Background/Purpose: Psoriasis patients with enthesitis can classify as psoriatic arthritis since the introduction of the CASPAR classification criteria in 2006. However, the presence of a tender enthesis is not necessarily indicative for underlying inflammatory disease as it could be related to overuse, metabolic disease or ageing. Therefore, we need a better way to identify the inflammatory component of entheseal involvement in psoriasis. To detect these inflammatory components and structural changes in the entheses, ultrasonographic examination can be applied to identify inflammatory disease of the entheses. Our objective was to determine the prevalence of ultrasound abnormalities among psoriasis patients in primary care.

Methods: Adult patients with psoriasis (ICPC S91) were identified from 97 general practitioners in the Rotterdam area. These patients were invited to participate in the SENSOR study. Patients who reported pain in joints, entheses or the lower back were eligible and invited for clinical evaluation. If physical examination indicated a painful enthesis on the LEI/MASES or arthritis, ultrasonographic examination of the entheses was performed. The six entheses of the Madrid Sonographic Enthesis Index (MASEI) and  the lateral epicondyle tendon insertion (elbow) were evaluated according to the MASEI scoring system. Positive inflammatory components on ultrasound included the presence of power Doppler signal (<2mm of the bony cortex) and increased thickness of the enthesis of the plantar fascia (>4.4mm).
Results: In total, 527 patients with psoriasis who reported musculoskeletal symptoms were clinically evaluated. 83 patients (47 female, mean age: 54 years) had at least one tender enthesis on the LEI/MASES and were evaluated by ultrasound. Another 23 patients (9 female, mean age: 54 years) suspected for presence of arthritis were evaluated by ultrasound as well. In 98 (92%) patients we detected ultrasound abnormalities [Table 1].  In 47 (44%) patients we found abnormalities indicating inflammatory disease at the enthesis. 28 (26%) patients were power Doppler positive on ultrasound, 4 (4%) patients had a thickened plantar fascia and in 15 (14%) patients both inflammatory components were present. In 51 (48%) patients we found structural changes without indication for inflammatory disease. There was no difference in ultrasound findings between patients suspected for enthesitis and patients suspected for arthritis.

Conclusion: In 44% of primary care psoriasis patients (n=106) we observed ultrasound abnormalities (presence of power Doppler and/or thickened plantar fascia) indicating inflammatory disease. Additionally, one or more structural ultrasound changes in the enthesis were observed in the majority of the patients. Whether this also indicates inflammatory disease requires further exploration.