Peripheral neuropathy refers to the many conditions that involve damage to the peripheral nervous system, the vast communication network that sends signals between the central nervous system (the brain and spinal cord) and all other parts of the body. Peripheral nerves send many types of sensory information to the central nervous system (CNS), such as a message that the feet are cold. They also carry signals from the CNS to the rest of the body.
Best known are the signals to the muscles that tell them to contract, which is how we move, but there are different types of signals that help control everything from our heart and blood vessels, digestion, urination, sexual function, to our bones and immune system.
The peripheral nerves are like the cables that connect the different parts of a computer or connect the Internet. When they malfunction, complex functions can grind to a halt.
Nerve signaling in neuropathy is disrupted in three ways:
- loss of signals normally sent (like a broken wire)
- inappropriate signaling when there shouldn’t be any (like static on a telephone line)
- errors that distort the messages being sent (like a wavy television picture)
Symptoms can range from mild to disabling and are rarely life-threatening. The symptoms depend on the type of nerve fibers affected and the type and severity of damage. Symptoms may develop over days, weeks, or years.
In some cases, the symptoms improve on their own and may not require advanced care. Unlike nerve cells in the central nervous system, peripheral nerve cells continue to grow throughout life.
How are the peripheral neuropathies classified?
More than 100 types of peripheral neuropathy have been identified, each with its own symptoms and prognosis. Symptoms vary depending on the type of nerves—motor, sensory, or autonomic—that are damaged.
- Motor nerves control the movement of all muscles under conscious control, such as those used for walking, grasping things, or talking.
- Sensory nerves transmit information such as the feeling of a light touch, temperature, or the pain from a cut.
- Autonomic nerves control organs to regulate activities that people do not control consciously, such as breathing, digesting food, and heart and gland functions.
- Most neuropathies affect all three types of nerve fibers to varying degrees; others primarily affect one or two types. Doctors use terms such as predominantly motor neuropathy, predominantly sensory neuropathy, sensory-motor neuropathy, or autonomic neuropathy to describe different conditions.
About three-fourths of polyneuropathies are “length-dependent,” meaning the farthest nerve endings in the feet are where symptoms develop first or are worse.
In severe cases, such neuropathies can spread upwards toward the central parts of the body. In non-length dependent polyneuropathies, the symptoms can start more toward the torso, or are patchy.
What are the symptoms of peripheral nerve damage?
Symptoms are related to the type of nerves affected.
Motor nerve damage is most commonly associated with muscle weakness.
Other symptoms include painful cramps, fasciculations (uncontrolled muscle twitching visible under the skin) and muscle shrinking.
Sensory nerve damage causes various symptoms because sensory nerves have a broad range of functions.
Damage to large sensory fibers harms the ability to feel vibrations and touch, especially in the hands and feet.
You may feel as if you are wearing gloves and stockings even when you are not. This damage may contribute to the loss of reflexes (as can motor nerve damage).
Loss of position sense often makes people unable to coordinate complex movements like walking or fastening buttons or maintaining their balance when their eyes are shut.
The “small fibers” without myelin sheaths (protective coating, like insulation that normally surrounds a wire) include fiber extensions called axons that transmit pain and temperature sensations.
Small-fiber polyneuropathy can interfere with the ability to feel pain or changes in temperature. It is often difficult for medical caregivers to control, which can seriously affect a patient’s emotional well-being and overall quality of life.
Neuropathic pain is sometimes worse at night, disrupting sleep. It can be caused by pain receptors firing spontaneously without any known trigger, or by difficulties with signal processing in the spinal cord that may cause you to feel severe pain (allodynia) from a light touch that is normally painless. For example, you might experience pain from the touch of your bedsheets, even when draped lightly over the body.
There are several types of peripheral neuropathies, the most common of which is linked to diabetes.
What are the causes of peripheral neuropathy?
Most instances of neuropathy are either acquired, meaning the neuropathy or the inevitability of getting it isn’t present from the beginning of life, or genetic. Acquired neuropathies are either symptomatic (the result of another disorder or condition; see below) or idiopathic (meaning it has no known cause).
What treatments are available through physical therapy?
Treatments depend entirely on the type of nerve damage, symptoms, and location. Your doctor will explain how nerve damage is causing specific symptoms and how to minimize and manage them.
With proper education, some people may be able to reduce their medication dose or manage their neuropathy without medications.
Definitive treatment can permit functional recovery over time, as long as the nerve cell itself has not died.
Exercise can deliver more blood, oxygen, and nutrients to far-off nerve endings, improve muscle strength, and limit muscle atrophy.
Self-care skills in people with diabetes and others who have an impaired ability to feel pain can alleviate symptoms and often create conditions that encourage nerve regeneration.
Specific symptoms can usually be improved
For motor symptoms, mechanical aids such as hand or foot braces can help reduce physical disability and pain.
Orthopedic shoes can improve gait disturbances and help prevent foot injuries. Splints for carpal tunnel problems can help position the wrist to reduce pressure of the compressed nerve and allow it to heal.
Transcutaneous electrical nerve stimulation (TENS) is a noninvasive intervention used for pain relief in a range of conditions. TENS involves attaching electrodes to the skin at the site of pain or near associated nerves and then administering a gentle electrical current. Although data from controlled clinical trials are not available to broadly establish its efficacy for peripheral neuropathies, in some studies TENS has been shown to improve neuropathic symptoms associated with diabetes.
Infrared light therapy can increase in blood flow, which provides nutrients, oxygen and proteins to the area to relieve pain and inflammation.
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