Peripheral Neuropathy

Causes

Peripheral neuropathy may be either inherited or acquired through disease processes or trauma. In many cases, however, a specific cause cannot be identified. Doctors usually refer to neuropathies with no known cause as idiopathic.

Symptoms

Symptoms vary depending on whether motor, sensory, or autonomic nerves are damaged. Motor nerves control voluntary movement of muscles such as those used for walking, grasping things, or talking. Sensory nerves transmit information such as the feeling of a light touch or the pain from a cut. Autonomic nerves control organ activities that are regulated automatically such as breathing, digesting food, and heart and gland functions. Some neuropathies may affect all three types of nerves; others primarily affect one or two types. Doctors may use terms such as predominantly motor neuropathy, predominantly sensory neuropathy, sensory-motor neuropathy, or autonomic neuropathy to describe the types of nerves involved in an individual’s condition.

Diagnosis

The symptoms of peripheral neuropathy are highly variable. A thorough neurological examination is required to sort out the cause of the symptoms and involves taking an extensive medical history (covering symptoms, work environment, social habits, exposure to toxins, alcohol use, risk of HIV or other infectious diseases, and family history of neurological diseases). In addition, tests are usually performed to identify the cause of the neuropathy as well as the extent and type of nerve damage.

A physical examination and various tests may reveal the presence of a systemic disease causing the nerve damage. Tests of muscle strength, as well as evidence of cramps or fasciculations, indicate motor fiber involvement. Evaluation of the person’s ability to sense vibration, light touch, body position, temperature, and pain reveals any sensory nerve damage and may indicate whether small or large sensory nerve fibers are affected.

Blood tests can detect diabetes, vitamin deficiencies, liver or kidney dysfunction, other metabolic disorders, and signs of abnormal immune system activity. An examination of cerebrospinal fluid that surrounds the brain and spinal cord can reveal abnormal antibodies associated with some immune-mediated neuropathies. More specialized tests may reveal other blood or cardiovascular diseases, connective tissue disorders, or malignancies. Genetic tests are becoming available for a number of the inherited neuropathies.

Treatment

Address underlying conditions

The first step in treating peripheral neuropathy is to address any contributing causes such as infection, toxin exposure, medication-related toxicity, vitamin deficiencies, hormonal deficiencies, autoimmune disorders, or compression that can lead to neuropathy. Peripheral nerves have the ability to regenerate axons, as long as the nerve cell itself has not died, which may lead to functional recovery over time. Correcting an underlying condition often can result in the neuropathy resolving on its own as the nerves recover or regenerate.

The adoption of healthy lifestyle habits such as maintaining optimal weight, avoiding exposure to toxins, exercising, eating a balanced diet, correcting vitamin deficiencies, and limiting or avoiding alcohol consumption can reduce the effects of peripheral neuropathy. Exercise can reduce cramps, improve muscle strength, and prevent muscle wasting. Various dietary strategies can improve gastrointestinal symptoms. Timely treatment of injuries can help prevent permanent damage. Smoking cessation is particularly important because smoking constricts the blood vessels that supply nutrients to the peripheral nerves and can worsen neuropathic symptoms. Self-care skills such as meticulous foot care and careful wound treatment in people with diabetes and others who have an impaired ability to feel pain can alleviate symptoms and improve quality of life. Such changes often create conditions that encourage nerve regeneration.

Systemic diseases frequently require more complex treatments. Strict control of blood glucose levels has been shown to reduce neuropathic symptoms and help people with diabetic neuropathy avoid further nerve damage.

Inflammatory and autoimmune conditions leading to neuropathy can be controlled in several ways. Immunosuppressive drugs such as prednisone, cyclosporine, or azathioprine may be beneficial. Plasmapheresis — a procedure in which blood is removed, cleansed of immune system cells and antibodies, and then returned to the body — can help reduce inflammation or suppress immune system activity. Large intravenously administered doses of immunoglobulins (antibodies that alter the immune system, and agents such as rituximab that target specific inflammatory cells) also can suppress abnormal immune system activity.

Symptom Management

Neuropathic pain, or pain caused by the injury to a nerve or nerves, is often difficult to control. Mild pain may sometimes be alleviated by over-the-counter analgesics such as nonsteroidal anti-inflammatory drugs (NSAIDs). More chronic and discomforting pain may need to be addressed through the care of a physician. Medications that are used for chronic neuropathic pain fall under several classes of drugs: antidepressants, anticonvulsant medications, antiarrythmic medications, and narcotic agents. The antidepressant and anticonvulsant medications modulate pain through their mechanism of action on the peripheral nerves, spinal cord, or brain and tend to be the most effective types of medications to control neuropathic pain. Antidepressant medications include tricyclic antidepressants such as amitriptyline or newer serotonin-norepinephrine reuptake inhibitors such as duloxetine hydrochloride or venlafaxine. Anticonvulsant medications that are frequently used include gabapentin, pregabalin, topiramate, and carbamazepine, although other medications used for treating epilepsy may also be useful. Mexiletine is an antiarrythmic medication that may be used for treatment of chronic painful neuropathies.

For pain that does not respond to the previously described medications, the addition of narcotic agents may be considered. Because the use of prescriptionobtained pain relievers that contain opioids can lead to dependence and addiction, their use is recommended only after other means of controlling the pain have failed. One of the newest narcotic medications approved for the treatment of diabetic neuropathy is tapentadol, a drug with both opioid activity and norepinephrine-reuptake inhibition activity of an antidepressant.

Topically administered medications are another option for neuropathic pain. Two agents are topical lidocaine, an anesthetic agent, and capsaicin, a substance found in hot peppers that modifies peripheral pain receptors. Topical agents are generally most appropriate for localized chronic pain such as herpes zoster neuralgia (shingles) pain. Their usefulness for treating diffuse chronic diabetic neuropathy is more limited.

Transcutaneous electrical nerve stimulation (TENS) is a non-invasive intervention used for pain relief in a range of conditions, and a number of studies have described its use for neuropathic pain. The therapy 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, TENS has been shown in some studies to improve peripheral neuropathy symptoms associated with diabetes.

Other complementary approaches may provide additional support and pain relief. 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. Acupuncture, massage, and herbal medications also are considered in the treatment of neuropathic pain.

Surgical intervention can be considered for some types of neuropathies. Injuries to a single nerve caused by focal compression such as at the carpal tunnel of the wrist, or other entrapment neuropathies, may respond well to surgery that releases the nerve from the tissues compressing it. Some surgical procedures reduce pain by destroying the nerve; this approach is appropriate only for pain caused by a single nerve and when other forms of treatment have failed to provide relief. Peripheral neuropathies that involve more diffuse nerve damage, such as diabetic neuropathy, are not amenable to surgical intervention.