Diagnosing polymyalgia rheumatica on ¹⁸F-FDG PET/CT: typical uptake patterns

The diagnosis of polymyalgia rheumatica (PMR) is often challenging, since similar clinical features and laboratory findings can be observed in several inflammatory conditions. PMR involves affected sites in a specific manner, and ¹⁸F-FDG PET/CT has the advantage for assessing the disease activity of each site. The purpose of this study was to identify the patterns of ¹⁸F-FDG uptake that suggest the diagnosis of PMR.

We studied 60 patients who had undergone ¹⁸F-FDG PET/CT scans for workup of suspected PMR, arthritis, enthesitis, or myopathy. Final diagnoses were made by board-certified rheumatologists. The incidence of significant ¹⁸F-FDG uptake, higher than mediastinal blood pool, of the following sites were compared among PMR patients and patients with other diseases: wrists, elbows, shoulders, sternoclavicular joints, acromioclavicular joints, spinous processes, ischial tuberosities, and greater trochanters. For the spinous processes, the incidence of "Y"-shaped uptake along the interspinous bursae was also evaluated.

A definitive diagnosis of PMR was given to 16 of 60 patients. The incidence of significant ¹⁸F-FDG uptake in the definitive PMR group was 6% for wrists and for elbows, 88% for glenohumeral and sternoclavicular joints, 25% for acromioclavicular joints, 81% for spinous processes, 69% for ischial tuberosities, and 81% for greater trochanters. Patients with PMR showed a significantly higher incidence of "Y"-shaped uptake along the interspinous bursae than the other patients (38 vs. 9%) (P = 0.016).

¹⁸F-FDG uptake distribution patterns and morphology can contribute to the diagnosis of PMR. Significant ¹⁸F-FDG uptake in the sternoclavicular joints is one of the characteristic findings in patients with PMR as well as the uptake in the shoulders, ischial tuberosities, and greater trochanters. "Y"-shaped spinous process uptake may be one of the specific findings for PMR.