Early Versus Late Onset Familial Mediterranean Fever: Similarities, Discrepancies, and the Value of Neutrophil to Lymphocyte Ratio in Detecting Autoinflammation.

Objective: The objective of this study was to compare the clinical and laboratory characteristics of early-onset familial Mediterranean fever patients (EOFPs), adult-onset familial Mediterranean fever (FMF) patients (AOFPs), and late-onset FMF patients (LOFPs). Materials and Methods: This study included a total of 202 FMF patients aged 18 years and above. Mediterranean fever (MEFV) gene mutations, demographic data, clinical characteristics, medications patients are on, neutrophil to absolute lymphocyte ratio (NLR), and C-reactive protein (CRP) levels obtained during an attack period, and three weeks after the attack were recorded. Based on the age of symptom onset, patients were divided into three groups: <20 years (EOFPs), 20-39 years (AOFPs), and ≥40 years (LOFPs). Results: The most common symptom was abdominal pain, followed by fever. Fever was statistically significantly more common in EOFPs compared to LOFPs (p=0.001). Most patients with the M694V homozygous mutation had a disease onset below 20 years of age, whereas no compound heterozygous mutation was found in LOFPs. The body mass index (BMI) in EOFPs was lower than in AOFPs and LOFPs (p=0.002). In the attack-free group, patients with the M694V homozygous mutation had significantly higher NLRs (median, 2.36 vs. 2.01, p=0.042). Conclusion: LOFPs had a milder form of the disease with less frequent abdominal pain and fever. We would like to advise clinicians that the NLR can be used to detect acute and subacute inflammation, especially in patients with the M694V homozygous mutation among EOFPs.