The complexities of insulin allergy: a case and approach

BACKGROUND: Insulin hypersensitivity is rare, but challenging for individuals with diabetes. The prevalence of insulin allergy has decreased since the introduction of human recombinant insulin preparations. Hypersensitivity reactions range from injection site erythema and swelling, to anaphylaxis. While some reactions are to excipients (zinc, protamine, metacresol), many are to recombinant insulin itself. We present a case of type 1 hypersensitivity to various preparations of insulin in a patient with insulin-dependent type 2 diabetes mellitus (T2DM). CASE PRESENTATION: A 61-year-old woman with a 30-year history of insulin-dependent T2DM was referred for evaluation of reactions to insulin. She had two episodes over 5-months; both required Emergency Department visits and epinephrine administration. The first episode entailed a burning sensation of the extremities and nausea, immediately after injecting NovoRapid(®) insulin. The second event entailed a similar reaction but this time there was also angioedema of the upper airway with difficulty breathing and hypotension, immediately after injecting Levemir(®) and NovoRapid(®), and taking metformin. There were no cofactors such as exercise, infectious illness, or NSAIDs use. Skin testing was performed with metformin, Lantus(®), Humalog(®), NovoRapid(®), glulisine, insulin regular, NPH, Levemir(®) and the excipient protamine, as per published testing concentrations. Metacresol was not tested as its use was restricted by the hospital pharmacy. Insulin preparations with and without metacresol were included in testing however. A clinic staff served as a negative control. The patent had negative testing with protamine, but sensitization to all insulin preparations. Metformin skin testing and challenge along with latex IgE were negative. Subsequently, she underwent intentional weight loss of 70 lb, and was started on oral hypoglycemics with good effect. CONCLUSIONS: Our case highlights the importance of diagnosing insulin allergy through a detailed history and focused testing. Therapeutic strategies include avoidance and insulin alternatives, alternate insulin preparations, or desensitization. In severe recurrent hypersensitivity reactions, Omalizumab or pancreatic transplantation have been effective.