Transthyretin cardiac amyloidosis - what left ventricle pattern to expect on 99mTc-Diphosphonate scintigraphy?

The diagnostic significance of [99mTc]Tc-Diphosphonate scintigraphy in transthyretin cardiac amyloidosis (TTR-CA) has become pivotal. The widespread adoption of single-photon emission computed tomography (SPECT) and SPECT/CT acquisitions, in accordance with guidelines, has highlighted the non-uniform distribution of the radiopharmaceutical in the left ventricle (LV). Despite its importance, there is limited literature addressing this phenomenon, leaving several questions unanswered.

This study aims to examine the regional distribution of [99mTc]Tc-Diphosphonate in the left ventricle of patients diagnosed with transthyretin cardiac amyloidosis (TTR-CA).

Between December 2018 and November 2023, 26 TTR-CA patients (mean age=82,4±5,9; 5 females) underwent [99mTc]Tc-Diphosphonate scintigraphy with [99mTc]Tc-DPD or [99mTc]Tc-HMDP. Planar images provided Visual Perugini scores and Heart/Contralateral ratio (H/CL). Additionally, 17 patients had a 180º SPECT acquisition, while 9 had a 360º SPECT/CT acquisition. Tomographic studies, processed using QGS/QPS software (GE Xeleris), segmented the left ventricle into 17 parts, and average segment scores were calculated relative to the maximum pixel value. Nine patients underwent both non-attenuated corrected (NAC) and attenuated corrected (AC) reconstruction. Statistical analysis employed the SPSS package (IBM SPSS statistics 27), using Mann-Whitney and Wilcoxon tests for myocardial segmental comparison and Spearman correlation analysis for variable relationships. A significance level of p<0,05 was considered.

Perugini scores were 1 (1 patient), 2 (12 patients), and 3 (13 patients), with a mean H/CL of 1,7±0,3. Figure 1 illustrates segmental [99mTc]Tc-Diphosphonate uptake in the left ventricle for the entire population. Septal region uptake (segments 2+3+8+9+14) was higher (mean uptake=73%) than the rest of the left ventricle (segments 1+4+5+6+7+10+11+12+13+15+16+17; mean uptake=59%); (p=0,004 - Mann-Whitney test).

There was no correlation between LV H/CL ratio and segmental [99mTc]Tc-Diphosphonate uptake (Spearman correlation analysis).

Segmental uptake showed a significant difference between AC and NAC reconstruction in segments 1 (p=0,008), 2 (p=0,013), 3 (p=0,008), 4 (p=0,008), 5 (p=0,008), 6 (p=0,008), 9 (p=0,015), 10 (p=0,012), 11 (p=0,011), 12 (p=0,008), 13 (p=0,079), 15 (p=0,017), 16 (p=0,047), 17 (p=0,008) - Wilcoxon test.

[99mTc]Tc-Diphosphonate uptake in CA-TTR was higher in septal segments, consistent with prior studies. No correlation between H/CL and segmental uptake was observed across all Perugini scores, which isn’t in concordance with some other studies published, suggesting the need for further investigations in this area.

The attenuation reconstruction correction altered, as expected, the [99mTc]Tc-Diphosphonate uptake on the inferior wall and apex, but also on other segments, located on septal, anterior e lateral walls.Fig 1