Isolated Tricuspid Valve Dysplasia in a Patient with Behçet's Disease: An Unusual Mimic of Carcinoid Heart Disease and Arrhythmogenic Right Ventricular Cardiomyopathy

Isolated tricuspid valve dysplasia (ITVD) is a rare congenital abnormality of the tricuspid valve that may remain clinically silent until adulthood and can resemble acquired causes of severe tricuspid regurgitation. This case report describes a 28-year-old man with established Behçet's disease who presented with progressive exertional dyspnoea, palpitations, and bilateral lower-limb oedema. Clinical examination showed features of right-sided heart failure and a pansystolic murmur consistent with severe tricuspid regurgitation. Electrocardiography demonstrated complete right bundle branch block, and 48-hour Holter monitoring showed frequent premature atrial contractions without sustained supraventricular or ventricular tachycardia. Transthoracic echocardiography revealed severe tricuspid regurgitation caused by diffuse thickening, retraction, and malcoaptation of the tricuspid valve leaflets, with marked right atrial and right ventricular dilatation and mildly reduced right ventricular systolic function. The initial differential diagnosis included carcinoid heart disease, arrhythmogenic right ventricular cardiomyopathy, Ebstein's anomaly, and Behçet's-related inflammatory valvulopathy. Mild biochemical abnormalities were not accompanied by clinical features of carcinoid syndrome, and 18F-FDG PET-CT and 68Ga-DOTATATE PET-CT showed no neuroendocrine tumour or hepatic metastases. Cardiac magnetic resonance imaging demonstrated severe right ventricular dilatation and apical aneurysms but no evidence supporting arrhythmogenic right ventricular cardiomyopathy. The absence of apical leaflet displacement excluded classic Ebstein's anomaly. After multidisciplinary evaluation, isolated tricuspid valve dysplasia was diagnosed, and the patient underwent successful bioprosthetic tricuspid valve replacement. Recovery was uneventful, and discharge occurred on postoperative day 10. This case highlights the need for structured multimodality assessment of primary severe tricuspid regurgitation in young adults with systemic inflammatory disease, particularly when congenital and acquired right-sided valvular disorders have overlapping clinical and imaging features.