Familial Mediterranean Fever as a Cause of Recurrent Pleurisy in a Child With Crohn's Disease: A Case Report.

Introduction: Familial Mediterranean fever (FMF) and Crohn's disease (CD) are chronic autoinflammatory disorders that share similar clinical and biological features. Both disorders are characterized by chronic and relapsing symptoms. In some cases, FMF can coexist with CD, which makes diagnosis and treatment challenging. Case Presentation: A 9-year-old Egyptian child was diagnosed with CD at the age of 5, based on clinical symptoms and endoscopic histopathologic findings. Initially, the patient responded well to biological therapy (anti-TNFα), showing improvements in symptoms along with declines in inflammatory markers and fecal calprotectin levels. At the age of 7, the child began experiencing frequent episodes of fever accompanied by pleuritic chest pain. Right-sided pleural effusion was identified on repeated chest X-rays. The patient was diagnosed with recurrent acute bacterial pneumonia due to immune suppression and was managed with multiple courses of oral antibiotics. During the last presentation, in one of these episodes, further investigation was pursued due to a lack of response to antibiotics, indicated by persistently elevated inflammatory markers (CRP, ESR) and nonresolving mild right-sided pleural effusion. FMF was suspected based on the patient's clinical presentation and chest imaging. A detailed family history revealed a positive FMF diagnosis in a first-degree cousin. Genetic testing was performed, which revealed two heterozygous pathogenic mutations that support the FMF diagnosis. Treatment with colchicine prevented further episodes. The patient continued to receive follow-up care from the GI team for CD and was maintained on adalimumab. Conclusions: FMF should be considered for children with CD who exhibit pulmonary symptoms that do not respond to CD treatment.