This study aimed to evaluate the prevalence and characteristics of arthritis in pediatric familial Mediterranean fever (FMF) patients with biallelic pathogenic MEFV mutations on exon 10 and to assess the impact of axial joint involvement on disease progression.

This cross-sectional study included 808 pediatric FMF patients with biallelic exon 10 mutations, followed for at least 12months. Data on demographics, clinical features, genetic variants, and treatment responses were analyzed. Patients were grouped based on arthritis presence, duration, and axial joint involvement for comparative analysis.

Arthritis was observed in 19.2% of patients, with acute and chronic arthritis in 17.9% and 6.4%, respectively. The M694V allele frequency was significantly higher in the arthritis group (82%, P<0.01), with a predominance of the M694V/M694V genotype (70.3%). In contrast, V726A and R761H alleles were less frequent. Chronic arthritis with axial involvement was associated with older age at diagnosis (P<0.01), increased polyarticular involvement (P<0.01), and elevated colchicine resistance (22.6%, P<0.01). The most frequently affected joints included the knee and sacroiliac joints. HLA-B27 positivity was higher in axial arthritis cases, but the need for advanced therapies did not differ significantly.

Our study highlights the diverse arthritis presentations in pediatric FMF patients with biallelic pathogenic genotypes. The M694V allele was more prevalent in the arthritis group, suggesting a potential genetic link. Specifically, the reduced frequency of common FMF attack symptoms, such as fever and abdominal pain, in patients with arthritis suggests that this may lead to diagnostic delays. Chronic arthritis with axial involvement was associated with higher colchicine resistance and a greater need for advanced treatments. These findings emphasize the importance of tailored management strategies and long-term follow-up in pediatric FMF patients with arthritis to optimize outcomes.