Cardiac phenotype in hereditary transthyretin amyloidosis: correlations between fibril types and 99mTc-DPD uptake

Variant transthyretin amyloidosis is a systemic disease. In Sweden, the Val30Met variant is the most prevalent. Val30Met presents in two phenotypes: an early-onset form dominated by polyneuropathy and a late-onset form frequently accompanied by cardiomyopathy. These phenotypes are associated with two amyloid fibril types. Type A fibrils, contain both fragmented and full-length transthyretin, whereas type B fibrils contain only full-length transthyretin. Fibril type has been linked to differences in cardiac tracer uptake on 99mTc-DPD scintigraphy. A total of 152 patients with confirmed variant transthyretin amyloidosis evaluated at Umeå University Hospital, Sweden, were included. Age at disease onset and cardiac involvement, investigated by echocardiography, Troponin-T, and NT-proBNP, were assessed in relation to fibril type in abdominal fat and scintigraphic findings. Eighty-five patients had type A fibrils and sixty-seven had type B fibrils. Type A patients were older at diagnosis and had pathologic scintigraphies and more severe cardiac involvement. A subset of type B patients (15%) exhibited cardiac tracer uptake and had cardiac characteristics and age at disease onset similar to those with type A fibrils. Even though there was a strong correlation with findings in abdominal fat pad biopsies, results from 99mTc-DPD scintigraphy correlated better with clinical phenotype.