Peripheral neuropathies (PN) happen when damage or an injury occurs to the nerves that connect the central nervous system (CNS) — the brain and spinal cord — to the rest of the body. These most often affect the arms, legs, hands, feet, and toes. The peripheral nervous system has three types of nerves. Each has a different job to do in keeping your body healthy. This article will explore the peripheral neuropathy basics and help you learn more about management and treatments.
Sensory nerves relay information from your senses on the outer parts of the body to the brain, such as whether you are touching something hot. Motor nerves carry messages from the brain to your muscles, telling them where to move. Autonomic nerves control the automatic functions of your body such as sweating and blood pressure.
“At its most basic, PN simply means any disease or injury that impacts on the sensory, motor, or autonomic nerves in the body,” says John England, M.D., Richard Paddison Professor and chair of the Department of Neurology at the Louisiana State University School of Medicine in New Orleans. “This is different from the diseases of the CNS that involve only the brain and spinal cord.”
Estimates suggest that between 25 and 30 percent of the U.S. population will have a neuropathy of some kind over the course of their lives. Diabetic neuropathy is seen in 66 percent of those with Type 1 diabetes and around 59 percent of those with Type 2. Carpal tunnel syndrome, caused by chronic entrapment of the median nerve in the carpal tunnel, is another common PN with a prevalence estimated to be between three and five percent of adults. (Read more about carpal tunnel syndrome.)
At Least 100 Types of Peripheral Neuropathy
More than 100 kinds of PN have been identified, and their causes and presentations vary significantly. Hereditary neuropathies are linked to genetics and often run in families from one generation to the next. They tend to be fairly rare, but newer research indicates that they may be more common than first thought. Acquired neuropathies develop after birth and are much more common.
“A lot of different things can cause PN,” says Adam Loavenbruck, M.D., director of the Neuromuscular Program at Hennepin County Medical Center in Minneapolis. “The most common cause is diabetes because high blood sugars are toxic to nerves. Other often-seen triggers for neuropathies include chemotherapy, excessive use of alcohol, tumors, malnutrition, and inflammatory diseases such as rheumatoid arthritis.”
Your symptoms will be different depending on the kind of neuropathy you have. If the damage is mainly to sensory nerves, you will often have tingling or numbness in the hands and feet, loss of coordination or reflexes, burning sensations, or changes in sensation — from severe pain to an inability to feel pain, pressure, or touch.
People with motor-nerve neuropathy are more likely to have muscle weakness and twitching and difficulty moving their arms and legs. Patients may also experience muscle cramps or spasms, and they may have a hard time picking things up because of loss of dexterity or muscle control.
“The damage usually affects the longest nerves of the body first,” says Loavenbruck. “Those nerves that run to your skin will often result in loss of sensation, tingling and burning pain. It may start at the lowest point like the toes and work its way up the limb.”
Steps Toward a Peripheral Neuropathy Diagnosis
The first step in diagnosing PN is helping your physician develop a complete medical history. The symptoms you are having and where they are located can give important clues to the type of neuropathy and which nerves are affected. Your doctor will also need to know about any diseases you have such as diabetes and any medications you’ve been prescribed that can contribute to PN.
Your health-care provider will ask about other parts of your life and lifestyle. For instance, does your workplace expose you to harsh chemicals that might damage your nerves? Is your diet likely to be low in certain vitamins (an indicator of neuropathies)? How about your alcohol intake?
Your doctor will likely order a battery of blood and urine tests. He or she will be looking for the presence of heavy metals, vitamin deficiencies, liver or kidney disease, and signs of abnormal immune system function consistent with autoimmune diseases.
The next step is often a physical examination. You will likely be asked to do things that test your balance and muscle strength. Usually your physician will use a pin to prick different parts of your body to see if you can feel pain, vibration, temperature, or pressure.
“These indicators are good, but they are subjective or can be influenced by your understanding of the physician’s question,” says Loavenbruck. “They are also not very precise because there isn’t a good way to precisely measure how much sensation loss is present.”
For this reason, specialized nerve studies will often be completed as part of the diagnostic work up. These tests may include:
- nerve conduction velocity (NVC). This stimulates a nerve fiber to generate its own electrical impulse. An electrode farther along the path measures the speed of transmission;
- electromyography (EMG). In this procedure, a fine needle is inserted into a muscle to record electrical activity in motor nerves both at rest and during contraction. This is used to determine if the disorder is related to nerves or the muscle;
- magnetic resonance imaging (MRI). This is used to identify vertebral spinal disk injuries and other abnormalities that can compress nerve roots and mimic neuropathies;
- nerve biopsy. The doctor takes a small sample of nerve tissue to look for any cause of neuropathy such as inflammation; and
- skin biopsy. The doctor removes a 3-mm piece of skin to identify any reduction in the number of nerve fibers.
