I had an EMG and nerve conduction test done to find out what's causing the painful numbness and tingling in my left hand. The tests came out all normal but the carpal tunnel surgery I had done worked great. Why is that?

Electrodiagnostic tests are used to help diagnose carpal tunnel syndrome (CTS). These include electromyography (EMG) and nerve conduction study (NCS). These tests show how well the nerves are working to send messages to the muscles and skin of the wrist, hand, and fingers.

These tests are done in order to avoid doing unnecessary surgery. But sometimes the tests are normal even when there is a problem. Early changes in the nerve may not show up with this type of testing. Waiting until there's enough nerve damage to have positive electrodiagnostic tests isn't a very good option.

As in your case, the true diagnostic test was the treatment. After surgery, your symptoms were improved. Doctors could use a simple but sensitive and reliable test to diagnose CTS. So far, this hasn't happened.

There is a wide range of tests. The results can often be confusing or contradictory. Each patient must be evaluated individually. The doctor takes into consideration age, body weight and size, signs and symptoms, and the results of any other tests done. Ultrasound or MRI testing can be done but these are usually saved for difficult cases.

Reference: 

Aaron M. Freilich and A. Bobby Chhabra, M.D. Diagnosis and Pathophysiology of Carpal Tunnel Syndrome. In Clinical Opinion in Orthopaedics. July 2007. Vol. 18. No. 4. Pp. 347-351.

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