Background Psoriatic Arthritis (PsA) is often associated with hand involvement including synovitis and tenosynovitis and dactylitis. At the micro anatomical level PsA is strongly linked to disease localisation to entheses and other sites of high mechanical stressing. Recently high resolution MRI has shown prominent abnormalities at the mini-entheses of the flexor tendon pulleys, a site of high physical stressing during finger flexion

Objectives This study tested the hypothesis that sonographic abnormalities were common at the hand flexor tendon mini-entheses in PsA including the A1, A2 and A4 in patients without active hand arthritis or dactylitis at the moment of ultrasound (US) scanning

Methods Consecutive patients affected by psoriasis (PsO) (23 cases), PsA (17) and healthy controls (HC) (19) were collected. The demographic charateristics are shown in Table 1. The cases were matched for sex, age and BMI. We excluded PsA patients with active arthritis or dactylitis at the moment of US study, the majority being under therapy with conventional DMARDs. The 2nd to 4th flexor tendons of the dominant hand were scanned with a high resolution linear probe (10–22 MHz) using an Esaote MyLab Twice machine. The sonograrapher was expert in muscolo skeletal ultrasound (MSKUS) and was blinded to the clinical details.The following changes were scored: tenosynovitis, A1, A2 and A4 pulley tendon thickness and pseudotensynovitis (peritendinous oedema). Pulleys were explored with transverse e longitudinal scan

Results The A1, A2 and A4 pulleys were significantly thicker in PsA compared to PsO and healthy controls measuring both longitudinal and transverse scan (table 2 shows mean±SD value of transverse measures).In PsA patients A1, A2 and A4 pulleys thickness were above than the 95th percentile of HCs values respectively in 84%,80% and 100% of cases.Considering HCs and PsA we found that having a A1 thickness over the 95th percentile of HCs shows a sensibility of 82% and specificity of 100% for PsA. Using ROC curve analysis we found that the presence of one A1 thickness over the 95th percentile of HCs have a sensibility of 82% and specificity of 100% for PsA. Peritendinous oedema evaluated scanning the palmar side of proximal and intermediate phalanx was common in PsA patients (6/17) and absent in PsO and HCs

Conclusions This study suggests that PsA cases have a much higher burden of abnormalities in the mini-entheses of the flexor tendons on the hand. With the improving resolution and capabilities of MKUS these findings may be relevant to understand the involvment of flexor tendon in PsA expecially in sites with high mechanical stressing. Measuring A1, A2 and A4 thickness could be useful in detecting PsA cases without clinical signs of sinovitis or dactylitis

Disclosure of Interest None declared