Insulin autoimmune syndrome: not just one but two different diseases with therapeutic implications.

Summary: We present a young woman with treatment resistant insulin autoimmune syndrome (IAS) with a protracted course. Her serum insulin level was 6945 pmol/l (<160), C-peptide 4042 pmol/L (<1480), anti-insulin antibodies 5305 U/mL (<0.4) were monoclonal IgG kappa. After 12 h of fasting, her blood glucose fell to 1.2 mmol/L. Post-meal blood glucose peaked at 12.2 mmol/L with reactive hypoglycaemia below 2 mmol/L. Frequent meals and continuous blood glucose monitoring were helpful, but further treatments advocated in the literature with prednisolone, rituximab, plasmapheresis, cyclophosphamide and ciclosporin were without beneficial effect. Based on this case and a review of the literature, we propose that IAS is not one but two different diseases with different therapeutic strategies. The first disease, polyclonal IAS, predominates in Asia and is characterized by polyclonal anti-insulin antibodies, association with certain HLA genotypes and other autoimmune conditions, medications and viral infections possibly triggering the disease, a possible female predominance among young patients and a tendency towards spontaneous remission. The other disease, monoclonal IAS, predominates in Caucasians. Typical features are monoclonal anti-insulin antibodies, only weak HLA association, no drug predisposition, no sex difference, rare remission and conventional therapy often being without any clinical effect. We suggest that monoclonal IAS with IgG or IgA anti-insulin antibodies should receive therapy targeting plasma cells rather than lymphocytes.

Learning points: IAS may be considered as two separate diseases, polyclonal and monoclonal. The presence of either polyclonal or monoclonal antibodies should determine the choice of treatment for IAS. In polyclonal IAS, discontinuation of a triggering medication and treatment of triggering conditions should be the backbone of therapy. Monoclonal IAS should receive treatment targeting plasma cells.