Extracardiac Biopsy Sensitivity in Transthyretin Amyloidosis Cardiomyopathy Patients With Positive 99 mTc-Labeled Pyrophosphate Scintigraphy Findings.

Background: The accurate sensitivity of amyloid deposition in extracardiac tissue (subcutaneous tissue and gastrointestinal tract) has not been evaluated in transthyretin amyloidosis cardiomyopathy (ATTR-CM) patients. This study aimed to evaluate the sensitivity of amyloid deposition in obtained endomyocardial and extracardiac biopsies.

Methods and results: This study retrospectively evaluated 175 consecutive ATTR-CM patients (wild-type [ATTRwt]: 134, hereditary [ATTRv]: 41) who had positive findings on ^{99 m}Tc-labeled pyrophosphate (^{99 m}Tc-PYP) scintigraphy and underwent tissue biopsy of at least one organ (subcutaneous tissue, gastrointestinal tract, and endomyocardium). Amyloid deposition was observed in the subcutaneous tissue of 57/150 patients (38%), gastrointestinal tract of 80/131 patients (61%), and endomyocardium of 108/109 patients (99%). Compared to patients with ATTRv, ATTRwt had significantly lower sensitivity in subcutaneous tissue (73% vs. 25%, P<0.01) and tended to be lower in the gastrointestinal tract (74% vs. 57%, P=0.08) biopsies. Among 124 patients who underwent both subcutaneous tissue and gastrointestinal tract biopsies, amyloid was detected in at least 1 specimen in 91 (73%) patients. The sensitivity of the combination of extracardiac biopsies was 66% and 94% in ATTRwt-CM and ATTRv-CM, respectively. Multivariate analysis reveals that ATTRv was the only significant predictor of amyloid deposition in the subcutaneous tissue.

Conclusions: Subcutaneous tissue and gastrointestinal tract biopsy sensitivity are inadequate, especially in patients with ATTRwt; however, the combination of these extracardiac biopsies contributes to increased sensitivity in patients with positive ^{99 m}Tc-PYP scintigraphy findings.