Protracted Febrile Myalgia Syndrome as Initial Presentation of Familial Mediterranean Fever in a Patient of Northern European Extraction Thought to have Ulcerative Colitis.

Introduction: Protracted febrile myalgia syndrome is a rare vasculitic manifestation of familial Mediterranean fever that presents as the initial familial Mediterranean fever manifestation in one-third of cases. While familial Mediterranean fever is classically autosomal recessive and associated with Mediterranean ancestry, the p.Met694del variant demonstrates autosomal dominant inheritance with a Northern European founder effect. MEFV-related enterocolitis can produce histologic features indistinguishable from inflammatory bowel disease. Case description: A 24-year-old European American man with no Mediterranean, Middle Eastern or Armenian ancestry, with biopsy-confirmed ulcerative colitis on upadacitinib, presented with six weeks of high-grade fevers, incapacitating myalgias, a 30-pound weight loss and pericardial effusion. Faecal calprotectin was markedly elevated (>8,000 μg/g) without gastrointestinal symptoms. Inflammatory markers were noticeably elevated with normal creatine kinase; extensive infectious and malignancy workup was negative. Bone marrow biopsy demonstrated focal haemophagocytosis without malignancy. Dramatic improvement occurred within 24-48 hours of corticosteroid initiation. Genetic testing revealed heterozygous p.Met694del, confirming autosomal dominant familial Mediterranean fever. At six-month follow-up on colchicine monotherapy without inflammatory bowel disease-directed therapy, inflammatory markers, faecal calprotectin and pericardial effusion had completely normalised, fulfilling Tel Hashomer criteria. Conclusion: This case highlights protracted febrile myalgia syndrome as an under-recognised initial presentation of autosomal dominant familial Mediterranean fever in non-Mediterranean populations. Colchicine-responsive normalisation of faecal calprotectin raises the possibility that MEFV-mediated enterocolitis contributed to intestinal inflammation initially attributed to ulcerative colitis. Early recognition enables amyloidosis prevention and essential genetic counselling for first-degree relatives. LEARNING POINTS: Protracted febrile myalgia syndrome - prolonged fever, incapacitating myalgia and normal creatine kinase, should prompt consideration of familial Mediterranean fever regardless of ancestry, as the p.Met694del variant follows autosomal dominant inheritance with a Northern European founder effect.Colchicine-responsive normalisation of faecal calprotectin (>8,000 to normal) without inflammatory bowel disease-directed therapy in a patient with biopsy-confirmed ulcerative colitis and a pathogenic MEFV variant, raises the possibility that MEFV-mediated enterocolitis contributed to intestinal inflammation initially attributed to inflammatory bowel disease, a distinction with direct therapeutic implications.Autosomal dominant MEFV variants carry critical implications for family counselling: first-degree relatives have a 50% risk of inheriting the variant and developing familial Mediterranean fever, including phenotype II amyloidosis (renal amyloidosis without preceding typical attacks).