small blood vessels.
MICROVASCULAR COMPLICATIONS
Retinopathy
DIABETES IS THE leading cause of blindness in the United States.1 Eye disease—characteristically retinal damage (retinopathy)—is one of the most frequent complications of diabetes. The retina is the light-sensitive nerve layer at the back of the eye that sends its “picture” to the brain. Diabetes weakens the small, retinal blood vessels, which causes blood and other fluids to leak out. During routine physical eye examinations, this leakage can be visualized with a standard ophthalmoscope.
In response to this damage, new retinal blood vessels form, but they are fragile and easily broken. The result is more bleeding and the eventual formation of scar tissue. In severe cases, this scar tissue can lift the retina and pull it away from its normal position, ultimately leading to blindness. Laser treatment can prevent retinopathy by sealing or destroying the leaky new blood vessels.
Approximately 10,000 new cases of blindness in the United States are caused by diabetic retinopathy each year.2 Whether retinopathy develops depends on how long a person has had diabetes as well as how severe the disease is.3 In type 1 diabetes, most patients develop some degree of retinopathy within twenty years. In type 2 diabetes, retinopathy may actually develop up to seven years before the diabetes itself is diagnosed.
Nephropathy
THE MAIN JOB of the kidneys is to clean the blood. When they fail, toxins build up in the body, which leads to loss of appetite, weight loss, and persistent nausea and vomiting. If the disease goes untreated, it eventually leads to coma and death. In the United States, more than 100,000 patients are diagnosed with chronic kidney disease annually, costing $32 billion in 2005. The burden is not only financially enormous, but emotionally devastating.
Diabetic kidney disease (nephropathy) is the leading cause of end stage renal disease (ESRD) in the United States, accounting for 44 percent of all new cases in 2005.4 Patients whose kidneys have lost over 90 percent of their intrinsic function require dialysis to artificially remove the accumulated toxins in the blood. This procedure involves removing the patient’s “dirty” blood, running it through the dialysis machine to clean out its impurities, and then returning the clean blood to the body. To stay alive, patients require four hours of dialysis, three times per week, indefinitely, unless they receive a transplant.
Figure 3.1. Adjusted prevalence rates of end stage renal disease5
Diabetic kidney disease often takes fifteen to twenty-five years to develop, but, like retinopathy, it may occasionally be diagnosed before type 2 diabetes, itself. Approximately 2 percent of type 2 diabetic patients develop kidney disease each year. Ten years after diagnosis, 25 percent of patients will have evidence of kidney disease.6 Once established, diabetic nephropathy tends to progress, leading to more and more kidney impairment until eventually the patient requires dialysis or transplantation.
Neuropathy
DIABETIC NERVE DAMAGE (neuropathy) affects approximately 60–70 percent of patients with diabetes.7 Once again, the longer the duration and severity of diabetes, the greater the risk of neuropathy.8
There are many different types of diabetic nerve damage. Commonly, diabetic neuropathy affects the peripheral nerves, first in the feet, and then progressively in the hands and arms as well, in a characteristic stocking-and-glove distribution. Damage to different types of nerves will result in different symptoms, including
•tingling,
•numbness,
•burning, and
•pain.
The incessant pain of severe diabetic neuropathy is debilitating, and the symptoms are commonly worse at night. Even powerful painkillers such as narcotic medications are often ineffective. Instead of pain, patients may sometimes experience complete numbness. Careful physical examination reveals decreased sensations of touch, vibration, and temperature, and a loss of reflexes in the affected parts of the body.
While a loss of sensation may seem innocuous, it is anything but. Pain protects us against damaging trauma. When we stub our toes, or lie in the wrong position, pain lets us know that we should quickly adjust ourselves in order to prevent further tissue damage. If we are unable to feel pain, we may continue to experience repeated episodes of trauma. Over years, the damage becomes progressive and sometimes deformative. A typical example is the foot. Significant nerve damage can lead to the complete destruction of the joint—a condition called Charcot foot—and may progress to the point where patients are unable to walk, and may even require amputation.
Another nerve disorder affecting the large muscle groups is called diabetic amyotrophy, which is characterized by severe pain and muscle weakness, particularly in the thighs.9
The autonomic nervous system controls our automatic body functions, such as breathing, digestion, sweating, and heart rate. Damage to these nerves may cause nausea, vomiting, constipation, diarrhea, bladder dysfunction, erectile dysfunction, and orthostatic hypotension (a sudden, severe drop of blood pressure on standing up). If the nerves to the heart are affected, the risk of silent heart attacks and death increases.10
No current treatment reverses diabetic nerve damage. Drugs may help the symptoms of the disease but do not change its natural history. Ultimately, it can only be prevented.
MACROVASCULAR COMPLICATIONS
Atherosclerosis (hardening of the arteries)
ATHEROSCLEROSIS IS A disease of the arteries whereby plaques of fatty material are deposited within the inner walls of the blood vessel, causing narrowing and hardening. This condition causes heart attacks, strokes, and peripheral vascular disease, which are collectively known as cardiovascular diseases. Diabetes greatly increases the risk of developing atherosclerosis.
Atherosclerosis is popularly but incorrectly imagined as cholesterol slowly clogging the arteries, much as sludge might build up in a pipe. In actuality, it results from injury to the artery, although the exact cause of the injury is unknown. There are many contributing factors, including but not limited to age, genetics, smoking, diabetes, stress, high blood pressure, and lack of physical activity. Any breach of the artery’s walls can initiate an inflammatory cascade. Cholesterol (a waxy, fat-like substance found in all cells of the body) infiltrates the damaged area and narrows the blood vessel. The smooth muscle that supports the tissue of the blood vessel proliferates, and collagen, a structural protein found abundantly in the body, also accumulates in response to this injury. Again, the result is a further narrowing of the blood vessel. Rather than a single episode that can be simply repaired, this response occurs in reaction to chronic injuries to the vessel wall.
The end result is the development of plaque, known as the atheroma, which is a pocket of cholesterol, smooth muscle cells, and inflammatory cells inside the blood vessel wall. This progressively limits the flow of blood to affected organs. If this atheroma ruptures, a blood clot forms. The sudden blockage of the artery by the clot prevents normal blood circulation and starves the downstream cells of oxygen, causing cell death and cardiovascular disease.
Heart disease
HEART ATTACKS,
