Diabetic Neuropathy:
The Nerve Damage of Diabetes
What Is Diabetic Neuropathy?
Diabetic neuropathy is a nerve disorder caused by diabetes. Symptoms
of neuropathy include numbness and sometimes pain in the hands, feet,
or legs. Nerve damage caused by diabetes can also lead to problems with
internal organs such as the digestive tract, heart, and sexual organs
causing indigestion, diarrhea or constipation, dizziness, bladder infections,
and impotence. In some cases, neuropathy can flare up suddenly, causing
weakness and weight loss. Depression may follow. While some treatments
are available, a great deal of research is still needed to understand
how diabetes affects the nerves and to find more effective treatments
for this complication.
DCCT: Can Diabetic Neuropathy Be Prevented?
A 10-year clinical study that involved 1,441 volunteers with insulin-dependent
diabetes (IDDM) was recently completed by the National Institute of Diabetes
and Digestive and Kidney Diseases. The study proved that keeping blood
sugar levels as close to the normal range as possible slows the onset
and progression of nerve disease caused by diabetes. The Diabetes Control
and Complications Trial (DCCT) studied two groups of volunteers: those
who followed a standard diabetes management routine and those who intensively
managed their diabetes. Persons in the intensive management group took
multiple injections of insulin daily or used an insulin pump and monitored
their blood glucose at least four times a day to try to lower their blood
glucose levels to the normal range. After 5 years, tests of neurological
function showed that the risk of nerve damage was reduced by 60 percent
in the intensively managed group. People in the standard treatment group,
whose average blood glucose levels were higher, had higher rates of neuropathy.
Although the DCCT included only patients with IDDM, researchers believe
that people with noninsulin-dependent diabetes would also benefit from
maintaining lower levels of blood glucose.
How Common Is Diabetic Neuropathy?
People with diabetes can develop nerve problems at any time. Significant
clinical neuropathy can develop within the first 10 years after diagnosis
of diabetes and the risk of developing neuropathy increases the longer
a person has diabetes. Some recent studies have reported that:
- 60 percent of patients with diabetes have some form of neuropathy,
but in most cases (30 to 40 percent), there are no symptoms.
- 30 to 40 percent of patients with diabetes have symptoms suggesting
neuropathy, compared with 10 percent of people without diabetes.
Diabetic neuropathy appears to be more common in smokers, people over
40 years of age, and those who have had problems controlling their blood
glucose levels.
What Causes Diabetic Neuropathy?
Scientists do not know what causes diabetic neuropathy, but several
factors are likely to contribute to the disorder. High blood glucose,
a condition associated with diabetes, causes chemical changes in nerves.
These changes impair the nerves' ability to transmit signals. High blood
glucose also damages blood vessels that carry oxygen and nutrients to
the nerves. In addition, inherited factors probably unrelated to diabetes
may make some people more susceptible to nerve disease than others.
How high blood glucose leads to nerve damage is a subject of intense
research. The precise mechanism is not known. Researchers have discovered
that high glucose levels affect many metabolic pathways in the nerves,
leading to an accumulation of a sugar called sorbitol and depletion of
a substance called myoinositol. However, studies in humans have not shown
convincingly that these changes are the mechanism that causes nerve damage.
More recently, researchers have focused on the effects of excessive
glucose metabolism on the amount of nitrous oxide in nerves. Nitrous oxide
dilates blood vessels. In a person with diabetes, low levels of nitrous
oxide may lead to constriction of blood vessels supplying the nerve, contributing
to nerve damage. Another promising area of research centers on the effect
of high glucose attaching to proteins, altering the structure and function
of the proteins and affecting vascular function.
Scientists are studying how these changes occur, how they are connected,
how they cause nerve damage, and how to prevent and treat damage.
What Are the Symptoms of Diabetic Neuropathy?
