A case report of an uncommon presentation of 99mtechnetium pyrophosphate scintigraphy in transthyretin cardiac amyloidosis: A potential diagnostic pitfall, pseudo-positive or pseudo-negative?

Abstract

^99mTechnetium pyrophosphate (^99mTc-PYP) scintigraphy has shown utility for diagnosis of transthyretin (ATTR) cardiac amyloidosis with a high sensitivity and specificity. However, in clinical practice, a protocol and a method of analysis of this modality are not yet unified. We present a case of ATTR cardiac amyloidosis showing a positive cardiac uptake in planar imaging but no myocardial uptake in single-photon emission computed tomography/computed tomography (SPECT/CT) fusion imaging on ^99mTc-PYP scintigraphy. We considered this tracer accumulation in the cardiac blood pool to be an inconclusive study. In this report, we focus on an inconclusive study case as a potential pitfall of ^99mTc-PYP scintigraphy and discuss the interpretation of ^99mTc-PYP scintigraphy findings with using both planar and SPECT/CT imaging for improvement of diagnostic accuracy for ATTR cardiac amyloidosis. <Learning objective: The present report describes the importance of distinguishing myocardial uptake from the cardiac blood pool by both planar and single-photon emission computed tomography/computed tomography fusion imaging on ^99mtechnetium pyrophosphate (^99mTc-PYP) scintigraphy for diagnosis of transthyretin cardiac amyloidosis. To improve diagnostic accuracy, the ^99mTc-PYP scintigraphy protocol including the method of evaluation and interpretation of the findings should be unified.>.

Keywords: 99mTechnetium pyrophosphate scintigraphy; Planar and single-photon emission computed tomography imaging; Transthyretin cardiac amyloidosis.

Fig. 1

An electrocardiogram showed atrial fibrillation, low voltage in limb leads, and poor R-wave progression in leads V1–V2 at the initial evaluation (A). The low voltage in limb leads progressed and T inversion in leads V3–V6 appeared 8 months later (B). A transthoracic echocardiogram showed left ventricular hypertrophy and severe biatrial dilatation (C, D).

Fig. 2

^99mTechnetium pyrophosphate (^99mTc-PYP) scintigraphy and semiquantitative analysis on planar images using heart retention (done 3 h after injection of ^99mTc-PYP) showed grade 1 uptake in the heart (A-1, B-1). Single-photon emission computed tomography/computed tomography fusion imaging showed cardiac blood pool uptake (A-2,3,4, B-2,3,4) on the first and second examinations, but local patchy uptake in the myocardium of left ventricle septal wall was also revealed in the second examination (B-2, 4; yellow arrows).

Fig. 3

Results of ^99mTc-PYP scintigraphy in our 133 patients suspected of having ATTR cardiac amyloidosis. ^99mTc-PYP, technetium pyrophosphate; ATTRwt, wild-type transthyretin cardiac amyloidosis (biopsy-proven TTR amyloid deposition and negative genetic testing); ATTRm, mutated transthyretin amyloidosis (biopsy-proven TTR amyloid deposition and positive genetic testing); HF, heart failure.