Magnetic Nerve Stimulation Used to Diagnose Piriformis Syndrome
In this study, scientists compare the results of needle electromyography (EMG) tests with magnetic nerve conduction velocity (NCV) tests to diagnose piriformis syndrome.

Piriformis syndrome is a group of symptoms caused by pressure on the sciatic nerve as it passes through the piriformis muscle in the buttocks. Symptoms include buttock and/or leg pain, numbness, tingling, and muscle weakness.

MRI or ultrasound studies are not always able to pinpoint the cause of buttock pain. NCV to measure the speed of signals along the sciatic nerve are invasive and can be painful. Magnetic stimulation of the nerve is painless and can be used to test the deep nerves such as the sciatic nerve.

Testing was done on 23 patients with piriformis syndrome. Results were compared when the same tests were done on 15 normal, healthy adults (control group). Both electrical and magnetic testing of the sciatic nerve was performed. The authors describe how much stimulation is needed to get the most accurate results.

Magnetic NCV showed that nerve impulses were slowed along the sciatic nerve from the L5 nerve root to the bottom of the buttocks. No such change was measured at the S1 nerve segment. Slower magnetic NCV were observed more often in patients who have had sciatic nerve compression for a longer period of time.

The authors conclude magnetic NCV is an accurate measure of sciatic nerve function in patients with piriformis syndrome. This test offers a painless, noninvasive way to test patients with piriformis syndrome. It can be used instead of the more painful, invasive needle EMG studies.
References
Chein-Wei Chang, MD, et al. Measurement of Motor Nerve Conduction Velocity of the Sciatic Nerve in Patients with Piriformis Syndrome: A Magnetic Stimulation Study. In Archives of Physical Medicine and Rehabilitation. October 2006. Vol. 87. No. 10. Pp. 1371-1375.