Carpal tunnel syndrome

by Dr. Russ Hornstein

Probably the most over-diagnosed of all upper body problems

While pain in the arm and wrist are very common in today’s typing/mousing intensive workplace, it is rarely attributed to carpal tunnel syndrome. Let’s first get to know the anatomy of the area and then I’ll jump into the process of diagnosing and treating it.

The hand itself has relatively few muscles in it. The muscles that are there only control the action of spreading the fingers apart (and a few small ones for the thumb). The rest of the finger and wrist motions are controlled by muscles in the forearm via long tendons. These long tendons which pass through the palm side of the wrist all move very close to one another but are allowed to move without too much friction due to fluid filled sacs called synovial sheaths which surround them.

Carpal tunnel syndrome and its symptoms is generally agreed to be a result of swelling in this small space. This is most common in women when pregnant, hypothyroidism, arthritis, diabetes and obesity. When swelling occurs here, there is a potential to have nerve impingement (pinching) of the median nerve. The median nerve supplies sensation of the thumb, index, middle and part of the ring finger and numbness, tingling or pain in this area are the classic carpal tunnel symptoms. The median nerve also supplies motor control to muscles of the thumb especially the one that allows you to press the pads of your thumb and little finger together. Weakness in the hand is another common symptom. The greatest difficulty that doctors face in diagnosing ‘true’ carpal tunnel syndrome is that the same symptoms can be caused by other problems not in the carpal tunnel. For instance, the median nerve can be pinched by a muscle in the middle of the forearm called the pronator teres. This will create almost exactly the same symptoms but of course has a very different treatment (not wrist surgery!). Another example which is very common is repetitive strain (or microtrauma) of the muscles on the inside of the forearm occurring as a result of overuse and creating a shortening of the muscles. This puts the tendons under a constant tension which can also create irritation in the carpal tunnel but for a different reason and again with a different treatment.

The challenge to properly diagnose one from another is great and far too often not met. The most common way to determine whether the median nerve has been pinched in the carpal tunnel is either to do a biopsy of it; take a piece of it out (this hurts a bit) and look for damage under the microscope or to do a nerve conduction velocity test (NCV). NCVs measure how well electrical signals pass through nerves. Injured nerves will not pass the signals very well so this is quite a good test when done properly.

The common treatment for carpal tunnel syndrome is rest, ice and anti-inflammatory medication. When this does not resolve enough of the symptoms, surgery is often the next step. The success rate of ‘decompression’ surgery is quite poor, maybe due to the symptoms originating from some other area or not having enough benefit in rehabilitating the nerve.

Obviously all possible causes must be investigated with utmost scrutiny, yet absolute accuracy of diagnosis is only granted to the best of the field. When the diagnosis cannot be decided with complete assurance, a common practice is to apply treatments for all of the possible causes from least invasive to most invasive. In practical terms, if the doctor cannot decide whether the cause is due to median nerve damage in the carpal tunnel or due to tendon irritation from repetitive strain micro trauma (the history should tell you this (not rocket science) they would first treat it as though it was the latter as this treatment is of a milder nature (massage and stretching exercises). This is a common methodology and generally a reasonable thing to do.

 

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