Somatosensory Evoked Potential Studies (SSEP):

Somatosensory evoked potential studies (SSEP or SEP) are helpful in the evaluation of large sensory nerve compromise.  The studies can be used to measure the speed of sensory nerve transmission through the peripheral nerve, the plexus, the spinal nerve, spinal cord, the brainstem and to specific areas of the brain.  Sensory nerve signal transmission across a site of compromise may be slowed, altered in quality or diminished in strength. SSEP studies may be utilized to monitor spinal nerve root and spinal cord signal integrity and quality during spinal surgical procedures.

Evoked potentials are electrical manifestations of the brain’s response to external stimulus.  Interpretation of somatosensory evoked potentials is based upon the speed of transmission (latency) and amplitude.

Dermatomal Somatosensory Study: This study refers to the electrical assessment of the sensory fibers of specific spinal nerve roots.  Most spinal nerves, which exit the spine, contain sensory nerve fibers that connect with specific skin regions called dermatomes.  The test is performed by placing superficial stimulating electrodes over a skin area innervated by a specific spinal nerve that is to be tested.  The nervous system response to the stimulus is applied to the skin is recorded over the spine and/or scalp.  The nerve signal responses that are measured include the speed of nerve conduction, the strength of the evoked thalamus/brain response, and the quality of nerve signal transmission.

The DSEP study is often performed after the EMG/NCV study if the later study does not provide conclusive findings in a patient believed to have spinal nerve root compromise.  Nerve root compromise is more often associated with predominating sensory complaints with muscle weakness typically occurring later due to progressive nerve damage.  The DSEP assessment may provide greater insight than the more traditionally used needle EMG study to confirm and localize the level of nerve root compromise.  The nerve root responses should be compared to levels not involved and the same nerve root on the opposite (contralateral) side.  The study can also be used to help detect spinal cord compromise.