What do neck pain and carpal tunnel syndrome (CTS) have in common? 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. And as this review shows, a nerve in the wrist is 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.
Without a clear mechanism of development of the double crush syndrome, treatment cannot be as specific as possible. Up until now, researchers have paid attention to types of treatment applied and then looked back to see which patients improved. By working backwards in this way, it may be possible to understand the mechanism underlying the loss of nerve function in more than one place along the nerve.
But the problem is a bit more complex than it seems. Some studies show that patients with just carpal tunnel syndrome have better results after carpal tunnel release surgery compared with individuals who have the double crush syndrome. This would lead one to think it is necessary to have surgery at both sites of the nerve compression (neck and wrist).
Yet other patients with double crush syndrome who have cervical decompressive surgery (without carpal tunnel release) have equally good results. Those results would suggest the need for cervical decompression before (or even alone without) carpal tunnel release.
Not everyone agrees but some experts in this area suggest the following when faced with the dilemma of treating a double crush syndrome. First, look at symptoms, results of clinical exams, and perform electrodiagnostic testing. Second, correlate all results together and keep the big picture in mind. Third, when there is a double crush syndrome present, perform the least invasive surgical procedure first.
Then reassess the patient’s symptoms, goals, and expectations and plan accordingly. The patient who continues to have pain and other nerve symptoms should be re-evaluated for a more proximal (closer to the neck) disorder of the nerve(s). 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 then be developed.