Diabetic Neuropathy

Diabetic neuropathies are a family of nerve disorders that occur as a complication of diabetes. It affects the nerves outside the central nervous system, and results in impaired conduction of electrical signals along the nerve. People with diabetes can, over time, develop nerve damage throughout the body. Some people with nerve damage have no symptoms. Others may have symptoms such as pain, tingling, or numbness—loss of feeling—in the hands, arms, feet, and legs. Nerve problems can occur in every organ system, including the digestive tract, heart, and sex organs.

About 60-70 % of people with diabetes have some form of neuropathy. People with diabetes can develop nerve problems at any time, but risk rises with age and longer duration of diabetes. The highest rates of neuropathy are among people who have had diabetes for at least 25 years. Diabetic neuropathies also appear to be more common in people who have problems controlling their blood glucose, also called blood sugar, as well as those with high levels of blood fat and blood pressure and those who are overweight.

Other Names

• Diabetic polyneuropathy

Types

There are two types of diabetic neuropathy.

1. Sensorimotor diabetic neuropathy involves chiefly the nerves of the arms and legs, especially the feet, and causes pain, tingling, numbness, and/or muscular weakness. Usually this type occurs in a symmetric, "stocking-glove distribution," because the longest nerves (i.e., those that go all the way to the fingers and toes) are affected first.
2. Autonomic diabetic neuropathy involves the nerves of the sympathetic and parasympathetic nervous systems, which control the whole body and many organs. Nerves affected include those that go to the heart, intestines, bladder, sweat glands, genitals, and blood vessels.^[1]

Within the above two categories are many more subcategories that describe what part of the body is affected by the neuropathy.^[1]

Signs and Symptoms

The symptoms of diabetic neuropathy are often slight at first. In fact, some cases may go unnoticed for a long time. Numbness, pain, or tingling in the feet, or legs may, after several years, lead to weakness in the muscles of the feet. Occasionally, diabetic neuropathy can flare up suddenly and affect nerves that innervate specific organs and tissues. These flareups produce symptoms specific to the tissue the nerve supplies. For example, neuropathy that affects nerves in the eyes can cause double vision or drooping eyelids (ptosis).

Nerve damage caused by diabetes generally occurs over a period of years and may lead to problems with the digestive tract and sexual organs, which can cause indigestion, diarrhea or constipation, dizziness, bladder infections, and impotence. The loss of sensation in the feet increases the possibility that foot injuries will go unnoticed and develop into ulcers or lesions that become infected. The pain of diabetic neuropathy may become severe enough to cause depression.

A leg or foot affected by diabetic neuropathy will typically show some signs, such as hair loss, calluses, or redness.^[1]

Causes

The primary effect of diabetes is elevated blood glucose levels. This results from either inadequate secretion of insulin from the pancreas or inadequate action of insulin due to resistance to the action of insulin by peripheral tissues like muscles, fat, etc. One of the many consequences of chronically high blood sugar is diabetic neuropathy. Several mechanisms are thought to underlie this neuropathy.

Diabetes often causes blood vessels to constrict. This vasoconstriction can severely limit blood flow to nerves, and as a result, the nerves do not get enough nutrients and oxygen. Essentially the nerves starve and cannot function properly.

Glucose binds to proteins on or in nerve cells in a process called glycosylation. These glycosylated proteins impair nerve function. In people with diabetes, the high blood glucose levels can increase the amount of glycosylated proteins.

Insulin is needed for most cells to take up glucose. This glucose is metabolized into ATP, a form of energy for the cell. Cells in the kidneys and retina and nerves, however, do not need insulin to take up glucose from the blood. These cells also metabolize glucose, but when glucose levels are too high an alternate metabolic pathway is used. This alternate pathway does not produce ATP. Instead, glucose metabolism leads to the production of free radicals. Free radicals are molecules that damage proteins and cell membranes. The free radicals can attack nerve cells and impair their function.

Diagnosis

Diagnosis of diabetic neuropathy is made based on symptoms as well as the examination of the body. Physical exams can detect sensory symptoms, such as tingling and numbness, as well as motor symptoms, such as impaired walking or other movements.

Examination

On physical examination, diabetic neuropathy may show up as loss of sensation, muscle weakness, hair loss or other skin changes, trouble with balance, orthostatic hypotension (a drop in blood pressure when a person stands up), and other signs.^[1]

Monofilament test

A simple device called a 5.07 Semmes-Weinstein monofilament, which consists of a nylon filament attached to a handle, can be used to test for diabetic neuropathy. The filament's tip is pressed against certain areas of the foot to see if the patient can feel the mild pressure.^[2]

Vibration tests

Either a simple musical tuning fork or a device called a biothesiometer can be used to test a diabetic person's ability to feel a vibration. The vibrating device is placed against a toe.^[2]

Treatment

The goal of treating diabetic neuropathy is to relieve discomfort and prevent further tissue damage. The existing nerve damage cannot be reversed, except if the neuropathy is detected early and glucose levels are controlled well.

Medications

The first step in treatment is to bring blood sugar levels under control by diet and medication. Another important part of treatment involves taking special care of the feet. Analgesics(pain killers), low doses of antidepressants, and some anticonvulsant medications are used to relieve pain, burning, or tingling.^[3] Avoid NSAIDS, as they increase the incidence of kidney injury. Safer analgesics are paracetomol, up to 3 grams per day in divided doses. Some antidepressants used to relieve pain in diabetic neuropathy include imipramine, amitriptyline, and duloxetine (Cymbalta). Some anticonvulsants used include gabapentin (Neurontin) and carbamazepine (Tegretol) are also used.

Therapies

Walking regularly, warm baths, or elastic stockings sometimes help relieve leg pain.

Prevention

Main Article: Diabetes and the Nervous System

A study called the Diabetes Control Complications Trial (DCCT) found that careful control of blood sugar reduces the risk that a person with diabetes will develop neuropathy.^[4]

Expected Outcome

The prognosis for diabetic neuropathy depends largely on how well the underlying condition of diabetes is handled. Treating diabetes may halt progression and improve symptoms of the neuropathy, but recovery is slow.

One of the more common complications of diabetic neuropathy is damage to the feet, which can manifest as pain and infections. Severe damage sometimes necessitates amputation.

Research

The National Institute of Neurological Disorders and Stroke (NINDS) conducts and supports research on diabetic neuropathy to increase understanding of the disorder and find ways to prevent and cure it. New medications are currently being examined to assess improvement or stabilization of neuropathic symptoms.

Clinical Trials

Studies on Diabetic Neuropathy from clinicaltrials.gov can be found here.

References

1. ↑ ^{1.0 1.1 1.2 1.3} Aring AM, Jones DE, Falko JM. Evaluation and prevention of diabetic neuropathy. Am Fam Physician. 2005 Jun 1;71(11):2123-8. Abstract | Full Text
2. ↑ ^{2.0 2.1} Singh N, Armstrong DG, Lipsky BA. Preventing foot ulcers in patients with diabetes. JAMA. 2005 Jan 12;293(2):217-28. Abstract | Full Text
3. ↑ Wong MC, Chung JW, Wong TK. Effects of treatments for symptoms of painful diabetic neuropathy: systematic review. BMJ. 2007 Jul 14;335(7610):87. Epub 2007 Jun 11. Abstract | Full Text
4. ↑ National Diabetes Information Clearinghouse: The Diabetes Control and Complications Trial and Follow-up Study