Potential Causes of a Numb or Tingling Thumb

Nerve Compression as a Common Cause of Thumb Numbness

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Numbness and tingling are common problems, and the nerve supply to the thumb is complicated. If you feel a numbness in your thumb, you are probably wondering what may be causing it.

First, it's important to know if the cause of your thumb numbness is something dangerous. Numbness that comes on suddenly, is accompanied by other problems such as weakness, has no obvious cause such as falling asleep on the arm, has no apparent cause (such as lying on the arm before it "falls asleep"), or is associated with neck or chest discomfort should be evaluated as soon as possible.

Hand numbness may indicate serious problems such as stroke, or even a heart attack or aortic dissection. However, the numbness is often associated with other symptoms in these cases.

What Exactly is Numb?

This question means two things: what is meant by the term numbness, and what parts of the thumb have the unusual sensation?

By numbness, do you mean a "pins and needles" feeling, known as paresthesia, or do you mean a total lack of feeling? Are all areas of the thumb equally affected, or is it just the front, side or back of the thumb? The latter question can be very important in helping distinguish the cause of the numbness.

Understanding The Median Nerve

The hand receives its peripheral nerve supply from cords that branch out between the bones in the neck. These branches twist and interlock in a complicated plexus, then become well-defined nerves such as the median, radial, and ulnar nerve.

While all three nerves are involved with moving the thumb, only the radial and median nerve are involved with sensation to the thumb. 

The median nerve provides sensation to the so-called "palmar" part of the thumb -- the part with the thumbprint and the part that is hidden when you make a fist. The nerve also supplies the palmar face of the index and middle fingers.

The median nerve often gets pinched, resulting in a diminished ability to carry electrical signals back from the skin to the spinal cord and brain. The result is numbness. Sometimes, weakness can also result, particularly of the muscles that bend the thumb towards the little finger.

The most common place for the median nerve to become pinched is in the carpal tunnel, a narrow passage in the wrist where the median nerve travels along several tendons to the fingers. If the tendons become inflamed, the swelling in the narrow tunnel can lead to a pinched nerve. This is sometimes painful, but not always. 

The median nerve can also be pinched in a location somewhere in the arm, but this usually causes numbness or weakness in the arm or wrist as well as the hand and thumb.

Understanding the Radial Nerve

The superficial branch of the radial nerve is responsible for delivering sensation from the back of the hand, thumb, and first two fingers to the brain. If the radial nerve is interrupted, numbness of the back of the hand can result.

Damage to the radial nerve is less common than the medial nerve. The trauma is also more obvious, as well. Rather than a subtle swelling pinching the nerve, the cause may be a bone fracture in the hand, for example.

Unless the damage is just to the superficial branch, there will likely be some degree of muscle weakness as well. In the thumb, this is most noticeable in the muscle that pulls the thumb away from the first finger as if mimicking the cocked hammer of a gun.

Understanding the Spinal Cord, Nerve Roots, and Brachial Plexus 

As mentioned, the nerves run from the hand to the arm, and then to the spinal cord. Like roads approaching a major city, more and more traffic (in this case electrical information) becomes intertwined the closer you get to the center of the action that is the brain. Nerves that were once completely separate begin to run side by side, ultimately converging in the brainstem, an area no bigger around than your thumb, through which flows all information between the body and brain.

For this reason, the closer a problem is to the brain, the more likely it is that more than one flow of information will be disrupted, like cars piling up on a freeway.

Before entering the allegorical freeway of the spinal cord, electrical information essentially travels through a very complicated on-ramp known as the brachial plexus. While it's possible that a very small lesion here could produce numbness of just one thumb, it's unlikely, and generally becomes even less likely when information enters the spinal cord. Not only would other parts of the body be numb, but weakness would likely result as well.

It's worth mentioning a few exceptions to the rule. Sensory and motor information are separated in the spinal cord, beginning from where the nerve roots enter. Motor information enters at the front and sensory information into the back of the spinal cord. For this reason, it's possible to have only numbness result from a cord lesion. Still, that numbness would most likely affect a higher percentage of the body.

Bottom Line

Most of the time, thumb numbness just results from compression of a peripheral nerve. While annoying, it isn't dangerous, provided no other warning signs are present. While it's always possible that something more serious is actually the cause, not only is it less likely, but so long as the numbness is the only problem, no really aggressive treatment is generally called for. For example, a strong blood thinner can be given for stroke, but this increases the risk of bleeding in the brain, and so doctors usually won't give this medication unless more serious symptoms are already present.

If the numbness in your thumb or other fingers persists, it's a good idea to visit your doctor for an evaluation, but unless other signs of weakness or sudden onset are present, it's unlikely to be an emergency.


Hal Blumenfeld, Neuroanatomy through Clinical Cases (2nd ed.). Sinauer Associates, Inc.; 2011.

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