Two forms of evoked potentials are utilized in the evaluation of patients referred to GDA when clinically indicated. They include the Somatosensory Evoked Potential and the Dermatomal Evoked Potential.
Somatosensory evoked potentials are generated from transcutaneous stimulation of the peripheral nerve using electrodes placed over the distribution of which nerve is being studied. Surface electrodes placed on the scalp record the potentials generated in the cerebral cortex.
The potentials recorded are obtained by averaging several hundred responses. SEPs help to determine if there are demyelinating lesions in the peripheral nervous system and can also be useful in evaluating the proximal portion of the nervous system including the nerve root, cord entry, spinal cord, brainstem and cerebral cortex.
Dermatomal evoked potentials are evaluated from transcutaneous stimulation of a sensory dermatome. The potentials generated in the patient's cerebral cortex are recorded with surface electrodes placed on the scalp. The recorded potentials are obtained by averaging several hundred responses. DEPs test specific nerve root levels.