Diabetes Mellitus Overview and Causes

Study Notes

Can be caused by intravenous glucose, severe stress (trauma, heart attack, stroke), diabetes, or impaired glucose regulation.
Diabetes mellitus results from an absolute or relative lack of insulin.

Defined by a fasting blood glucose of 7.0 mmol/L or higher (on more than one occasion with symptoms)
Or a random blood glucose of 11.1 mmol/L or higher.
Oral glucose tolerance tests (OGTT) may be needed for diagnosis.
Classified into several types including Type 1, Type 2, other specific types, and gestational diabetes.

Cause: Destruction of beta cells in the pancreas
Consequence: Lack of insulin production
Usually presents during childhood and adolescence
Requires insulin therapy.
Can be autoimmune (Type 1A) or with unknown cause (Type 1B)
Latent autoimmune diabetes of adults (LADA) sometimes considered a slow onset Type 1 diabetes

Insulin resistance with relative insulin deficiency or a secretory defect with insulin resistance.
Insulin therapy may be needed
Onset typically during adulthood with a familial tendency and often linked to obesity.

Inherited disorders affecting insulin secretion, action, or insulin receptor defects
Genetic defects of beta-cell function: Maturity-onset diabetes of the young (MODY)
Genetic defect of insulin action: Type A insulin resistance (insulin receptor defect), for example, leprechaunism, lipoatrophy, and Rabson-Mendenhall syndrome
Insulin deficiency due to pancreatic disease: Chronic pancreatitis, Pancreatectomy, Haemochromatosis, Cystic fibrosis
Endocrinopathies: Relative insulin deficiency due to high growth hormone (acromegaly), phaeochromocytoma, or high cortisol (Cushing's Syndrome)
Drugs: Thiazide diuretics, Interferon alpha, Glucocorticoids
Infections: Septicaemia, Congenital rubella, Cytomegalovirus
Rare autoimmune diabetes: Anti-insulin receptor antibodies, Stiff man syndrome (high GAD autoantibodies)
Genetic syndromes associated with diabetes: Down's syndrome, Turner's syndrome, Klinefelter's syndrome, Myotonic dystrophy.

High risk factors: previous high birth weight delivery , obesity, family history of diabetes, high-risk ethnic groups (Black or South Asian)
Screen as early as possible and repeat testing at 24-28 weeks
Diagnosis: Fasting blood glucose ≥ 7.0 mmol/L or random blood glucose ≥ 11.1 mmol/L
Reclassify after 6 weeks postpartum with repeat OGTT.

Fasting blood glucose < 7.0 mmol/L
Blood glucose between 7.8–11.1 mmol/L two hours after an oral glucose tolerance test (OGTT)
Some patients with IGT may develop diabetes mellitus later
Pregnancy IGT is treated as GDM due to the risks to the fetus.