Amyloidosis of pancreatic islets in primary amyloidosis (AL type).

Seven cases of primary amyloidosis (AL-type) were studied immunocytochemically for the possible involvement of pancreatic islets. The two cases with extensive organ involvement by AL-amyloidosis revealed amyloid deposits in pancreatic islets by routine HE and Congo red staining, which were positive for amyloid p and amyloid a, but were only focally positive for light chains kappa and lambda. Positive staining for amyloid p and amyloid a was also noted in the scattered pancreatic acinar tissues, and this positive staining was not specifically located in pancreatic islets as seen in type 2 diabetes mellitus. It is concluded that amyloid deposits in pancreatic islets occur in systemic AL-amyloidosis by a different mechanism from type 2 diabetes. Islet amyloidosis in AL-amyloidosis appears to deposit via circulation, depositing in both pancreatic islets and acinar tissue through blood vessels. In type 2 diabetes, beta islet cells die by cytotoxic effects of smaller amylin (islet amyloid polypeptide, IAPP) aggregates, and the interstitial space created by the necrotic beta cells is replaced by larger IAPP aggregates, to form complex, polymerized islet amyloid. In AL-amyloidosis, the amount of amyloid and light chain deposits in pancreatic islets is much less than that of the other organs and appears to have no connection to type 2 diabetes because the patients did not present diabetes or hyperglycemia. However, considerable islet amyloidosis can be seen in severe AL-type amyloidosis.