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Familial Mediterranean Fever mimics

Familial Mediterranean fever (FMF) is an inherited autoinflammatory disease characterized by recurrent attacks of fever and acute inflammation of the membranes lining the abdomen, joints and lungs. These attacks are often short-lasting, around 1-3 days. It is important to recognise these presenting symptoms so that appropriate investigations and management can be implemented to our patients.

Although there is no cure for FMF, early treatment is often effective. Thus, better phenotyping of our patients are needed. 

At the ACR22, Dr Baspinar et al. (Abstract #1839) performed a large case-control study in Turkey to assess whether acute abdomen episodes which led to appendectomies could be misdiagnosed as appendicitis rather than FMF-associated serositis. They defined FMF patients who underwent unindicated appendectomies as case while those who did not as control. 303/1958 (15%) had appendectomies. The authors reported that FMF diagnosis was made much later in case vs control group i.e. up to double the time. M694V homozygous mutation of the MEFV gene was more common in the former. This mutation has been associated with severe disease features. During this acute abdomen attack, the CRP levels were much higher in case than control group. However, it would be difficult to distinguish the two accurately. This study reminded us to consider FMF as a differential diagnosis in patients presenting with recurrent short-lasting fever and acute abdomen. Better and clinically useful biomarkers than CRP levels and molecular genetic testing are needed so that unnecessary appendectomies can be prevented. 

Since musculoskeletal symptoms are common in FMF, can we define the pattern of joint involvement better? Dr Ayla AY et al. (Abstract #1830) performed a cohort study in Turkey and showed that 40% out of over 2000 patients had arthralgia or arthritis. This occurred during the first FMF attack in 73% of patients. Combining features that occurred more than 50% of the patients, we should think of FMF in patients presenting with red, mono or oligo arthritis in the lower limbs (ankles and knees). Thus, reactive arthritis, crystal arthropathy and peripheral spondyloarthropathy jump to my mind and could be FMF mimickers. About ¼ of patients had concomitant diagnosis of axial spondyloarthropathy, so this is another mimicker and we should be wary patients presenting with short, acute episode of inflammatory back pain.

Better recognition of FMF may improve short- and long-term outcomes since the majority (80%) of patients with arthralgia/arthritis responded to a course of colchicine. 

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