Background Idiopathic inflammatory myopathies (IIM) and eosinophilic fasciitis (EF) are defined as idiopathic inflammation of muscle or fascia. In patients clinically suspected of having those entities, Magnetic Resonance Imaging (MRI) is performed to assess muscle involvement, and 18F- Fluorodeoxyglucose Positron Emission Tomography (PET) to exclude a paraneoplastic origin of the symptoms.
Objectives In this study, we aimed to compare the relative performance of MRI and PET in the detection of muscle and/or fascia inflammation.
Methods This retrospective board – approved study included 18 patients suspected of MII (12) or EF (6) in which both MRI and an 18F-FDG PET were available and performed within a interval ≤3 months, and in which no therapeutic changes occurred between the two exams. The mean interval between MR and PET was 7 days [range -62 (PET performed between MRI) to +91].
For each subject, muscular involvement was independently evaluated on MRI and PET in up to 17 possible predefined muscular groups, subdivided on 3 categories: upper limbs, lower limbs and trunk. A total of 220 corresponding muscular groups were analyzed. A group was considered abnormal on MR when a high signal was seen on fat saturated T2w images (either in muscle or fascia) and, on PET, when high uptake was present. The Kappa statistics between the two imaging modalities were calculated.
Results MRI detected significantly more lesions than 18F-FDG PET in the 3 categories (upper limbs, lower limbs and trunk) (p<0.001). The overall agreement between MRI and 18F-FDG PET was 0.67 (95% confidence interval 0.57 to 0.77); it was 0.81 (CI 95 0.70–0.93), 0.50 (CI 95 0.31–0.68) and 0.65 (CI 95 0.34–0.97) for upper limbs, lower limbs and trunk, respectively.
Conclusions MRI seems more accurate to detect inflammatory changes of muscle or fascia than 18FDG PET when myositis or fasciitis is clinically suspected.
Disclosure of Interest None declared