Objectives

To investigate spinal and cortical somatosensory evoked potentials (SEPs) in normal dogs and dogs with cauda equina compression.

Materials & Methods

SEPs were recorded in 11 normal dogs and 21 dogs with cauda equina compression due to lumbosacral interverbral disc protrusion confirmed on computed tomography. Clinical signs included lumbosacral pain, pelvic limb lameness, muscle weakness and atrophy. Following tibial nerve stimulation, spinal SEPs were recorded percutaneously under anesthesia from L7-S1 to T13-L1. Cortical SEPs were recorded from the scalp. SEPs were analysed for waveform, latency, and amplitude.

Results

Two prominent negative peaks were identified: N1, reflecting the ascending volley of impulses in the dorsal roots of the cauda equina, and N2, reflecting postsynaptic activity in the spinal cord and spinal cord interneurons. Both negative peaks were followed by positive deflections P1 and P2. Latencies of N1-P1 and N2-P2 complex were significantly prolonged in the patient group compared with the control group. Amplitudes of N1 and N2 were not significantly different between control and patient group. Top-top amplitudes were significantly higher in the patient group than in control group. Cortical SEPs were not different between control and patient group.

Conclusion

Cauda equina compression delays nerve conduction as evidenced by prolonged latencies of spinal SEPs.