The symptoms of diabetic neuropathy vary. Numbness and tingling in feet
are often the first sign. Some people notice no symptoms, while others
are severely disabled. Neuropathy may cause both pain and insensitivity
to pain in the same person. Often, symptoms are slight at first, and since
most nerve damage occurs over a period of years, mild cases may go unnoticed
for a long time. In some people, mainly those afflicted by focal neuropathy,
the onset of pain may be sudden and severe.
Diabetic Neuropathy Can Affect Virtually Every Part of the Body
Diffuse (Peripheral) Neuropathy
Diffuse (Autonomic) Neuropathy
- Heart
- Digestive System
- Sexual organs
- Urinary tract
- Sweat glands
Focal Neuropathy
- Eyes
- Facial muscles
- Hearing
- Pelvis and lower back
- Thigh
- Abdomen
What Are the Major Types of Neuropathy?
The symptoms of neuropathy also depend on which nerves and what part
of the body is affected. Neuropathy may be diffuse, affecting many parts
of the body, or focal, affecting a single, specific nerve and part of
the body.
Diffuse Neuropathy
The two categories of diffuse neuropathy are peripheral neuropathy affecting
the feet and hands and autonomic neuropathy affecting the internal organs.
Peripheral Neuropathy
The most common type of peripheral neuropathy damages the nerves of
the limbs, especially the feet. Nerves on both sides of the body are affected.
Common symptoms of this kind of neuropathy are:
- Numbness or insensitivity to pain or temperature
- Tingling, burning, or prickling
- Sharp pains or cramps
- Extreme sensitivity to touch, even light touch
- Loss of balance and coordination.
These symptoms are often worse at night.
The damage to nerves often results in loss of reflexes and muscle weakness.
The foot often becomes wider and shorter, the gait changes, and foot ulcers
appear as pressure is put on parts of the foot that are less protected.
Because of the loss of sensation, injuries may go unnoticed and often
become infected. If ulcers or foot injuries are not treated in time, the
infection may involve the bone and require amputation. However, problems
caused by minor injuries can usually be controlled if they are caught
in time. Avoiding foot injury by wearing well-fitted shoes and examining
the feet daily can help prevent amputations.
Autonomic Neuropathy
(also called visceral neuropathy)
Autonomic neuropathy is another form of diffuse neuropathy. It affects
the nerves that serve the heart and internal organs and produces changes
in many processes and systems.
Urination and sexual response
Autonomic neuropathy most often affects the organs that control
urination and sexual function. Nerve damage can prevent the bladder from
emptying completely, so bacteria grow more easily in the urinary tract
(bladder and kidneys). When the nerves of the bladder are damaged, a person
may have difficulty knowing when the bladder is full or controlling it,
resulting in urinary incontinence.
The nerve damage and circulatory problems of diabetes can also lead
to a gradual loss of sexual response in both men and women, although sex
drive is unchanged. A man may be unable to have erections or may reach
sexual climax without ejaculating normally.
Digestion
Autonomic neuropathy can affect digestion. Nerve damage can cause
the stomach to empty too slowly, a disorder called gastric stasis. When
the condition is severe (gastroparesis), a person can have persistent
nausea and vomiting, bloating, and loss of appetite. Blood glucose levels
tend to fluctuate greatly with this condition.
If nerves in the esophagus are involved, swallowing may be difficult.
Nerve damage to the bowels can cause constipation or frequent diarrhea,
especially at night. Problems with the digestive system often lead to
weight loss.
Cardiovascular system
Autonomic neuropathy can affect the cardiovascular system, which
controls the circulation of blood throughout the body. Damage to this
system interferes with the nerve impulses from various parts of the body
that signal the need for blood and regulate blood pressure and heart rate.
As a result, blood pressure may drop sharply after sitting or standing,
causing a person to feel dizzy or light-headed, or even to faint (orthostatic
hypotension).
Neuropathy that affects the cardiovascular system may also affect the
perception of pain from heart disease. People may not experience angina
as a warning sign of heart disease or may suffer painless heart attacks.
It may also raise the risk of a heart attack during general anesthesia.
