Proliferative Synovitis of the Shoulder Bursae is a Key Feature for Discriminating Elderly Onset Rheumatoid Arthritis Mimicking Polymyalgia Rheumatica From Polymyalgia Rheumatica.

Semiquantitative scoring for subacromial bursa (SAB), subdeltoid bursa (SDB), and subcoracoid bursa by both gray-scale (GS) and power Doppler (PD) ultrasonography was performed in 15 patients with polymyalgia rheumatica (PMR) (72.6 ± 7.7 years old) and 15 patients with elderly onset rheumatoid arthritis with PMR-like onset (pm-EORA) (70.7 ± 7.0 years old) before starting treatment. The GS grades of SAB were significantly higher in the shoulders with pm-EORA than in the shoulders with PMR. The GS and PD scores of SAB and the PD scores of SDB were significantly higher in pm-EORA than in PMR cases. The sums of GS and/or PD scores for the three bursae were significantly higher in pm-EORA than in patients with PMR. The sums of GS and PD scores for SAB were significantly higher in pm-EORA than in PMR cases. Moderate to severe proliferative synovitis of the shoulder bursae, especially in SAB, is a key feature for discriminating pm-EORA from PMR.