Blockmans D et al. (2007) Repetitive 18-fluorodeoxyglucose positron emission tomography in isolated polymyalgia rheumatica: a prospective study in 35 patients. Rheumatology (Oxford) 46: 672–677

The exact cause of polymyalgia rheumatica (PMR) is unknown. Studies of patients with PMR and giant-cell arteritis indicate that PMR could be a vasculitis limited to the subclavian or axillary arteries, or a synovitis or perisynovitis of the shoulders and hips. A new study has now shown that PMR is mainly a synovitis of the large joints.

The study included 35 patients with isolated PMR. Patients received methylprednisolone 12 mg/day, which was tapered and discontinued at 6 months. Fluorodeoxyglucose (FDG) deposition was measured by PET scans before treatment, and 3 and 6 months after treatment if possible. FDG uptake was scored at seven vascular regions, and at the shoulder region, hip region, and the processi spinosi of the vertebrae.

Low vascular involvement was noted in 31% of patients at baseline. By contrast, 94% of patients had increased FDG uptake in the shoulder, 89% in the hip and 51% in the processi spinosi. PET scans at 3 months showed a decrease in the intensity of FDG uptake at both the vascular and proximal joint regions; PET scans at 6 months were difficult to interpret as disease relapse occurred in 58% of patients. Relapse was not related to specific FDG-PET findings, and therefore repeat FDG-PET scans for PMR follow-up are not recommended.

Although this study indicates that PMR is a manifestation of a synovitis of the proximal joints, distinction between perisynovitis and synovitis was not possible because of the low resolution of the PET scans.