Table 3.

Potential causes of inconsistencies between planar ^99mTc‐PYP scintigraphy and biopsy findings in suspected ATTR‐CM

Planar 99mTc‐PYP scintigraphy	Biopsy	Potential causes of inconsistencies
Positive	Negative	Sampling errors in biopsy Errors in scintigraphy imaging time or evaluation Errors in pathological diagnosis Cardiac pools Deposit of proteins other than transthyretin (e.g. AL)
Negative	Positive	Errors in scintigraphy evaluation Errors in pathological diagnosis Deposit of proteins other than transthyretin (e.g. AL) ATTRv‐CM with a low sensitivity in 99mTc‐PYP scintigraphy (Phe64Leu mutation)

A positive ^99mTc‐PYP scintigraphy result refers to Grade 2 (moderate cardiac uptake equal to rib uptake) or Grade 3 (high cardiac uptake greater than rib uptake), and a negative result refers to Grade 0 (no cardiac uptake) or Grade 1 (mild cardiac uptake less than rib uptake).

^99mTc‐PYP, ^99mtechnetium‐pyrophosphate; AL, light chain; ATTR‐CM, transthyretin amyloid cardiomyopathy; ATTRv‐CM, variant ATTR‐CM.