Other important diagnostic tests are the classical nerve studies.  These can be broken down into two basic classifications; sensory nerve action potential studies and motor conduction velocity studies.  The priors are sometimes referred to as “SNAP studies”.21  

     Axonotmesis may, in rare cases, indicate that the nerve was severed; however, it generally indicates that regeneration can occur because the endoneurial coverings maintain their proper alignment, indicating that this patient will recover with conservative care.  Neuropraxis however is found when conduction is locally blocked (for example focal demyelination), and recovery is relatively rapid.  With neuropraxia think of some local, focal blockage to nerve conduction, such as a carpal tunnel syndrome.  Finally neurotmesis can be distinguished for the other two states because when distally stimulated, normal conduction is maintained.4  

      The most sophisticated of all Neurodiagnostic tests is Somatosensory evoked potentials, also called Somatosensory evoked responses, short-latency Somatosensory evoked potential, Somatosensory EPs, SL-Eps, SEPs, SSEPs, SSERs or SERs 6-17.  

      Functional impairment is uniformly assessed by the performance of a quality physical, orthopedic and neurological examination and special tests, and obtaining the patient’s history then forming the consistent patient status.  Imaging procedures allow you to actually study a picture revealing structural evidence, which is then correlated to determine functional changes.  The search for a relatively noninvasive, simple test of brain function has brought about the development of sensory evoked potentials recorded from the scalp as low-risk, clinically-applicable procedures capable or providing new and objective evidence about a variety of nervous system functions.  Generally, Somatosensory evoked responses are used to test the visual system, the auditory system and somatosensory tracts and pathways 7,14.   

      Somatosensory evoked response specificity concerns posterior column disease, such as posterolateral column disease or sclerosis of the spine, to test the integrity of the rostral projections of the central nervous system, the cervical roots, the lumbar roots, the brachial plexes, specific upper extremity nerves such as the median nerve and cervical and lumbar radiculopathy. 7,8,14,21  

      This examiner previously discussed the fact that we could gain tremendous insight into the integrity of the afferent pathways by use of Neurodiagnostic procedures, yet we were unable to test the stretch and vibratory receptors.  With the use of SL-SEPs, we can now test those stretch and vibratory afferent receptors.  Sensory evoked potentials provide an objective measurement of the functional state of the afferent sensory pathways including the receptors, primary afferent sensory neurons into the central nervous system, ascending sensory pathways within the nervous system, specific sensory cortex, and nonspecific sensory cortex functions. 7,21     In fact, it has been determined that sensory evoked potentials can a) determine whether or not our patient has a disorder of sensory function, b) localize the anatomical site of the patient’s disorder, c) implicate specific etiologies for sensory impairment, and d) provide an objective index of the efficacy of various therapies. 7 

     Neuroscientists have been exploring additional uses for SSEPs.  Desmedt, in 1971, revealed that peripheral nerve function can be determined by a neurologist by measurement of the change in latency of the initial scalp-derived negative component form stimulation at various points along a peripheral nerve, which will provide a measure of the nerve’s conduction velocity. 2,8  This application of somatosensory evoked potentials is particularly applicable to individuals with advanced peripheral neuropathies in whom compound nerve-action potentials may be difficult to detect by other means.                                                                         

     Cracco (1975) proved that SSEPs could be used to localize the level of spinal cord pathology in infants.9,10  Perot used SSEPs as a rapid and objective clinical measure of spinal cord function in individuals rendered unconscious, or who were uncooperative from trauma.14

     The presences of potentials were recorded from the scalp following stimulation of nerves in the legs.   Perot determined that normal SSEPs indicate integrity of dorsal column function, whereas their absence, prolonged latency, or diminished amplitude alerts the clinician to the presence of a spinal cord lesion.14 

      Starr 14  discussed the use of SSEPs to monitor spinal cord function in the operating room in individuals undergoing correction of spinal column curvature.

      Synek and Cowen12 proved that somatosensory-evoked potentials could be effectively used in the evaluation of traumatic lesions of the brachial plexus, especially in young people.  They studied 12 patients with traumatic lesions of the brachial plexus using SSEPs by simulation of the median and radial nerves, cervical spinal cord and contralateral cerebral cortex.  Their results revealed that patients with C5-C6 root avulsion had either normal, delayed or absent responses at the cervical cord and cortex, depending on the involvement of C7 roots that were abnormal after radial nerve stimulation.  In-patients with multiple root avulsions and flail anesthetic arms, no potentials could be recorded from the cervical cord or contralateral cortex, regardless of which nerve was stimulated.  To determine relevant information, it was important to stimulate the nerves having roots near the anatomic site of the lesion, as determined clinically and electromyographically.  Thus SSEPs are effective in the evaluation of peripheral injuries to the brachial plexus, median and radial nerves, and cervical spinal cord. 12,13,21 

      SSER’s have also demonstrated slowed conduction in somatosensory pathways of the spinal cord and the brain stem in diseases such as demyelinating disease, multiple sclerosis, and vascular lesions of the brainstem and infiltrating tumors that affect the ascending pathways.7,8

      Cerebral hemisphere lesions which result in a loss of sensations such as pin and positional sense as well as touch have been associated with a loss of evoked potentials from both the affected and normal hemispheres if the stimulus is applied to the limbs with decreased sensibility. 15

      Cervical spondyloslysis has demonstrated an abnormal latency difference between the brachial plexus and lower medullary components following upper limb stimulation. 8,16  SSEPs have demonstrated abnormality in-patients with vitamin B12 deficiency, Friedreich’s ataxia, and hereditary sensorimotor neuropathies and in children with degenerative CNS diseases such as juvenile diabetes and renal diseases.  Even intrinsic brain stem tumors, infarctions and hemorrhages of the brain have been found by short-latency SSEPs.7  

     Separating fact from fiction relative to cervical and lumbar radiculopathy with actual case studies using SSEPs, Electroencephalographhy, Stroboscopic examination, Biofeedback, surface EMG’s etc will be discussed in parts 4 and 5.