Neuropathy

The Facts

Peripheral neuropathy refers to damage to the peripheral nerves – nerves that carry information between the central nervous system (the brain and spinal cord) and the rest of the body. Peripheral neuropathy occurs in about 2% to 8% of people and is more common as we age.

Peripheral neuropathy may be caused by a number of different medical conditions, such as diabetes, cancer, and nutritional deficiencies. Peripheral neuropathy can also be caused by medications and chemicals. It can interfere with the senses, with movement, or with the function of internal organs.

Damage to one nerve is called mononeuropathy, while damage to many nerves all at once is called polyneuropathy.

Causes

Mononeuropathies are usually caused by pressure on a nerve that is just under the skin and near the knee, elbow, shoulder, or wrist. Mononeuropathies may also be caused by trapped or injured nerves. Sudden onset is most commonly caused by trauma such as forcible overextension or repeated tight gripping. Gradual onset may be caused by compression (e.g., from a tumor, crutches, or a cast).

Some nerves close to the surface of the body, such as the median nerve in the wrist, the ulnar nerve in the elbow, the radial nerve in the upper arm, and the peroneal nerve in the calf, are more easily injured than other nerves. The injuries result in the following mononeuropathies: carpal tunnel syndrome, ulnar nerve palsy, radial nerve palsy, and peroneal nerve palsy.

For example, repetitive wrist movements can put pressure on the median nerve in the wrist, causing carpal tunnel syndrome. There are several conditions (e.g., infections, sarcoidosis, connective tissue disorders) that can cause mononeuropathies in several places at a time–these are called multiple mononeuropathies.

Polyneuropathy has many causes, including alcoholism; diseases such as diabetes, cancer, and end-stage kidney failure; autoimmune diseases; infections; and exposure to poisonous toxic chemicals, heavy metals such as lead or mercury, and chemotherapeutic agents such as vincristine.

Hypothyroidism, a hormonal condition in which the thyroid gland doesn't work normally, can also cause neuropathy. Some neuropathies are due to inherited medical conditions that get worse with time, and others can be caused by certain medications (e.g., didanosine, dapsone, metronidazole, isoniazid, vincristine, amiodarone). Vitamin deficiencies (e.g., B12, folic acid) can also cause polyneuropathy.

Guillain-Barré syndrome is a very serious form of polyneuropathy. Sometimes people with the disease become paralyzed. It is probably caused by an autoimmune reaction. The body's immune system attacks the nerve's myelin sheath, a coating that helps carry a signal along the nerve. Guillain-Barré syndrome can develop suddenly between 5 days and 3 weeks after a person has had a respiratory infection or a gastroenteritis, a vaccine (the chance is less than 1 per 1,000,000 people vaccinated), or a surgery.

Symptoms and Complications

The symptoms of neuropathy depend on the location and seriousness of the nerve damage.

Mononeuropathy appears as pain, weakness, or immobilization in the localized area of the affected nerve. If the affected nerve is purely a sensory nerve, there will be numbness but no weakness; if a motor nerve is involved, there will be weakness but no numbness.

Symptoms of polyneuropathy may develop suddenly or gradually. The first symptom of polyneuropathy is often mild tingling, which gets worse over time until the area becomes numb. People with diabetes often have neuropathy of the feet. This is a serious condition because they could get an infection or injure a foot and not be able to feel it.

Along with the tingling and numbness, people with chronic polyneuropathy may feel burning or shooting pain. Since they can't sense changes in temperature or feel pain caused by injuries, theyoften burn themselves or develop open sores from injuries they don't realize they have. They may also have trouble walking and standing because they can't tell what position their joints are in.

Neuropathy can also cause muscle weakness.

Sometimes the nerves controlling automatic functions of the body such as bowel and bladder contraction or blood pressure control are affected by neuropathy. When this happens, a person can have constipation, diarrhea, erectile dysfunction, bladder dysfunction, and high or low blood pressure.

The main symptom of Guillain-Barré syndrome is weakness that gets progressively worse over 2 to 3 weeks. The weakness starts in the legs and moves to the arms. The breathing and swallowing muscles can also become weak. Between 5% and 10% of people with the disease have to breathe using a respirator, and 1 in 10 can't swallow. Hearts of people with a serious case of the disease may beat with an abnormal rhythm, and their blood pressure may go up and down in an irregular and unpredictable way.

Making the Diagnosis

Your doctor can usually diagnose neuropathy from the pattern of symptoms and the neurological examination.

Electromyography (EMG), a technique that measures electrical activity in the muscles, may provide more information about the neuropathy. In this technique, small needles are put into the muscle. Every time the muscle contracts, it creates electricity. The electrical signals are recorded as spikes on a screen and are also played back as sound. People with neuropathy have abnormal electrical activity in their muscles because of the damaged nerves that control those muscles. Nerve conduction studies can also be used. They measure how quickly electrical signals travel through the nerves that control movement (motor nerves) or sensation (sensory nerves).

It's also important for the doctor to find out what is causing the neuropathy. Blood tests can sometimes tell if it's due to metal poisoning, diabetes, a vitamin deficiency, kidney failure, or a genetic disease. Urine tests may diagnose heavy metal poisoning or cancer.

Unfortunately, none of these tests alone can diagnose Guillain-Barré syndrome. In suspected Guillain-Barré syndrome patients, lab tests are done mainly to rule out other possible causes. Sometimes a small amount of spinal fluid is removed through a very fine needle (lumbar puncture) to look for increased amounts of protein or abnormal cells. In rare cases, a muscle or nerve biopsy may be done.

Treatment and Prevention

Avoiding repetitive movements that could put pressure on the nerves can prevent mononeuropathy. For example, if you use a computer all day, make sure to adjust the angle of the keyboard so you don't hyperextend your wrists.

You need to release the pressure on the damaged nerve in order to relieve mononeuropathy. You can do this either with physical therapy, by avoiding the cause of the pressure, with the use of splints (especially when sleeping), or with surgery. In mild cases, over-the-counter pain relievers (e.g., ibuprofen*, naproxen) may also be helpful.

The treatment of polyneuropathy depends on what caused it. Polyneuropathy related to diabetes requires that the blood sugar levels be carefully controlled. If cancer related, treating the underlying cancer may alleviate the neuropathy. If a specific treatment isn't available, the pain associated with the neuropathy can usually be helped with medications. Several medications such as amitriptyline, carbamazepine, gabapentin, duloxetine, lamotrigine, pregabalin, and topiramate, as well as cannabis and its derivatives, have been used to relieve the pain of neuropathy. Lidocaine injections and patches may be useful when applied over the painful area. Capsaicin cream can also be helpful, but many people do not tolerate the initial burning sensation associated with it. Neuropathic pain that does not respond to usual treatment may require treatment with opioid pain medications (e.g., oxycodone, morphine, tramadol).

Since it can get worse very quickly, people with suspected Guillain-Barré syndrome should be rushed to the hospital. Their breathing will be monitored, and they will need physiotherapy to loosen tight muscles. Once the doctors are sure it is Guillain-Barré syndrome, the person may receive treatment with plasmapheresis (to remove antibodies from the blood) and immunoglobulins. If someone with Guillain-Barré syndrome is treated early, they can get better in a matter of days or weeks. Otherwise, it may takes a few months, but most people do recover.

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