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 the United 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.