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

Abstract

Objective: 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.

Methods: 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.

Results: 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).

Conclusion: 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.

Keywords: 18F-FDG PET/CT; Interspinous bursa; Polymyalgia rheumatica; Spinous processes; Sternoclavicular joints.