AIS occurs mainly in Japan, where it is recognised as one of the most common causes of symptomatic spontaneous hypoglycaemia, especially in people with thyroid disease that has been treated with methimazole. It is characterised by the presence in plasma of autoantibodies to endogenous human insulin and high total plasma immunoreactive insulin. Plasma C-peptide levels may be normal, high, or very high, even during hypoglycaemic episodes that tend to be of the rebound variety more often than of the fasting variety. AIS is thought to be due to insulin that is secreted during the absorptive phase of a meal being bound by anti-insulin antibodies and then being released from them during the postabsorptive phase when all the carbohydrate in the meal has been absorbed (Fig. 20.29).
