Desensitization for insulin allergy: a useful treatment also for local forms.

Insulin allergy is now a rare condition thanks to the introduction of human recombinant proteins in the 1980s. As a high-molecular-weight protein, insulin induces mainly type I hypersensitivity reactions, which can range from local erythema to anaphylaxis. Desensitization is the treatment of choice for systemic reactions in patients who require insulin and many authors recommend symptomatic treatment for local reactions [1]. Local forms of insulin allergy, however, can progress to systemic forms [2], and there has even been a report of fatal anaphylaxis in a patient who had previously experienced only local reactions [3]. We report the case of a 62-year old man who, in 2003, was diagnosed with type 2 diabetes mellitus, which was controlled with oral treatment for 7 years. In 2010, during admission to hospital due to hyperglycemic decompensation, he received intravenous insulin, which he tolerated well. On discharge, it was decided to initiate subcutaneous administration of insulin aspart plus protamine (12 units-0-12 units). Immediately after receiving the fi rst dose, the patient developed a pruritic, erythematous nodule (5 cm diameter) that lasted for 48 hours. Treatment was changed to insulin glargine (12 units-0-12 units) and insulin detemir (14 units-0-14 units), but the lesion returned. Insulin was replaced by oral treatment and the patient was referred to our outpatient clinic. Skin prick tests (SPTs) performed with all available insulin preparations in Spain, including insulin lispro [3,4], were positive in all cases. Specifi c immunoglobulin (Ig) E for insulin was 14.8 kUA/L (ImmunoCap Phadia). SPTs with latex and protamine were both negative. Patch tests with insulin aspart plus protamine, insulin detemir, insulin glargine, latex and zinc were all negative at 48 and 96 hours. A diagnosis of type I hypersensitivity to insulin was established. A target dose of 6 units of subcutaneous insulin a day was established by an endocrinologist in accordance with the patient’s insulin needs. We started by administering simultaneous fractionated doses (2 by 2) of the total target Table. Desensitization Protocol