But that blessing can become a curse when your body's signaling system goes awry. This happens if you develop diabetic nerve disease (neuropathy).

On the one hand, you may not feel pain when you need to. For example, you might get a blister on your foot, but because you don't feel it, you keep walking on it and make it worse.

On the other hand, you may feel a lot of pain for no good reason. For example, you might have chronic pain in your feet and legs when there is no injury.

Either way, you'll want to do all you can to avoid developing neuropathy. But if it does develop, there are ways to treat it.

What Causes Neuropathy?

There are many causes of diabetic nerve disease in the feet and legs, and they can work alone or in combination to produce neuropathy.

* High Blood Glucose

It makes sense that high blood glucose levels have something to do with diabetic nerve disease: Neuropathy occurs in people with high blood glucose levels, and good control can slow or prevent it. But what's really going on?

You know that insulin helps glucose get into muscle cells and fat cells. But some types of cells don't require insulin to take in glucose. Nerve cells are one example. When there's too much glucose in the blood, a lot of glucose goes into these cells. Once inside the nerve cells, the excess glucose forms sugar alcohols. The sugar alcohols build up. This can affect the production of other nutrients that the nerve cells need to function. The nerves slow down. After many years of living with too much glucose, the nerves suffer permanent damage.

* Smoking

Your nerves are fed by small blood vessels. When these blood vessels are damaged, the nerves are deprived of oxygen and suffer damage.

Smoking makes neuropathy worse. This may be because smoking further damages blood vessels, which have already suffered damage from diabetes.

* Alcohol

People with diabetes who drink a lot of alcohol are more likely to develop nerve disease than people who consume little or no alcohol. Among those individuals who have nerve disease, heavy drinkers often develop more severe neuropathies.

* High Blood Pressure and High Cholesterol Levels

* Autoimmunity

Insulin-dependent (type 1) diabetes occurs when the body treats the insulin-producing cells of the pancreas as invaders. This is called an autoimmune attack. In some people with type I diabetes, the body treats the nerves in the same way--as invaders. This is a rare but often disabling problem in young people.

How Can I Avoid Getting Neuropathy?

There's no surefire way. Some people may have an inherited predisposition to nerve damage, and blood glucose levels that are not that far above normal will set it off. But you will help your chances of avoiding diabetic nerve disease by

* keeping your blood glucose levels under control

* keeping your cholesterol levels and blood pressure down

* not smoking

* not drinking alcohol, other than in moderation.

What Are My Chances Of Developing Neuropathy?

This depends on how you define "having neuropathy." Your doctor may be able to uncover evidence of nerve damage with a lot of testing, but you may not have any symptoms. About 7 percent of people will have signs of neuropathy one year after diagnosis of diabetes, and 50 percent after five years. These are signs detected by a doctor. However, only 30 percent of those people develop symptoms of diabetic neuropathy. (Most experts believe that this percentage is higher in people who drink too much alcohol.

Is It Important For Me To Get Checked For Neuropathy?

Yes, for three reasons:

1. You'll want to be sure that your symptoms are not due to another cause, such as poor circulation, back problems, gout, degenerative arthritis, pernicious anemia, or hypothyroidism.

2. If you have neuropathy and you don't know it, you're in danger of damaging your feet without realizing it.

3. You can get treatment for pain, if needed, and you can take steps to slow the progression of neuropathy.

How Will I Know I Have Neuropathy?

* Through tests done by your doctor. Every year, have a complete physical performed by a specialist in diabetes care. During this physical your doctor will check to see if you are developing neuropathy.

Your doctor may use a tuning fork to see if you can feel vibrations in your feet. This is usually the first sensation to decrease with diabetic neuropathy.

Your doctor might also test your reflexes with a hammer, and touch your feet and lower legs with a pin to see if you still have pain sensation.

* You'll develop symptoms. These symptoms usually start in your feet. Your full foot may be involved or just one area, such as your toe. Symptoms move up your legs as time goes on.

You might describe your symptoms as coldness, itching, burning, tingling, or a feeling like insects are crawling over your skin. Usually these symptoms are worse at night and often get better if you get out of bed and walk around a bit.

Though some symptoms disappear when you walk around, you may feel as if you're walking on cotton or that the floor feels strange. Your feet may feel numb. You may also have a deep aching in the muscles of your calf, especially at night.

At a later stage, a deep pain (often described as a toothache in the foot) develops. Again, it's worse at night and is relieved by getting out of bed and walking around. Often at this time the skin of the legs and feet becomes oversensitive. Contact with clothing, pajamas, or even your other leg is very unpleasant.

At an even more advanced stage, momentary but unpleasant electric shock-like sensations traveling up and down your leg may occur. These are usually described as "lightning pains."

How Can Neuropathy Be Treated?

First, try to get your blood glucose levels under control. As you get better control, the symptoms of neuropathy may decrease.

Simple treatments may work for you, such as wearing elastic (support) hose. An over-the-counter pain killer, such as acetaminophen (Tylenol), may relieve your symptoms.

Use of a TENS unit, which provides nerve stimulation, may also relieve your pain. This can be fitted by your doctor or physical therapist.

If your symptoms are in your skin rather than deep in your muscles or bones, you may get pain relief from capsaicin cream. Capsaicin is an extract from red peppers. It acts against substance P, the chemical in nerves that causes pain.

Take care when you use this cream. If you overuse it, it may cause redness and irritation of the skin. Inhaling the dried cream has, on occasion, caused asthma attacks.

Capsaicin can be purchased without a prescription, but this means it's not covered by health insurance.

Prescription Drugs

If these measures don't help, then you'll need prescription medicines. No drug has been approved by the Food and Drug Administration specifically for the treatment of diabetic neuropathy. However, drugs approved for other uses appear to do some good in treating neuropathy as well.

Drugs called tricyclics are usually used to treat depression, but in smaller doses they may relieve the symptoms of neuropathy. Thus, your doctor may prescribe medicines such as amitriptyline or imipramine to relieve your symptoms. An added advantage is that these drugs may help you sleep.

If antidepressants alone aren't successful, medicines called phenothiazines, usually used for psychological problems, may be added. An example is a drug called fluphenazine.

Another group of drugs that may help your symptoms are those that are usually used to treat epilepsy, such as carbamazepine and clonazepam. Again, these drugs are used in much smaller doses when they are used to treat neuropathy.

Another group of drugs, usually used to treat irregular beating of the heart, may help too. For example, a dose of the local anesthetic lidocaine given in your vein may improve your symptoms for anywhere from just a few days up to one or two weeks. Mexiletine, a drug similar to lidocaine but which you take by mouth, may also help your symptoms.

Remember that the pain from neuropathy doesn't last forever, though no one can say how long your symptoms will last. It could be a month, or it could be years. Often the more acute and severe the symptoms are, the sooner they will end.

Even when you know this, you'll likely get depressed because of your chronic pain. With depression, your pain may be worse. If you're feeling depressed, tell your doctor. The insomnia that often goes with it can be relieved quickly with medication.

Remember that the pain from neuropathy is not treated the same way as the pain that occurs with a bone fracture, a bad tooth, or a kidney stone. The strong pain killers used for these other conditions don' t work well for neuropathy. They are meant to be used for only a short time. You would need high doses of them for your chronic pain, and you'd risk getting addicted to them.

The best advice is to work closely with a specialist in diabetes care who has experience treating pain.

David S. H. Bell, MB, is a professor of medicine at the University of Alabama at Birmingham.

COPYRIGHT 1995 American Diabetes Association Inc.