Rituximab Therapy for Insulin Allergy in Type-1 Diabetes Mellitus.

Background/Objective: Allergic reactions to insulin have decreased significantly since the introduction of human insulin preparation, but up to 2.4% of insulin-treated patients can still be affected. Rituximab is a monoclonal antibody against the surface antigen CD20 on B lymphocytes, and it is largely used to treat lymphoproliferative and rheumatological conditions. In a very few published case reports, rituximab has been used as an investigational drug to treat severe insulin allergy refractory to conventional therapy. Here, we present an unusual case of a 40-year-old woman with T1DM and severe insulin allergy that was successfully treated with rituximab. Case Report: The patient was diagnosed with T1DM at age 37. Three years later, skin reactions developed at insulin administration sites. These consisted of pruritic and painful erythema and wheals that appeared within 1 to 4 h of insulin administration, followed by induration, subcutaneous nodules, and surrounding lipodystrophy that lasted several days with spontaneous resolution in 1 to 2 weeks. Extensive immunologic evaluation suggested the reaction was related to insulin allergy. Skin biopsy revealed sublobular panniculitis. After failed conventional treatment with antihistamines, glucocorticoid, and various insulins, rituximab infusion as an investigational approach was initiated. This was very successful, leading to prolonged remission of her insulin allergy. Discussion: First-line management of insulin allergy should focus on second-generation antihistamines and switching insulin preparation. In refractory cases, systemic immunotherapy with rituximab can be a viable option. Conclusion: Practitioners should be aware that in patients with insulin allergy who fail conventional treatment, immunotherapy with rituximab can be a viable option.