Numbness refers to the partial or complete loss of sensation. People with numbness may be unable to feel light touch, pain, temperature, or vibration or to know where parts of their body are (position sense). When people do not know where parts of their body are, they have problems with balance, coordination, and walking.
Many people mistakenly use the term numbness when they have abnormal sensations such as tingling, prickling, or a pins-and-needles sensation or when a limb feels weak or is paralyzed—perhaps partly because people with numbness often also have such abnormal sensations and symptoms. The presence of other symptoms depends on what is causing numbness.
If numbness has been present a long time, particularly in the feet, it can lead to other problems. People may have difficulty walking and driving and may be more likely to fall. They may not notice infections, foot sores (ulcers), and injuries because they cannot sense pain as well. In such cases, treatment may be delayed.
Pathway for sensation:
For a person to feel sensations normally, sensory receptors (specialized ends of sensory nerve fibers in the skin) must detect information in and around the body. These receptors must then send a signal along the following pathway:
For some parts of the body, the pathway includes a plexus or the cauda equina.
Plexuses are networks of sensory nerve fibers and motor nerve fibers (which carry signals from the brain and spinal cord to muscles and other body parts—see Plexus Disorders). In plexuses, these nerve fibers are combined and sorted to serve a particular area of the body. The fibers then branch off from the plexus to become peripheral nerves. There are four plexuses in the torso.
The cauda equina is a bundle of spinal nerve root fibers at the bottom of the spinal cord. This structure resembles a horse's tail, which is what its name means in Latin. It supplies sensation to the thighs, buttocks, genitals, and the area between them, which are called the saddle area because they are the area of the body that would touch a saddle.
Numbness results when one part of the pathway for sensation malfunctions, usually because of a disorder or drug. Many conditions can cause numbness in various ways. For example, they may
Pressure on different parts of the pathway has various causes (see see Table 5: Some Causes and Features of Numbness), as in the following:
Because so many disorders can cause numbness, doctors ask questions systematically, focusing on more likely causes.
In people with numbness, the following symptoms are cause for concern:
When to see a doctor:
People who have warning signs should go to a hospital immediately. People without warning signs should call their doctor. The doctor can decide how rapidly they need to be seen based on their symptoms.
What the doctor does:
Doctors begin by asking which body parts are affected. The pattern of body parts affected by numbness often indicates which part of the nerve pathway is malfunctioning:
Then doctors ask about the person's other symptoms and medical history. Doctors also do a physical examination. What they find during the history and physical examination often suggests a cause and the tests that may need to be done (see see Table 5: Some Causes and Features of Numbness).
Doctors first ask the person to describe the numbness. Then doctors may ask specific questions:
Knowing how quickly numbness and other symptoms began helps doctors determine the type of disorder.
The person is asked about symptoms that may suggest a cause. For example, back and/or neck pain suggests osteoarthritis, a ruptured disk, or another disorder that puts pressure on the spinal cord. Doctors also ask whether the person has had a disorder that can cause numbness, particularly diabetes, chronic kidney disease, infections (such as HIV infection or Lyme disease), a stroke, or arthritis. Doctors may ask whether any family members have had similar symptoms or have a hereditary disorder that affects the nervous system. They ask the person about use of drugs, including recreational drugs, and about possible exposure to toxins.
The physical examination includes a complete evaluation of the nervous system (neurologic examination—see Physical Examination), focusing on testing sensation (whether the person can feel stimuli, such as touch and temperature, normally), as well as reflexes and muscle function.
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Tests are done based on where doctors think the problem is:
Nerve conduction studies and electromyography are often done at the same time. Nerve conduction studies use electrodes or small needles to stimulate a nerve. Then doctors measure how fast the nerve transmits signals (see Electromyography and Nerve Conduction Studies). For electromyography, small needles are inserted into a muscle to record its electrical activity when the muscle is at rest and when it is contracting.
Other tests are then done to identify the specific disorder. For example, if results suggest a polyneuropathy, doctors do blood tests to check for its various causes (such as diabetes or kidney disorders).
The condition causing numbness is corrected or treated when possible.
General measures can help relieve symptoms and prevent additional problems. Precautions to prevent injury are needed because people with numbness are less likely to feel discomfort. If their feet are numb, particularly if circulation is impaired, they should wear socks and shoes that fit well and should check their shoes for pebbles or other foreign material before putting their shoes on. People should inspect their feet frequently for sores and signs of infection, such as redness. If hands or fingers are numb, people should be careful when handling objects that could be hot or sharp.
If people are having difficulty walking or have lost their sense of position (where body parts are), physical therapy can help them learn to walk more safely and to prevent falls (see Prevention). People should be aware that they may have problems driving, and if they do, they should talk to their doctor about the problems.
Last full review/revision August 2012 by Michael C. Levin, MD