Systemic Oxalosis Mimicking Transthyretin Amyloid Cardiomyopathy: A Cause of False Positive Tc-99m PYP Scintigraphy.

BACKGROUND: Technetium-99m pyrophosphate (Tc-99m PYP) scintigraphy is a noninvasive imaging modality in the diagnosis of transthyretin amyloid cardiomyopathy (ATTR-CM), though false positive results may result in adverse clinical outcomes. CASE SUMMARY: A 53-year-old man with a history of heart failure with reduced ejection fraction and end-stage renal disease presented with upper extremity weakness and hypervolemia. Tc-99m PYP scintigraphy was suggestive of ATTR-CM. However, transthyretin genetic testing was negative, and endomyocardial biopsy was without evidence of amyloid deposition. The patient later died, and autopsy revealed myocardial oxalate deposition concerning for primary vs secondary hyperoxaluria. DISCUSSION: Although Tc-99m PYP scintigraphy is a sensitive and specific modality for the detection of ATTR-CM, clinicians should recognize other infiltrative cardiomyopathies causing false positivity such as systemic oxalosis.