Introduction
According to WHO, Diabetes Mellitus is a group of metabolic disorders characterized by long-term high blood sugar (chronic hyperglycemia) along with disturbances in the metabolism of carbohydrates, proteins and fats. It occurs either due to lack of insulin, reduced insulin action, or both.
Types of Diabetes Mellitus
A) Type 1 Diabetes Mellitus
Type 1 DM occurs due to decreased insulin secretion from the pancreas. It is also known as insulin-dependent diabetes or juvenile-onset diabetes because it usually starts in childhood.
Two subtypes exist:
- Subtype IA: Autoimmune destruction of pancreatic beta cells causing complete insulin deficiency.
- Subtype IB (Idiopathic): Insulin deficiency without clear autoimmune cause; patients often develop ketosis.
Etiopathogenesis of Type 1 DM
The development of Type 1 DM involves three main factors:
1) Genetic Factors
- Multiple genes determine susceptibility to Type 1 DM.
- If one identical twin develops Type 1 DM, the other has around 50% chance of developing it.
- High-risk individuals often carry HLA genes on chromosome 6, especially HLA-DR3, HLA-DR4 and HLA-DQ.
- Beta cells behave as auto-antigens and activate CD4+ T cells, leading to destruction of beta cells.
2) Autoimmune Factors
- Presence of autoantibodies such as anti-GAD (glutamic acid decarboxylase), anti-insulin antibodies.
- Inflammatory cells (CD4+, CD8+ cells) infiltrate pancreatic islets — known as “insulitis”.
- Selective destruction of beta cells by T-cell mediated apoptosis.
- Associated autoimmune disorders like Hashimoto’s thyroiditis, Addison’s disease, pernicious anemia and Graves’ disease.
3) Environmental Factors
- Viral infections such as measles, mumps, Coxsackie B virus, cytomegalovirus.
- Drugs like alloxan, streptozotocin can experimentally destroy beta cells.
- Seasonal and geographical patterns may influence onset.
Clinical Features of Type 1 DM
- Usually occurs before age 35 years
- Polyuria (frequent urination)
- Polydipsia (excessive thirst)
- Polyphagia (increased hunger)
- Weight loss
- Ketoacidosis
- Hypoglycemic episodes
Type 2 Diabetes Mellitus
Type 2 DM is the most common type, accounting for nearly 80% of all diabetes cases. It occurs due to delayed or insufficient insulin secretion and insulin resistance in body tissues such as muscle and liver. It typically appears after 40 years of age but is now increasingly seen in overweight teenagers.
Symptoms develop slowly and many patients remain asymptomatic until diagnosed during routine tests for high blood sugar or glucose in urine.
Etiopathogenesis of Type 2 DM
1) Genetic Factors
- Genetic influence is stronger in Type 2 than in Type 1 DM.
- If one identical twin has Type 2 DM, the other has 80% chance of developing it.
- Children of diabetic parents have 40% higher risk.
2) Constitutional Factors
- Obesity is the strongest risk factor.
- Hypertension and lack of physical activity contribute to insulin resistance.
3) Insulin Resistance
Peripheral tissues such as muscle, liver and fat become less responsive to insulin. Obesity (especially central obesity) is closely linked to insulin resistance.
4) Impaired Insulin Secretion
Initially the pancreas compensates by secreting excess insulin. Over time, beta cell function declines, causing inadequate insulin release.
5) Increased Hepatic Glucose Production
The liver becomes resistant to insulin’s action and continues to produce glucose through gluconeogenesis even when sugar levels are high.
Complications of Diabetes Mellitus
Long-term uncontrolled diabetes can damage various organs:
1) Diabetic Retinopathy
A leading cause of blindness due to damage to retinal blood vessels. About 2% of diabetics may become blind after 15 years of disease.
2) Diabetic Nephropathy
A major cause of chronic kidney failure. Early detection through screening helps prevent progression.
3) Cardiovascular Diseases
About 50% of diabetic deaths occur due to heart diseases. Risk factors include high blood pressure, high cholesterol, smoking and obesity.
4) Diabetic Neuropathy
The most common complication affecting up to 50% of diabetics. It leads to nerve damage, sensory loss, limb weakness and male impotence.
5) Diabetic Foot Disease
Poor blood flow and nerve damage lead to ulcers, infections and risk of amputation. More common in people without proper footwear.
6) Skin Infections
Fungal and bacterial infections occur more frequently in diabetics.
7) Hearing Problems
Hearing impairment is more common in people with diabetes.
8) Dementia Risk
Type 2 DM increases the risk of conditions like Alzheimer’s disease. Poor sugar control further raises the risk.
9) Depression
Common in both Type 1 and Type 2 diabetics. Depression may worsen diabetes management.
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