Conclusive Diagnosis of Transthyretin Cardiac Amyloidosis Is Dependent on Ruling Out Light Chain Amyloidosis

Distinguishing between amyloidosis types is critical because the therapeutic modalities and prognosis for light chain amyloidosis (AL) and transthyretin amyloidosis (ATTR) differ significantly.¹ AL cardiomyopathy (AL-CM) can occasionally lead to a significant myocardial uptake on 99mTcpyrophosphate (99mTc-PYP) scan, defined as grade ≥2 on qualitative scoring.

In a retrospective review of patients with AL-CM seen at the Cleveland Clinic between 2015 and 2019, Andrej Gabrovsek, MD, and colleagues identified patients with AL-CM who underwent 99mTc-PYP scan to determine the prevalence and degree of myocardial uptake in these patients.² The planar imaging grading scheme is defined at the Cleveland Clinic as grade 0 (no myocardial uptake), grade 1 (uptake less than rib), grade 2 (equal to rib), or grade 3 (greater than rib). A heart-to-contralateral (H/CL) ratio was calculated for each patient. To ascertain if the uptake was in the myocardium (defined either as focal or diffuse) or in the blood pool, SPECT imaging was utilized. An H/CL ratio >1.3 and grade ≥2 myocardial uptake indicated a positive scan.

During the study period, a total of 227 patients who underwent a 99mTc-PYP scan were positive, with 26 patients being diagnosed with AL-CM. Fifteen percent (4/26) of patients with AL-CM had grade ≥ 2 myocardial uptake and an H/CL ratio >1.3 on planar imaging, confirmed with SPECT imaging. Endomyocardial biopsy revealed 1 patient with grade 3 uptake who had significant amounts of AL and ATTR amyloid deposits; however, this patient had a negative TTR genetic test. The researchers reported that AL-CM contributed to 2.2% of the positive scans.

The authors concluded that 15% of patients with AL-CM who underwent a 99mTc-PYP scan had significant myocardial uptake. They noted that when using a 99mTc-PYP scan for noninvasive diagnosis, it is critical for AL-CM to be ruled out to make a conclusive diagnosis of transthyretin cardiac amyloidosis.

References

1. Donnelly JP, Gabrovsek A, Sul L, et al. Evidence of concurrent light chain and transthyretin cardiac amyloidosis in 2 patients. J Am Coll Cardiol CardioOnc. 2020;2:127-130.
2. Gabrovsek A, Hussain M, Collier P, et al. AL amyloidosis causing positive technetium-99m pyrophosphate imaging. Presented at: 2020 International Symposium on Amyloidosis; September 14-18, 2020. Abstract PT118.