Persistent local insulin allergy in a diabetic with chronic lymphatic leukaemia.

A 75 year old maturity-onset diabetic developed persistent local allergy to insulin. She had coexistent asymptomatic chronic lymphatic leukaemia. All species of insulin provoked a recurrence of the allergy and attempts at hyposensitization and treatment of the leukaemia produced only marginal benefit. Administration of subcutaneous steroids with insulin relieved the problem, but could not be stopped without relapse. Immunological investigations suggested an immune complex-mediated hypersensitivity reaction to insulin. The later development of immune complex-mediated arthropathy tended to support this suggestion. The lack of histological and immunological evidence of an IgE-mediated reaction suggested that in this case the mechanism of insulin allergy and arthralgia was IgG mediated. We suggest that the chronic leukaemia was implicated in both processes by interfering with homeostatic mechanisms that normally prevent the development of autoallergic disorders.