Value of Hands Ultrasonography in the Differential Diagnosis Between Psoriatic Arthritis and Rheumatoid Arthritis

Psoriatic arthritis (PsA) can mimic rheumatoid arthritis (RA) at an early stage, especially when psoriasis is lacking. In the absence of specific radiological and immunological markers, the differential diagnosis between these two diseases can be challenging. We aimed to determine whether hands ultrasonography (US) may be useful in the differential diagnosis between PsA and RA.

We conducted a cross-sectional study including patients with PsA and RA. All wrists and small joints of the hands were examined using gray-scale and Power Doppler US. The evaluated US lesions were: synovitis, tenosynovitis of extensor carpi ulnaris, extensor communis and flexor tendons, enthesitis of extensor tendons at distal interphalangeal joints, peritendon inflammation of extensor tendons, and soft tissue edema.

Six hundred joints in 20 PsA patients and 900 joints in 30 RA patients were assessed. Extensor enthesitis was significantly more observed in PsA compared with RA (39.4 vs 26.3%, P = .006) with a significant higher frequency of enthesophytes and calcifications (P = .022 and P = .002, respectively). Peritendon inflammation of extensor digitorum tendons was observed in 13% of metacarpophalangeal joints in PsA patients versus 3% in RA patients with a significant difference (P < .001). Soft tissue edema was exclusively observed in PsA (1.5 vs 0%, P = .033). Power Doppler synovitis was significantly more frequent in RA (9.2 vs 5%, P = .002). Extensor carpi ulnaris tenosynovitis was significantly more frequent in RA (18.3 vs 2.5%, P = .017).

Extrasynovial US findings may be helpful to distinguish PsA from RA especially in patients with immunonegative polyarthritis and no evidence of psoriasis.