Characteristics of adult-onset auto-immune type 1 diabetes

Classically described as a disease of childhood and adolescence, diabetes mellitus type 1 (T1DM) can occur in adulthood. Adult-onset T1DM is poorly documented and is often misdiagnosed. This study aims to describe the epidemiological aspect of T1DM with adult-onset and detail its clinical, paraclinical, and therapeutic characteristics.

A 9-year retrospective longitudinal study (2011-2019) was conducted including adult patients (age >20 years) with confirmed diabetes and at least one of the auto-antibodies (auto-Abs) to glutamic-acid-decarboxylase (GAD), to islet-tyrosine-phosphatase 2 (IA2) or islet-cell-antibodies (ICA) positive.

A total of 166 patients were included (sex-ratio M/F: 1.34; mean age: 28.6 years [20-56 years]). At the onset, 50.6% of patients presented with diabetic ketosis and 13.3% with diabetic ketoacidosis. Cardinal symptoms of diabetes were present in 30.7% of patients only at diagnosis, while the discovery was fortuitous in 5.4% of cases. 27.7% of patients developed an additional auto-immune disease mainly autoimmune thyroid disease. The risk of developing another AUTO-IMMUNE DISEASE was highest in females (p = 0.010) and increased with age (p = 0.011). GAD-Abs, IA2-Abs, and ICA were positive in 98.2%, 13.3%, and 17.4% of cases respectively. Only GAD-Abs were found positive in 73.1%. Upon diagnosis, 75.9% of patients were treated with insulin, while 24.1% of patients were initially put on oral anti-diabetic drugs before requiring insulin within an average of 7.42 months.

Adult-onset T1DM has a different clinical course (slower onset, less abrupt symptoms, more insidious presentation, and more prolonged progression to insulin) that has to be known. Misdiagnosis of adult-onset T1DM can have serious consequences.