What is Diabetes Mellitus?
Diabetes mellitus is a group of metabolic diseases characterized by chronic hyperglycemia (elevated blood glucose) resulting from defects in insulin secretion, insulin action, or both 1.
Core Pathophysiology
The fundamental problem in diabetes is deficient insulin action on target tissues, which stems from:
- Inadequate insulin secretion from pancreatic β-cells
- Diminished tissue response to insulin (insulin resistance)
- Both mechanisms frequently coexist in the same patient 1
This deficient insulin action disrupts the metabolism of carbohydrates, fats, and proteins throughout the body 1.
Clinical Presentation
Acute Symptoms
When hyperglycemia becomes marked, patients develop classic symptoms:
- Polyuria (excessive urination)
- Polydipsia (excessive thirst)
- Weight loss (sometimes with polyphagia/increased appetite)
- Blurred vision
- Impaired growth and increased infection susceptibility in chronic cases 1
Life-Threatening Acute Complications
- Diabetic ketoacidosis (DKA)
- Nonketotic hyperosmolar syndrome 1
Long-Term Organ Damage and Mortality Risk
The chronic hyperglycemia of diabetes causes progressive damage, dysfunction, and failure of multiple organ systems, directly impacting morbidity and mortality 1:
Microvascular Complications
- Retinopathy → potential blindness
- Nephropathy → renal failure requiring dialysis
- Peripheral neuropathy → foot ulcers, amputations, Charcot joints
- Autonomic neuropathy → gastrointestinal, genitourinary, cardiovascular symptoms, and sexual dysfunction 1
Macrovascular Complications
- Atherosclerotic cardiovascular disease
- Peripheral arterial disease
- Cerebrovascular disease (stroke)
- Hypertension and dyslipidemia are commonly associated 1
Major Types of Diabetes
Type 1 Diabetes (5-10% of cases)
- Absolute insulin deficiency due to autoimmune destruction of pancreatic β-cells
- Can be identified by autoantibody markers and genetic factors
- Requires insulin for survival 1, 2
Type 2 Diabetes (Most prevalent)
- Combination of insulin resistance and inadequate compensatory insulin secretion
- Often has a prolonged asymptomatic period where hyperglycemia exists without symptoms
- May be managed with lifestyle modifications, oral agents, and/or insulin depending on disease severity 1
Other Types
- Gestational diabetes mellitus (diagnosed during pregnancy)
- Monogenic diabetes syndromes (e.g., MODY, neonatal diabetes)
- Secondary diabetes from diseases of the exocrine pancreas, drug-induced, or other causes 2
Disease Progression
The degree of hyperglycemia reflects the severity of the underlying metabolic process and can change over time 1. The disease may progress through stages:
- Normal glucose regulation
- Impaired fasting glucose (IFG) or impaired glucose tolerance (IGT)
- Overt diabetes mellitus 1
Clinical Significance
Understanding that diabetes is fundamentally a disease of deficient insulin action leading to chronic hyperglycemia with devastating multi-organ complications is essential. The primary clinical goals are preventing acute metabolic crises and reducing long-term microvascular and macrovascular complications that drive diabetes-related morbidity and mortality 1.