Ankle retinacula abnormalities as features of psoriatic arthritis: An ultrasound study.

OBJECTIVE: To compare the ultrasonography (US) assessment of the retinacula of ankles in patients with rheumatoid arthritis (RA) and psoriatic arthritis (PsA). METHODS: This cross-sectional study included RA or PsA patients with ankle pain and healthy controls. The following US features were recorded: presence of synovitis, tenosynovitis and abnormalities of two retinacula (the superior peroneal retinaculum [SPR] and the flexor retinaculum [FR] evaluated in mode B and power Doppler). RESULTS: Among the 80 included patients, 37 (46%) and 23 (29%) had RA and PsA; 20 (25%) patients were healthy controls. The FR was thicker in PsA than RA ankles 0.96±0.39 vs. 0.64±0.15, P<0.001 with no difference between RA patients and HCs. Other FR abnormalities such as hypoechogenicity, PD positivity or periostosis were more frequent in PsA than RA patients, P<0.001. On receiver-operating-characteristic curve analysis, a cut-off of 1mm FR thickness provided a sensitivity of 49% and specificity of 97% for the diagnosis of PsA. Overall, 39 and 3% of PsA and RA ankles exhibited retinaculitis of FR (thickness≥1mm with hypervascularization or hypoechogenicity). The two disease groups did not differ in the evaluation of SPR. CONCLUSIONS: US abnormalities of FR were more frequent in PsA than RA and appeared to be specific for PsA. US assessment of FR might be useful to distinguish RA and PsA.