Joint inflammation in polymyalgia rheumatica is regarded primarily as a disease of the synovial cavities and bursae, but the adjacent capsules and soft tissues have not been evaluated using sensitive imaging methods. We used fat suppression magnetic resonance imaging (MRI) to determine anatomical sites of inflammatory change in the shoulders of patients with early polymyalgia rheumatica (PMR) and a control group of patients with rheumatoid arthritis (RA).
Fourteen patients with PMR and 14 with RA (a total of 20 shoulders in each group) were evaluated. T2 SPIR (fat suppressed) coronal oblique MRI sequences of the shoulders were performed. Scans were assessed for sites of joint effusion, bursitis, tenosynovitis, bone edema, and extracapsular soft tissue edema. Statistical analysis was performed using Fisher's test.
Nine of 14 patients (10/20 joints) with PMR but only 2/14 (2/20 joints) with RA had prominent edema at extracapsular sites adjacent to the joint capsule or in the soft tissues (p = 0.02). Both groups had a comparable degree of joint effusion (18 PMR, 17 RA), bursitis (18 PMR, 16 RA), and tenosynovitis (3 PMR, 2 RA).
The only significant difference between the 2 groups was the presence of inflammatory change outside the joint cavity in patients with PMR. This may contribute to the diffuse nature of symptoms in PMR and have implications for its pathogenesis.