Familial Mediterranean fever phenotype progression into anti-cyclic citrullinated peptide antibody-positive rheumatoid arthritis: a case report

Familial Mediterranean fever (FMF) is caused by dysfunction of the MEFV gene product, pyrin. Here we report a case of FMF phenotype which developed into rheumatoid arthritis (RA), based on a positive result for anti-cyclic citrullinated peptide (CCP) antibody (Ab). A 42-year-old woman presented to our clinic with more than 6 months of intermittent arthralgia in the wrists, feet, and fingers associated with menstruation. No fever was reported and there was no family history of FMF or other autoimmune diseases. Laboratory tests revealed elevated C-reactive protein (CRP) and rheumatoid factor (RF). Tests for autoantibodies including anti-CCP Ab, antinuclear Ab, and anti-DNA Ab were all negative. Genetic analysis identified an R304R homozygous mutation in MEFV; however, the pathological significance is unclear because this mutation does not cause amino acid substitution. We diagnosed incomplete FMF phenotype despite the lack of fever due to periodic arthritis, lack of autoantibodies, and complete resolution of arthritis following colchicine treatment within a day. Several months later, increased stiffness and arthralgia persistently occurred in finger joints on both sides. Ultrasonography revealed synovitis at the metacarpophalangeal and metatarsophalangeal joints. Laboratory analysis revealed the patient to be positive for anti-CCP Ab. Therefore, we finally diagnosed RA. Her arthritis diminished following administration of methotrexate and salazosulfapyridine. We consider the possibility that pyrin dysfunction may have affected the acquired immunity, contributing to the onset of RA as an autoimmune disease. This is an interesting case of equivalent FMF progressing into RA and will be valuable to raise awareness of a continuum from autoinflammatory to autoimmune disease.