Part 3 

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, 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 non insulin-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 is 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

·        Legs

·        Feet

·        Arms

·        Hands

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. 

AutonomicNeuropathy (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-aresponse
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.

Next Week Part 4

How Do Doctors Diagnose Diabetic Neuropathy?

How Is Diabetic Neuropathy Usually Treated?

Why Is Good Foot Care Important for People with Diabetic Neuropathy?

Are There Any Experimental Treatments for Diabetic Neuropathy?

Overview of a new device to measure sub-clinical neuropathy.

Studies on new device.

New study for your participation with new device.

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