Donut Morphology of Cardiac Amyloidosis: A Glazed Over Diagnosis.

BACKGROUND: Transthyretin cardiac amyloidosis (ATTR-CM) typically manifests with diffuse biventricular wall thickening, and technetium-99m pyrophosphate scintigraphy is highly accurate in this setting. False-negative results may occur, however, in early-stage disease when amyloid infiltration is nondiffuse. CASE SUMMARY: A 74-year-old man with heart failure with preserved ejection fraction, atrial fibrillation, and bilateral carpal tunnel syndrome was referred after negative cardiac amyloid radionuclide imaging (CARI) performed elsewhere. Cardiac magnetic resonance revealed isolated circumferential basal wall thickening with localized subendocardial late gadolinium enhancement and extracellular volume of 38%, forming a donut-shaped morphology. Repeat CARI with technetium-99m pyrophosphate confirmed nondiffuse grade 2 uptake in the basal left ventricle, establishing wild-type ATTR-CM. Tafamidis 61 mg daily was started alongside optimized heart failure therapy. DISCUSSION: Amyloid deposition progresses base to apex, producing nondiffuse scintigraphy patterns in early disease. Cardiac magnetic resonance identified the unusual morphology and directed repeat scintigraphy, extending beyond current diagnostic guidelines and avoiding diagnostic delay. TAKE-HOME MESSAGE: When clinical suspicion for ATTR-CM is high, negative CARI should prompt further evaluation rather than premature exclusion of the diagnosis.