Ultrasonographic evaluation of FMF patients with exertional leg pain: an overlooked component of the disease

OBJECTIVES: Exertional leg pain (ELP) is an underrecognized manifestation of FMF with unclear pathophysiology. This study performed a comprehensive ultrasonographic evaluation of lower-extremity joints, tendons and entheses in paediatric FMF patients with ELP, comparing findings with non-ELP patients and matched healthy controls. METHODS: Paediatric FMF patients carrying homozygous or compound heterozygous pathogenic MEFV variants were enrolled in this prospective study. Demographic, anthropometric and clinical data were collected, while a blinded operator performed standardized ultrasonographic evaluations. RESULTS: A total of 50 patients and 25 heathy controls were included (25 with ELP, 25 without). No differences were observed between the groups in demographic, anthropometric or FMF-related factors, including MEFV mutations and ISSF scores. Among the evaluated parameters, Achilles tendon thickness was significantly increased in children with ELP, independent of demographic or anthropometric factors, compared with both healthy and non-ELP group (P < 0.01). Nine patients exhibited grade 1 knee synovial effusions, predominantly in the ELP cohort, most with subclinical inflammation. One patient with ELP demonstrated enthesitis and was diagnosed with HLA-B27-negative ERA. Patellar tendon and plantar fascia thickness were comparable. CONCLUSION: Paediatric FMF patients with ELP demonstrated increased achilles tendon thickness. Although no standardized cut-off exists for tendinopathy, this may reflect tendon structural changes related to ELP. Moreover, FMF patients, particularly those with ELP, exhibited inter-attack knee effusions which may serve as a marker for subclinical inflammation. Larger longitudinal cohorts are needed to define ELP, elucidate its underlying pathways and clarify the clinical significance of Achilles tendon thickening.