Diagnostic tools for amyloidosis.

Demonstration of amyloid deposits in biopsy specimens is the only means of confirming the diagnosis of amyloidosis. In experienced hands, nonsurgical biopsies of the rectal mucosa or, preferably, of the abdominal fat pad or labial salivary glands provide the diagnosis in 80 to 85% of cases. Immunolabeling studies help to determine the histological type of amyloidosis but are not performed routinely in everyday practice. In patients with a family history of amyloidosis, studies of the genome and amyloid protein can identify the protein variants capable of causing systemic amyloidosis. Once the diagnosis of amyloidosis is established, the extent of systemic involvement with amyloid should be evaluated by performing renal and hepatic function tests, a proteinuria assay, and an echocardiogram. Scintigraphy with radiolabeled serum amyloid P (SAP) component is a rapid and specific investigation that provides a map of the amyloid deposits. Deposits are usually seen in the liver and spleen. SAP component scintigraphy can provide support for the diagnosis of amyloidosis in patients with negative histological studies. Tissue retention of radioactivity predicts survival.