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Chronic Nerve Compression: What's Going On?

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Ever felt nervous, jittery, or just plain irritable? You might think those are all emotional responses but in fact, that's your nervous system responding to whatever is happening in your life. The central nervous system (CNS) is made up of the brain and spinal cord. But there's another part of the nervous system called the peripheral nervous system (PNS). It's made up of all the nerves coming from the spinal cord and going out to the rest of your body. The peripheral nerves can be sensory only, motor only, or mixed (both sensory and motor).

Nerves in the peripheral nervous system can also become irritated when they are impinged or pressed upon by bone spurs, protruding discs, tumors, inflammation, and so on. In other situations, those nerves are damaged by injuries that cause chronic (long-term) changes in nerve function. It's the chronic nerve compression (CNC) injuries also known as compressive neuropathies that are the focus of this review article.

Nerve injury or damage of this type can occur as a result of trauma - the nerve gets pinched (compressed), crushed, cut, or stretched. When sensory nerves are affected the result can be symptoms of pain, burning, altered sensation, numbness and tingling, or even complete loss of sensation (paresthesia). Muscle weakness and atrophy are more likely to develop with motor nerve impairment. And a combination of these two sets of symptoms occur with compression of mixed nerves. Chronic nerve compression can also develop as a result of degenerative conditions or health problems like diabetes and chronic alcohol abuse that lead to nerve damage.

Diagnosis and treatment of compressive neuropathies have presented quite a challenge to physicians. The best treatment is always one that provides a cure for the problem. But what we understand about how nerves function and what's happening biologically at the cellular level in these injuries is very limited right now. In fact, we only really have theories and models of what scientists think is going on to use when planning treatment.

Part of the problem is that there are so many different parts to the nerve that could be affected. For example, there's the lining around the nerve and the connective tissue between the lining and the nerve. There are individual nerve cells that could be damaged. The nerve can be injured anywhere from where it connects to the spinal cord all the way down to where the nerve integrates with the skin or muscle it communicates with.

Treatment and prognosis vary depending on which part of the nerve is damaged and how severe is the damage. But it's not like a cut on the finger that can be seen and a bandaid applied. You can't see the nerves. They can't be X-rayed. So how does the physician diagnose the problem? Well, first the patient's symptoms help identify which nerve is affected. Sensory or motor changes (or both) provide helpful information.

Then special electrodiagnostic tests can be applied. There are nerve conduction velocity (NCV) tests that measure the speed that messages are sent along the nerve. Another test called compound muscle action potential (CMAP) measures the messages sent along nerves to the muscles. Sensory nerve action potential (SNAP) tests are used to assess nerves that only pick up sensory (not motor) input. There's also the compound nerve action potential (CNAP) used to test nerves that are both sensory and motor nerves. The results of these tests can help determine where the nerve is damaged and how serious the injury might be.

The authors of this article go into great depth discussing each one of these test measures, the results, and the interpretation of the results. Electrodiagnostic findings are also compared for trauma (both the acute and chronic phases) as well as in chronic compressive injuries from diabetes. From what scientists have found so far, it looks like the biologic and physiologic responses within the damaged nerve(s) differs depending on how the injury occurred.

What can we expect to get from all these nerve studies? Physicians hope to find ways to treat nerve injuries without surgery. Understanding the underlying biology of healing for each type of injury may help scientists find faster and more successful ways to foster healing and full recovery. At the very least, if a way can be found to prevent nerve pain or stop it once it gets started, patients would be eternally grateful.

Right now, scientists are very focused on healing central nervous system damage from spinal cord injuries. The spinal cord injury of the late actor Christopher Reaves (Superman) spurred that research on in a big way. It's possible that some of the techniques used in spinal cord research such as cell transplantation and the use of growth factors to foster nerve regrowth might work with the peripheral nervous system as well.

Reference: Minal Tapadia, JD, MA, et al. Compressive Neuropathies of the Upper Extremity: Update on Pathophysiology, Classification, and Electrodiagnostic Findings. In Journal of Hand Surgery. April 2010. Vol. 35-A. No. 4. Pp. 668-677.

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