[Benefit of ultrasound in the phenotype recognition of psoriatic arthritis]

To explore the difference in phenotype recognition of PsA patients in two clinical scenarios, physical examination with and without ultrasound assessment.

PsA patients who visited the rheumatology and clinical immunology department of Peking University First Hospital between January 2010 and October 2020, with complete data of clinical and ultrasound assessment were enrolled. The phenotypes were first identified based on physical examination only, and then combined with enthesitis and dactylitis shown on power doppler and gray-scale ultrasound. The phenotype groupings without and with ultrasound assessment were presented with Wayne diagram. The distributions of different clinical phenotypes were compared by using χ² test or Fisher's exact test. The differences of clinical phenotypes with and without ultrasound assessment were compared by using Wilcoxon signed rank test.

A total of 227 patients with PsA were enrolled with one or more clinical domains. Physical examination revealed that psoriasis was in 209 (92.1%, 209/227) patients, nail involvement in 98 (43.2%, 98/227) patients, peripheral arthritis in 219 (96.5%, 219/227) patients, axial involvement in 25 (11.0%, 25/227) patients, dactylitis in 80 (35.2%, 80/227) patients, and enthesitis in 18 (7.9%, 18/227) patients. Besides 18 patients with clinical enthesitis, ultrasound scan revealed acute enthesitis in 80 patients, with hypoechogenicity (55 cases), tendon thickening (62 cases), and presence of Doppler signals (48 cases). Similarly, dactylitis on ultrasound was found in 18 patients besides those patients with clinical dactylitis. Compared with the phenotypes recognized based on physical examination only, the additional ultrasound assessment revealed that the most common phenotypes, peripheral arthritis was significantly less frequently recognized (49.8% vs. 27.8%, P < 0.001), however on the other hand, the proportion of the patients with peripheral arthritis and enthesitis was significantly increased (4.4% vs. 18.1%, P < 0.001). The phenotype of peripheral arthritis combined with enthesitis, and dactylitis was also dramatically increased (1.8% vs. 17.6%, P < 0.001).

Ultrasound is a useful tool to identify enthesitis and dactylitis. With the aid of ultrasound assessment, rheumatologists can better identify the lesions of PsA, accurately identify the phenotypes, and further guide the subsequent treatment.