Basics of Diabetes

Pathophysiology of Diabetes Mellitus

Diabetes = Hyperglycemia, which is defined as:

                        --fasting plasma glucose above 126 mg/dl

                        --oral glucose tolerance test (OGTT) above 200 mg/dl

Pre-Diabetes is defined as:

                        --impaired fasting glucose (IFG) of 100-125 mg/dl

                        --impaired glucose tolerance (IGT) of 140-199 mg/dl

Acute Complications of Uncontrolled Diabetes (all directly caused by hyperglycemia)

--Polydypsia due to plasma glucose hyperosmolarity

--Polyuria due to excess fluid intake and glucose-induced osmotic diuresis

--Weight loss due to calories lost as glucosuria, leaving a negative calorie balance

--Polyphagia due to glucosuria and negative calorie balance

--Poor wound healing, gingivitis, blurred vision

Chronic Complications of Uncontrolled Diabetes

Chronic complications may be due to mitochondrial superoxide overproduction in response to hyperglycemia.

Macrovascular Atherosclerosis:  diabetics have a high incidence of coronary, cerebral, and       peripheral artery diseases.  Caused by dyslipidemias including elevated LDL and   triglycerides, low HDL, and reduced fibrinolytic activity.  Management includes foot care.

Microvascular Diseases of Diabetes

1.  Diabetic Retinopathy has many manifestations, including microaneurysms, microhemorrhages,         proliferative vessel changes, and vitreous bleeds (cause blindness).  Diabetic retinopathy is caused by basement membrane deterioration and ischemia.

2.  Nephropathy progresses from microalbuminuria to proteinuria to uremia to ESRD.  Nephropathy     is caused by hyperfiltration, increased glomerular pressure, and BM thickening.

3.  Neuropathy can be peripheral (symmetrical stocking-glove numbness/tingling), autonomic    (erectile dysfuntion, enteropathy, gastroparesis, orthostatic hypotension), or             mononeuropathic (single nerve pain/palsy).  Peripheral and autonomic neuropathies are       caused by metabolic schwann cell defects and axonal degeneration.  Mononeuropathies             are caused by ischemia, and resolve on their own within a year.

The Diabetic Foot

This is a combination of Peripheral Neuropathy (leads to undetected trauma, blisters, ulcers) and            Peripheral Vascular Disease (impairs healing, allows infection).

Endstage Complications of Uncontrolled Diabetes

1.  Diabetic Ketoacidosis results from complete lack of insulin and reliance on fatty acids for             energy.  There is unrestrained lipolysis and ketone synthesis, causing acidosis and             ketonemia.  Patients will show Kussmaul respiration.  This is a medical emergency.

2.  Non-Ketotic Hyperosmolarity is an extreme hyperglycemia without acidosis.  It is caused by     insufficient insulin resulting in poor glucose uptake and increased hepatic glucose output.  There is just enough insulin to suppress ketone synthesis.  The extreme hyperglycemia   leads to osmotic diuresis and vascular collapse.

Diabetic Control

1.  Self-monitoring of blood glucose

2.  Hemoglobin A1c (“glycohemoglobin”) monitoring measures glycemia over the last 2-3 months.

            Hemoglobin A1c < 7 is good.  Hemoglobin A1c > 9 is bad.

Type 1 Diabetes Mellitus

Characterized by Beta cell deficiency, leading to complete insulin deficiency.  This leads to severe         metabolic lability and ketoacidosis.  Metabolic lability is hard to treat.

DM type 1 is almost always an autoimmune disease caused by anti-islet, anti-GAD, or anti-insulin

            antibodies.  These cause lymphocytic inflitration and destruction of the pancreas islets.    Although the destruction is gradual, the clinical onset is usually acute.

DM type 1 is associated with other autoimmune conditions including vitiligo and hypothyroidism.

DM type 1 usually occurs in people <35 yo who are of thin-to-normal body weight.  It is much less common than DM type 2, and shows some HLA associations.  Family history is rare.

DM type 1 always requires insulin therapy, and will not respond to insulin-stimulating oral drugs.

Remember that metabolic lability and glucose swings are a hallmark of DM type 1.

*End-stage DM type 1 is ketoacidosis.

Type 2 Diabetes Mellitus

Characterized by insulin resistance and relative, not complete insulin deficiency.

DM type 2 is caused by Beta cell deficiency coupled with peripheral insulin resistance.

            --Peripheral insulin resistance is the hallmark of DM type 2.  Although insulin levels may                         be high, this does not cause hypoglycemia.  This is due to receptor density and                                 post-receptor changes in response to chronic hyperinsulinemia.

            --Obesity is the main cause of insulin resistance.

            --Beta cell deficiency occurs over years as islets fail from insulin overproduction.  Insulin                        levels become inadequate to overcome the peripheral resistance.

