Unexpected Abdominal Fat Pad Biopsy: Answer

Abstract

Granulomatous vasculitis secondary to AIns (insulintype) amyloidosis.Amyloid typing by liquid chromatography-tandem mass spectrometry was positive for AIns (insulin-type) amyloidosis. The histopathologic findings are very unusual for AIns amyloidosis, which previous reports show to be diffuse deposition of pink amorphous material in the dermis and subcutis. However, in this case, insulin-type amyloid presented as a granulomatous vasculitis. The material to which the foreign body reaction was engendered was proven to be amyloid by Congo red staining and by amyloid typing. Stains were negative for fungal vasculitis, and acid-fast bacillus and Fite stains were not performed as the pattern was not that of a mycobacterial infection. Similar histologic presentations as this have been reported with cerebral amyloid angiopathy and as rare drug reactions, such as to infliximab. 1,2 Insulin-type amyloidosis is a phenomenon in which subcutaneous masses develop at the site of repetitive insulin injections. This type of amyloid is a rare complication of chronic insulin therapy, and most patients present with a hard mass or an "insulin ball" at the site of their insulin injections. 3 It is known that insulin-type amyloid is not associated with systemic amyloidosis. 4 The patient in this case report did not present with any skin abnormalities, and instead, his insulintype amyloid was diagnosed during a systemic workup for amyloidosis. 5 This case report brings up a novel histologic and clinical presentation of insulin-type amyloid. The cause of the formation of these insulin-type amyloid masses has not been described, and the awareness of this condition is limited. By our research, this is the second case report that discovered insulin-type amyloid without a concurrent diagnosis of an "insulin ball." More importantly, this is the first case report that found insulin-type amyloid presenting as a deep dermal vasculitis. This finding suggests that pathologists should be aware of this novel presentation of insulin-type amyloid to accurately make this diagnosis. 5