Background To search for association between ultrasound (US) enthesis abnormalities and disease activity, spine and sacro-iliac joints (SIJ) MRI inflammatory lesions and spine structural changes in a cohort of patients suspected for axial spondyloarthritis (SpA).

Methods Patients: Of 708 patients included in the DESIR(Devenir des Spondyloarthrites Indifférenciées Récentes) cohort, 402 had an US enthesis assessment and were selected for this study. Imaging: Achilles, lateral epicondyles, superior patellar ligament, inferior patellar ligament entheses were systematically US scanned and abnormalities were summed in US structural and power Doppler (PDUS) scores. Spine radiographs, SIJ and spine MRI scans were centrally scored modified Stoke Ankylosing Spondylitis Spine Score (mSASSS), presence of MRI sacro-iliitis, Spondyloarthritis Research Consortium of Canada and Berlin scores. Analysis: The associations between the US structural/PDUS scores and disease activity, C reactive protein (CRP), MRI SIJ and spine inflammatory lesions and mSASSS were tested by Spearman's correlation tests.

Results Among the 402 patients included (median age: 33.5 years, males: 48.5%), 55% had US enthesis structural abnormalities while 14% had PDUS abnormalities. There was no association between US scores and Bath Ankylosing Spondylitis Disease Activity Index, CRP or inflammatory lesions on SIJ and spine MRI. There was a correlation between US structural and PDUS scores and the mSASSS (respectively, r=0.151, p=0.005; r=0.143, p=0.007). The proportion of patients with syndesmophytes was higher in the case of US enthesophytes (26% of syndesmophytes vs 6% in the absence of US enthesophytes, p<0.0001).

Conclusion While the US abnormalities do not seem to be a helpful tool for monitoring disease activity in axial SpA, US enthesophytes, strongly associated with axial syndesmophytes, might be a marker of interest for disease severity.

Trial registration number NCT01648907, date of registration : 20 July 2012.