Familial Mediterranean fever in patients with inflammatory bowel diseases: a nationwide study from the epi-IIRN

Inflammatory bowel diseases (IBD) and familial Mediterranean fever (FMF) are auto-inflammatory diseases with common clinical and biological features. We aimed to determine their association and characterize the natural history in patients with both diagnoses.

Utilizing data from the epi-IIRN cohort, which includes 98% of Israel's population, we calculated the adjusted prevalence of FMF among IBD patients vs non-IBD controls. Case ascertainment of IBD was determined according to validated algorithms and for FMF by ICD-9 codes and colchicine purchase.

In total, 34 375 IBD patients (56% Crohn's disease [CD] and 44% ulcerative colitis [UC]) were compared with 93 602 matched controls. Among IBD patients, 157 (0.5%) had FMF compared with 160 (0.2%) of non-IBD controls (OR = 2.68 [95%CI 2.2-3.3]; P < 0.001). Pediatric-onset IBD had a higher prevalence of FMF compared with adult-onset IBD (30/5243 [0.6%] vs 127/29 132 [0.4%]), without statistical significance (OR = 1.31 [0.88-1.96]; P = 0.2). FMF was more prevalent in CD (114/19 264 [0.6%]) than UC (43/15 111 [0.3%]; OR = 2.1 [1.5-3.0], P < 0.001). FMF diagnosis preceded that of IBD in 130/157 cases (83%). FMF was associated with a more severe disease activity in UC patients at diagnosis, but not in CD patients. Outcomes were comparable between patients with CD+FMF vs CD alone; however, in patients with UC+FMF, time to biologic treatment was shorter.

FMF is more prevalent in IBD patients than in the general population, particularly in CD. The diagnosis of FMF precedes the diagnosis of IBD in most cases, and may be associated with a more severe course in UC.