Injection Site Reaction to Various Insulins as Type III Allergy With Urticarial Vasculitis in a Patient With Type I Diabetes Mellitus.

Injection site reactions are defined as skin reactions at the injection site to drugs administered subcutaneously. Pathophysiologically, these reactions are based on different immunological mechanisms. We report the case of a 49-year-old patient with type 1 diabetes mellitus (first diagnosis in 1994 at the age of 23 years). Continuous subcutaneous insulin infusion using an insulin pump has been used for many years. The patient presented to the department of dermatology with progressive symptoms in the area of the insulin injection sites on the lower abdomen, accompanied by pain, burning, erythema, tenderness, and the formation of subcutaneous nodules. Previous attempts to use different insulins and to change the injection sites did not improve his symptoms. Furthermore, the symptoms appeared within hours after the insulin pump was attached, so that the injection site has to be changed as soon as every 48 hours. No anaphylactic shock was reported at any time. Multiple histological specimens were obtained from an older lesion on the abdomen as well as from test sites after standard allergological tests (prick and intradermal tests) of various insulins. Histologically, these biopsies showed the image of an extensive deep-reaching small vessel vasculitis with the aspect of an urticarial vasculitis and confirmed the diagnosis of an injection-site reaction that can be characterized as a type III hypersensitivity reaction.