TO THE EDITOR:

Diagnosis of amyloidosis, with the possible exception of cardiac transthyretin amyloidosis (ATTR) in patients without monoclonal components, requires demonstration of tissue amyloid deposits and identification of the amyloidogenic protein.2,3  The gold standard for amyloid detection is Congo red (CR) staining, based on amyloid’s congophilia and birefringence under polarized light (PL; CR-PL). When systemic amyloidosis is suspected, subcutaneous abdominal fat, acquired by fine-needle aspiration or punch biopsy, is considered the tissue of choice, given the high sensitivity (up to 80% to 90%)5-7  and low risk of major complications.

Although birefringence under PL is a defining feature of amyloid, CR-PL interpretation critically depends on equipment quality, the pathologist’s expertise, and connective tissue abundance.8,9  This may translate into low specificity in nonspecialized centers and unnecessary second-level testing. In our experience,...

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