Ultrasound assessment of enthesis thickness in psoriasis and psoriatic arthritis: A cross-sectional study

Background: The inflammatory involvement of the enthesis in the course of psoriasis is accompanied by structural abnormalities detectable by ultrasound. The most common of these abnormalities is the thickening of the tendon at the insertion site. Aims: The aim of the present study was to compare the thickness of entheses of patients with psoriatic arthritis, only skin psoriasis, and healthy controls. Methods: A cross-sectional study was conducted in a cohort of patients affected with either only skin psoriasis or psoriatic arthritis as well as in a control group. Eight entheses sites were scanned by ultrasound bilaterally. The following entheseal characteristics were collected and recorded in a predefined database: entheseal thickness, bone erosions, enthesis calcifications (enthesophytes), presence of blood flow, and presence of bursitis. All the detected entheseal changes were scored, and the data was statistically analyzed. Results: The major differences in enthesis thickness between only skin psoriasis and psoriatic arthritis patients were found at the following sites: (i) olecranon tuberosity, (ii) superior pole of the patella, and (iii) medial epicondyle of femur. The thickness of the medial collateral ligament at the site of the femoral origin was increased in psoriatic arthritis, but not in both only skin psoriasis and healthy controls. The score obtained by adding the thickness of all the 8 examined entheses for each patient showed significant differences among the three groups (psoriatic arthritis: 81.3; only skin psoriasis 74.4; Controls: 67.6; P < 0.0001). Interestingly, we found that in psoriatic arthritis patients, the highest enthesis thickening was seen in entheses affected by bone erosions. Limitations: The small sample of patients studied is a limiting factor in this study. Conclusions: Our data demonstrated that the ultrasound measurement of the enthesis thickness enables a distinction between patients with psoriatic arthritis from those with only skin psoriasis. It is a useful method to improve diagnostic accuracy, especially in patients without clear clinical signs of enthesitis.