18F-fluoro deoxy glucose PET scanner (18F-FDG-PET-CT) has shown its interest in the diagnosis of polymyalgia rheumatica (PMR) and makes possible to evaluate the metabolic activity of the entire musculoskeletal system and in particular muscular structures. The purpose of this study was to evaluate muscle involvement using 18F-FDG-PET-CT in the case of PMR, compared to a non PMR population.

This is a monocentric retrospective study of patients with PMR (ACR/EULAR 2012 criteria) who had an 18F-FDG-PET-CT examination. A control group composed of subjects without rheumatological manifestations who had such an examination as part of neoplastic research or follow-up of neoplastic diseases was also evaluated. The PET assessment included 17 sites suggesting a PMR, as previously reported. Areas of muscle hypermetabolism were classified in the same way according to the same semi quantitative classification. Muscle activity sites were identified. A comparison of patients with PMR with and without muscle damage was performed using the exact Mann–Whitney or Fisher test.

Two hundred and one cases were examined, involving 101 PMRs (mean age 68.6 years) and 100 controls (mean age 67.7 years). Overall, PET muscle damage was observed in 34 cases (34%) in PMR and 10 cases (10%) in controls (P=0.004). Lesions are bi or multi-focal in half of the cases. The affected muscle sites are: spinal muscles 19, scapular girdle 14, pelvic girdle 13, and thigh 6. Fasciitis was found in 3 cases. In patients with PMR, PET muscle involvement was not associated with age, CRP or overall PMR PET score.

Muscle damage assessed by 18F-Fluorodeoxyglucose PET-CT is common in PMR (1/3 of cases), located at the usual sites of disease symptoms, without association with age, CRP levels or the overall PET PMR score. The muscle must be carefully evaluated during a PET examination in cases of PMR.