Numbness and tingling is one of the most common reasons why people come in to see a neurologist. Figuring out the cause of the numbness can be a difficult task, but most neurologists have an approach to determining the cause of the numbness and offering some kind of relief.
Ruling Out an Emergency
The first step is to figure out whether or not your numbness or tingling is caused by something that is an emergency. Numbness that comes on suddenly, is accompanied by weakness, has no apparent cause (such as lying on the arm before it “falls asleep”), or that does not improve quickly could very well be an emergency like a stroke, and should be checked out by a medical professional as soon as possible.
Is the Problem in the Peripheral Nervous System?
The most common cause of numbness is a problem with a peripheral nerve. Knowing which nerve supplies different areas of the body can help a neurologist figure out where the problem is, and how it might be fixed.
An easy example is when you whack your “funny bone” in your elbow and feel an uncomfortable tingling shoot down to your fingers. When this happens, you’ve lightly injured your ulnar nerve as it travels from your neck down to your fingers, especially your ring finger and little finger.
Your thumb, index finger and middle finger are innervated by a different nerve, called the median nerve. This is the nerve that is affected in carpal tunnel syndrome, for example. There are dozens of other nerves, each supplying a slightly different area of the body. Different combinations of affected areas of the body can help a doctor determine the source of numbness. For this reason, it is good to be as precise as possible when describing where your feelings are occurring.
It's also important to describe any other symptoms that are going on. Back and neck pain can indicate an area of stenosis (narrowing) that leads to compression of a nerve as it exits the spinal cord. This is known as radiculopathy.
Peripheral nerves are very sensitive to toxins, nutritional deficiencies, and some infections. These are problems that affect the entire body at once, and so it would be a little unusual for one side of the body to be more affected than another. Usually, longer nerves are affected first, and the longest nerves in your body run down your legs into your feet.
In general, tingling that happens in the fingers and toes is less concerning than when just one side of the body is affected. There are exceptions, however, such as Guillain-Barre Syndrome (although this is usually also associated with weakness).
Diabetes is the most common cause of a peripheral neuropathy that gradually affects both feet, then spreads up the body. This can result in pain and numbness, and eventually can become so debilitating that a person can hardly walk, or may seriously injure their feet and have no way to know about it. A very common cause of a more sudden feeling of tingling all over is when you are breathing too quickly, such as when you get anxious.
Is the Problem in the Brain or Spinal Cord?
While not every lesion in the brain or spinal cord is an emergency, neurologists are usually more concerned when these structures are damaged because they are so closely tied to other critical functions of the body. While numbness and tingling are annoying, neurologists are more concerned about ensuring nothing more debilitating happens.
A neurologist will usually rely on your medical history and your physical exam to determine whether an injury to the brain or spinal cord is causing your numbness. For example, if you tell the neurologist that you type a lot, your wrist hurts, and the exam shows that just your thumb, index finger, and middle finger are numb, you most likely have carpal tunnel syndrome, and there’s no need to evaluate you for something like stroke.
On the other hand, if your entire arm is numb, you have no pain, and your symptoms came on all at once, the neurologist would be more concerned about a lesion in your brain or spinal cord, and might order further testing to confirm.
What Kinds of Tests Are Used to Evaluate Numbness and Tingling?
If it sounds like your problem is caused by peripheral nerve damage, your doctor may order an electromyogram (EMG) or nerve conduction study. These test certain electrical properties of the nerves in your arms and legs. In unusual cases, other nerves, such as those in your face, can also be tested.
Tests on your blood may be ordered to investigate for signs of toxins or infections that could affect your nervous system. In some cases, such as if your doctor is concerned about Guillain-Barre Syndrome, a lumbar puncture may be called for as well.
While I’ve gone into a brief description of how doctors think about numbness and tingling, please remember that this article is no substitute for a medical evaluation. Use your judgment, and if you have any concerns, don’t hesitate to call a doctor.
Neurologic Emergencies: A Symptom Oriented Approach. 2nd edition. By Greg L. Henry, Andy Jagoda, Neal E. Little and Thomas R. Pellegrino. 2003. Pp. 346. New York: McGraw‐Hill.
Braunwald E, Fauci ES, et al. Harrison's Principles of Internal Medicine. 16th ed. 2005.