Numbness refers to the partial or complete loss of sensation. It can be a symptom of nervous system malfunction Introduction to Symptoms of Brain, Spinal Cord, and Nerve Disorders Disorders that affect the brain, spinal cord, and nerves are called neurologic disorders. Neurologic symptoms—symptoms caused by a disorder that affects part or all of the nervous system—can... read more .
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 and coordination.
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 Spinal Cord Is Organized 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 Plexus Disorders Plexuses (networks of interwoven nerve fibers from different spinal nerves) may be damaged by injury, tumors, pockets of blood (hematomas), or autoimmune reactions. Pain, weakness, and loss... read more 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 Cauda Equina Syndrome Cauda equina syndrome occurs when the bundle of nerves that extends from the bottom of the spinal cord is compressed or damaged. The most common cause of cauda equina syndrome is a herniated... read more 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.
Causes of Numbness
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 Overview of Vasculitis Vasculitic disorders are caused by inflammation of the blood vessels (vasculitis). Vasculitis can be triggered by certain infections or drugs or can occur for unknown reasons. People may have... read more
, or in the brain, as results from stroke Overview of Stroke A stroke occurs when an artery to the brain becomes blocked or ruptures, resulting in death of an area of brain tissue due to loss of its blood supply (cerebral infarction). Symptoms occur suddenly... read more Damage part of the pathway for sensation, as may result from injuries Injuries of the Spinal Cord and Vertebrae A spinal cord injury is damage to the bundle of cells and nerves that carry incoming and outgoing messages between the brain and the rest of the body. Most spinal cord injuries result from motor... read more
or from hereditary disorders that affect nerves Hereditary Neuropathies Hereditary neuropathies affect the peripheral nerves, causing subtle symptoms that worsen gradually. (See also Overview of the Peripheral Nervous System.) Hereditary neuropathies may affect... read more (neuropathies), such as Friedreich ataxia Friedreich ataxia Coordination disorders often result from malfunction of the cerebellum, the part of the brain that coordinates voluntary movements and controls balance. The cerebellum malfunctions, causing... read more Put pressure on (compress) part of the pathway
Infect a nerve, as occurs in leprosy Leprosy Leprosy is a chronic infection usually caused by the bacteria Mycobacterium leprae or Mycobacterium lepromatosis. It results in damage primarily to the peripheral nerves (the nerves... read more
, HIV infection Human Immunodeficiency Virus (HIV) Infection Human immunodeficiency virus (HIV) infection is a viral infection that progressively destroys certain white blood cells and is treated with antiretroviral medications. If untreated, it can cause... read more 
, or Lyme disease Lyme Disease Lyme disease is a tick-transmitted infection caused by Borrelia species, primarily by Borrelia burgdorferi and sometimes by Borrelia mayonii in the United States. These... read more 
Cause nerves in part of the pathway to become inflamed and lose their outer layer (called demyelination), as occurs in multiple sclerosis Multiple Sclerosis (MS) In multiple sclerosis, patches of myelin (the substance that covers most nerve fibers) and underlying nerve fibers in the brain, optic nerves, and spinal cord are damaged or destroyed. The cause... read more or Guillain-Barré syndrome Guillain-Barré Syndrome (GBS) Guillain-Barré syndrome is a form of polyneuropathy causing muscle weakness, which usually worsens over a few days to weeks, then slowly improves or returns to normal on its own. With treatment... read more
Cause metabolic abnormalities, which may occur in diabetes Diabetes Mellitus (DM) Diabetes mellitus is a disorder in which the body does not produce enough or respond normally to insulin, causing blood sugar (glucose) levels to be abnormally high. Urination and thirst are... read more , vitamin B12 deficiency Vitamin B12 Deficiency Vitamin B12 deficiency can occur in vegans who do not take supplements or as a result of an absorption disorder. Anemia develops, causing paleness, weakness, fatigue, and, if severe, shortness... read more , or poisoning due to heavy metals (such as lead) or another toxin or when chemotherapy drugs are used
Pressure on different parts of the pathway has various causes, depending on which part of the pathway is affected (see table Some Causes and Features of Numbness Some Causes and Features of Numbness 
