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, KNOWN medically as myocardial infarctions, are the most well-recognized and feared complication of diabetes. They are caused by atherosclerosis of the blood vessels supplying the heart. The sudden blockage of these arteries starves the heart of oxygen, resulting in the death of part of the heart muscle.
The Framingham studies of the 1970s established a strong association between heart disease and diabetes.11 Diabetes increases the risk of cardiovascular disease two- to fourfold, and these complications develop at a younger age compared to nondiabetics. Sixty-eight percent of diabetics aged sixty-five or older will die of heart disease, and a further 16 percent will die of stroke.12 Reducing the risk of macrovascular disease is therefore of primary importance. The extent of death and disability resulting from cardiovascular diseases is many times greater than that resulting from microvascular diseases.
Over the past three decades, there have been significant improvements in the treatment of heart disease, but gains for diabetic patients have lagged far behind. While the overall death rate for nondiabetic men has decreased by 36.4 percent, it has only decreased 13.1 percent for diabetic men.13
Stroke
A STROKE IS caused by atherosclerosis of the large blood vessels supplying the brain. A sudden disruption of the normal blood flow starves the brain of oxygen and a portion of the brain may die. Symptoms vary depending upon which part of the brain is affected, but the devastating impact of stroke cannot be underestimated. In the United States, it is the third leading cause of death and the biggest contributor to disability.
Diabetes is a strong independent risk factor in stroke, meaning that, on its own, diabetes increases a person’s risk of having a stroke by as much as 150–400 percent.14 Approximately a quarter of all new strokes occur in diabetic patients.15 Every year of diabetes increases the risk of stroke by 3 percent,16 and the prognosis is also far worse.
Peripheral vascular disease
PERIPHERAL VASCULAR DISEASE (PVD) is caused by atherosclerosis of the large blood vessels supplying the legs. The disruption of normal blood flow starves the legs of oxygen-carrying hemoglobin. The most common symptom of PVD is pain or cramping that appears with walking and is relieved by rest. As the blood vessels narrow and circulation worsens, pain may also appear at rest and especially at night. PVD significantly reduces mobility, which can lead to long-term disability.
Skin with a poor blood supply is more likely to be damaged and takes longer to heal. In diabetics, minor cuts or injuries to the feet may become non-healing foot ulcers. In severe cases, these areas where the skin has broken down, revealing underlying tissue, can progress to gangrene. At this point, blood supply has been greatly reduced or completely lost, the tissue dies, and amputation of the affected limb—a treatment of last resort—often becomes necessary to treat chronic infections and relieve pain.
Diabetes, along with smoking, is the strongest risk factor for PVD. Approximately 27 percent of diabetic patients with PVD will progressively worsen over a five-year period, and 4 percent of them will need an amputation.17 Patients with gangrene and those requiring amputation may never walk again, which can result in a cycle of disability. A loss of function of the limbs leads to less physical activity, which in turn leads to progressive deconditioning of the muscles. Weaker muscles lead to less physical activity, and the cycle repeats.
OTHER COMPLICATIONS
Alzheimer’s disease
ALZHEIMER’S DISEASE IS a chronic, progressive, neurodegenerative disease that causes memory loss, personality changes, and cognitive problems. It is the most common form of dementia, and the sixth leading cause of death in the United States.18 Alzheimer’s disease may reflect the inability to use glucose normally, perhaps a type of selective insulin resistance in the brain. The links between Alzheimer’s disease and diabetes have grown so strong that many researchers have suggested Alzheimer’s disease can be called type 3 diabetes.19 These arguments go far beyond the scope of this book, however.
Cancer
TYPE 2 DIABETES increases the risk of most common cancers, including breast, stomach, colorectal, kidney, and endometrial cancers. This may be related to some of the medications used to treat diabetes and will be further discussed in chapter 10. The survival rate of cancer patients with pre-existing diabetes is far worse than for nondiabetics.20