Clinically Probable Late-Onset Familial Mediterranean Fever Presenting as Recurrent Pericarditis and Suggestive of Evolving Constrictive Physiology.

Familial Mediterranean fever (FMF) is a rare genetic autoinflammatory disorder that usually appears in childhood. It is marked by recurrent episodes of fever and inflammation of the serous membranes. Late-onset cases are rare and often misdiagnosed due to symptoms similar to those of other infections or inflammatory diseases. We report the case of a 65-year-old man who presented with recurring fever, pleural effusions, and pericarditis over two months, suggestive of evolving constrictive physiology. Despite being hospitalized several times, tests for infections and cancers ruled out other causes. This included thoracenteses, a pericardial window, a pleural biopsy, and bone marrow analysis. Pathology showed fibrinous pericarditis and chronic pleuritis with fibrosis, without signs of cancer. The patient was started on colchicine, which led to a quick improvement in his condition. Considering the symptom presentation and response to colchicine, we diagnosed clinically probable FMF based on established criteria, noting that late-onset presentations over the age of 60 represent fewer than 5% of all FMF cases. This case emphasizes the need to suspect FMF in patients with unexplained recurrent serositis, even in older individuals. Although heart involvement in FMF is uncommon, it can imitate serious conditions and delay proper treatment. Colchicine is the main treatment, and regular follow-ups are important to check for response and side effects. A team approach is vital, especially in unusual cases, to lower the risk of complications such as amyloidosis and heart problems.