Neuropathy is a collection of disorders that occurs when nerves of the peripheral nervous system (the part of the nervous system outside of the brain and spinal cord) are damaged. The condition is generally referred to as peripheral neuropathy, and it is most commonly due to damage to nerve axons. Neuropathy usually causes pain and numbness in the hands and feet. It can result from traumatic injuries, infections, metabolic disorders, and exposure to toxins. One of the most common causes of neuropathy is diabetes.
Neuropathy can affect nerves that control muscle movement (motor nerves) and those that detect sensations such as coldness or pain (sensory nerves). In some cases - autonomic neuropathy - it can affect internal organs, such as the heart, blood vessels, bladder, or intestines.
Pain from peripheral neuropathy is often described as a tingling or burning sensation. There is no specific length of time that the pain exists, but symptoms often improve with time - especially if the neuropathy has an underlying condition that can be cured. The condition is often associated with poor nutrition, a number of diseases, and pressure or trauma, but many cases have no known reason (called idiopathic neuropathy).
In theUnited States, about 20 million people suffer from neuropathy. Over half of diabetes patients also suffer from the condition.
How is neuropathy classified?
Peripheral neuropathy can be broadly classified into the following categories:
- Mononeuropathy - involvement of a single nerve. Examples include carpal tunnel syndrome, ulnar nerve palsy, radial nerve palsy, and peroneal nerve palsy.
- Multiple mononeuropathy - two or more nerves individually affected.
- Polyneuropathy - generalized involvement of peripheral nerves. Examples include diabetic neuropathy and Guillain-Barre syndrome.
Neurophathies may also be categorized based on a functional classification (motor, sensory, autonomic, or mixed) or the type of onset (acute - hours or days, subacute - weeks or months, or chronic - months or years).
The most common form of neuropathy is (symmetrical) peripheral polyneuropathy, which mainly affects the feet and legs on both sides of the body.
What causes neuropathy?
About 30% of neuropathy cases are considered idiopathic, which means they are of unknown cause. Another 30% of neuropathies are due to diabetes. In fact, about 50% of people with diabetes develop some type of neuropathy. The remaining cases of neuropathy, called acquired neuropathies, have several possible causes, including:
- Trauma or pressure on nerves, often from a cast or crutch or repetitive motion such as typing on a keyboard
- Nutritional problems and vitamin deficiencies, often from a lack of B vitamins
- Alcoholism, often through poor dietary habits and vitamin deficiencies
- Autoimmune diseases, such as lupus, rheumatoid arthritis, and Guillain-Barre syndrome
- Tumors, which often press up against nerves
- Other diseases and infections, such as kidney disease, liver disease, Lyme disease, HIV/AIDS, or an underactive thyroid (hypothyroidism)
- Inherited disorders (hereditary neuropathies), such as Charcot-Marie-Tooth disease and amyloid polyneuropathy
- Poison exposure, from toxins such as heavy metals, and certain medications and cancer treatments
Who gets neuropathy?
Risk factors for peripheral neuropathy include several conditions and behaviors. People with diabetes who poorly control their blood sugar levels are very likely to suffer from some neuropathy. Autoimmune diseases such as lupus and rheumatoid arthritis also increase one's chance of developing a neuropathy. People who have received organ transplants, AIDS patients, and others who have had some type of immune system suppression have a higher risk of neuropathy. In addition, those who abuse alcohol or have vitamin deficiencies (especially B vitamins) are at an increased risk. Neuropathy is also more likely to occur in people with kidney, liver or thyroid disorders.
What are the symptoms of neuropathy?
Neuropathy symptoms depend on several factors, chiefly where the affected nerves are located and which type of nerves are affected (motor, sensory, autonomic). Several types of neuropathy affect all three types of nerves. Some neuropathies suddenly arise while others come on gradually over the course of years.
Motor nerve damage usually leads to symptoms that affect muscles such as muscle weakness, cramps, and spasms. It is not uncommon for this type of neuropathy to lead to a loss of balance and coordination. Patients may find it difficult to walk or run, feel like they have heavy legs, stumble, or tire easily. Damage to arm nerves may make it difficult to do routine tasks like carry bags, open jars, or turn door knobs.
Sensory nerve damage can cause various symptoms, such as an impaired sense of position, tingling, numbness, pinching and pain. Pain from this neuropathy is often described as burning, freezing, or electric-like, and many report a sensation of wearing an invisible "glove" or "stocking". These sensations tend to be worse at night, and can become painful and sever. On the contrary, sensory nerve damage may lead to a lessening or absence of sensation, where nothing at all is felt.
Autonomic nerve damage affects internal organs and involuntary functions and can lead to abnormal blood pressure and heart rate, reduced ability to perspire, constipation, bladder dysfunction, diarrhea, incontinence, sexual dysfunction, and thinning of the skin.
How is neuropathy diagnosed?
Peripheral neuropathy is often not easy to diagnose. It is not a single disease, but a symptom with often several potential causes. The standard diagnostic process begins with a full medical history with physical and neurological exams that will examine tendon reflexes, muscle strength and tone, the ability to feel sensations, and posture and coordination. Blood tests are also common in order for doctors to measure levels of vitamin B-12. Other common tests include urinalysis, thyroid function tests, and a nerve conduction study that includes electromyography (to measure electrical discharges produced in muscles). Physicians may also recommend a nerve biopsy, where a small portion of nerve is removed and examined under a microscope.
How is neuropathy treated?
There are a variety of treatments available for peripheral neuropathy. They range from traditional pills and creams to special diets and therapies that stimulate the nervous system. Antidepressants, especially tricyclics and selective serotonin-norepinephrine re-uptake inhibitors (SNRI's), are a favored treatment for neuropathies. They will relieve neuropathic pain in non-depressed persons.
In June 2012, researchers from the University of Michigan School of Nursing reported that Cymbalta (duloxetine), an antidepressant, can relieve the symptoms of chemotherapy-induced peripheral neuropathy.
Another class of medicines commonly prescribed for neuropathy is that of anticonvulsants. These medicines block calcium channels on neurons to limit pain. Opioid narcotic treatments for neuropathy are used as well to treat the condition, but are less favored because of the risk of dependency. However, opioids have been the most consistently effective in reducing pain.
For some types of neuropathy, such as post-herpes neuralgia, physicians recommend treatment with a topical anesthetic such as lidocaine. Topical applications of capsaicin (the chemical that makes peppers hot) has also been used to treat neuropathic pain.
Alternative therapies for peripheral neuropathy include cannabinoids (an class of chemicals found in marijuana), Botulinum Toxin Type A (better known as Botox), NMDA antagonists (such as ketamine), dietary supplements (such as alpha lipoic and benfotiamine), chiropractic massages, yoga, meditation, cognitive therapy, and accupuncture.
A final class of therapies for neuropathy are called neuromodulators. These include both implantable and non-implantable technologies (electrical and chemical) such as spinal cord stimulators, implanted spinal pumps, electrodes that stimulate the motor cortex of the brain, and methods called deep brain stimulation.
How can neuropathy be managed and prevented?
There are several ways to manage neuropathy and prevent its symptoms. Good foot health is important, especially for diabetics. Patients should check feet for blisters, cuts, or calluses and avoid tight fitting shoes and socks. Doctors can recommend an exercise plan that will reduce neuropathy pain and control blood sugar levels. Patients should also quit smoking and eat healthful meals. Massages of hands and feet may also aid neuropathy management by stimulating nerves and temporarily relieving pain. Finally, it is advised to avoid prolonged pressure on knees or elbows in order to prevent new nerve damage.