3 Discordant Extracardiac Amyloid Proteins Highlighting Bystander Deposition in a Case of Light-Chain Amyloid...

Accurate differentiation of immunoglobulin light-chain (AL) from transthyretin (ATTR) amyloid cardiomyopathy is critical, as misclassification may delay appropriate therapy and worsen outcomes.

An 80-year-old woman with incidental gallbladder AL lambda and ApoA-IV amyloid deposits had elevated cardiac biomarkers and lambda monoclonal gammopathy. Bone marrow biopsy demonstrated AL and ATTR deposits. Echocardiography showed increased wall thickness, apical-sparing strain, and elevated filling pressures. Given these discordant findings, endomyocardial biopsy (EMB) was performed; proteomic analysis confirmed AL lambda deposition without ATTR, prompting anti-plasma cell therapy.

This is a rare case of mixed extracardiac amyloid required EMB with proteomic analysis to resolve discordant findings and confirm AL cardiomyopathy.

Amyloid cardiomyopathy subtyping is essential because AL and ATTR amyloidosis treatment differ fundamentally. Underrecognized codeposited "bystander" proteins may confound typing; therefore, discordant extracardiac findings may not represent the myocardial subtype. When uncertainty persists, particularly with monoclonal gammopathy, EMB is essential to define cardiac amyloid subtype.