Human insulin allergy-immediate and late type III reactions in a long-standing IDDM patient

Abstract Human insulin allergy—immediate or late type III reaction—is a rare event. We report the case of a 33-year-old female patient with insulin-dependent diabetes mellitus for 25 years who presented, in the last 8 years, mild but generalized urticaria partially controlled with oral antihistamines. There was no improvement after changing from mixed beef-pork to human insulin. In the last 3 years another allergic manifestation began: small, localized, subdermal and painful non-erythematous nodules with central hematomas at injection sites, occurring 6–8 h after the insulin injection and lasting for 48 h. The following maneuvers had no benefit: (1) Human insulin (NPH or Lente) administered with dexametasone or xylocain locally. (2) Short acting human insulin with or without previous boiling. (3) Anti-histamine cetirizine dihydrochloride—10 mg/day. The allergic symptoms disappeared only after treatment with short acting human insulin (up to 100 U/day) associated to prednisone—40 mg/day and cetirizine dihydrochloride for 4 months. However, after stopping prednisone the urticaria reappeared and it was relieved with insulin desensitization. The pain at the site of injections persisted. Conclusion: This long-standing IDDM patient presented two types of reactions to human insulin: the immediate type (systemic urticaria), treated with antihistamines and desensitization, and the Arthus' type III reaction (nodules and hematomas occurring 6–8 h after the insulin injection) that required glucocorticoid therapy for more than 4 months.