All that glitters is not gold; due diligence when interpreting pyrophosphate cardiac scans to avoid misdiagnosis of transthyretin cardiac amyloidosis.
Butera B, Modi K, Klingler D, McCord J, and Ananthasubramaniam K. All that glitters is not gold; due diligence when interpreting pyrophosphate cardiac scans to avoid misdiagnosis of transthyretin cardiac amyloidosis. Journal of the American College of Cardiology 2020; 75(11):3132.
J Am Coll Cardiol
Background Technetium-99m pyrophosphate (PYP) nuclear scan is currently considered the noninvasive test of choice for transthyretin cardiac amyloidosis (TTRCA) with a heart to lung ratio greater than 1.5 suggesting TTRCA. Case An 81 year old female presented to cardiology clinic for evaluation of previously diagnosed TTRCA. Her electrocardiogram (Figure 1A) showed bifasicular block and an echocardiogram (Figure 1B-D) demonstrated diffuse left ventricular hypertrophy. As part of the workup a PYP scan (Figure 1E) was performed and interpreted to have a planar ratio of 1.5 with Grade 2 Tc-99m pyrophosphate uptake, consistent with TTRCA. Decision-making While planar images appeared to show some cardiac uptake equal to that of bone in the contralateral thorax, review of the single-photon emission computed tomography (SPECT) images (Figure 1F) and blood pool reconstruction images (Figure 1G) demonstrated only bone uptake of the tracer, on a background of blood pool activity with no myocardial uptake. Subsequent testing revealed elevated free kappa light chains and the patient was referred to a hematologist for further evaluation. Conclusion Light chain amyloidosis should be first ruled out given implications for treatment. Furthermore, errors in diagnosis of TTRCA can occur when only planar images and ratio cutoffs are used. Due diligence to evaluate SPECT data to confirm myocardial Tc-99m PYP uptake is important to confirm the diagnosis of TTRCA.