Somatosensory potentials in dogs with naturally acquired thoracolumbar spinal cord disease

Somatosensory evoked potentials (SEP) were recorded at the scalp and at various levels along the lumbar and caudal thoracic parts of the spine in response to tibial nerve stimulations. The SEP were observed in 24 diseased dogs, 2 with a vertebral fracture, 1 with a spinal cord tumor, 1 with a vertebral tumor, and 20 with disk herniation. Cord compression location was confirmed by myelography, laminectomy, or both. The clinical state had significant (P < 0.0001) influence on SEP characteristics. The scalp-recorded SEP latency changed only in association with the most severe lesions; spine-recorded SEP conduction velocity was lower in association with mild lesions; scalp-recorded SEP amplitude changed with lesions of intermediary severity. Because these 3 electrophysiologic variables were influenced differently by cord damage, it was possible to discriminate the various clinical grades by use of these techniques. However, dogs with signs of pain only could not be differentiated from clinically normal dogs. The evoked injury potential was observed in all but 4 diseased dogs, and its maximal amplitude corresponded, in all cases, with cord damage location. Increased duration (P < 0.05) of the spine-recorded SEP was associated with long-standing problems, but not necessarily with clinically detectable malfunction. Use of SEP and evoked injury potential for identifying lateralized cord damage may be of value.