Proof-of-concept for the application of Raman spectroscopy in differentiating the subtypes of cardiac amyloidosis.

Cardiac amyloidosis is a clinically severe condition classified into three major subtypes based on the precursor protein: immunoglobulin light-chain (κ) (ALκ) amyloidosis, immunoglobulin light-chain (λ) (ALλ) amyloidosis, and transthyretin (ATTR) amyloidosis. To improve patient outcomes, subtype-specific treatment must be initiated promptly. Therefore, rapid differentiation is required. In this study, we aimed to differentiate cardiac amyloidosis subtypes using Raman spectroscopy, which enables rapid, non-destructive, label-free and preparation-free sample analysis. Raman spectra were acquired from amyloid-deposited areas in cardiac tissue sections obtained from autopsy cases of each disease subtype and compared with spectra from non-deposited areas. An increase in the high-wavenumber component of the Amide I band, assigned to β-sheet structures, was observed across all subtypes. Focusing on this band, principal component analysis was performed, resulting in the identification of five loading spectra useful for distinguishing between disease subtypes. A multinomial logistic regression model, utilizing the principal component scores derived from these loading spectra, achieved an overall accuracy of approximately 94% for differentiating disease subtypes in the training dataset, and 85% in the validation dataset based on spectra acquired from different areas within the same samples. This proof-of-concept study is limited by the small sample size, and the findings should be validated in studies with a larger sample size. Nevertheless, given the rapidity of Raman spectroscopy, our results may have practical future utility, such as enabling rapid differentiation of disease subtypes using surgical specimens from patients with carpal tunnel syndrome, which often precedes the onset of cardiac amyloidosis.