Magnetic Motor Evoked Potentials for Assessing Spinal Cord Integrity in Dogs with Intervertebral Disc Disease

Abstract

Magnetically elicited transcranial motor evoked potentials (MEPs) were studied in 37 dogs with type 1 intervertebral disc (IVD) disease. The waveforms were recorded from both cranial tibial muscles before and after surgery. The latencies and amplitudes obtained were compared to those of a control population (n = 14). MEPs were recordable in all dogs with mild or no neurologic deficits, but they were recordable in only 50% of ambulatory dogs that were severely ataxic. MEPs could not be elicited from nonambulatory dogs. There was a significant attenuation of the amplitudes in all clinical cases, even if the dogs demonstrated back pain alone. Significantly prolonged latencies were associated with neurologic deficits. MEPs were not good predictors of neurologic recovery. The responses obtained from the side where the disc material was found were not different from those recorded from the opposite side. MEPs were very sensitive to lesions of the spinal cord, as indicated by the significant changes in the waves in patients with mild or no neurologic deficits and in the loss of response in dogs that still demonstrated purposeful movement. Neurologic exams provided more accurate diagnoses and prognoses than did MEPs in dogs with IVD disease.

Acute Spinal Cord Injury

“…82 Such electrophysiologic data available in companion animals remains extremely limited. In dogs, one study found transcranial MMEPs difficult to record in the acute phase of SCI in nonambulatory dogs, 83 but little attempt has been made so far to replicate this finding or further develop these techniques to analyze acute injury. Recent data from humans suggest that this should be pursued: recently, and for the first time in a large cohort of 255 human patients with SCI, it has been shown that recovery of motor-evoked potential amplitude closely paralleled the clinical recovery of walking function following incomplete and complete SCI.…”

Neurophysiological assessment of spinal cord injuries in dogs using somatosensory and motor evoked potentials

“…Normal thoracic limb MEPs with altered pelvic limb MEP latency and amplitude should be expected in thoracolumbar spinal injuries. As with SSEPs, recording abnormalities are consistent with lesion severity [30, 31], (i.e., the more severe the injury, the grater the latency and the lower the amplitude), although they do not seem to correlate with prognosis for recovery. MEPs may not be recorded caudal to the injury site [32, 33] (Fig.…”

“…More investigation and standardization should be determinant for better and more trustable results, and more information extracted from human medicine should be of great benefit to application in animals. SSEPs and MEPs have been used alone or in combination to complement neurological examination, as well as for disease characterization and functional classification of spinal cord injuries [15–17, 20, 26, 31, 37, 40–42]. Several aspects need to be further investigated and defined before results can be compared between studies.…”

“…In dogs, extensive anatomical variability in head shape (e.g., brachycephalic vs. dolichocephalic breeds) is likely to interfere with correct location of stimulation and signal capture sites. Latency and amplitude reference values are also open to question, given the wide variability even between individuals of the same breed [11, 31]. A single study describes the use of SSEPs for intraoperative monitoring of dogs with spinal cord dysfunction [19].…”

Clinical canine spinal cord injury provides an opportunity to examine the issues in translating laboratory techniques into practical therapy

“…In addition, normal values for sensory and transcranial magnetic motor-evoked potentials have been established in dogs, [76][77][78][79] although not in routine clinical use. Domestic dogs are generally highly amenable to training and functional testing and this feature permits future subtle analysis of their recovery after SCI.…”