Prevalence and characteristics of patients with incidental cardiac uptake on bone scintigraphy

Background: Bone scintigraphy is emerging as a confirmatory diagnostic tool for transthyretin cardiac amyloidosis (ATTR-CA). This study aimed to investigate the frequency and clinical characteristics of patients with incidental cardiac uptake and incidental ATTR-CA on bone scintigraphy. Methods: All bone scintigraphic studies performed at a tertiary teaching hospital between 2011 and 2022 were reviewed retrospectively. Patients who underwent bone scintigraphy to confirm ATTR-CA were excluded. Patients with cardiac uptake of grade 2 or 3 were included and divided into two groups: possible ATTR-CA group and noncardiac amyloidosis (non-CA) group. Results: Of the 61,432 bone scintigraphic studies performed on 32,245 patients, 23 (0.07%) had grade 2 or 3 cardiac uptake. Nine of 23 patients (39.1%) were assigned to the non-CA group because they showed cardiac uptake from definite other causes or focal uptake that did not match CA. The remaining 14 patients (60.9%) were classified as the possible ATTR-CA group, and five patients were referred to cardiologists and finally diagnosed with ATTR-CA. Two patients were treated with tafamidis. Patients in the ATTR-CA group were significantly older and had a less frequent history of end-stage renal disease than those in the non-CA group. Other characteristics were comparable in both groups. Conclusions: Although incidental ATTR-CA in patients undergoing bone scintigraphy for noncardiac reasons is uncommon, if cardiac uptake is observed in elderly patients without metastatic calcification associated with end-stage renal disease, further diagnostic work-up for ATTR-CA as a cause of undiagnosed heart failure should be considered.