What Is Causing My Numb Thumb or Hand?

Nerve compression is a common culprit of thumb numbness

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Numbness and tingling are common problems, and the nerve supply to the thumb and hand is complicated. If you feel a numbness in your thumb and/or hand, it's likely causing your concern.

First, it's important to know if the cause of your thumb or hand 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 Numb Actually Means

There are two issues at play: the meaning of the term numbness and the parts of the hand that 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? When thinking of your thumb, 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 called 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 in 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.

In addition, 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 Ulnar Nerve

Injury to the ulnar nerve as it travels from your neck down to your fingers can cause numbness and tingling along the side of your hand, especially your ring finger and little finger. One example is when you whack your “funny bone” and feel an uncomfortable tingling shoot down to your fingers. Like the median nerve, the ulnar nerve can get pinched too, especially as it passes below the elbow.

When this occurs, a person develops cubital tunnel syndrome, which can cause numbness and tingling in the ring and little finger, as well as muscle weakness in the hand.

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.

In other words, 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.

Tests That Evaluate Numbness and Tingling

The tests ordered are often directed at finding the exact cause of numbness and tingling, with the goal of determining the best treatment plan. You should not expect to have all of these tests, but only a select few that are most likely to be helpful in your individual situation.

  • Electromyography (EMG) or nerve conduction study (NCV): These tests evaluate the function of the nerves in your arms and legs. EMG is a test that involves using needles in the affected muscles, while NCV involves applying electrodes to the skin and using a small shock effect. Both of these tests are mildly uncomfortable for a few seconds, but most people are able to tolerate the tests without difficulty, and there should not be any pain or discomfort remaining after the tests are completed.
  • You might need to have a brain CT scan or a brain MRI if there is a possibility that the numbness or tingling is caused by a stroke, multiple sclerosis, head trauma, a brain tumor, or another medical condition involving the brain.
  • lumbar puncture would be needed in rare cases, such as if your doctor is concerned about a rapidly worsening illness called Guillain-Barre Syndrome (GBS). GBS is characterized by severe weakness of the legs, followed by hand weakness and weakness of the muscles of the body, including the muscles that control breathing. GBS often begins with mild numbness or tingling of the feet or hands.

Since toxins, nutritional deficiencies, and some infections can damage the peripheral nerves, your doctor may order blood tests. However, these conditions tend to affect the entire body at once, so it would be a little unusual for one side of the body to be more affected than another.

Examples include lead toxicity and vitamin B12 deficiency. Diabetes and thyroid disease too can cause a peripheral neuropathy.

A Word From Verywell

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.

Sources:

Azhary H, FarooQ MU, Bhanushali M, Majid A, Kassab MY. Peripheral Neuropathy: Differential Diagnosis and Management. 2010 Apr 1;81(7):887-92.

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

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