Clinical and ultrasonography assessment of peripheral enthesitis in ankylosing spondylitis

Objective. The aim of this study was to compare clinical examination with power Doppler US (PDUS) in the detection of entheseal abnormalities in patients with AS. Methods. Thirty-six AS patients underwent clinical and PDUS examination of the following bilateral entheseal sites: common extensor tendon at its insertion at the lateral humeral epicondyle; gluteus tendons at their insertion at the greater trochanter; quadriceps tendon at its insertion at the superior pole of the patella; patellar tendon at its proximal insertion at the inferior pole of the patella; patellar tendon at its distal insertion at the tibial tuberosity; Achilles tendon at its insertion at the calcaneus; and plantar aponeuroses at its insertion at the calcaneus. Results. Clinical and PDUS examination revealed at least one abnormal enthesis in 23 (63.9%) and 35 (97.2%) AS patients, respectively. Furthermore, of 432 entheses examined in our 36 AS patients, 64 (14.8%) were considered abnormal by clinical examination and 192 (44.4%) by PDUS. US abnormalities most commonly found were enthesophytes (31.7%), calcifications (33.7%), thickening (29.8%) and hypoechogenicity (26.6%). We found erosions and PD signals in 9.7 and 6% of examined entheseal sites, respectively. The evidence of entheseal abnormalities by clinical examination has a poor likelihood ratio (LR) for the presence of US abnormalities with vascularization (LR = 1.61), without vascularization (LR = 1.24) or erosions (LR = 1.51) at all sites. Conclusions. PDUS permits detection of structural and inflammatory abnormalities of the enthesis in AS and may complement the physical examination in order to better evaluate enthesitis.