Understanding Peripheral Neuropathy -- the Basics

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The Basics | Symptoms | Detection & Treatment

What Is Peripheral Neuropathy?

The name of the condition tells you a bit about what it is:

Peripheral: Beyond (in this case, beyond the brain and the spinal cord.)

Neuro-: Related to the nerves

-pathy: Disease

Put these concepts together and you'll find peripheral neuropathy refers to the variety of conditions that result when the nerves from the rest of the body that connect to the brain and spinal cord are damaged or diseased

The peripheral nerves make up an intricate network that connects the brain and spinal cord to the muscles, skin and internal organs.ï¿½ Peripheral nerves come out of the spinal cord and are arranged along lines in the body called dermatomes.ï¿½ Typically, damage to a nerve will affect one or more dermatomes, which can be tracked to specific areas of the body.ï¿½ Damage to these nerves interrupts communication between the brain and other parts of the body and can impair muscle movement, prevent normal sensation in the extremities, and cause pain.

Types of Neuropathy

There are many different kinds of peripheral neuropathy with many different causes -- from carpal tunnel syndrome (an injury common after chronic repetitive use of the hands and wrists -- such as computer use) to Guillain-Barre syndrome (a rare, sudden paralysis).

As a group, peripheral neuropathies are common, especially among people over the age of 55. The conditions collectively affect 3% to 4% of people in this group.

Neuropathies are typically classified according to the problems they cause or what is at the root of the damage.

There also are terms that express how extensively the nerves have been damaged.ï¿½ These describing words include:

Mononeuropathy

Damage to a single peripheral nerve is called mononeuropathy.ï¿½ Physical injury or trauma such as from an accident is the most common cause.ï¿½ Prolonged pressure on a nerve, caused by extended periods in sedentary positions such as in a wheelchair or bed, or continuous, repetitive motions can trigger mononeuropathy. ï¿½If the fibrous, shock-absorbing discs that lie between the bones in the back are damaged, they could press on a nerve and cause this type of neuropathy.

Carpal tunnel syndrome is a common type of mononeuropathy.ï¿½ It is called an overuse strain injury, which occurs when the nerve that extends through the wrist is compressed.ï¿½ People whose work requires repeated motions with the wrist extended (such as assembly-line workers, physical laborers, and those who use computer keyboards for prolonged periods) can be particularly susceptible.

This damage to the nerve can result in numbness, tingling, unusual sensations and pain in the first three fingers on the thumb side of the hand, particularly while sleeping.ï¿½ In time, carpal tunnel injuries can weaken the muscles in the hand. You may also feel pain, tingling, or burning in your arm and shoulder.

Here are more examples whichï¿½can cause weakness in the affected parts of the body, such as hands and feet:

Ulnar nerve palsy occurs when the nerve that passes close to the surface of the skin at the elbow is damaged.
Radial nerve palsy is caused by injury to the nerve that runs along the underside of the arm.
Peroneal nerve palsy results when the nerve at the top of the calf behind the knee is compressed.ï¿½ This leads to a condition called "foot drop".

Neuropathy can affect a variety of nerves, those that affect muscle movement (motor nerves) and those that detect sensations such as coldness or pain (sensory nerves). ï¿½In some cases, it can affect internal organs, such as the heart, blood vessels, or the bladder and intestines.ï¿½ Neuropathy that affects internal organs is called an autonomic neuropathy.

Mononeuropathy multiplex is when several isolated nerves are involved.

Polyneuropathy

Polyneuropathy accounts for the greatest number of peripheral neuropathy cases.ï¿½ It is caused when many peripheral nerves throughout the body malfunction at the same time.ï¿½ Polyneuropathy can have a wide variety of causes, including exposure to certain toxins, poor nutrition (particularly vitamin B deficiency), and complications from diseases such as cancer or kidney failure.

One of the most common forms of chronic polyneuropathy is diabetic neuropathy, a condition that occurs in diabetics that is the result of poorly controlled blood sugar levels.ï¿½ Though less common, diabetes can also cause mononeuropathy, often characterized by weakness of the eye or of the thigh muscles.

The most common symptoms of polyneuropathy are tingling, numbness, burning pain and loss of sensation in the arms and legs.ï¿½ Because people with chronic polyneuropathy often lose their ability to sense temperature and pain, they can burn themselves and develop open sores as the result of injury or prolonged pressure.ï¿½ If the nerves serving the organs are involved, diarrhea or constipation may result, as well as loss of bowel or bladder control.ï¿½ Sexual dysfunction and abnormally low blood pressure also can occur.

Joints are particularly vulnerable to stress in people with polyneuropathy because they are often insensitive to pain.

One of the most serious polyneuropathies is Guillain-Barre syndrome, a rare disease that strikes suddenly when the body's immune system attacks nerves in the body.ï¿½ Symptoms tend to appear quickly and worsen rapidly, sometimes leading to paralysis.ï¿½ Early symptoms include weakness, tingling, and loss of sensation in the legs that eventually spreads to the arms.ï¿½ Blood pressure problems, heart rhythm problems and breathing difficulties may occur in critical cases.ï¿½ However, despite the severity of the disease, recovery rates are good when patients receive treatment early.

Who Gets Peripheral Neuropathies?ï¿½

Neuropathiesï¿½occur by one of three methods:

Acquired neuropathies, for example, are caused by environmental forces like poisoning, diabetes, trauma, infection or an illness.
Hereditary neuropathy is not as common.ï¿½ It is caused by inherited genetic defects.
Idiopathic neuropathy is from an unknown cause.ï¿½ As many as a third of all neuropathies are classified this way, where the cause can't be explained.

What Causes Peripheral Neuropathy?

Many things can cause peripheral neuropathies so it is often difficult to discern the cause.ï¿½ In fact, in up to one in three cases, the cause cannot be determined. ï¿½Diabetes is responsible for another third.ï¿½ Other known causes include several rare inherited diseases, alcoholism, toxins and certain environmental agents, poor nutrition or vitamin deficiency, trauma due to compression, herniated discs in the back, certain kinds of cancer, conditions where nerves are mistakenly attacked by the body's own immune system or damaged by an overaggressive response to injury, particular medications, kidney disease, thyroid disease, and infections such as Lyme disease, shingles or AIDS.

Hereditary Neuropathy

Hereditary neuropathies are diseases of the peripheral nerves that are genetically passed from parent to child.ï¿½ The most common of these is Charcot-Marie-Tooth disease type 1, which is characterized by weakness in the legs and, to a lesser degree, the arms.ï¿½ Caused by degeneration of the insulation that normally surrounds the nerves and helps them conduct the electrical impulses needed for them to trigger muscle movement, symptoms usually appear between mid-childhood and age 30.

Medically reviewed by Michael Aronson, MD, August 2005.

SOURCES: Bromberg M., "An approach to the evaluation of peripheral neuropathies," Seminars In Neurology, June 2005, Issue: 25(2):153-9. National Institute of Neurologic Disorders and Stroke (NINDS). The Official Patient's Sourcebook on Peripheral Neuropathy: A Revised and Updated Directory for the Internet Age, Icon Health Publications, October 1, 2002. Sghirlanzoni A,; Pareyson D,; Lauria G.; "Sensory neuron diseases," Lancet Neurology, June 2005, 4(6):349-61.

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