AHL amyloidosis mimicking transthyretin amyloidosis on cardiac Tc-99 m pyrophosphate scan: A diagnostic challenge.

Background: Amyloidosis is a multisystem disease characterized by the deposition of amyloid fibrils, leading to organ dysfunction. When cardiac amyloidosis is suspected, it is essential to screen for light chain amyloidosis (AL) and transthyretin amyloidosis (ATTR), the two most common subtypes.

Methods: We report a patient with advanced heart failure and mild kidney dysfunction as initial symptoms. Preliminary testing revealed a slightly abnormal light chain ratio and a strong positive Tc-99 m pyrophosphate (PYP) scan. Biopsies of the heart, bone marrow, and kidney confirmed amyloidosis. Further immunofluorescence and mass spectrometry analysis identified immunoglobulin G and lambda light chain deposits. The patient was diagnosed with multiple myeloma and heavy and light chain amyloidosis (AHL) and initiated treatment with cyclophosphamide, bortezomib, and dexamethasone, rather than tafamidis, an oral transthyretin kinetic stabilizer used for ATTR.

Conclusions: AHL amyloidosis is a rare subtype. This case demonstrates that a positive PYP scan, even with intense uptake, is not entirely specific for ATTR. Tissue confirmation is essential for a definitive diagnosis, particularly when light chain disease or other rare forms are suspected, because AL/AHL and ATTR have distinct treatments and prognoses and may coexist.