Hypoglycemia
Autonomic neuropathy can hinder the body's normal response to
low blood sugar or hypoglycemia, which makes it difficult to recognize
and treat an insulin reaction.
Sweating
Autonomic neuropathy can affect the nerves that control sweating.
Sometimes, nerve damage interferes with the activity of the sweat glands,
making it difficult for the body to regulate its temperature. Other times,
the result can be profuse sweating at night or while eating (gustatory
sweating).
Focal Neuropathy
(including multiplex neuropathy)
Occasionally, diabetic neuropathy appears suddenly and affects specific
nerves, most often in the torso, leg, or head. Focal neuropathy may cause:
- Pain in the front of a thigh
- Severe pain in the lower back or pelvis
- Pain in the chest, stomach, or flank
- Chest or abdominal pain sometimes mistaken for angina, heart attack,
or appendicitis
- Aching behind an eye
- Inability to focus the eye
- Double vision
- Paralysis on one side of the face (Bell's palsy)
- Problems with hearing.
This kind of neuropathy is unpredictable and occurs most often in older
people who have mild diabetes. Although focal neuropathy can be painful,
it tends to improve by itself after a period of weeks or months without
causing long-term damage.
People with diabetes are also prone to developing compression neuropathies.
The most common form of compression neuropathy is carpal tunnel syndrome.
Asymptomatic carpal tunnel syndrome occurs in 20 to 30 percent of people
with diabetes, and symptomatic carpal tunnel syndrome occurs in 6 to 11
percent. Numbness and tingling of the hand are the most common symptoms.
Muscle weakness may also develop.
How Do Doctors Diagnose Diabetic Neuropathy?
A doctor diagnoses neuropathy based on symptoms and a physical exam.
During the exam, the doctor may check muscle strength, reflexes, and sensitivity
to position, vibration, temperature, and light touch. Sometimes special
tests are also used to help determine the cause of symptoms and to suggest
treatment.
A simple screening test to check point sensation in the
feet can be done in the doctor's office. The test uses a nylon filament
mounted on a small wand. The filament delivers a standardized 10-gram
force when touched to areas of the foot. Patients who cannot sense pressure
from the filament have lost protective sensation and are at risk for developing
neuropathic foot ulcers. Physicians may order the filament (with instructions
for use) free from the Gillis W. Long Hansen's Disease Center, LEAP Program,
5445 Point Clair Road, Carville, Louisiana 70721; telephone (504) 642-4714.
Nerve conduction studies check the flow of electrical
current through a nerve. With this test, an image of the nerve impulse
is projected on a screen as it transmits an electrical signal. Impulses
that seem slower or weaker than usual indicate possible damage to the
nerve. This test allows the doctor to assess the condition of all the
nerves in the arms and legs.
Electromyography (EMG) is used to see how well muscles
respond to electrical impulses transmitted by nearby nerves. The electrical
activity of the muscle is displayed on a screen. A response that is slower
or weaker than usual suggests damage to the nerve or muscle. This test
is often done at the same time as nerve conduction studies.
Ultrasound employs sound waves. The sound waves are too
high to hear, but they produce an image showing how well the bladder and
other parts of the urinary tract are functioning.
Nerve biopsy involves removing a sample of nerve tissue
for examination. This test is most often used in research settings.
If your doctor suspects autonomic neuropathy, you may also be referred
to a physician who specializes in digestive disorders (gastroenterologist)
for additional tests.
How Is Diabetic Neuropathy Usually Treated?
Treatment aims to relieve discomfort and prevent further tissue damage.
The first step is to bring blood sugar under control by diet and oral
drugs or insulin injections, if needed, and by careful monitoring of blood
sugar levels. Although symptoms can sometimes worsen at first as blood
sugar is brought under control, maintaining lower blood sugar levels helps
reverse the pain or loss of sensation that neuropathy can cause. Good
control of blood sugar may also help prevent or delay the onset of further
problems.
