Atypical gastrointestinal presentation of hereditary transthyretin amyloidosis: a case report highlighting the diagnostic challenge.

Background: Hereditary transthyretin amyloidosis (ATTR) is a rare, progressive multisystem disease, often underdiagnosed due to its heterogeneous presentation. This case highlights an atypical presentation of ATTR amyloidosis dominated by gastrointestinal symptoms and the diagnostic pitfalls associated with certain genetic subtypes that may escape standard imaging modalities. Case summary: We present a 68-year-old man with severe gastrointestinal symptoms and extreme weight loss, over a prolonged period. Initial investigations were inconclusive across multiple centres. A deep intestinal biopsy eventually revealed amyloid deposition, and subsequent genetic testing confirmed hereditary ATTR amyloidosis. Cardiac magnetic resonance imaging revealed myocardial involvement despite a negative 99mTc-HDP scintigraphy. The patient was referred for targeted therapy. Discussion: This case underscores the need for high clinical suspicion and a multidisciplinary approach when encountering unexplained gastrointestinal and cardiac symptoms. It also demonstrates the value of the European Society of Cardiology guidelines as a reliable reference point for guiding further management when diagnostic uncertainty arises.