A rare case of insulin-derived amyloidoma emerging outside typical injection sites raises questions about tissue trauma and amyloid formation, highlighting the potential of proteomic analysis for accurate diagnosis.
A rare case report published in the journal The Journal of Dermatology has described an insulin-derived amyloidoma developing in an unexpected place: the right groin of a man in his 50s with type 1 diabetes. Unlike the more familiar “insulin ball”, which forms at repeated injection sites, this lesion appeared as a 35mm by 20mm subcutaneous nodule in an area where the patient said he had never injected insulin.
The report adds an unusual twist to a condition usually linked to long-term insulin therapy. In most published cases, insulin-derived amyloidosis arises where injections are repeatedly given, often as firm, painless lumps that can be mistaken for lipohypertrophy or other soft-tissue lesions. Reviews of the condition have noted that these deposits can interfere with insulin absorption and worsen glycaemic control, making recognition clinically important.
In this case, histopathology showed degenerated tissue with amorphous eosinophilic material in a fibrofatty background, and Congo red staining confirmed amyloid. Standard immunohistochemistry did not identify a major amyloid type, but liquid chromatography-tandem mass spectrometry detected peptides from both human insulin and insulin aspart. According to the authors, that proteomic result established the diagnosis of insulin-derived amyloidosis.
The patient had undergone two operations for epidermoid cysts in the same region, and the authors suggest that prior surgical trauma may have altered the local tissue environment, perhaps through disrupted lymphatic drainage, allowing circulating insulin to deposit there. Similar reports in the literature have shown that proteomic analysis can be decisive when routine staining is inconclusive, reinforcing its growing role in amyloid typing.
The case is a reminder that insulin-derived amyloidosis should not be assumed to occur only at injection sites. For clinicians, the message is twofold: persistent subcutaneous nodules in people with diabetes deserve careful evaluation, and tissue proteomics may be the clearest route to diagnosis when conventional tests fail.
Disclaimer: This content is for informational purposes only and is not intended to be a substitute for professional medical judgment, advice, diagnosis, or treatment.
