Diabetes is the commonest cause of neuropathy in developed countries. Neuropathy affects roughly half of diabetics. It usually starts with burning sensation, itching or reduced sensation in the hands and feet, otherwise known as ‘gloves and socks’ neuropathy.
Vitamin problems are another cause of neuropathy, especially with respect to vitamins B-1, B-6 and B-12. These are important in nerve metabolism and when they are lacking the nerves suffer, leading to neuropathy with loss or impairment of neural function. Vitamin B-6 overdoses can damage nerves. This has been seen where megadoses of B-6 are included in some sports drinks, as well as in B-complex vitamins.
Alcoholism causes neuropathy two ways. The first is by direct toxicity to the nerves. Secondly, poor nutrition may play a role, since alcoholics often do not eat a nutritious diet, and this causes deficiencies in B vitamins and other nutrients necessary for nerve function. People with neuropathy from any cause should avoid heavy alcohol use, which can further impair the nerves.
Autoimmune diseases: Here the normal defenses of the body turn against the cells and tissues. Some autoimmune diseases only affect one part of the body; sometimes this is the nerves. In other autoimmune disorders, multiple body tissues are affected. Examples of autoimmune diseases include Guillain-Barré syndrome, chronic inflammatory demyelinating polyneuropathy (CIDP), Sjögren’s syndrome, multifocal motor neuropathy (MMN), lupus, rheumatoid arthritis, sarcoidosis, vasculitis and others.
Neurotoxins are chemicals that can damage the nerves and disrupt their functioning. Such toxins include lead, mercury, arsenic, cadmium, and botulinum and tetanus toxins and certain pesticides and industrial chemicals, as well as some medications (see below). Excess amounts of other normally helpful substances, such as zinc and vitamin B-6, harm nerves. Some sports drinks contain megavitamins and have been reported to cause vitamin B-6 toxicity.
Medications such as chemotherapeutics, some anticonvulsants, HIV medications (didanosine and stavudine), statin cholesterol-lowering drugs, several blood pressure medications and certain antibiotics can cause peripheral neuropathy.
Infections: Certain viral and bacterial infections can rarely cause neuropathy, either directly or indirectly, as antibodies produced by the body against the pathogens also attack normal body organs such as nerve fibers. Leprosy is a common cause of neuropathy in some tropical countries. At least ten percent of those infected with Human Immunodeficiency Virus (HIV) develop neuropathy, some because HIV medications can be toxic to nerves. Other infections associated with neuropathy include hepatitis C, Herpes varicella-zoster (shingles), diphtheria, West Nile virus, Epstein-Barr virus and Lyme disease.
Trauma or compression: A common cause of nerve injury is physical trauma to the nerves, such as by injuries, falls, sports activities or surgery. Nerve function can also be compromised by other body parts pressing on the nerve. An example is sciatica, which is caused by a degenerated disc which allows a vertebra to press on a nerve root, causing pain in one or both legs. Another example is carpal tunnel syndrome, in which wrist structures press on nerves. This often comes from repeated activities like typing or hammering. Tumors, scars or bone spurs can also press on nerves and cause damage. Tight casts can inflict external compression that impacts nerve function.
Cancers such as lymphoma and monoclonal gammopathy (abnormal blood proteins) cause neuropathies too. As mentioned above, some medications, called chemotherapeutics, that are used to treat cancer, can damage nerves and cause neuropathy.
Inherited/genetic: Most neuropathies resulting from inherited disorders start in childhood. Many are due to lack of a protein necessary for the production of the myelin sheath. They may also be caused by a defective process leading to accumulation of neurotoxic substances. Examples are Charcot-Marie-Tooth disease, Fabry, metachromatic leukodystrophy and Krabbe disease. Recent research has found that in some cases of neuropathy, genes for certain proteins in the nerve cell membrane are abnormal, leading to chemical changes in the nerve cells that result in neuropathic pain. In other types of neuropathy, defects in genes can cause the nerves to be overexcitable, so that the person feels pain despite lack of injury. Genetic testing may be appropriate for some patients, if their symptoms or test results suggest they may have an inherited/genetic basis for their neuropathy.
Other medical conditions, including amyloidosis and liver, thyroid and kidney diseases can also cause neuropathy.