Wild-type transthyretin amyloid cardiomyopathy diagnosed by 99mTc-HMDP scintigraphy and an endomyocardial biopsy despite inconclusive 99mTc-PYP findings.

UNLABELLED: Transthyretin amyloid cardiomyopathy (ATTR-CM) is a progressive but under-diagnosed disease. With the emergence of novel therapies, including transthyretin (TTR) stabilizers and RNA silencers, an accurate diagnosis and timely therapeutic intervention have become increasingly important. 99mTechnetium (99mTc)-labeled bone radiotracer scintigraphy, using pyrophosphate (PYP) or hydroxymethylene diphosphonate (HMDP), is a key noninvasive diagnostic tool. We herein report a case of wild-type ATTR-CM in an 87-year-old woman who presented with heart failure with a preserved ejection fraction (HFpEF) and a history of bilateral carpal tunnel release surgery. Despite strong clinical suspicion, 99mTc-PYP scintigraphy demonstrated only a cardiac blood pool without a definite myocardial uptake, and was ultimately interpreted as inconclusive. However, subsequent 99mTc-HMDP scintigraphy revealed distinct myocardial tracer accumulation (Perugini grade 2). An endomyocardial biopsy confirmed TTR-positive amyloid deposits, and a genetic analysis identified wild-type ATTR-CM. This case highlights the need for careful analysis of cardiac blood pool patterns on 99mTc-PYP scintigraphy, and underscores that when 99mTc-PYP scintigraphy is inconclusive, an endomyocardial biopsy should be considered in patients with clinical features suggestive of ATTR-CM (e.g. HFpEF, left ventricular hypertrophy, and a history of carpal tunnel syndrome) to avoid a missed or delayed diagnosis.

LEARNING

OBJECTIVE

To recognize that even though 99mTc-PYP scintigraphy generally has high diagnostic accuracy for ATTR-CM, inconclusive cardiac blood-pool 99mTc-PYP scintigraphy requires a careful analysis rather than being assumed to be negative. When ATTR-CM is strongly suspected based on clinical findings, an endomyocardial biopsy should be considered. This case underscores the importance of integrating imaging findings with clinical judgment to avoid a missed or delayed diagnosis of ATTR-CM.