Diagnostic value of bone scintigraphy versus CMR in cardiac amyloidosis.

Abstract

Objectives and background: Accurate diagnosis of transthyretin amyloidosis cardiomyopathy (ATTR-CM) and its differentiation from light-chain (AL) cardiac amyloidosis (CA) cases (AL-CM) is of paramount importance, since treatment strategies are totally different and obviously more successful in case of early disease detection. Surprisingly, comparative imaging data based on concurrent cardiovascular magnetic resonance (CMR) and bone scintigraphy in the same patients with biopsy-proven diagnosis of CA are still rare.

Methods: This was a real-world retrospective single-centre study based on a local clinical care pipeline and we carefully analysed clinical, laboratory, CMR, bone scintigraphy data (and if necessary additional endomyocardial biopsy (EMB) data) in patients with suspected CA. As a major inclusion criterion, we only looked at those patients who underwent both a CMR study and a bone scintigraphy - with a clear-cut imaging finding detected by at least one imaging method.

Results: N=123 patients in whom the final diagnosis was obtained either non-invasively based on combined findings from bone scintigraphy and monoclonal protein studies or invasively based on additional EMB findings were included. A positive CMR result indicating presence of CA was found in 121 patients - suggesting a CMR sensitivity of 98.4% for the diagnosis of any CA. Bone scintigraphy identified 18 patients with low to moderate uptake (Perugini-score = 0-1) and 105 patients with high uptake (Perugini-score ≥2) - resulting in a sensitivity for bone scintigraphy of 85.4% for the diagnosis of any CA. There was an agreement ("diagnostic match") between CMR and bone scintigraphy results in 103 patients (84%) of the total study cohort, while a discrepancy ("diagnostic mismatch") was observed in 20 patients (16%). In 18 out of these 20 diagnostic mismatch cases, CMR correctly diagnosed the presence of CA despite a negative or inconclusive result on bone scintigraphy (eight with AL-CM, eight with ATTR-CM, and two with EMB-proven but unspecified CA).

Conclusion: CMR shows a substantially higher diagnostic yield for the diagnosis of CA compared to bone scintigraphy, if a real-world cohort of patients comprising different subtypes of CA is looked at, since CMR does not only detect ATTR-CM but also depicts other CA subtypes such as AL. In case of a clear-cut positive CMR result unequivocally indicative of CA, there is no incremental diagnostic value of an additionally performed bone scintigraphy.

Relationship with industry policy: No financial support or influence of any pharmaceutical company.