Localized amyloidosis at the site of repeated insulin injection in a diabetic patient

A 60-year-old woman diabetic patient presented with a subcutaneous mass in right lower abdominal quadrant where recombinant human insulin or insulin analogue had been injected for 16 years. Her diabetes has been insulin resistant with insufficient blood glucose control. The mass was extirpated under the suspicion of neoplasm but it was found to consist of diffuse deposition of eosinophilic amorphous materials mixed with inflammatory change. Congo-red staining demonstrated positive red color and yielded green birefringence by polarized microscopy. Pre-digestion with potassium permanganate was incomplete to quench positive Congo-red stains. Immunostains with insulin antibody were positive for this deposition but not so with amylin or AA or AL amyloid. Thus, the mass was considered to be localized amyloidosis composed of iatrogenic A-Ins type amyloid. Thus, the case suggested that her insulin resistance, i.e. refractoriness of insulin treatment, may be ascribed to poor penetration of injected insulin and human insulin itself or its analogue is amyloidogenic to form a local mass.