The most reliable investigation in amyloid disease is-

The best sites from which to obtain a biopsy specimen in systemic amyloidosis are the abdominal fat pad and rectal mucosa (approaching 90% sensitivity for fat pad and 73-84% for rectal mucosa) While some imaging modalities can strongly suggest amyloidosis, a tissue sample showing birefringent material is still the criterion standard. This is definitely the case in terms of cardiac-specific amyloid. While endomyocardial biopsy is the best confirmatory > test for local cardiac amyloid deposition, it can be very- risk averse and requires a centre of excellence with the full complement of immunohistochemical and molecular-based testing