DM type 2 develops when insulin production can no longer overcome peripheral insulin resistance.

            Patients become unresponsive to insulin-stimulating oral drugs, and ultimately require      insulin injections.  But because there is always some residual insulin secretion, there is little metabolic lability and glucose levels tend to stay stable.

DM type 2 usually occurs in people >35 yo who are obese.  Family history is very common, and       twin concordance is extremely high. 

*End-stage DM type 2 is Non-Ketotic Hyperosmolarity.

	Type 1 Diabetes	Type 2 Diabetes
Etiology	Autoimmune	Peripheral resistance
Formerly known as	IDDM	NIDDM or “adult onset” diabetes
Age of onset	Younger	Older
Obesity	Rare	Common
Family History/Twin concordance	Rare	Common
HLA association	Yes	No
Ketosis	Yes	No
Insulin resistance	No	Yes
Endogenous insulin	No	Yes
Respond to Oral Agents	No	Yes
Metabolic lability	Labile	Not labile

(Raymond removed image of natural history of type 2 diabetes: glucose levels, insulin resistance and secretion.)

Other causes of hyperglycemia

1.  Gestational diabetes is caused by excess counter-insulin hormones of pregnancy, which lead to    insulin resistance.  The resulting maternal hyperglycemia is transmitted to the fetus, causing        fetal pancreatic hypertrophy.  The baby will be large and fat, with neonatal complications.

2.  Defective insulin receptors or post-receptor signal transduction.

3.  “Glucose toxicity” in which hyperglycemia itself causes more insulin resistance. 

            This is a feedforward cycle that leads to ketoacidosis and severe hyperglycemia.

Carbohydrate Metabolism and Hypoglycemia

Increased blood glucose stimulates insulin secretion. 

High insulin will promote glucose uptake, glycolysis, and glycogenesis, as well as uptake and      synthesis of amino acids, proteins, and fat.

Low insulin will promote gluconeogenesis, glycogenolysis, lipolysis, and proteolysis.

	Liver	Adipose Tissue	Muscle
High insulin	Glycolysis Glycogenesis	Triglyceride synthesis	Amino acid uptake Protein synthesis
Low insulin	Gluconeogenesis Glycogenolysis	Lipolysis	Proteolysis

Normal Responses to Eating and Fasting

1.  CHO fed state:  increased insulin secretion, causing glycolysis, glycogen storage, fatty acid    synthesis/storage, and protein synthesis.

2.  Overnight fast:  low insulin and high glucagon cause glycogen breakdown, hepatic     gluconeogenesis, and lipolysis. 

3.  Prolonged fast:  extremely low insulin and low glucagon cause lipolysis to take over.  Lipids   are the main fuel source.  Gluconeogenesis is minimized, as it causes nitrogen wasting,       ammonia build-up, and loss of muscle mass.

Counter-Regulatory Hormones

The following hormones raise blood glucose and oppose insulin:

            --Glucagon

            --Epinephrine/Norepinephrine

            --Cortisol

            --Growth Hormone

These are “fight or flight” hormones that raise glucose to fuel muscles.  They cause anxiety,         alertness, apprehension, sweating, and tachycardia.

These hormones are released due to stress.  Therefore, stress worsens diabetic control, raises   blood glucose, and generally worsens diabetes.

Hypoglycemia

Hypoglycemia is defined by “Whipple’s Triad”:

            1.  Documented low plasma glucose

            2.  Symptoms of hypoglycemia

            3.  Response to administered carbohydrate

There are two classes of hypoglycemic symptoms:

            1.  Adrenergic symptoms due to catecholamine release and counter-regulatory hormones.                    These symptoms include tremor, blurred vision, weakness, palpitations, anxiety,                                   emotional lability, headache.  Adrenergic symptoms mildly dangerous.

            2.  Neuroglucopenic symptoms due to inadequate glucose to the brain.  These symptoms                                 include confusion, slurred speech, siezures, somnolence, and coma.  Very dangerous.

Reactive versus Fasting Hypoglycemia

It is not normal to become symptomatically hypoglycemic, even during a prolonged fast!

Reactive/postprandial Hypoglycemia occurs a few hours after a meal.  It is common, and not associated with disease.  May be caused by overly rapid gastric emptying (“alimentary     hypoglycemia”).

Fasting Hypoglycemia occurs post-absorptively (>10 hours after a meal).  It is abnormal, and is          usually caused by excess insulin.  This may be exogenous insulin (over-injection during     diabetes therapy) or endogenous insulin (insulinoma).  Insulinomas may be detected by             putting patients on a prolonged fast and looking for persistently high insulin levels or symptoms of hypoglycemia.

Other causes of fasting hypoglycemia include defective gluconeogenesis (liver failure,   alcoholic hypoglycemia) and counter-regulatory hormone deficiency (adrenal insufficiency).