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

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 (SUVmean-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, SUVmean-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.