Q: I have neck pain and discomfort from a pinched nerve at the C56 and C67 levels. I seem to be able to manage this with positioning, posture, and some stretching exercises. Now I'm starting to have hand and finger numbness and tingling. The doctor isn't sure if this is coming from the neck or the wrist. Could the original compressive nerve damage in the neck lead to this kind of carpal tunnel syndrome?

A: Neck pain and carpal tunnel syndrome may have a common cause. They could be coming from damage, injury, or compression of the same spinal nerve root. In fact, compression in one region has been shown to increase the likelihood of damage at another location along the nerve. Studies have shown that the nerves in the wrist are actually more susceptible to problems when there is compression in the neck.

Although the link between cervical spine arthritis and carpal tunnel syndrome has been proven, the exact mechanism by which this comes about remains unknown. The condition is referred to as double crush syndrome (DCS). Many experts have suggested various different ways in which this syndrome develops.

It could have to do with the damaged nerve's ability to transport information further down. Perhaps there is a loss of blood supply. Or maybe the initial nerve damage leaves it stiff and no longer elastic enough to transmit messages along its length. Sometimes, another condition such as diabetes or thyroid disease is the missing link. But again, the exact mechanism by which carpal tunnel syndrome follows the initial neck pain remains a mystery.

Physicians have found that electrodiagnostic testing is the most valid and reliable way to document nerve impairment linked with carpal tunnel syndrome. The same type of testing is not as reliable for documenting a double crush syndrome. Commonly used tests (e.g., Phalen's, Tinel's) that point to carpal tunnel syndrome and are confirmed with electrodiagnostic tests cannot be used reliably to diagnose a double crush syndrome.

Sometimes the diagnosis is confirmed when treatment is/is not successful. If decompressive surgery of the neck doesn't change the carpal tunnel symptoms but carpal tunnel release does, then the problem was located in the wrist. But choosing whether to start with treatment distally (at the wrist and hand) versus more proximally (treating the neck) is sometimes just a judgment call without firm evidence of which way is best to go.

If and when a clearer understanding of the mechanism underlying double crush syndrome is discovered, patient management can be re-visited. More appropriate and more consistently successful treatment can be developed.

Reference: William J. Molinari III, MD, and John C. Elfar, MD. The Double Crush Syndrome. In The Journal of Hand Surgery. April 2013. Vol. 38A. No. 4. Pp. 799-801.