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Over time, high blood sugar can damage nerves and blood vessels. This damage often affects the feet and legs. Diabetes is responsible for more than 60% of lower limb amputations not caused by accidental injuries, and people with diabetes are 10 times more likely to have an amputation as those without the disease.

Nerve damage makes it harder to feel things happening to your feet, while blood vessel damage can slowly choke off blood flow through arteries feeding them. When these conditions coincide, a simple cut or blister on the bottom of the foot or even an ingrown toenail can become so severely infected that a toe or foot must be amputated.

Diabetes can cause three types of nerve damage:

  • Peripheral neuropathy. This is the most common type of nerve damage. It affects the long nerves that extend from your spine to your arms and legs. Symptoms include numbness, tingling, and reduced sensitivity to light touch. Burning, shooting, or stabbing pain may also occur.

  • Focal neuropathy. This refers to damage to a specific nerve or set of nerves, causing a weakness in facial, leg, arm, or eye muscles. The condition can appear as hand weakness, an inability to lift a leg, or double vision.

  • Autonomic neuropathy. This type of damage involves the autonomic nervous system—the nerves controlling automatic body functions such as heart rate, blood pressure, digestion, sweating, and erections. Autonomic neuropathy may produce a variety of unpleasant effects, such as a racing heartbeat, profuse sweating, bloating, dizziness or nausea, vomiting, diarrhea, and constipation. People with autonomic neuropathy affecting the genitourinary system may not be able to empty their bladders completely (which can predispose them to bladder infections), and as many as half of diabetic men may develop erectile dysfunction (impotence).

One consequence of peripheral neuropathy is loss of pain sensation. When this occurs, a foot injury can go unnoticed, worsen, and become a feeding ground for invasive bacteria. Altered sweating patterns with autonomic neuropathy can also affect the skin's ability to fight infections. Poor circulation contributes to the problem by making it harder for the body's infection fighters—white blood cells, antibodies, and other defenders—to reach the infected area. Poor circulation can also cause ulcers to develop around a wound. Foot ulcers are dangerous and require immediate attention. If not treated, they can penetrate deep below the skin and spread infection into bone.

Toes are very vulnerable to infection. People with severe peripheral neuropathy are also more prone to Charcot's foot, a condition in which joint destruction and deformity interfere with walking. Charcot's foot develops when daily wear and tear cause a minor injury to a joint or bone, and the problem goes unnoticed. Unless changes are made in the individual's stride, footwear, or exercise program, the damage continues and the tissues are eventually destroyed.

Detection and treatment

Because people with peripheral neuropathy can't rely on symptoms to tell them something is wrong, they must carefully check their feet and toes for a possible injury every day. It also helps to wear shoes that have been carefully fitted. A podiatrist can be an excellent resource for help with foot care and footwear.

If a foot ulcer or sore becomes infected, oral or intravenous antibiotics can help fight the infection. But healing can take anywhere from weeks to months, and may require bed rest and elevation of the affected limb.

When circulatory problems inhibit healing, procedures like those used to treat cardiovascular problems may be necessary. For example, if an artery in your foot is blocked, your doctor may recommend angioplasty plus stent insertion or bypass surgery. In angioplasty, a doctor opens a narrowed or blocked artery in the foot by inserting a thin flexible catheter into the artery above the blockage, maneuvering it into the blockage, and then inflating a tiny balloon to open the artery. The balloon expands a tube-like stent that keeps the artery open after the catheter is removed. In bypass surgery, a surgeon takes a length of blood vessel from elsewhere in the body and uses it to construct a new channel that allows blood to get around the blockage.

If all treatment options are exhausted, or if an infection penetrates to the bone or gangrene sets in, part of the foot or leg may need to be amputated. A prosthesis can usually be fitted afterward to make walking possible.

Putting your best foot forward

The adage "An ounce of prevention is worth a pound of cure" applies to many diabetes complications. Damage to the feet and legs is no exception. The best way to avoid these problems is to keep your blood sugar level tightly controlled and to practice good foot care:

  • Put on clean socks or stockings each day.

  • Wear well-fitting, comfortable shoes. If neuropathy makes it hard to tell how a shoe feels, consult an expert in fitting footwear for people with diabetes.

  • To minimize the chance of injuring your feet, avoid going barefoot.

  • Examine your feet every day for any sores, cuts, scratches, breaks in the skin, or swollen areas. Don't forget to check between your toes.

  • Massage your feet with a moisturizing cream to prevent dryness and reduce the chance of cracking, which can lead to skin infection.

  • Wash your feet with warm water and soap every day, and dry them carefully. Never soak feet, because this can dry and crack skin.

  • Keep your toenails well cared for to avoid ingrown nails. If this problem does develop, don't try to fix the ingrown nail yourself—see your doctor instead.

  • Have all calluses, corns, warts, and other common foot ailments treated by a podiatrist.

  • Treat any foot injury immediately, and seek professional help for any wound that seems unusual or doesn't heal.

Last Annual Review Date: 2011-12-05 Copyright: Harvard Health Publications

Reference: Diabetes section on Better Medicine

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Neuropathy is most commonly seen in people who have had diabetes for at least 25 years.