Transcranial magnetic motor evoked potentials and magnetic resonance imaging findings in paraplegic dogs with recovery of motor function

Abstract

Background: Transcranial magnetic motor evoked potentials (TMMEP) are associated with severity of clinical signs and magnetic resonance imaging (MRI) findings in dogs with spinal cord disease.

Hypothesis: That in initially paraplegic dogs with thoracolumbar intervertebral disc herniation (IVDH), MRI findings before surgery and TMMEPs obtained after decompressive surgery are associated with long-term neurological status and correlate with each other.

Animals: Seventeen client-owned paraplegic dogs with acute thoracolumbar IVDH.

Methods: Prospective observational study. TMMEPs were obtained from pelvic limbs and MRI (3T) of the spinal cord was performed at initial clinical presentation. Follow-up studies were performed ≤ 2 days after reappearance of motor function and 3 months later. Ratios of compression length, intramedullary hyperintensities' length (T2-weighted hyperintensity length ratio [T2WLR]), and lesion extension (T2-weighted-lesion extension ratio) in relation to the length of the 2nd lumbar vertebral body were calculated.

Results: TMMEPs could be elicited in 10/17 (59%) dogs at 1st and in 16/17 (94%) dogs at 2nd follow-up. Comparison of TMMEPs of 1st and 2nd follow-up showed significantly increased amplitudes (median from 0.19 to 0.45 mV) and decreased latencies (from 69.38 to 40.26 ms; P = .01 and .001, respectively). At 2nd follow-up latencies were significantly associated with ambulatory status (P = .024). T2WLR obtained before surgery correlated with latencies at 2nd follow-up (P = .04).

Conclusions: TMMEP reflect motor function recovery after severe spinal cord injury.

Keywords: canine; magnetic resonance imaging; spinal cord injury; therapy monitoring; transcranial magnetic stimulation.

Figure 1

Design of the prospective study. After naturally occurring thoracolumbar intervertebral disc herniation, dogs were presented at the clinic within 7 days. At initial presentation, a neurological examination (NE), transcranial magnetic stimulation (TMS) to obtain transcranial magnetic motor evoked potentials from the pelvic limbs and magnetic resonance imaging (MRI) of the spinal cord were performed before hemilaminectomy (surgery). First follow‐up included a NE and TMS within 2 days after observable motor function reappearance (range 4–35 days after surgery). Second follow‐up was performed 3 months after the 1st follow‐up (range 80–128 days after surgery) comprising repeated NE, TMS, and MRI

Figure 2

Sagittal T2‐weighted MR image of an 11‐year‐old Shih Tzu with intervertebral disc herniation and marked spinal cord compression at the level of Th11/12. Solid lines indicate intramedullary hyperintensities (T2WL), whereas the dotted line indicates spinal cord compression length (CL). Summation of solid and dotted lines represents T2W‐LE; division of these lengths by the lengths of L2 (not depicted here) create the dimensionless ratios T2‐weighted hyperintensity length ratio, compression length ratio, and T2‐weighted‐lesion extension ratio. The latter of the 3 ratios was calculated separately to account for possible overlapping of hyperintensities and regions of spinal cord compression

Figure 3

Comparison of peak‐to‐peak amplitudes and stimulus conduction velocity (normalized latencies) of transcranial magnetic motor evoked potentials (TMMEPs) recorded at 1st and 2nd follow‐up in 9 dogs. Comparison of these values revealed a significant increase of peak‐to‐peak amplitudes (3A; P = .01) and an increase of normalized latencies (3B; P = .001). Each plot represents 1 dog, dotted lines connect data of the same dog at 1st and 2nd follow‐up. At 1st follow‐up, TMMEPs could be obtained from the cranial tibial muscle in 16 pelvic limbs of 9 dogs; at 2nd follow‐up TMMEPs were recorded in 18 pelvic limbs of 9 dogs