Differentiation between early rheumatoid and early psoriatic arthritis by the ultrasonographic study of the synovio-entheseal complex of the small joints of the hands.

OBJECTIVES: To determine whether ultrasonographic findings of the synovio-entheseal complex of the hand small joints could be used to differentiate between early rheumatoid and early psoriatic arthritis.
METHODS: Thirty-four early rheumatoid and 26 early psoriatic arthritis patients with a prevalent involvement of the hands were examined with ultrasound (US). All exams were performed at the first visit by evaluating synovitis, peritendon extensor digitorum tendon oedema, enthesitis of the central slip of extensor tendon, flexor tenosynovitis and soft tissue oedema. In the same patient, the two most clinically involved joints, if possible of the same digit, were evaluated.
RESULTS: Sixty-eight clinically involved joints were evaluated in 34 early rheumatoid arthritis patients and 52 joints in 26 early psoriatic arthritis patients.Synovitis was significantly more frequently detected in early rheumatoid arthritis compared to early psoriatic arthritis patients (p=0.0001), in 91.1% joints of the former and in 59.6% joints of the latter. At metacarpohalangeal joint, the presence of peritendon extensor digitorum tendon inflammation was observed in 2.5% of the joints in the early rheumatoid arthritis group and in 54.1% of the joints in the early psoriatic arthritis group (p=0.0001). At PIP joints, central slip enthesitis was exclusively observed in EPsA (p=0.0045). When considering the most clinically involved finger per patient, soft tissue oedema was detected almost exclusively in psoriatic arthritis (p=0.0002).
CONCLUSIONS: The US involvement of synovio-entheseal complex and US extrasynovial features may be helpful in the differential diagnosis between early rheumatoid and early psoriatic arthritis.