The most simple cause of numbness in the foot is positional. We have all experienced numbness in the foot at one time as a result of sitting, standing or lying in the same position for too long. This can block off the blood supply to the foot, causing it to feel numb. This type of numbness is easily alleviated by changing position and as the blood flow returns to the foot, the feeling of numbness disappears.
Direct Nerve Injury
Sometimes, numbness is caused by abnormal pressure being put on one or more of the nerves supplying sensation to the feet. A herniated disc in the lower back can bulge out and compress the nerves of the spinal cord. If the pressure is great enough, it can cause an injury to the nerves supplying the foot, leading to numbness in the foot. Wearing shoe gear that is too tight, especially high heels, can lead to a condition called Morton's neuroma in the foot. This condition is thought to result from abnormal pressure on the nerves in the ball of the foot, which can result in numbness. Medication, and sometimes surgery, may be necessary to relieve the pressure. In most cases, once the pressure is relieved, the numbness will slowly go away.
Medical conditions such as peripheral vascular disease and Raynaud's syndrome restrict blood flow to feet, resulting in numbness. Peripheral vascular disease is caused by a narrowing of the arteries, causing reduced blood flow to extremities. This can cause numbness in the feet, particularly while walking. Raynaud's syndrome is a condition that causes numbness in the feet when they are exposed to cold temperatures. Once blood flow is returned to the feet, this numbness can dissipate.
Diabetes is a serious medical condition that affects many parts of the body. This condition often causes numbness in the foot, called peripheral neuropathy. Numbness develops from poorly controlled blood sugar levels. The excess sugar in the blood causes nerve damage, resulting in numbness. This type of nerve damage is irreversible. Diabetics need to take special care of their feet because this numbness leads to an impaired ability to feel pain, heat or cold. Diabetics must visually inspect their feet every day to look for cuts or open sores -- numbness may mask these injuries.
Multiple sclerosis, also called MS, is an autoimmune disease that causes the body's immune system to destroy the protective sheath that covers the peripheral nerves. This can affect the nerves in the feet, causing numbness. Damage to the nerves as a result of multiple sclerosis is progressive. Although this nerve damage is irreversible, numbness in the feet may come and go. Severe numbness may impair walking abilities.
Tarsal Tunnel Syndrome
Tarsal tunnel syndrome is caused by the pinching of the posterior tibial nerve on the inside part of the ankle as it enters the foot. The nerve passes through a small, tight channel to get into the foot. This nerve is easily compressed if it becomes irritated or inflamed. This can lead to tingling and numbness in the foot. Rest, ice and ant-inflammatory medication are used to treat this, but in extreme cases surgery may be needed to relieve the pressure on the nerve.
Alcoholism is a chronic disease that causes the body to become dependent on alcohol and affects many parts of the body. Excessive drinking affects the nervous system, which can cause numbness in the hands and feet.
Some medications can directly affect the nerves providing sensation to the feet, which can lead to numbness. Nerve damage is caused by certain toxic effects of the medications. Certain heart medications such as hydrolazine and indapamide, some cancer drugs such as vincristine, antibiotics including metronidazole and INH and anti-HIV drugs such as stavudine and zidovudine can all cause numbness in the feet.
Vitamin B12 deficiency can cause anemia, resulting in a low red blood cell count. A longstanding B12 deficiency can cause damage to the myelin sheath covering the peripheral nerves of the extremities, leading to numbness in the feet. Treatment with vitamin B12 may help reverse the condition. Abnormal levels of calcium, sodium or potassium can also lead to nerve damage, causing numbness in the feet.
- Diabetes Care: Diabetic Neuropathies -- Update on Definitions, Diagnostic Criteria, Estimation of Severity, and Treatments
- Deutsches Arzteblatt International: Posterior Tarsal Tunnel Syndrome
- The Mount Sinai Journal of Medicine, New York: Axonal Damage in Multiple Sclerosis
- British Journal of Clinical Pharmacology: Alcoholic Neuropathy -- Possible Mechanisms and Future Treatment Possibilities
- Mayo Clinic Proceedings: Peripheral Artery Disease: Current Insight Into the Disease and Its Diagnosis and Management