Michael C. Levin, MD, Saskatchewan Multiple Sclerosis Clinical Research Chair and Professor of Neurology and Anatomy-Cell Biology;Adjunct Professor of Neurology, College of Medicine, University of Saskatchewan;University of Tennessee Health Science Center
Numbness refers to the partial or complete loss of sensation. It can be a symptom of nervous system dysfunction.
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, walking, and driving, and they are more likely to fall.
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:
Through sensory nerves (nerves from the skin to the spinal cord)
Through spinal nerve roots, formed by sensory nerves joined together into thick short branches that pass through the backbones (vertebrae) to connect with the spinal cord (see Figure: How the Spine Is Organized)
Up the spinal cord
Through the brain stem
To the part of the brain that perceives and interprets these signals (in the cerebrum)
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). 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
Reduce or block the blood supply to nerves in the body, as occurs in vasculitis, or in the brain, as results from stroke
Damage part of the pathway for sensation, as may result from injuries or from hereditary disorders that affect nerves (neuropathies), such as Friedreich ataxia
Put pressure on (compress) part of the pathway
Infect a nerve, as occurs in leprosy, HIV infection, or Lyme disease
Cause nerves in part of the pathway to become inflamed and lose their outer layer (called demyelination), as occurs in multiple sclerosis or Guillain-Barré syndrome
Cause metabolic abnormalities, as may occur in diabetes, vitamin B12 deficiency, or arsenic poisoning or with use of chemotherapy drugs
Pressure on nerves: Repeating specific movements over and over, causing swelling, as occurs in carpal tunnel syndrome, or remaining in one position too long, as when people sit with their legs crossed a long time
Pressure on spinal nerve roots: Rupture or herniation of a disk in the spine, osteoarthritis, or narrowing of the passageway for the spinal cord (spinal stenosis)
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:
Numbness that begins suddenly (within minutes or hours)
Weakness that begins suddenly or rapidly (within hours or days)
Numbness or weakness that rapidly spreads up or down the body, involving more and more parts of the body
Numbness in the thighs, buttocks, genitals, and the area between them (saddle area) and loss of bladder and bowel control (incontinence)
Numbness on both sides below a specific level of the body (such as below the midchest)
Numbness of an entire leg or arm
Loss of sensation in the face and torso
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:
Part of a limb: Peripheral nerve or sometimes spinal nerve root malfunction
Arm and leg on the same side of the body: Brain malfunction
Both sides of the body below a specific level of the body: Spinal cord malfunction
Both sides, mainly in the hands and feet: Simultaneous malfunction of many peripheral nerves throughout the body (a polyneuropathy)
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 Table: Some Causes and Features of Numbness).
Doctors first ask the person to describe the numbness. Then doctors may ask specific questions:
When numbness began
How quickly it began
Whether the person also has other symptoms such as abnormal sensations, weakness or paralysis, loss of bowel or bladder control, retention of urine, vision problems, difficulty swallowing, or deterioration of mental function
Whether any event, such as pressure on a limb, an injury, sleeping in an awkward position, or an infection, triggered the symptoms
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), focusing on testing sensation (whether the person can feel stimuli, such as touch and temperature, normally), as well as reflexes and muscle function.
Some Causes and Features of Numbness
Numbness in both limbs (arm and leg) on one side of the body
Disorders that affect the outer layer of the cerebrum (the largest area of the brain), such as
Often weakness and reduced or absent reflexes in an area supplied by one nerve
A doctor's examination
Sometimes nerve conduction studies and electromyography
*Features include symptoms and results of the doctor's examination. Features mentioned are typical but not always present.
CT = computed tomography; MRI = magnetic resonance imaging.
Testing is not needed if the diagnosis is obvious and treatment involves only general measures (such as rest or a splint)—for example, in some cases of carpal tunnel syndrome.
In other cases, tests are done based on where doctors think the problem is:
For sensory nerves, plexuses, or spinal nerve roots: Nerve conduction studies and electromyography
For plexuses: Sometimes magnetic resonance imaging (MRI) after a contrast agent is injected into a vein
For the brain or spinal cord: MRI or, if MRI is not readily available, computed tomography (CT)
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. For electromyography, a small needle is 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, kidney disorders, or vitamin deficiencies).
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.
People should be aware that they may have problems driving, and if they do, they should talk to their doctor about the problems.
Numbness refers to partial or complete loss of sensation and is often accompanied by abnormal sensations, such as tingling.
Numbness, which has many causes, occurs when one part of the pathway from sensory receptors in the skin to the brain malfunctions.
If people have any warning sign, they should see a doctor immediately.
Telling doctors which parts of the body are affected and how quickly symptoms develop helps doctors identify the location and cause of the malfunction.
Testing usually starts with nerve conduction studies and electromyography if the sensory nerves, plexuses, or spinal nerve roots are thought to be affected or with MRI if the brain or spinal cord is thought to be affected.