Enthesitis may be one of the signs of severe disease in familial Mediterranean fever.

Objective: Familial Mediterranean fever (FMF) is an auto-inflammatory disease that is also characterized with some of the common musculoskeletal features of spondyloarthritis (SpA). Enthesitis is the hallmark of SpA. Recently, it was postulated that exertional leg pain is a possible sign of lower extremity enthesitis associated with FMF severity. In this study, we have evaluated the association between the enthesitis, enthesitis score and disease severity in FMF patients.

Methods: We enrolled 238 FMF patients that fulfilled the modified Tel-Hashomer criteria. We assessed the presence of enthesitis at the Maastricht Ankylosing Spondylitis Enthesitis Score (MASES) defined sites with standard palpation method. Then, FMF patients dichotomised two groups as enthesitis group and controls. Herein, we evaluated the enthesis extensity with MASES. FMF disease severity was determined via the international severity scoring system for FMF (ISSF). Firstly, we have compared demographic properties, disease-related features and ISSF scores of the groups. Then, we have correlated ISSF with MASES in enthesitis group.

Results: We showed that 54 (22.6%) of 238 patients had enthesitis. The demographic features were similar between the groups. The enthesitis group had higher ISSF scores (p < 0.001); higher frequency of fever (p = 0.004), exertional leg pain (p < 0.001), myalgia (p < 0.001) and arthritis (p = 0.01); and more intense, widespread, frequent and longer attacks compared with controls. Moreover, there was a weak correlation between ISSF and MASES in the patients with enthesitis.

Conclusion: Enthesitis may be a sign of more severe FMF phenotype and frequently associated with other musculoskeletal manifestations resemble SpA. Key points •More than one-fifth of the patients with FMF would suffer from enthesitis. •The FMF patients with enthesitis had higher ISSF scores; higher frequency of fever, exertional leg pain, myalgia and arthritis; and more intense, widespread, frequent and longer attacks as compared with controls. •Enthesitis may be a sign of more severe FMF phenotype and frequently associated with other SpA-like musculoskeletal feature.