Clinical Diagnosis and Subtyping of Cardiac Amyloidosis by Mass Spectrometry

Purpose Medical treatment for cardiac amyloidosis (CA) is evolving rapidly. Heart transplantation can be a valid option when followed by transplantation of bone marrow or liver, dependent on the type and origin of the amyloid protein. Thus, accurate typing of amyloidosis has implications for treatment, prognosis, and genetic counseling. Although non-invasive diagnostic techniques can type CA, endomyocardial biopsy (EMB) may be needed in the case of equivocal imaging findings or discordant data. We aimed to define the role of mass spectrometry (MS) for diagnosis and subtyping of CA. Methods Nineteen previously diagnosed CA cases, who underwent EMB at Sahlgrenska University Hospital (SU), Gothenburg, between the beginning 1990s and 2016, were selected. MS analysis, modified from was conducted on duplicate samples from myocardial tissue for each case included.1 Clinical features and diagnoses were used as gold standard and compared to the MS findings. Results Clinical diagnosis and the MS analysis agreed in 14 cases (73.7 %); in 3/19 (15.8 %) diagnosis was unclear or discordant (Fig.1). MS analysis revealed that transthyretin (TTR) amyloidosis was the most abundant amyloid protein in the samples examined (9/19; 47.3 %), whereas the AA subtype only occurred in 1 case (5.2 %). The AL κ type amyloidosis occurred in 3 cases (15.8 %), and AL λ type in six cases (31.6 %). These results strongly correlated with the clinical features in all patients. Clinical diagnosis could not be retrieved from the medical records in 2 cases (10.4 %). Additional 20 patients with clinical CA are presently under study. Conclusion MS analysis of a small amount of endomyocardial tissue can be used to subtype CA with a high diagnostic validity. The method differentiated between TTR, SAA and Ig light chain amyloidosis. AL κ and AL λ identities correlated to those found in serum and urine electrophoreses. MS can therefore be of use to subtype CA for cases in which clinical findings are inconclusive. 1) Brambilla F et al. Blood. 2012 Feb 23;119(8):1844-7