), as in the following:
Pressure on nerves Compression of the Spinal Cord Injuries and disorders can put pressure on the spinal cord, causing back or neck pain, tingling, muscle weakness, and other symptoms. The spinal cord may be compressed by bone, blood (hematomas)... read more : Repeating specific movements over and over, causing swelling, as occurs in carpal tunnel syndrome Carpal Tunnel Syndrome Carpal tunnel syndrome is a painful compression (pinching) of the median nerve as it passes through the carpal tunnel in the wrist. The cause of most cases of carpal tunnel syndrome is unknown... read more
, or remaining in one position too long, as when people sit with their legs crossed a long timePressure on spinal nerve roots: Rupture or herniation of a disk Herniated Disk A herniated disk occurs when the tough covering of a disk in the spine tears or ruptures. The soft, jelly-like interior of the disk may then bulge out (herniate) through the covering. Aging... read more
in the spine, osteoarthritis Osteoarthritis (OA) Osteoarthritis is a chronic disorder that causes damage to the cartilage and surrounding tissues and is characterized by pain, stiffness, and loss of function. Arthritis due to damage of joint... read more 
, or narrowing of the passageway for the spinal cord (spinal stenosis)Pressure on the spinal cord Compression of the Spinal Cord Injuries and disorders can put pressure on the spinal cord, causing back or neck pain, tingling, muscle weakness, and other symptoms. The spinal cord may be compressed by bone, blood (hematomas)... read more : A tumor, an injury, or a pocket of blood (hematoma) or pus (abscess) near the spinal cord
Evaluation of Numbness
Because so many disorders can cause numbness, doctors ask questions systematically, focusing on more likely causes.
Warning signs
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
Difficulty breathing
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, as occurs in transverse myelitis Acute Transverse Myelitis Acute transverse myelitis is inflammation that affects the spinal cord across its entire width (transversely) and thus blocks transmission of nerve impulses traveling up or down the spinal cord... read more (which causes inflammation across the entire width of the spinal cord)
Both sides, mainly in the hands and feet: Simultaneous malfunction of many peripheral nerves throughout the body (a polyneuropathy Polyneuropathy Polyneuropathy is the simultaneous malfunction of many peripheral nerves throughout the body. Infections, toxins, drugs, cancers, nutritional deficiencies, diabetes, autoimmune disorders, and... read more )
Then doctors ask about the person's other symptoms and medical history Medical History in Neurologic Disorders Before doing a physical examination, doctors interview the person to obtain information about the person's current and past health (medical history). The history is the most important part of... read more . 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 Some Causes and Features of Numbness ).
Doctors 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 Neurologic Examination When a neurologic disorder is suspected, doctors usually evaluate all of the body systems during the physical examination, but they focus on the different parts of the nervous system. Examination... read more ), focusing on testing sensation (whether the person can feel stimuli, such as touch and temperature, normally), as well as reflexes and muscle function.
Testing
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: Nerve conduction studies and electromyography and 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 Electromyography and Nerve Conduction Studies Diagnostic procedures may be needed to confirm a diagnosis suggested by the medical history and neurologic examination. Imaging tests commonly used to diagnose nervous system (neurologic) disorders... read more 
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).
Treatment of Numbness
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 Prevention Most falls occur when older people with one or more physical conditions that impair mobility or balance encounter an environmental hazard. Although many people have no symptoms before a fall... read more .
People should be aware that they may have problems driving, and if they do, they should talk to their doctor about the problems.
Key Points
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 Warning signs Numbness refers to the partial or complete loss of sensation. It can be a symptom of nervous system malfunction. People with numbness may be unable to feel light touch, pain, temperature, or... read more , 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.
