Non-immune-mediated versus immune-mediated type 1 diabetes: diagnosis and long-term differences-retrospective analysis.

Background: The American Diabetes Association proposed two subcategories for type 1 diabetes mellitus: type 1A or immune-mediated diabetes (IDM) and type 1B or idiopathic diabetes. The absence of β-cell autoimmune markers, permanent insulinopenia and prone to ketoacidosis define the second category, whose pathogenesis remains unclear. Only a minority of patients fall into this category, also designated non-immune-mediated (NIDM), which is considered by several authors similar to type 2 diabetes. The aim of this study is to evaluate differences at the diagnosis and 10 years later of two categories.

Methods: Retrospective cohort study of patients with β-cell autoimmune markers performed at diagnosis and undetectable c-peptide. Were excluded patients with suspicion of another specific type of diabetes. We obtained two groups: IDM (≥ 1 positive antibody) and NIDM (negative antibodies). Age, family history, anthropometry, duration of symptoms, clinical presentation, blood glucose at admission, A1C, lipid profile, arterial hypertension, total diary insulin dose (TDID), microvascular and macrovascular complications were evaluated. Results were considered statistically significant with p < 0.05.

Results: 37 patients, 29 with IDM and 8 patients with NIDM. The age of diagnosis of IDM group (23 years) was significantly different (p = 0.004) from the NIDM group (38.1). The body mass index (BMI) at the diagnosis did not differ significantly (p = 0.435). The duration of symptoms was longer in the NIDM (p = 0.003). The disease presentation (p = 0.744), blood glucose (p = 0.482) and HbA1c (p = 0.794) at admission and TDID at discharge (p = 0.301) did not differ significantly. Total and LDL cholesterol levels were higher in NIDM group but did not differ significantly (p = 0.585 and p = 0.579, respectively). After 10 years BMI did not differ between groups (p = 0.079). Patients with IDM showed a significantly higher HbA1c (p = 0.008) and TDID (p = 0.017). Relative to the lipid profile, there was no significant difference, however the LDL cholesterol and triglycerides were higher on the NIDM group, as the percentage of hypertension. Microvascular complications were higher in the IDM group, but no significant difference was found.

Conclusion: Patients with IDM had a poor metabolic control and higher insulin requirement. Patients with NIDM were older and showed higher cardiovascular risk, resembling a clinical phenotype of type 2 diabetes.