Types of Diabetes
Diabetes is classified into four major categories: Type 1 diabetes, Type 2 diabetes, Gestational diabetes mellitus (GDM), and Specific types of diabetes due to other causes, which include monogenic diabetes syndromes, diseases of the exocrine pancreas, and drug or chemical-induced diabetes. 1
Major Types of Diabetes
Type 1 Diabetes
- Results from autoimmune β-cell destruction, usually leading to absolute insulin deficiency 2, 1
- Characterized by the presence of autoantibodies to insulin, glutamic acid decarboxylase (GAD), islet antigen 2 (IA-2), or zinc transporter 8 (ZnT8) 1
- Can be staged as:
- Typically presents with classic symptoms of polyuria/polydipsia, with approximately one-third of children presenting with diabetic ketoacidosis (DKA) 2
- Includes latent autoimmune diabetes of adulthood (LADA) 1, 3
Type 2 Diabetes
- Due to progressive loss of β-cell insulin secretion, often occurring on the background of insulin resistance 1
- Frequently associated with metabolic syndrome 1
- Pathophysiology involves:
- Insulin resistance as a primary defect leading to compensatory hyperinsulinemia
- Alternative model suggests hyperinsulinemia as the primary event promoting obesity and insulin resistance 1
- Adipose tissue dysfunction with release of inflammatory mediators
- Ectopic fat deposition in liver, muscle, and pancreas 1
Gestational Diabetes Mellitus (GDM)
- Diabetes diagnosed in the second or third trimester of pregnancy that was not clearly overt diabetes prior to gestation 2, 1
- Affects approximately 8.3% of pregnancies 1
- Approximately 70% of females with GDM will develop diabetes over time 1
Specific Types of Diabetes Due to Other Causes
Monogenic diabetes syndromes:
Diseases of the exocrine pancreas:
Drug or chemical-induced diabetes:
Diagnostic Considerations
- Diagnosis is not always straightforward at presentation, and misdiagnosis is common (occurring in up to 40% of adults with new-onset type 1 diabetes) 2, 1
- The traditional paradigm that type 1 diabetes occurs only in children and type 2 diabetes only in adults is no longer accurate, as both diseases occur in both age groups 2, 1
- Diagnostic criteria according to the American Diabetes Association include:
- A1C ≥6.5% (48 mmol/mol)
- Fasting plasma glucose ≥126 mg/dL (7.0 mmol/L)
- 2-hour plasma glucose ≥200 mg/dL (11.1 mmol/L) during OGTT
- Random plasma glucose ≥200 mg/dL (11.1 mmol/L) with classic symptoms 1
Clinical Pearls and Pitfalls
- Common pitfall: Misdiagnosis of diabetes type is frequent, especially in adults with type 1 diabetes misdiagnosed as having type 2 diabetes 2, 1
- Important consideration: Testing for islet autoantibodies (GAD, IA-2, ZnT8) can help determine the type of diabetes when the diagnosis is unclear 1
- Useful test: C-peptide testing can help distinguish between type 1 and type 2 diabetes after disease duration of >3 years 1
- Critical awareness: All forms of diabetes require monitoring for and prevention of long-term complications, including microvascular (retinopathy, nephropathy, neuropathy) and macrovascular (cardiovascular disease) complications 1
- Key practice point: Regular reassessment of diabetes classification is important, especially when treatment response is suboptimal, as the true diagnosis may become more evident over time 1
Treatment Approaches Based on Diabetes Type
- Type 1 diabetes: Insulin therapy is essential and lifelong, with options including multiple daily injections or continuous subcutaneous insulin infusion 1
- Type 2 diabetes: Lifestyle modifications (weight loss, physical activity, dietary modifications) are cornerstone treatments, with pharmacological therapy typically starting with Metformin 1
- GDM: Management includes dietary measures, regular blood glucose monitoring, and insulin therapy in 20-30% of cases 1
- Monogenic diabetes: Treatment is directed at the underlying cause and tailored to the specific genetic etiology 1, 4