Dooley Noted: 9/6/2015
Carpal tunnel syndrome is one of the most misdiagnosed neuropathies of the human body.
While I am always appreciative of patients dropping anatomical terms, any type of numbness and tingling of the hand is usually deemed carpal tunnel syndrome.
But it’s not the patient’s fault.
I’ve seen more cases than I can count of patients presenting to me with a misdiagnosis of carpal tunnel syndrome from a healthcare professional.
This is particularly frustrating, because out of all of these cases, I see a very few that presented with true carpal tunnel syndrome.
Let me explain.
First, let’s discuss the anatomy of the carpal tunnel.
Since “carpal” is the Latin term for “wrist,” the floor of the carpal tunnel is made of tiny wrist bones.
The roof of this tunnel is known as the flexor retinaculum, a soft tissue retainer that keeps flexor tendons from bowstringing during wrist and finger flexion.
Nine tendons lay in this carpal tunnel that control digital and wrist flexion.
One nerve exists in this tunnel: the median nerve.
The median nerve is an important peripheral nerve composed of axons from the C5-T1 ventral rami (branches of spinal nerves). This nerve is responsible for innervation of the medial (flexor) forearm compartment, as well as five muscles in the hand that mostly affect the thumb, second, and third digits.
What’s particularly helpful in diagnosis of median neuropathy is the fact that this nerve provides skin sensation to the palmar aspect of the first, second, third, and lateral parts of the fourth digit, as well as the lateral and middle palm of the hand. The nerve even stretches to the back of our hand to the level of around your nailbeds on the same digits.
Another hand nerve, the ulnar nerve, supplies the medial fourth and fifth digits on the front and back of the hand. So if you’re tingling is present here, there’s no way on earth it’s carpal tunnel syndrome.
The back of the thumb side to fourth finger is largely supplied by the radial nerve. So, if the back of your hand is numb, it’s not carpal tunnel syndrome.
In true carpal tunnel syndrome, the palm of the hand will be spared from numbness. The palmar branch from median nerve actually branches before the median nerve enters the carpal tunnel. In fact, this nerve travels OVER the carpal tunnel.
If your palm is also also numb, you don’t have carpal tunnel syndrome as your sole diagnosis. You know for sure, at minimum, the median nerve is being compressed elsewhere.
The most common place I’ve seen the median nerve compressed is the forearm, particularly at the location of the flexor digitorum superficialis (FDS) muscle.
This muscle is mostly superficial to the median nerve, then travels distally alongside it in the carpal tunnel. This muscle controls wrist and digital flexion up to the second knuckle for digits 2-5.
Since we all are typically glued to our computers and phones, we can fall into excessive use of FDS. This leaves us prone to median neuropathy.
Only median nerve compression caused by FDS will not spare the palm from numbness.
If you are concerned about your numbness and tingling, by all means see a neurologist. Get an EMG/NCV test to see if the median nerve is conducting and delivering electricity.
However, please note this test will not tell you exactly where the median nerve is entrapped.
If you received a carpal tunnel diagnosis off an EMG/NCV, demand a quality neurological exam that includes the testing of the palm with the pinwheel or blind sharp test.
In some cases, the nerve can be crushed at the carpal tunnel and at the forearm.
And if numbness exists only in the first and second fingers, with the palm also numb on the thumb side, this is more indicative of a C6 nerve root issue. The common location for this problem is actually up at the neck!
Since you may not be able to trust your healthcare professional to remember the anatomy, it’s better to arm yourself with knowledge.
Or, show them this article to assure an appropriate assessment.
As always, it’s your call.
– Dr. Kathy Dooley
P.S. Stay tuned for more discussions of nerve entrapment sites, for median nerve and beyond!