Behçet's disease‬ and familial Mediterranean fever: Two sides of the same coin or just an association? A cross-sectional study‬.

BACKGROUND: Familial Mediterranean fever (FMF) is a genetic disease, characterized by attacks of fever, arthritis, serositis and pain. Behçet's disease (BD) is an inflammatory disorder with a genetic basis, characterized by oral and genital ulcers, uveitis, pustular erythematous cutaneous lesions, arthritis, central nervous system involvement and possible vascular manifestations such as venous thrombosis, arteritis and aneurysms.

OBJECTIVES: To investigate the association and actual differentiation between these two entities in a large-scale population-based study.

METHODS: Data for this study was collected from the databases of "Clalit Health Services", the largest state-mandated health service organization in Israel. All adult members diagnosed with BD were included (n=892) and as well as their age- and sex-matched controls (n=4444), creating a cross-sectional population-based study. Medical records of all subjects were analyzed for documented FMF. A logistic regression model was done to estimate how BD, age, gender, BMI, ethnicity and socioeconomic status contributed as risk factors for FMF.

RESULTS: The proportion of FMF in patients with BD increased compared with those reported in controls (5.83% and 0.23%, respectively, P<0.001). This coexistence was prominent among both sex groups but was much stronger among female BD patients (females with OR of 177 and of 8.4 in males, P<0.001). In a multivariate analysis, BD was identified as an independent risk factor for FMF (OR 25.16, 95% CI 13-53.3).

CONCLUSION: BD diagnosis was found to be independently associated with higher incidence of FMF, especially in females, people of Arab descent and BMI>30. Our data imply that understating the differentiation between FMF and BD is not evident and clear in a real-life population of patients with BD.