Shoulders are often involved in spondyloarthritis (SpA) and rheumatoid arthritis (RA). The diagnosis of peripheral SpA and its differential diagnosis with RA could be challenging. A recent ultrasound study showed that ultrasonography (US) of the hands might differentiate psoriatic arthritis to RA. The aim of the study was to compare different US features in SpA, RA and healthy controls.

A total of 38 SpA and 43 RA patients with clinical involvement of shoulders were included and compared to 33 controls. One blinded rheumatologist performed US examinations. The following items were assessed: gleno-humeral effusion, long-head biceps tendon tenosynovitis, subacromial and subdeltoid bursitis, acromio clavicular (AC) synovitis and humeral bone erosion.

Thirty-eight SpA (mean age: 49.9±15.4years, 58% of male), 43 RA patients (52.9±16.6years, 26% of male) and 33 controls (55.2±16.9years, 42% of male) were assessed. In comparison to RA, SpA patients had higher frequency of AC synovitis (66% vs 5%, P<0.0001) but lower prevalence of subacromial and subdeltoid bursitis (39% vs 67%, P=0.015), gleno-humeral effusion (5% vs 28%, P=0.008) and humeral bone erosion (10% vs 56%, P<0.0001). Unilateral abnormalities were found more frequently in SpA patients than in RA (64% vs 26%, P<0.0001).

Our results suggest that AC synovitis is highly evocative of SpA in patients with inflammatory painful shoulders. Thus, US might help to diagnose SpA and to differentiate with RA.