99mTechnetium-pyrophosphate bone scan: A potential biomarker for the burden of transthyretin amyloidosis in skeletal muscle: A preliminary study

Introduction/Aims: Transthyretin amyloidosis (ATTR) proteins can infiltrate skeletal muscle and infrequently cause a myopathy. ^99mTechnetium-pyrophosphate (^99mTc-PYP) is a validated biomarker for cardiac involvement in variant and wild-type ATTR (ATTRv and ATTRwt, respectively). The aim of this study was to test the hypothesis that ^99mTc-PYP is a biomarker for muscle burden of ATTR.

Methods: Radioisotope uptake in the deltoid muscles of patients with ATTR was compared to uptake in control subjects without amyloidosis in a retrospective study. ^99mTc-PYP scans were evaluated in 11 patients with ATTR (7 ATTRv, 4 ATTRwt) and 14 control subjects. Mean count (MC) values were measured in circular regions of interest (ROIs) 2.5–3.8 cm2 in area. Tracer uptake was quantified in the heart, contralateral chest (CC), and deltoid muscles.

Results: Tracer uptake was significantly higher over the deltoids and heart but not the CC, in patients with ATTR than in control subjects. MC values were 120.1 ± 43.7 (mean ± SD) in ATTR patients and 78.9 ± 20.4 in control subjects over the heart (p = 0.005), 73.3± 21.0 and 63.5 ± 14.4 over CC (p = 0.09), and 37.0 ± 11.7 and 26.0 ± 7.1 averaged over both deltoid muscles (p = 0.014).

Discussion: ^99mTc-PYP is a potential biomarker for ATTR amyloid burden in skeletal muscle.