| Summary: | Abstract Background Various inflammatory conditions may present with musculoskeletal symptoms similar to those of polymyalgia rheumatica (PMR). We investigated findings on 18F-fluorodexoxyglucose (FDG)-positron emission tomography/computed tomography (PET/CT) images that may differentiate PMR from polymyalgia-like illnesses. Methods We analyzed data from 25 patients with new-onset polymyalgia-like illnesses who fulfilled Bird’s diagnostic criteria for PMR and had undergone FDG–PET/CT scan. To assess the uptake by major joints and synovial bursae, particularly at PMR-specific sites (shoulder, sternoclavicular, and hip joints, interspinous bursae, ischial tuberosities, and greater trochanters), we used visual scoring system to score FDG uptake: 0, no uptake (same as bone); 1, slight uptake; 2, moderate uptake (same as the liver); 3, greater uptake than the liver; and 4, uptake as strong as in the cerebellum. Results The final diagnoses were PMR in 17 patients and non-PMR in eight patients (three malignancies, two infections, one cholesterol crystal embolism, one ANCA-associated vasculitis, and one undefined diagnosis). Although the serum MMP-3 levels were significantly higher in patients with PMR, C-reactive protein and erythrocyte sedimentation rate mean values did not differ between the two groups. In PMR-specific sites, FDG accumulations were observed in all cases of PMR, with a high PET-positive score of 2.00 (range, 0–3), but it was low in non-PMR cases, with a PET-positive score of 1.00 (range, 0–3). Conclusions The FDG accumulation patterns in polymyalgia-like illness differ from those in PMR, despite the similar clinical presentations of both conditions. An FDG–PET/CT scan is useful for differentiating PMR from other polymyalgia-like illnesses.
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