Short Stories from Dr. Z’s Think Tank
Dr. Z (M. Zannakis PhD)
Award-winning neurophysiologist specializing in hand pain & nerve injury repair
- 21+ medical device patents
- 100+ peer reviewed publications
Wondering why your carpal tunnel symptoms differ from others?
Most people immediately associate hand pain, tingling or numbness with carpal tunnel syndrome.
These sensations are well known because they’re the hallmark symptoms of this neurological condition.
But why aren’t they consistent across the board? For example, some people start off with occasional pain while others have constant numbness.
Still others feel finger tingling from time to time but never have pain. What’s going on?
It’s all in the nerves!
How nerves work
Carpal tunnel syndrome is a disease centering around the major nerve in your wrist joint. Named the median nerve, it’s the source of all those unpleasant to debilitating sensations.
Like all nerves, this nerve is a bundle of tiny, microscopic fibers. Magnified thousands of times, they’re like a bundle of drinking straws.
There are tens of thousands of fibers in each nerve. And each individual fiber carries only one sensation from one specific point on the fingers or hand.
Take a look at the image above. There are 4 colors and each color represents a symptom:
- Red = Pain
- Pink = Numbness
- Blue = Tingling
- Yellow = Burning
Therefore, each color straw (representing a fiber) carries a certain sensation from only one location, like a fingertip or knuckle. Thus, a red straw representing pain might arise from a pinprick in the fingertip or knuckle (or someplace else).
Essentially, each group of fibers in the nerve specializes in carrying one particular sensation like pain. In reality, there are many more sensations, like vibration, tickling, burning, cold, etc.
All of these feelings travel within the fiber bundle that makes up the median nerve. The sensations travel from the skin of the fingers and hand, through the wrist joint, and finally to the brain.
The carpal tunnel space
On its way to the brain from the fingers and hand, the fibers of the median nerve pass through the wrist joint. At its narrowest, the nerve travels through a very cramped space called the “carpal tunnel”. That space is actually a passageway whose walls are the wrist bones. Not only does the median nerve pass through here, but so do the tendons which flex the fingers. This jam-packed space is no wider than a finger, and is one of the most overcrowded spaces in the body.
In carpal tunnel syndrome, the tendons inside that tight passageway gradually swell up. Scientists still don’t understand exactly why tendons swell up to begin with. But the result is that the slow, steady tendon swelling pushes against the adjacent median nerve inside that tight space.
Eventually, as swelling continues, the pushing on the nerve results in a crushing action. Basically, nerves don’t like being crushed. When they are, they produce an abnormal sensation doctors call “paresthesia”. For instance, let’s say a nerve fiber normally carries vibration sensation. But when crushed, the paresthesia might feel like burning or prickling instead.
Why hand and/or finger strength is usually a sign of worsening carpal tunnel
Muscles are activated by signals from the brain. And good muscle strength involves two important interrelated components. First, the muscle itself has to be healthy. Second, the signals that travel from the brain and into the muscle must be intact. That means the nerve going to the muscle must be normal. However, in carpal tunnel syndrome, the median nerve is compromised. Enough pressure on the median nerve ultimately damages the fibers responsible for activating hand muscles.
Usually, the fibers carrying motor (movement) commands to the muscles are thicker in diameter. In a sense, they are heartier or heftier than sensory fibers. Thus, they are more resistant to damage. That’s why motor problems like loss of hand strength and dexterity generally occur later than sensory problems when you have carpal tunnel syndrome. Therefore, if a patient experiences any hand strength loss, their carpal tunnel syndrome (by definition) is more advanced.
Along the same lines, a patient’s motor fibers might be more densely located on the edges of the median nerve. In that case, the fibers would be more exposed to the crushing pressure of swelling tendons. In such instances, even though the patient’s carpal tunnel syndrome is not truly “advanced,” severe motor disturbances can nonetheless occur.
Arrangement of nerve fiber bundles
The arrangement of fibers within a nerve bundle is different in everybody. Let’s get back to the drinking straw analogy and the illustration. When you grab a bundle of straws, you might end up with more red straws on the outside of the bundle, as in the picture. That might translate into more pain fibers on the outer edges of the bundle. That’s shown as more red straws on the outside than inside the bundle. But somebody else might end up grabbing the bundle so more blue straws are on the inside of the bundle. That might translate into more tingling fibers on the bundle’s outer edge.
Essentially, everybody’s arrangement of nerve fibers in a bundle is as different as randomly grabbing colored straws. In other words, some people may have more pain fibers on the outside than inside their nerve bundle. In contrast, other people may have more vibration fibers on the outside than inside their nerve bundle.
This “individualized” arrangement is why some people feel one kind of abnormal (paresthesia) sensation with carpal tunnel syndrome that’s different than somebody else. If tendons start to crush a nerve bundle that has more pain fibers on the outside, then pain will be the primary unpleasant sensation. In time, as tendons crush more of the fiber bundle, additional sensations arise. This is why it’s common for other symptoms to appear in a short period of time. They include pain, numbness, tingling, burning, pins-and-needles, soreness, electric shock, and itching.
No two patients feel the signs of carpal tunnel syndrome exactly the same way. That’s because of how an individual’s median nerve is arranged. The median nerve is arranged in bundles of tiny fibers. Inside the wrist joint, where compression of the nerve occurs, that arrangement makes you more or less susceptible to certain sensations.
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