Quantitative 99mTc-Pyrophosphate SPECT/CT evaluation of tafamidis response in a case of transthyretin cardiac amyloidosis.

Transthyretin cardiac amyloidosis (ATTR-CA) is increasingly recognized as a cause of heart failure in elderly patients. Noninvasive diagnosis with technetium-99m pyrophosphate (99mTc-PYP) scintigraphy has become established, but quantitative approaches for therapy monitoring remain under investigation. We present a case of wild-type ATTR-CA in an 82-year-old man treated with tafamidis. Baseline echocardiography showed concentric left ventricular hypertrophy with preserved ejection fraction, impaired global longitudinal strain, and elevated B-type natriuretic peptide (BNP). Planar and SPECT/CT imaging with 99mTc-PYP demonstrated diffuse myocardial uptake (grade 3, H/CL 1.97). Quantitative analysis with GI-BONE software yielded SUVmax 4.2, amyloid deposition volume (AmyDV) 122 cm³, and total amyloid uptake (TAU) 313. Endomyocardial biopsy confirmed wild-type ATTR. After 18 months of tafamidis therapy, symptoms persisted with further GLS impairment and BNP elevation, while echocardiographic wall thickness remained increased. In contrast, repeat PYP imaging showed reduced uptake (grade 2, H/CL 1.64) with markedly decreased quantitative indices (SUVmax 2.3, AmyDV 2 cm³, TAU 4). This case demonstrates that volumetric indices can capture substantial therapy-related changes, although discordance with functional and biomarker findings highlights the need for integrated assessment. Quantitative 99mTc-PYP SPECT/CT may serve as a promising tool for therapy monitoring in ATTR-CA.