Abstract
A 66-year-old man presented for treatment of a previously biopsied hidradenoma of the lower mid abdomen. An excision was performed. In addition to focal residual tumor, histopathology was notable for prominent deposition of brightly eosinophilic material around subcutaneous blood vessels, as well as for focal extravascular deposits. The deposits were positive for Congo red and Congo red fluorescence, consistent with amyloidosis. Further history was obtained, and revealed that the patient regularly injected insulin subcutaneously on the abdomen for treatment of type 2 diabetes. Immunohistochemistry showed that the deposits were positive for insulin and negative for amyloid A. Serum and urine evaluation for monoclonal gammopathy was negative. Considering the clinical history in conjunction with laboratory testing, the dermal deposits were interpreted as insulin-derived amyloid due to subcutaneous insulin injection. Unlike the few previously reported cases of amyloid deposition associated with subcutaneous insulin injection1, our case represents an incidental finding within an excision specimen for an unrelated lesion, indicating that this process can be histopathologically prominent, but clinically undetected. Awareness of this phenomenon may facilitate correct diagnosis and reduce concern for systemic amyloidosis in similar future cases.
1. Bernárdez C, Schärer L, Molina-Ruiz AM, Requena L. Nodular amyloidosis at the sites of insulin injections. J Cutan Pathol. 2015 Jul;42(7):496-502. doi: 10.1111/cup.12501. Epub 2015 Jun 4. PMID: 25953111.