Diagnostic utility of ¹⁸F-FDG PET/CT in clinically suspected cases of polymyalgia rheumatica

Introduction: Polymyalgia rheumatica (PMR) is an inflammatory rheumatic disease manifested by typical clinical symptoms but is often a diagnostic challenge to differentiate it from various other rheumatological conditions, most common being rheumatoid arthritis¹. Recently studies have shown potential role of 18F-FDG PET/CT in the diagnostic work up of PMR². The current study aimed at identifying the distribution of tracer uptake pattern in suspected cases of PMR that can suggest the diagnosis of PMR.

Methods: We reviewed the whole body 18F-FDG PET/CT studies done in fifteen clinically suspected cases of PMR (M: F=10:5, mean age = 63.4 years, range 47-84). All the patients were symptomatic at time of undergoing PET/CT and had variable symptoms of muscle stiffness, multiple joint pains, myalgia etc. The mean erythrocyte sedimentation rate was elevated (53.8 mm/hr) and the C-reactive protein was 54.3 mg/L which were elevated. All patients underwent whole body 18F-FDG PET/CT for the initial evaluation. The incidence of significant ¹⁸F-FDG uptake in the joints/bursae higher than mediastinal blood pool was taken as positive for disease involvement.

Results: Increased FDG uptake in the multiple joints/skeletal muscles/bursae was noticed in all except four patients with/without joint effusion and synovial thickening. The typical distribution of abnormal increased FDG uptake was multiple joints along with FDG uptake in the bursae/ skeletal muscles. The most commonly affected joint was gleno-humeral (10/15; mean SUVmax 5.1, range 3.7-6.2) followed by hip and sterno-clavicular joints in 6 and 4 patients respectively. The less common involved joints included knee in 2 patients and elbow, wrist, acromio-clavicular, pubic symphysis, atlanto-odontoid joints in one patient each. In addition, there was increased FDG uptake in the thickened bursae most commonly ischial bursa in three and trochanteric bursa in one patient respectively. Three patients showed increased FDG uptake in the skeletal muscles namely paraspinal, quadratus lumborum and supraspinatus, not attributing to muscular activity. Association of co-existing active vasculitis was noted in 3/15 patients involving right superficial temporal artery, origin of CCA and abdominal aorta (one each; Fig 1).

Conclusions: Present study demonstrates the potential role of 18F-FDG PET/CT in mapping the distribution of involvement and extent in this diagnostically challenging entity. Additionally 18F-FDG PET/CT helped in identifying coexisting active vasculitis in these subsets of patients. Furthermore, it may be helpful in treatment response evaluation and more prospective studies are needed to establish the same.