Visceral technetium-99 m-labeled pyrophosphate uptake in patients with wild-type transthyretin cardiac amyloidosis

Abstract

Objectives

Technetium-99 m-labeled pyrophosphate (Tc-99 m-PYP) scintigraphy can image tracer uptake in the myocardium, subcutaneous fat, and skeletal muscles of patients with wild-type amyloid transthyretin (ATTRwt) cardiac amyloidosis (CA), which indicates ATTR deposition. However, there are few reports of visceral Tc-99 m-PYP uptake in patients with ATTRwt-CA. This study was conducted to determine whether Tc-99 m-PYP scintigraphy can image ATTR deposition in the viscera, particularly the liver, spleen, and gastrointestinal tract.

Methods

Chest- and abdomen-centered Tc-99 m-PYP scintigraphy with single-photon emission computed tomography-computed tomography fusion images were acquired 2 h after patients with clinically suspected CA were intravenously injected with 20 mCi of the tracer. The participants were divided into two groups: ATTR-CA and non-ATTR-CA groups. Semi-quantitative visual grade of hepatic tracer uptake and mean standardized uptake values in the liver (SUV_mean-L) were investigated. The presence or absence of tracer uptake in the spleen and alimentary tract (stomach, small intestine, and colon, excluding the rectum and anus) was also investigated.

Results

Of 209 participants (median age, 85 years; range, 79–90 years; 56.5% male), 72 patients, all of whom had ATTRwt-CA, were assigned to the ATTR-CA group, whereas 137 were assigned to the non-ATTR-CA group. Semi-quantitative visual grade of hepatic tracer uptake, SUV_mean-L, and the rate of splenic tracer uptake did not vary between both groups (p = 0.100, p = 0.904, and p = 0.356, respectively). However, the ATTR-CA group showed a higher rate of tracer uptake in the alimentary tract than the non-ATTR-CA group (p < 0.001). Within the digestive tract, the tracer uptake rates in the small intestine and colon were significantly higher in the ATTR-CA group than in the non-ATTR-CA group (p < 0.001 and p < 0.001, respectively); however, no significant difference was observed in gastric accumulation between the two groups (p = 0.305).

Conclusions

Tc-99 m-PYP scintigraphy may image ATTR deposition in the small intestine and colon of patients with ATTRwt-CA. In contrast, Tc-99 m-PYP uptake likely reflects blood pool activity rather than ATTR deposition in the liver, spleen, and stomach.