Another important part of treatment involves special care of the feet,
which are prone to problems.
A number of medications and other approaches are used to relieve the
symptoms of diabetic neuropathy.
Relief of Pain
For relief of pain, burning, tingling, or numbness, the doctor may suggest
an analgesic such as aspirin or acetaminophen or anti-inflammatory drugs
containing ibuprofen. Nonsteroidal anti-inflammatory drugs should be used
with caution in people with renal disease. Antidepressant medications
such as amitriptyline (sometimes used with fluphenazine) or nerve medications
such as carbamazepine or phenytoin sodium may be helpful. Codeine is sometimes
prescribed for short-term use to relieve severe pain. In addition, a topical
cream, capsaicin, is now available to help relieve the pain of neuropathy.
The doctor may also prescribe a therapy known as transcutaneous electronic
nerve stimulations (TENS). In this treatment, small amounts of electricity
block pain signals as they pass through a patient's skin. Other treatments
include hypnosis, relaxation training, biofeedback, and acupuncture. Some
people find that walking regularly or using elastic stockings helps relieve
leg pain. Warm (not hot) baths, massage, or an analgesic ointment such
as Ben Gay may also help.
Gastrointestinal Problems
Indigestion, belching, nausea or vomiting are symptoms of gastroparesis.
For patients with mild symptoms of slow stomach emptying, doctors suggest
eating small, frequent meals and avoiding fats. Eating less fiber may
also relieve symptoms. For patients with severe gastroparesis, the doctor
may prescribe metoclopramide, which speeds digestion and helps relieve
nausea. Other drugs that help regulate digestion or reduce stomach acid
secretion may also be used or erythromycine may be prescribed. In each
case, the potential benefits of these drugs need to be weighed against
their side effects.
To relieve diarrhea or other bowel problems, antibiotics or clonidine
HCl, a drug used to treat high blood pressure, are sometimes prescribed.
The antibiotic tetracycline may be prescribed. A wheat-free diet may also
bring relief since the gluten in flour sometimes causes diarrhea.
Neurological problems affecting the urinary tract can result in infections
or incontinence. The doctor may prescribe an antibiotic to clear up an
infection and suggest drinking more fluids to prevent further infections.
If incontinence is a problem, patients may be advised to urinate at regular
times (every 3 hours, for example) since they may not be able to tell
when the bladder is full.
Dizziness, Weakness
Sitting or standing slowly may help prevent light-headedness, dizziness,
or fainting, which are symptoms that may be associated with some forms
of autonomic neuropathy. Raising the head of the bed and wearing elastic
stockings may also help. Increased salt in the diet and treatment with
salt-retaining hormones such as fludrocortisone are other possible approaches.
In certain patients, drugs used to treat hypertension can instead raise
blood pressure, although predicting which patients will have this paradoxical
reaction is difficult.
Muscle weakness or loss of coordination caused by diabetic neuropathy
can often be helped by physical therapy.
Urinary and Sexual Problems
Nerve and circulatory problems of diabetes can disrupt normal male sexual
function, resulting in impotence. After ruling out a hormonal cause of
impotence, the doctor can provide information about methods available
to treat impotence caused by neuropathy. Short-term solutions involve
using a mechanical vacuum device or injecting a drug called a vasodilator
into the penis before sex. Both methods raise blood flow to the penis,
making it easier to have and maintain an erection. Surgical procedures,
in which an inflatable or semirigid device is implanted in the penis,
offer a more permanent solution. For some people, counseling may help
relieve the stress caused by neuropathy and thereby help restore sexual
function.
In women who feel their sexual life is not satisfactory, the role of
diabetic neuropathy is less clear. Illness, vaginal or urinary tract infections,
and anxiety about pregnancy complicated by diabetes can interfere with
a woman's ability to enjoy intimacy. Infections can be reduced by good
blood glucose control. Counseling may also help a woman identify and cope
with sexual concerns.
Why Is Good Foot Care Important for People with Diabetic Neuropathy?
