Background Enthesitis represents one of the most important peripheral musculoskeletal manifestations in patients with axial spondyloarthritis (axSpA). However, studies specifically evaluating Achilles tendon enthesitis and its impact over time are scarce. The objectives of this study were to evaluate the impact of Achilles’ tendon enthesitis found at baseline during physical examination on the outcome measures after 2 years of follow-up in patients with ankylosing spondylitis (AS). Methods This was an observational and prospective study conducted during 2 years of follow-up in the REGISPONSER-AS registry. Linear regression models adjusted for age, body mass index (BMI), and anti-TNF intake were conducted to evaluate the association between the presence of Achilles enthesitis at baseline and the patient-reported outcome (PRO) scores at baseline. The impact of this feature on PROs over 2 years of follow-up was evaluated using mixed models for repeated measures adjusted for age, BMI, and anti-TNF intake. Results Among the 749 patients included, 46 patients (6.1%) showed Achilles’ tendon enthesitis during physical examination at the baseline study visit. Patients with Achilles enthesitis had an increase in the global VAS score, BASDAI, mBASDAI, ASDAS-CRP, and BASFI scores in comparison with patients without this feature. In addition, the mean global VAS, BASDAI, and ASDAS-CRP scores were significantly higher among patients with Achilles enthesitis over the 2 years of follow-up after adjusting for age, BMI, and current anti-TNF intake. The percentage of patients achieving ASDAS low disease activity (ASDAS < 2.1) after 2 years of follow-up was 15.9% and 31.5% for patients with and without Achilles enthesitis, respectively (p = 0.030). Conclusions In patients with AS, the presence of Achilles’ tendon enthesitis was associated with worse scores on the outcome measures after 2 years of follow-up, leading to a lower probability of achieving low disease activity.

BackgroundSpondyloarthritis, (axial (axSpA), peripheral (pSpA)) and psoriatic arthritis (PsA)) share enthesitis as a hallmark clinical feature. Reliable clinical instruments have been developed to assess enthesitis: Spondyloarthritis Research Consortium of Canada Enthesitis (SPARCC), Leeds Enthesitis Index (LEI), Maastricht Ankylosing Spondylitis Enthesitis Score (MASES) and MEI (Mander Enthesitis Index). Since these four indexes include different enthesis locations, they may capture a different number of patients with enthesitis in the different SpA entities.Objectivesa) To describe the individual locations of enthesitis in axSpA, pSpA and PsA; b) to evaluate whether the prevalence of patients with at least one enthesitis across the three groups differs depending on the use of SPARCC, LEI, MASES and MEI indexes; c) to evaluate the level of agreement between these indexes for detecting patients with at least one enthesitis in axSpA, pSpA and PsA populations.MethodsPerSpA was a multinational observational, cross-sectional study with 24 participating countries worldwide. A total of 4185 patients with a diagnosis of axSpA (2719), pSpA (433) and PsA (1033) according to the Rheumatologist’s opinion were included in this analysis. Information on the location of enthesitis collected during the study visit was used according to the SPARCC, LEI, MASES and MEI indexes.The prevalence of patients with at least one enthesitis according to the different indexes were compared across the diseases (axSpA, PsA and pSpA), and pair-wise agreement between indexes were evaluated using the Cohen’s kappa in the global population and in the three groups.ResultsOut of 36 locations, the most prevalent enthesitis in the overall population were the lumbar spinous processes (6.5%), the thoracic spinous processes (4.9%) and the insertion of the Achilles tendon right (4.8%) and left (3.9%). A total of 10.7%, 8.3%, 13.5% and 17.2% of patients in the overall population showed at least one enthesitis according to the SPARCC, LEI, MASES and MEI indexes, respectively. Figure 1 shows that, among patients with axSpA, MEI and MASES indexes capture the majority of patients with at least one enthesitis (98.7% and 82.4%, respectively), while in pSpA and PsA, MEI and SPARCC are the indexes which capture the majority of patients with enthesitis (100% and 84.6% for MEI and SPARCC in pSpA, and 97.3% and 77% for MEI and SPARCC in PsA, respectively). In PsA, the LEI only captured 57.2% of the patients with at least one enthesitis. In the total population, MASES and MEI showed the strongest agreement for patients with at least one enthesitis (absolute agreement 96.3%; Cohen’s kappa: 0.86). Similarly, among axSpA patients, MASES and MEI showed an almost perfect agreement (97.3%; 0.90), while LEI and MEI showed a moderate agreement (90.4%; 0.54). In pSpA patients, SPARCC and MEI showed the strongest agreement (97.2%; 0.90), as well as among PsA patients (95.4%; 0.82). However, MASES and SPARCC showed a less agreement in PsA patients (94.2%; 0.67).Figure 1.Prevalence of enthesitis captured by different indexes.ConclusionThe most prevalent locations of enthesitis on the global SpA population are the lumbar spinous processes, the thoracic spinous processes and Achilles tendon. MEI and MASES are the two index that capture more patients with enthesitis in axSpA, while MEI and SPARCC are the two index that capture more patients in pSpA and PsA. The LEI index may underestimate the prevalence of enthesitis in these patients. MASES and MEI showed the largest level of agreement in the overall population and in axSpA, while MEI and SPARCC showed the largest level of agreement in pSpA and PsA. These results suggest that the prevalence of enthesitis across entities differs depending on the disease and on the use of the different index.References[1]Heuft-Dorenbosch L, et al. Assessment of enthesitis in ankylosing spondylitis. Ann Rheum Dis 2003;62:127-132Disclosure of InterestsNone declared

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