Comparison of extracapsular changes by magnetic resonance imaging in patients with rheumatoid arthritis and polymyalgia rheumatica

Objective. Joint inflammation in polymyalgia rheumatica is regarded primari ly as a disease of the synovial cavities and bursae, but the adjacent capsu les and soft tissues have not been evaluated using sensitive imaging method s. We used fat suppression magnetic resonance imaging (MRI) to determine an atomical sites of inflammatory change in the shoulders of patients with ear ly polymyalgia rheumatica (PMR) and a control group of patients with rheuma toid arthritis (RA). Methods. Fourteen patients with PMR and 14 with RA (a total of 20 shoulders in each group) were evaluated. T2 SPIR (fat suppressed) coronal oblique MR I sequences of the shoulders were performed. Scans were assessed for sites of joint effusion, bursitis, tenosynovitis, bone edema, and extracapsular s oft tissue edema. Statistical analysis was performed using Fisher's test. Results. Nine of 14 patients (10/20 joints) with PMR but only 2/14 (2/20 jo ints) with RA had prominent edema at extracapsular sites adjacent to the jo int 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 te nosynovitis (3 PMR, 2 RA). Conclusion. The only significant difference between the 2 groups was the pr esence of inflammatory change outside the joint cavity in patients with PMR . This may contribute to the diffuse nature of symptoms in PMR and have imp lications for its pathogenesis.