A high degree of suspicion is necessary to yield the diagnosis of cardiac amyloidosis. Cardiac amyloidosis should be suspected in patients with congestive heart failure or cardiomyopathy in the absence of ischemic or valvular heart disease.11 Diagnosis of amyloidosis begins with immunofixation of the serum and urine as a screening test.4 Ninety percent of patients with AL amyloidosis show monoclonal light chains with immunofixation.5 Positive immunofixation provides an indication for biopsy to establish a diagnosis. Congo red tissue stain will show an apple-green birefringence due to the beta-pleated protein structure when viewed under a polarizing microscope.1
Biopsy of the subcutaneous abdominal fat is a convenient, minimally invasive procedure that will yield a diagnosis in 70% to 80% of patients with amyloidosis.5 Deep rectal tissue biopsy is diagnostic in about 80% of cases; however, the specimen must be deep enough to include the submucosa.16 Bone marrow biopsy will prove positive for 50% to 60% of patients and will also assess the plasma cell type, which will aid in diagnosis of the amyloidosis type.5 Other possible sites for biopsy include the minor salivary glands, gingival tissue, and skin.4 Endomyocardial biopsy is virtually 100% sensitive for the diagnosis of cardiac amyloidosis and should be performed if less invasive types of biopsy prove nondiagnostic.1,10 However, cardiac biopsy poses certain risks and may not be necessary if echocardiographic findings are consistent with cardiac amyloidosis and histological diagnosis of AL amyloidosis has been confirmed from another tissue sample.1,4,10 Persistence in obtaining a diagnostic specimen is needed when cardiac amyloidosis is suspected.