Tibial nerve somatosensory evoked potentials in dogs with degenerative lumbosacral stenosis

OBJECTIVE: To determine somatosensory evoked potentials (SEPs) in dogs with degenerative lumbosacral stenosis (DLS) and in healthy dogs. STUDY DESIGN: Clinical and experimental study. ANIMALS: Dogs with DLS (n = 21) and 11 clinically normal dogs, age, and weight matched. METHODS: Under anesthesia, the tibial nerve was stimulated at the caudolateral aspect of the stifle, and lumbar SEP (LSEP) were recorded percutaneously from S1 to T13 at each interspinous space. Cortical SEP (CSEP) were recorded from the scalp. RESULTS: LSEP were identified as the N1-P1 (latency 3-6 ms) and N2-P2 (latency 7-13 ms) wave complexes in the recordings of dogs with DLS and control dogs. Latency of N1-P1 increased and that of N2-P2 decreased as the active recording electrode was moved cranially from S1 to T13. Compared with controls, latencies were significantly delayed in DLS dogs: .8 ms for N1-P1 and 1.7 ms for the N2-P2 complex. CSEP were not different between groups. CONCLUSIONS: Surface needle recording of tibial nerve SEP can be used to monitor somatosensory nerve function of pelvic limbs in dogs. In dogs with DLS, the latency of LSEP, but not of CSEP, is prolonged compared with normal dogs. CLINICAL RELEVANCE: In dogs with lumbosacral pain from DLS, the cauda equina compression is sufficient to affect LSEP at the lumbar level.