Uncertain Clinical Relevance of Serial Bone Scintigraphy Findings in Treated Transthyretin Amyloid Cardiomyopathy

Technetium-99m-labeled 3,3-diphosphono-1,2-propanodicarboxylic acid (^99mTc-DPD) scintigraphy is a critical part of the validated nonbiopsy diagnostic algorithm for transthyretin amyloid cardiomyopathy (ATTR-CM). With the advent of novel disease-modifying therapies for ATTR-CM, there is intense interest in establishing the utility of DPD scans as an indicator of treatment response.

The authors conducted a retrospective multimodality imaging study to determine the utility of ^99mTc-DPD to track treatment response in ATTR-CM.

ATTR-CM patients from the United Kingdom National Amyloidosis Centre who were receiving amyloid-specific disease-modifying therapy (DMT) and underwent pre- and post-treatment ^99mTc-DPD/single-photon emission computed tomography-computed tomography scans were included. Myocardial percentage injected dose (PID), a proposed scintigraphic indicator of cardiac amyloid burden, was measured at baseline and follow-up. Change from baseline in this variable was compared with that of other validated biomarkers of disease severity.

A total of 66 patients with ATTR-CM who received DMT underwent serial ^99mTc-DPD scans. At follow-up, with a median time between ^99mTc-DPD scans of 27.5 months (Q1-Q3: 21.9-33.1 months), there was a mean reduction from pre-DMT myocardial PID on ^99mTc-DPD scintigraphy of 1.5 ± 1.5%. No statistically significant correlation between the change in PID at follow-up and change in echocardiographic, biochemical, or cardiac magnetic resonance parameters was identified. Discordance in which there was an improvement on follow-up ^99mTc-DPD scintigraphy despite disease progression was observed in 28/66 patients (42.4%).

Our study indicates a poor correlation between reduction in ^99mTc-DPD uptake at follow-up and numerous established biomarkers of ATTR-CM treatment response. Changes in DPD uptake in ATTR-CM patients receiving DMT should be interpreted with caution.