Evaluating the Use of Technetium Pyrophosphate Imaging and Cardiac Biopsy

Cardiac SPECT with technetium pyrophosphate (99mTc-PYP) imaging is used to differentiate cardiac amyloid transthyretin (ATTR) from amyloid light chain (AL) subtypes when a diagnosis is unclear. Garcia and colleagues from the University Hospital Cleveland Medical Center presented a case study that underscores the critical clinical decision points healthcare providers need to consider to ensure accurate diagnosis.

An 83-year-old male presented with a chief complaint of dyspnea, and he was treated initially for acute decompensated heart failure.

He was assessed and found to have low-flow, low-gradient, severe aortic stenosis (AS) with severe left ventricular hypertrophy (LVH) on echocardiogram. The patient also had 6 years of smoldering amyloid, stage C heart failure with reduced ejection fraction, and a history of bilateral carpal tunnel surgery.

During the presentation, Garcia highlighted the key diagnostic decision-making point to consider in this case. Although cardiac AL was suspected, given the patient’s age, and the history of smoldering amyloid, the presenter urged caution; given the consistent history of the smoldering phase without any progression, the ATTR subtype must also be carefully considered.

A 99mTc-PYP scan was performed, revealing grade 3 uptake and a heart to contralateral lung (H/CL) ratio of 1.6, which could indicate ATTR. This was specifically based on the analysis comparing the visual density and uptake of technetium pyrophosphate in the heart to that of the visual density of the ribs. This uptake is then ranked from a visual grade of 0, 1, 2 or 3, with grade 0 reflecting no myocardial uptake of technetium pyrophosphate, grade 1 demonstrating that myocardial uptake is greater than that of the ribs, grade 2 demonstrating myocardial uptake that is equal to that of the ribs, and grade 3 demonstrating myocardial uptake that is greater than that of the ribs.

The results of a cardiac MRI confirmed bi-atrial, biventricular LVH, severe AS, and advanced cardiac amyloidosis. Subsequent endomyocardial biopsy revealed positive Congo-red staining, and immunofluorescence with lambda light chain–restrictive disease; these factors are consistent with a diagnosis of AL.

Based on these conflicting results, which did not provide a clear diagnosis, a pathology specimen was sent for mass spectrometry analysis, and the final diagnosis of ATTR was confirmed. The authors concluded that despite previous reports suggesting ATTR amyloidosis has been detected with 99mTc-PYP imaging with 97% sensitivity and 100% specificity in quantitative measure of H/CL, with a cutoff value >1.5, in this rare case, the initial biopsy results suggested the AL subtype. This case is a reminder that because the gold standard for diagnosing cardiac amyloidosis remains biopsy, further characterization may be necessary when discordance is present among investigative studies.

Source: Garcia RA, Osnard M, Sekulic M, et al. What to do next? Discordance between technetium pyrophosphate imaging and cardiac biopsy for AL versus ATTR cardiac amyloidosis. Presented at: ACC.21, American College of Cardiology 70th Annual Scientific Session & Expo, May 15-17, 2021. Poster 1086-07.

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