Spinal stenosis is one of the main causes of the low back pain and defined as any type of narrowing of spinal canal or nerve root canals of intervertebral foramina.

But, the value of electrodiagnostic study has been controversial due to variable clinical findings and electrodiagnostic findings and electrodiagnostic tests are not standardized as yet.

So to determine the electrodiagnostic features of the spinal stenosis and the sensitivities of the electrodiagnostic tests, we studied conventional electromyopraphy and somatosensory evoked potentials in 56 lumbar spinal stenosis patients and 13 cervical spinal stenosis patients and compared these electrodiagnostic findings with radiologic findings and surgical findings.

The conculusions are as follows;

1) The sensitivities of the electrodiagnostic tests when using radiologic findings as the gold standard are nerve conduction study 31%, needle EMG 61%, somatosensory evoked potential 76% and 90% when we combined the study of needle EMG and somatosensory evoked potentials. So, somatosensory evoked potentials are superior to conventional EMG in detecting clinical symptoms.

2) Somatosensory evoked potentials elicited by dermatomal or cutaneous nerve stimulation are more sensitive than somatosensory evoked potentials elicited by nerve trunk stimulation.

3) Posterior tibial nerve SEP is useful as a screening test in cervical spinal stenosis, especially in cervical myelopathy.

4) The electrodiagnostic characteristics of the spinal stenosis are bilateral multiradicular involvement and more frequent high radicular involvement than simple herniated nucleus pulposus in lumbar spinal stenosis.

So, electromyographer should explore bilateral and multiple nerve roots in spinal stenosis.