Diabetes mellitus is a metabolic disorder characterized by hyperglycemia and results from defective insulin production, secretion, or utilization.
Pathophysiology and Etiology
- There is an absolute or relative lack of insulin produced by the beta cell, resulting in hyperglycemia.
- Defects at the cell level, impaired secretory response of insulin to rises in glucose, and increased nocturnal hepatic glucose production (gluconeogenesis) are seen in type 2 diabetes.
- Etiology of type 1 diabetes is not well understood; viral, autoimmune, and environmental theories are under review.
- Etiology of type 2 diabetes involves heredity, genetics, and obesity
Type 1 Diabetes Mellitus
Type 1 diabetes mellitus was formerly known as insulin dependent diabetes mellitus and juvenile diabetes mellitus.
- Little or no endogenous insulin, requiring injections of insulin to control diabetes and prevent ketoacidosis.
- Five to 10% of all diabetic patients have type 1.
- Etiology: autoimmunity, viral, and certain histocompatibility antigens as well as a genetic component.
- Usual presentation is rapid with classic symptoms of polydipsia, polyphagia, polyuria, and weight loss.
- Most commonly seen in patients under age 30 but can be seen in older adults.
Type 2 Diabetes Mellitus
Type 2 diabetes mellitus was formerly known as noninsulin dependent diabetes mellitus or adult onset diabetes mellitus.
- Caused by a combination of insulin resistance and relative insulin deficiency- some individuals have predominantly insulin resistance, whereas others have predominantly deficient insulin secretion, with little insulin resistance.
- Approximately 90% of diabetic patients have type 2.
- Etiology: strong hereditary component, commonly associated with obesity.
- Usual presentation is slow and typically insidious with symptoms of fatigue, weight gain, poor wound healing, and recurrent infection.
- Found primarily in adults over age 30; however, may be seen in younger adults and adolescents who are overweight.
- Patients with this type of diabetes, but who eventually may be treated with insulin, are still referred to as having type 2 diabetes.
Prediabetes
Prediabetes is an abnormality in glucose values intermediate between normal and overt diabetes.
Impaired Fasting Glucose
- A new category adopted by the American Diabetes Association in 1997 and redefined in 2004.
- Occurs when fasting blood glucose is greater than or equal to 100 but less than 126 mg/dL.
Impaired Glucose Tolerance
- Defined as blood glucose measurement on a glucose tolerance test greater than or equal to 140 mg/dl but less than 200 in the 2-hour sample.
- Asymptomatic; it can progress to type 2 diabetes or remain unchanged.
- May be a risk factor for the development of hypertension, coronary heart disease, and hyperlipidemias.
Gestational Diabetes Mellitus
- Gestational diabetes mellitus (GDM) is defined as carbohydrate intolerance occurring during pregnancy.
- Occurs in approximately 4% of pregnancies and usually disappears after delivery.
- Women with GDM are at higher risk for diabetes at a later date.
- GDM is associated with increased risk of fetal morbidity.
- Screening for GDM for all pregnant women other than those at lowest risk (under age 25, of normal body weight, have no family history of diabetes, are not a member of an ethnic group with high prevalence of diabetes) should occur between the 24th and 28th weeks of gestation.
Diabetes Associated with Other Conditions
- Certain drugs can decrease insulin activity resulting in hyperglycemia- corticosteroids, thiazide diuretics, estrogen, phenytoin.
- Disease states affecting the pancreas or insulin receptors- pancreatitis, cancer of the pancreas, Cushing's disease or syndrome, acromegaly, pheochromocytoma, muscular dystrophy, Huntington's chorea.
