Background Positron emission tomography/computed tomography (PET/CT) possesses the unique potential to document whole body inflammation in polymyalgia rheumatica (PMR), however the precise anatomical structures involved have not been well characterised.
Objectives To characterise the pattern of 18F-fluorodeoxyglucose (18F-FDG) uptake on whole body PET/CT in patients with newly diagnosed PMR, and to precisely identify anatomic correlates of 18F-FDG uptake with magnetic resonance imaging (MRI).
Methods Patients with newly diagnosed PMR according to the 2012 EULAR/ACR classification criteria (1) were prospectively recruited. Participants with symptoms suggestive of giant cell arteritis were excluded. A whole body 18F-FDG PET/CT scan was performed at baseline in all untreated patients. Qualitative and semi-quantitative (standardised uptake value maximum [SUVmax]) scoring of 18F-FDG uptake was undertaken, with statistical analyses completed using Stata 13.0 (Statcorp, College Station, TX, USA). MRI of the pelvis, knee and hand/wrist was then performed in three patients with representative 18F-FDG PET/CT findings using a 1.5 Tesla magnet. Medview fusion software was utilised to anatomically correlate sites of 18F-FDG uptake.
Results Nineteen patients were recruited. Mean age was 67.52±6.36 years and there was a slight male predominance (63.16%). On whole body PET/CT, adjacent to the ischial tuberosities was the most common site of abnormal 18F-FDG uptake (18/19 patients [94.74%]) and showed the highest mean SUVmax value (3.95 ± 1.81). Eleven patients (11/18 [61.11%]) were found to have knee involvement, with intense 18F-FDG uptake in posteromedial knee structures in ten participants. 18F-FDG uptake was similarly appreciated at the hand/wrist in twelve patients (63.16%). At the hand/wrist, a volar distribution was typical. MRI of the pelvis demonstrated bilateral and symmetric high T2 signal surrounding the proximal hamstring tendon origins of semimembranosus and the conjoint tendon of semitendinosus and biceps femoris. At the knee, peri tendinous oedema surrounding the distal insertion of semimembranosus was similarly visualised. Hand/wrist MRI revealed synovial thickening and enhancement in the flexor compartment, in keeping with tenosynovitis. PET/MRI fusion at the pelvis and knee confirmed semimembranosus peri tendonitis as the anatomical correlate of 18F-FDG uptake adjacent to the ischial tuberosities and of posteromedial knee structures on whole body PET/CT.
Conclusions PET/MRI fusion demonstrates that hamstring peri tendonitis is a distinctive manifestation of PMR. This further characterise the imaging phenotype of PMR and highlights a predilection for tendon involvement in this condition.
Dasgupta B et al. 2012 Provisional classification criteria for polymyalgia rheumatica: a European League Against Rheumatism/American College of Rheumatology collaborative initiative. Arthritis & Rheumatism. 2012;64(4):943–54.
Disclosure of Interest None declared