Analysis of the clinical characteristics of insulin autoimmune syndrome induced by methimazole

What is known and objective: The number of case reports of insulin autoimmune syndrome (IAS) induced by methimazole (MMI) is increasing. The purpose of this study is to explore the clinical characteristics and provide a scientific reference for clinical diagnosis, treatment and prevention.

Methods: The literature on IAS cases and case series induced by MMI in Chinese and English was collected for retrospective analysis.

Results and discussion: A total of 106 patients (males 33, females 73) were described in the Chinese and English literature. The median age of patients with IAS induced by MMI was 37 years (range 15-76) occurring during both regular and irregular MMI therapy or after resumption of medication. The onset of symptoms occurred at night or early morning, within days in some and up to 6 months in others; the symptoms were neuropathic in 65.31% and related to the autonomic nervous system in 33.67%. Blood glucose concentration in samples presumably taken during the hypoglycaemic phase was 1.7 mmol/L (median; range 0.03-4.7); insulin concentrations were elevated ≥100 mU/L (ref range) and associated with low C-peptide levels (<10 μg/L; ref range). Tests for IgG insulin autoantibodies (IAA) were positive in 104 patients (98.02%) and negative in two patients (1.98%). The 75-g oral glucose tolerance test (OGTT) showed impaired glucose tolerance and diabetic curves. Pancreatic imaging was unremarkable on computed tomography (CT), magnetic resonance imaging (MRI) and ultrasound. Withdrawal of MMI alone or with corticosteroid treatment reduced hypoglycaemic episodes within days to 3 months. IAA decreased and became negative in 3 months (median; range 1-12). Follow-up showed no recurrent hypoglycaemic episodes at 5 months (median; range 1-60).

What is new and conclusion: Methimazole-induced IAS is a clinically rare autoimmune disease with hypoglycaemia that occurs during medication treatment that should be treated promptly.