SUV was measured in proximal muscles (SUV_PROX) that had the highest radiotracer uptake on visual grading as well as in the musculus longissimus thoracis (SUV_MLT), whereas mean SUV was measured for the liver (SUV_LIV). Muscle-to-liver SUV ratios for either muscle group were compared and a SUV_PROX/SUV_MLT ratio was calculated. SUV_PROX/SUV_MLT of DM patients were compared with age- and sex-matched control subjects (n = 24) with melanoma who had received FDG-PET scans. DM patients presented with proximal and symmetrical muscle uptake. Differences in SUV_PROX/SUV_LIV and SUV_MLT/SUV_LIV ratios in DM subjects were significant (p < 0.001). SUV_PROX/SUV_MLT ratios in DM and their controls also differed significantly (p = 0.0012). The SUV_PROX/SUV_MLT ratio threshold between DM subjects and controls was 1.73 with a sensitivity of 50% (CI95%, 29.1 to 70.9%) and specificity at 83.3% (CI95%, 62.6 to 95.3%). When amyopathic DM patients were removed from the analysis, specificity was increased to 95% (CI95%, 75.1 to 99.9%) with a likelihood ratio of 10 and an AUC of 83.4% (CI95%, 71.4 to 95.4%). A muscle-to-muscle SUV_PROX/SUV_MLT ratio with a cut-off value of 1.73 in FDG-PET imaging might serve as a non-invasive marker to determine disease activity in dermatomyositis. • [18F]-FDG PET-scanner standardised uptake value (SUV) could reflect disease activity in dermatomyositis (DM). • A ratio of SUV in proximal muscles (SUV_PROX) to SUV in musculus longissimus thoracis (SUV_MLT) could be used to determine active DM. • Active disease is suspected for SUV _PROX /SUV _MLT ratios greater than 1.73.