People with diabetes need to take special care of their feet. Neuropathy
and blood vessel disease both increase the risk of foot ulcers. The nerves
to the feet are the longest in the body, and are most often affected by
neuropathy. Because of the loss of sensation caused by neuropathy, sores
or injuries to the feet may not be noticed and may become ulcerated.
At least 15 percent of all people with diabetes eventually have a foot
ulcer, and 6 out of every 1,000 people with diabetes have an amputation.
However, doctors estimate that nearly three quarters of all amputations
caused by neuropathy and poor circulation could be prevented with careful
foot care.
To prevent foot problems from developing, people with diabetes should
follow these rules for foot care:
- Check your feet and toes daily for any cuts, sores, bruises, bumps,
or infections--using a mirror if necessary.
- Wash your feet daily, using warm (not hot) water and a mild soap.
If you have neuropathy, you should test the water temperature with your
wrist before putting your feet in the water. Doctors do not advise soaking
your feet for long periods, since you may lose protective calluses.
Dry your feet carefully with a soft towel, especially between the toes.
- Cover your feet (except for the skin between the toes) with petroleum
jelly, a lotion containing lanolin, or cold cream before putting on
shoes and socks. In people with diabetes, the feet tend to sweat less
than normal. Using a moisturizer helps prevent dry, cracked skin.
- Wear thick, soft socks and avoid wearing slippery stockings, mended
stockings, or stockings with seams.
- Wear shoes that fit your feet well and allow your toes to move. Break
in new shoes gradually, wearing them for only an hour at a time at first.
After years of neuropathy, as reflexes are lost, the feet are likely
to become wider and flatter. If you have difficulty finding shoes that
fit, ask your doctor to refer you to a specialist, called a pedorthist,
who can provide you with corrective shoes or inserts.
- Examine your shoes before putting them on to make sure they have no
tears, sharp edges, or objects in them that might injure your feet.
- Never go barefoot, especially on the beach, hot sand, or rocks.
- Cut your toenails straight across, but be careful not to leave any
sharp corners that could cut the next toe.
- Use an emery board or pumice stone to file away dead skin, but do
not remove calluses, which act as protective padding. Do not try to
cut off any growths yourself, and avoid using harsh chemicals such as
wart remover on your feet.
- Test the water temperature with your elbow before stepping in a bath.
- If your feet are cold at night wear socks. (Do not use heating pads
or hot water bottles.)
- Avoid sitting with your legs crossed. Crossing your legs can reduce
the flow of blood to the feet.
- Ask your doctor to check your feet at every visit, and call your doctor
if you notice that a sore is not healing well.
- If you are not able to take care of your own feet, ask your doctor
to recommend a podiatrist (specialist in the care and treatment of feet)
who can help.
Are There Any Experimental Treatments for Diabetic Neuropathy?
Several new drugs under study may eventually prevent or reverse diabetic
neuropathy. However, extensive testing is required by the U.S. Food and
Drug Administration to establish the safety and efficacy of drugs before
they are approved for widespread use.
Researchers are exploring treatment with a compound called myoinositol.
Early findings have shown that nerves in diabetic animals and humans have
less than normal amounts of this substance. Myoinositol supplements increase
the levels of this substance in tissues of diabetic animals, but research
is still needed to show any concrete lasting benefits from this treatment.
Another area of research concerns the drug aminoguanidine. In animals,
this drug blocks cross-linking of proteins that occurs more quickly than
normal in tissues exposed to high levels of glucose. Early clinical tests
are under way to determine the effects of aminoguanidine in humans.
One approach that appeared promising involved the use of aldose reductase
inhibitors (ARIs). ARIs are a class of drugs that block the formation
of the sugar alcohol sorbitol, which is thought to damage nerves. Scientists
hoped these drugs would prevent and might even repair nerve damage. But
so far, clinical trials have shown that these drugs have major side effects
and, consequently, they are not available for clinical use.
Some General Hints
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