Peripheral neuropathy: When nerves get damaged

You have had a foot or hand “fall asleep” because of the way you have been sitting, standing, or sleeping. The abnormal pressure pushes on the nerves and compresses the blood vessels that supply them. The nerves react to their distress by sending signals that cause an unpleasant, even painful tingling sensation. But it’s a temporary situation: the pins-and-needles go away after we change position so blood vessels open up and the pressure is off the nerves.

For people with peripheral neuropathy, that tingling sensation  along with pain, burning, numbness, and other uncomfortable feelings  doesn’t go away easily. Their symptoms aren’t a response to a fleeting lack of blood supply and pressure but to injury or damage to the nerves themselves. That damage may be related to any number of causes, ranging from a traumatic injury to an underlying health condition, such as diabetes.

Generally, early diagnosis and treatment offer the best chance of controlling symptoms and preventing more peripheral nerve damage.

Live wires disrupted

Your nervous system can be viewed in two broad categories. One is your central nervous system, which is your brain and spinal cord. The other is the peripheral nervous system, which includes the peripheral nerves (see illustration). It’s these nerves that are affected by peripheral neuropathy, including:

• Sensory nerves. These allow you to feel sensations such as heat, pain or touch, and contribute to your sense of balance.

• Motor nerves. These help control your muscles’ speed of contraction and their power.

• Autonomic nerves. These control involuntary body functions, such as heart rate, blood pressure, digestion, and bladder function.

It’s most common for the longest nerves  those that reach to your toes  to be affected first. Depending on which of these nerves are affected, signs and symptoms vary. You may encounter:

• Gradual numbness and tingling in your feet or hands that may progress up into your legs or into your arms.

• Burning pain.

• Pain that is sharp, jabbing or electric-like.

• Extreme sensitivity to touch, even light touch.

• Clumsiness or a lack of coordination.

Peripheral neuropathy affecting motor nerves can produce muscle weakness or even paralysis. Bowel or bladder problems are associated with damage to autonomic nerves.

Numbness or reduced feeling associated with peripheral neuropathy may pose some dangers. For instance, if you touch a hot pan or plate, your normal response is to pull back quickly, avoiding a more severe burn. If parts of your body lack feeling, you’re less likely to protect yourself from injury. Another potential danger is for infection or inflammation to go undetected and untreated. Normally, inflammation causes increased pain  but that pain sensitivity may be reduced if you have peripheral neuropathy. This makes it important to regularly check affected areas for minor injuries and treat them to avoid infection. Being proactive is especially important if you have diabetes, which tends to slow wound healing.

Peripheral neuropathy is a symptom, not a single disease. Determining its cause isn’t always easy. In many cases, a cause can’t be identified. Some peripheral neuropathies are due to genetic conditions. One of the most common acquired causes is diabetes, especially if your blood sugar level is poorly controlled. Many people who have diabetes eventually develop some type of neuropathy. Other conditions that can set off peripheral neuropathy include rheumatoid arthritis, lupus, kidney disease, and an underactive thyroid (hypothyroidism).

Certain viral or bacterial infections  including shingles (herpes zoster), hepatitis C, and HIV and AIDS  can cause or possibly make you more susceptible to peripheral neuropathy. Guillain-Barre syndrome affects peripheral nerves. Cancers, particularly blood-related cancers, may be a factor. Some tumors may develop into peripheral nerves. Nerves can also be injured as a result of growths in adjacent bones, tissue or ligaments.

Vitamin deficiencies, especially a lack of certain vitamin B vitamins, can cause peripheral nerve dysfunction. Alcoholism has been associated with peripheral neuropathy. Poor dietary habits of alcoholics may lead to vitamin deficiencies.

The potential for peripheral nerve damage is increased with exposure to toxic substances, such as heavy metals and certain medications. The side effects of certain chemotherapy drugs used to treat cancer can be particularly concerning.

For some, severed or damaged peripheral nerves may be caused by an accident or constant repetitive pressure or injury (e.g. carpal tunnel syndrome at the wrist).

Sorting it out

The usual starting point in diagnosing the cause of peripheral neuropathy is a full medical and family history, as well as physical and neurological exams. From there, your doctor may request blood tests to check blood sugar and vitamin levels and to evaluate for the presence of abnormal proteins (monoclonal proteins), which can cause or be associated with peripheral neuropathy. Blood tests also show how well your kidneys, liver or thyroid are functioning.

If you have signs or symptoms that indicate a nerve disorder such as a peripheral neuropathy, an electromyography (EMG) may be done. EMG is a diagnostic procedure that measures electrical signals in peripheral nerves and the transfer of those signals into muscles. A nerve conduction velocity (NCV) study, part of an EMG, uses surface electrodes  electrodes taped to the skin  to measure the speed and strength of signals traveling between two or more points along the course of the nerve or nerves. The electromyographer places surface electrodes at various locations on your skin depending on where you’re experiencing problems. The electrodes will at times transmit a tiny electrical current that you may feel as a twinge or a spasm.

Occasionally, doctors will order a biopsy of the nerves themselves. The information gleaned from this and other tests can help doctors determine the cause of the neuropathy, and thus provide more definitive treatment.

Treatment

Treatment is geared to managing the underlying condition causing the neuropathy. Doing so often improves the neuropathy on its own, or at least stops the damage from progressing. The other part of treatment is relieving painful symptoms. Your doctor may recommend several treatment options, such as:

• Pain relievers. Nonprescription pain relievers may help relieve mild symptoms. Prescription pain relievers may be helpful for more severe symptoms.

• Anti-seizure drugs. Medications such as gabapentin (Neurontin), topiramate (Topamax). pregabalin (Lyrica), carbamazepin (Tegretol), phenytoin (Dilantin), which were first developed to treat epilepsy, are often used to treat nerve pain.

• Lidocaine patches and topical gels or creams. Lidocaine products or products containing lidocaine and other topicals may be applied where hypersensitivity to light touch is most problematic.

• Certain antidepressants. Tricyclic antidepressants  such as amitriptyline and desipramine (Norpramin) and serotonin and norepinephrine reuptake inhibitors (SNRIs)  such as duloxetine (Cymbalta) and venlafaxine (Effexor)  can relieve pain by altering the chemical processes in your brain and spinal cord that cause you to feel pain. • Transcutaneous electrical nerve stimulation (TENS). Gentle electric current delivered through adhesive electrodes on the skin. TENS may be applied several times a day.

Various alternative treatments may help relieve symptoms of peripheral neuropathy. These include:

• Acupuncture. This may help reduce symptoms, although multiple sessions may be needed before improvement is noticed.

• Biofeedback. This allows you to practice techniques such as relaxation and guided imagery while monitoring your response. Doing so can help you deal with the stress of chronic pain.

Getting ahead of the problem

When nerves are damaged, you may encounter unusual or even unpleasant sensations in the area supplied by those nerves. Early treatment of peripheral neuropathy offers the best chance of preventing further damage and successfully treating symptoms.

Diabetes is thought to be the leading cause of peripheral neuropathy. On the plus side, there’s strong evidence that lifestyle interventions can significantly reduce the likelihood of type 2 diabetes developing in people at risk of the condition. Those interventions include a dedicated effort to eat a healthy diet  one that emphasizes fruits, vegetables, and whole grains  as well as do regular exercise and lose excess weight.