Usefulness of ¹⁸F-FDG PET/CT to distinguish polymyalgia rheumatica in elderly patients presenting with myalgia

To describe imaging features of ¹⁸F-FDG positron emission tomography/computed tomography (PET/CT) of polymyalgia rheumatica (PMR) and evaluate their ability to distinguish PMR in elderly patients presenting with myalgia.

Ninety-three elderly patients (male 29, female 64, age 66.3 ± 8.7 years) with myalgia underwent ¹⁸F-FDG PET/CT for suspected PMR. Based on final clinical diagnosis, clinical data of PMR patients and other subjects were compared. Diagnostic efficacy of 2012 EULAR/ACR classification criteria was assessed. PET/CT findings were reviewed to define PMR-related metabolic patterns. An imaging score algorithm was developed to discriminate PMR from rheumatoid arthritis (RA), the most common alternative diagnosis. The score algorithm's diagnostic performance was validated in the cohort.

Based on final clinical diagnosis, 44 (47.3%) patients were PMR and 49 (52.7%) were other rheumatic disorders. PMR often presented with fever and hip pain and was absent of other joint involvement. The EULAR/ACR classification criteria reached a maximum accuracy of 55.3%. PET/CT consistently demonstrated PMR-related uptake in the interspinous bursae, pubic tendon entheses, and ischial tuberosity bursae; some patients showed giant-cell arteritis (GCA) through abnormal vascular uptake. An 8-item PET/CT score (1 point per criterion) of ≥ 4 distinguished PMR from RA, with 95.5% sensitivity, 85.2% specificity, and 91.5% accuracy. For the entire cohort, a score ≥ 5 achieved 84.1% sensitivity, 94.8% specificity, and 88.2% accuracy.

¹⁸F-FDG PET/CT outperformed the EULAR/ACR criteria for early and accurate diagnosis of PMR in elderly individuals with myalgia. Key Points • FDG PET/CT assists in the diagnosis of PMR. • FDG PET/CT achieves higher diagnostic accuracy for PMR than the 2012 EULAR/ACR criteria. • Eight-item PET/CT score distinguishes PMR from RA with 91.5 % accuracy in elderly myalgia.