Nuclear Medicine Imaging for the Diagnosis of ATTR Cardiac Amyloidosis

Overview Bone scintigraphy is widely recognized as a useful tool for diagnosing cardiac amyloidosis, particularly transthyretintype (ATTR) cardiac amyloidosis.However, no consensus has been established regarding its optimal usage and evaluation methods.For instance, a combination of visual assessment using the Perugini Grade system and semi-quantitative evaluation of the heart-to-contralateral lung (H/CL) ratio using the Bokhari method is commonly employed.Imaging is performed either 1-hour or 3-hours post-administration, utilizing planar imaging, single photon emission computed tomography (SPECT) imaging, or SPECT/CT imaging.In Japan, two radiopharmaceuticals, 99m Tc-PYP (pyrophosphate) and 99m Tc-HMDP (hydroxymethylene diphosphonate), are used, yet a standardized approach remains lacking.Notably, given that probable diagnosis based on nuclear imaging has now been established as a diagnostic criterion for ATTR cardiac amyloidosis, a designated intractable disease, it is crucial to ensure accurate interpretation of imaging results.Misinterpretation may lead to clearly positive cases being overlooked or clearly negative cases being misdiagnosed as positive.The objective of this Working Group (WG) report is to establish a standardized diagnostic framework for ATTR cardiac amyloidosis using bone scintigraphy in Japan and to provide guidelines aimed at minimizing misdiagnosis. Background Basics of cardiac amyloidosisVarious guidelines for cardiac amyloidosis have been published (1), providing detailed descriptions of the disease.Therefore, this section presents a brief overview. Subtypes of cardiac amyloidosis relevant to cardiovascular careSeveral subtypes of amyloidosis exist; however, the two most relevant to cardiovascular care are ATTR amyloidosis and light-chain (AL) amyloidosis. ATTR amyloidosisATTR amyloidosis is further classified into wild-type (ATTRwt) and hereditary (ATTRv) forms.