When AL-amyloidosis is suspected, a tissue biopsy is required to establish the diagnosis. Congo red staining of a fat pad aspirate would reveal amorphous tissue deposits that appear pink using standard light microscopy and apple green under polarized light, but this test does not distinguish between AL, acquired, and familial/inherited subtypes of amyloidosis. In AL-amyloidosis, a plasma cell dyscrasia, the amyloid fibrils are composed of monoclonal light chains (usually ι). Performing both serum and urine protein electrophoresis with immunofixation reveals a monoclonal light chain in over 90% of patients with AL-amyloid but does not eliminate the need for κ/λ immunostaining of tissue amyloid deposits. Without confirming the Ig origin of the amyloid, one cannot rule out the possibility of another type of amyloidosis with an incidentally discovered monoclonal gammopathy of uncertain significance.1 An inherited form of predominantly cardiac amyloidosis resulting from a specific transthyretin mutation has been described in older African Americans. In this Caucasian patient, this diagnosis is unlikely.
- κ/λ Immunostaining of tissue amyloid deposits.
1. Lachmann HJ, Booth DR, Booth SE, et al. Misdiagnosis of hereditary amyloidosis as AL (primary) amyloidosis.
N Engl J Med 2002;346:1786-91.
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