The coexistence of rheumatoid arthritis (RA) and familial Mediterranean fever (FMF) has been rarely seen in case reports in the literature. Herein, we wanted to present a patient who had been followed up and treated as RA, but on investigation we concluded that he really had FMF and its joint complaints associated with sacroiliitis. Recovery was achieved by etanercept administered as if he was an RA patient. 1. Introduction Familial Mediterranean fever (FMF) is an autosomal recessive, autoinflammatory disease characterized by recurrent self-limiting attacks of fever, arthritis, and serositis [1]. Mutations in the pyrin-encoding gene Mediterranean fever (MEFV) on chromosome 16p13.3 are responsible for clinical findings and different phenotypical features [2, 3]. Pyrin proteins affected by these mutations alter inflammatory processes via some cytokines, especially interleukin-1β. Inflammatory processes can cause arthritis (in any joints, including the sacroiliac joint), fever, serositis, and erysipelas-like skin lesions. Nevertheless, phenotypical variations may be seen among patients having the same genotypes [2, 3]. Spinal (i.e., sacroiliitis) and peripheral joint (i.e., knee arthritis) involvements of FMF can be resembling spondyloarthropathies (SpA) features [4]. In addition, it has been notified that sacroiliitis could be seen in 7% of Turkish FMF patients [4]. M694V mutation can be encountered significantly higher frequencies in FMF patients with sacroiliitis [4]. Recently, antitumor necrosis factor (TNF) agents have been frequently used to produce a clinical response in patients with resistance to colchicine therapy [4–6]. The coexistence of rheumatoid arthritis (RA) and familial Mediterranean fever (FMF) has been rarely seen in case reports in the literature [6, 7]. Herein, we wanted to present a patient who had been followed-up and treated as RA, but on investigation we concluded that he really had FMF and its joint complaints associated with sacroiliitis. Recovery was achieved by etanercept administered as if he was an RA patient. 2. A Case Report A 45-year-old man had initially been admitted for arthritis in each knee in 2005. He was diagnosed as RA in another health center and treated with sulfasalazine (SSZ), methotrexate (MTX), and prednisolone. However, he did not use this therapy regularly. He suffered from abdomen, back, and low-back pain. His laboratory test results were as follows: erythrocyte sedimentation rate (ESR) 57？mm/h, C-reactive protein (CRP) 3.91 (0–0.8)？mg/dL, and RF 21.1？IU/mL in 2010. He had elevated AST, ALT, and ALP
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