What are the different types of diabetes?

Types of Diabetes

Diabetes mellitus 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. 1

Main Types of Diabetes

Type 1 Diabetes

• Due to autoimmune β-cell destruction, usually leading to absolute insulin deficiency
• Includes latent autoimmune diabetes of adulthood (LADA)
• Typically presents with classic symptoms of polyuria/polydipsia
• Approximately 40-50% of children with Type 1 diabetes present with diabetic ketoacidosis (DKA)
• Requires lifelong insulin therapy

Type 2 Diabetes

• Due to non-autoimmune progressive loss of β-cell insulin secretion
• Often occurs on the background of insulin resistance and metabolic syndrome
• Accounts for approximately 90% of all diabetes cases worldwide
• May occasionally present with DKA, particularly in ethnic and racial minorities
• Management includes lifestyle modifications and stepwise pharmacological therapy

Gestational Diabetes Mellitus (GDM)

• Diabetes diagnosed in the second or third trimester of pregnancy
• Not clearly overt diabetes prior to gestation
• Affects approximately 8.3% of pregnancies
• Approximately 70% of females with GDM will develop diabetes over time
• Management includes dietary measures, blood glucose monitoring, and insulin therapy in 20-30% of cases

Specific Types of Diabetes Due to Other Causes

1. Monogenic diabetes syndromes:

   • Maturity-onset diabetes of the young (MODY)
   • Neonatal diabetes
   • Often misdiagnosed as type 1 or type 2 diabetes
   • Treatment is directed at the underlying genetic cause

2. Diseases of the exocrine pancreas:

   • Cystic fibrosis
   • Pancreatitis
   • Pancreatectomy
   • Pancreatic tumors

3. Drug or chemical-induced diabetes:

   • Glucocorticoid use
   • Treatment for HIV/AIDS
   • After organ transplantation

4. Genetic syndromes associated with diabetes:

   • Down syndrome
   • Klinefelter syndrome
   • Turner syndrome
   • Wolfram syndrome
   • Friedreich ataxia

Diagnostic Considerations

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. Classification is not always straightforward at diagnosis, and misdiagnosis is common, occurring in up to 40% of adults with new-onset type 1 diabetes 1.

Diagnostic criteria for diabetes 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

Clinical Implications

All forms of diabetes require monitoring for and prevention of long-term complications, including:

• Microvascular complications: retinopathy, nephropathy, neuropathy
• Macrovascular complications: cardiovascular disease

Regular reassessment of diabetes classification is important, especially when treatment response is suboptimal, as the true diagnosis may become more evident over time 1.

Pitfalls to Avoid

1. Misdiagnosis: The clinical presentation of diabetes types can overlap, leading to misclassification and inappropriate treatment.

2. Overlooking monogenic forms: Monogenic diabetes accounts for approximately 1-2% of diabetes cases but is frequently mistakenly diagnosed as either type 1 or type 2 diabetes 3.

3. Ignoring atypical presentations: Adults with type 1 diabetes may not present with classic symptoms and may experience temporary remission from insulin requirements.

4. Relying solely on age for classification: Both type 1 and type 2 diabetes can occur at any age, challenging the traditional age-based classification.

5. Failing to consider secondary causes: Always consider other potential causes of diabetes, particularly in patients with atypical presentations or poor response to standard therapy.