First Treat Underlying Conditions
“The first option is usually addressing any treatable underlying condition,” says Elia L. Perez, RN, NP-BC, a nurse practitioner at the Helm Center for Pain Management in Laguna Woods, California. “If there is pressure on a spinal nerve, as we see in carpal tunnel syndrome, treating the cause also takes away the pain. When malnutrition is the reason for pain, helping a person improve their diet may be all that is needed. Working with you to better control your diabetes may alleviate some of the pain or at least keep it from getting worse.”
For most people with PN, their pain won’t resolve and will need to be controlled medically. Neuropathic pain doesn’t respond well to simple over-the-counter pain medications.
Medications for Pain Associated with Peripheral Neuropathy
The best drugs for PN-related pain are those used to stop seizures. Among this class of medications, the two that seem to have the best results are pregabalin (Lyrica) and gabapentin (Neurontin).
“The anti-seizure medications work by blocking sodium and calcium channels in the nerve,” says England. “By blocking these channels in sensory nerves that control pain, you decrease the pain impulses and lessen the perception of pain.”
Antidepressants are another class of medication that is effective in treating neuropathic pain. An older group of medicines known as tricyclic antidepressants (amitriptyline) and newer serotonin-norepinephrine reuptake inhibitors such as duloxetine hydrochloride (Cymbalta) or venlafaxine (Effexor) are most often prescribed.
“Both kinds of medications are thought to work by stopping nerve endings from taking in a neurotransmitter know as norepinephrine,” says England. “As you increase the amount of norepinephrine in the CNS, the transmission of pain impulses decreases along the nerve.”
Since pain related to PN is often chronic and can last for long periods of time, narcotic medications aren’t often used as first-line drugs. Due to addiction concerns, they are typically only prescribed after other medications and combinations of medicines have been tried but high levels of pain still persist.
Medications applied directly to the skin are another option. Two often used are topical lidocaine, an anesthetic agent, and capsaicin, a substance found in hot peppers that modifies peripheral pain receptors. The topical products are indicated for chronic, local pain, and their usefulness in treating diffuse chronic diabetic neuropathy is more limited.
Transcutaneous electrical nerve stimulation (TENS) is a non-invasive intervention that has been studied in PN-related pain. Electrodes are attached to the skin at the site of pain or near associated nerves. A gentle electrical current is used to disrupt electrical transmission of pain by the nerves. TENS has been shown in some studies to improve peripheral neuropathy symptoms associated with diabetes.
Other Treatment Options Are Available for Peripheral Neuropathy
Occupational and/or physical therapies can be useful in treating neuropathic pain in selected individuals. For example, mechanical aids such as hand or foot braces can help reduce pain and physical disability by compensating for muscle weakness or alleviating nerve compression. Orthopedic shoes can improve gait disturbances and help prevent foot injuries in people with a loss of pain sensation.
“We have also seen some success using acupuncture,” Perez says. “In most cases, though, the relief is temporary, and you have to go on a regular basis to get best results.”
Surgery is not generally advised, although it can be useful in specific circumstances. For PN related to compression of a single nerve such as in carpal tunnel syndrome, surgery to release the nerve, stopping the compression, can lead to a complete cure.
Certain procedures reduce pain by cutting the nerve in two. This is only used when a single nerve causes pain and other interventions haven’t worked. For PNs that are more widespread, such as diabetic neuropathy, surgery isn’t recommended.
What happens over the long term for people with peripheral neuropathies and their pain depends on the individual’s circumstances. For example, in nerve compression neuropathies, freeing the nerve usually takes care of the problem. Many kinds of PNs resulting from bad diets are resolved by better eating and/or vitamin supplements. The nerve damage related to chemotherapy medications often goes away within two years of completing the treatment.
In other instances, though, the damage is done, and the best that can be hoped for is that the pain doesn’t get worse. Better control of blood sugars in diabetes stops the progression but seldom relieves the pain.
Research is currently underway to help us better understand PN. Specific genetic mutations have been found for some inherited neuropathies. This could lead to identifying people who are at high risk before symptoms appear.
Other studies are trying to determine why nerves degenerate. The hope is that researchers can find new targets for therapies for treatment and prevention of the damage associated with PNs.
One promising area of research focuses on a class of molecules called neurotrophic factors that protect neurons from injury and enhance their survival. Neurotrophic factors also help maintain normal function in mature nerve cells, and some stimulate regeneration.
Finally, researchers are looking at new strategies for relieving pain. They are investigating the many pathways that carry pain signals to the brain. They hope to identify substances that will block this signaling with fewer side effects.
“The take-away for the general public is to be aware that if you have pain or sensory loss in your feet, it is important that you don’t ignore it and hope it goes away,” says England. “If it is persistent, go to a doctor and have it evaluated. The earlier you look for causes, the better it will be for you.”
Resources for Peripheral Neuropathy
Foundation for Peripheral Neuropathy