Misdiagnosis of 99mTc-PYP-positive Danon disease as ATTR-CA: a case report and molecular imaging pitfalls

This case exposes a critical diagnostic pitfall: intense 99mTc-PYP uptake (Perugini grade 3) may occur in non-amyloid conditions like Danon disease, likely due to myocardial microcalcification, challenging scintigraphy's specificity for ATTR-CA. Key discriminators include younger age, Wolff-Parkinson-White syndrome, marked creatine kinase elevation, and neurocognitive impairment in Danon disease versus elderly male predominance, low-voltage QRS complexes, and refractory heart failure in ATTR-CA. Pathological confirmation remains essential for young patients with "ATTR-like" scintigraphy, particularly when atypical features (e.g., skeletal muscle involvement or preexcitation syndromes) are present. Comprehensive integration of demographic, electrocardiographic, biomarker, and imaging data is imperative to prevent misdiagnosis and ensure appropriate management.