Abstract
Autoantibody to endogenous insulin was studied in a patient with rheumatoid arthritis (RA) and Sjögren's syndrome who was treated with tiopronin (α-mercaptopropionyl glycine: MPG). MPG has been used in patients with RA in recent years, because of its immunomoderating action. Although MPG has a good effect in some patients with RA, one patient was found to have autoantibody to endogenous insulin accidentally.
A 46-year-old female rheumatoid patient treated with MPG and with no history of previous exogenous insulin exposure, had frequent hypoglycemic episodes after 16 days of re-administration of MPG. The anti-insulin antibody was evaluated by the specific precipitation method, using radioisotope-labelled insulin. The antibodies to IgG. IgA, IgM, kappa and lambda were used in order to determine the immunoglobulin class and light chain type of anti-insulin antibody. The patient's serum showed 2, 974 μU/ml of total immunoreactive insulin (IRI), 22 μU/ml of free IRI and IgG (κ) type anti-insulin antibody. She was diagnosed as having insulin autoimmune syndrome (IAS). When MPG was stopped, her hypoglycemic attacks disappeared. She had a further mild hypoglycemic attack on the 11th day after challenge of MPG.
It was therefore concluded that MPG may produce autoantibody to endogenous insulin and induce IAS to patients with RA who have abnormalities of immune response.
