Transient Loss of TcMEP during L5-S1 posterior fusion?

In the following case report, a posterior lower lumbar surgical procedure done on a Spondylolisthesis (L5/S1) patient resulted in a transient loss of motor evoked potentials despite the patient had no neurological injury?. The motor loss was occurred after epidural injection of 2.4mg of morphine?. The authors believe it could be due to the pressure caused by the injection would have compressed cauda equina?.

Even a small injection of this kind could lead to evoked potential changes should be noted. Though the TcMEP recovered after 1h, care  must be taken to make sure prolonged compression does not take place!.

Case report

Transient loss of motor-evoked responses associated with caudal injection of morphine in a patient with spondylolisthesis undergoing spinal fusion

PETER R.J. GIBSON MBBS FANZCA*, Pediatric Anesthesia, Volume 16 Issue 5, Pages 568 - 572, 2005

A 7-year-old girl having posterior spinal fusion for Grade 3 anterior spondylolisthesis at the L5/S1 level was administered 2.5 mg of morphine in 10 ml saline via the caudal epidural route before surgery.

Motor-evoked responses were markedly diminished in her lower limbs for 1 h following this but returned spontaneously. She suffered no neurological injury. The cause for this is postulated to be transient cauda equina compression from the volume of injectate. This complication of caudal injection has not been reported before. The possible mechanisms for this are discussed. We believe that significant L5/S1 spondylolisthesis should be considered a contraindication to the use of caudal epidural injections.

Wave P300 (ERP) & Temporal Lobe Epilepsey

In this latest issue of the journal of Human Brain Mapping, the authors suggest that wave P300 an endogenous event related evoked potential seems to be altered in pateints with temporal lobe epilepsy, a change in the latency and amplitude of P300 was observed in 10 patients suffering from TLE (same number of normal recording was conduted for comparison). 

Hum Brain Mapp. 2008 Nov 25. [Epub ahead of print] 

Attention impairment in temporal lobe epilepsy: A neurophysiological approach via analysis of the P300 wave.

Bocquillon P, Dujardin K, Betrouni N, Phalempin V, Houdayer E, Bourriez JL, Derambure P, Szurhaj W.
Department of Clinical Neurophysiology, Lille University Medical Center, Lille, France.
Purpose:

Attention is often impaired in temporal lobe epilepsy (TLE). The P300 wave (an endogenous, event-related potential) is a correlate of attention which is usually recorded during an "oddball paradigm," where the subject is instructed to detect an infrequent target stimulus presented amongst frequent, standard stimuli.

Modifications of the P300 wave's latency and amplitude in TLE have been suggested, but it is still not known whether the source regions also differ. Our hypothesis was that temporal lobe dysfunction would modify the P3 source regions in TLE patients. Methods: A comparative, high density, 128-channel electroencephalographic analysis of the characteristics of P300 (P3b latency and amplitude) was performed in 10 TLE patients and 10 healthy controls during auditory and visual oddball paradigms. The P3b sources were localized on individual 3D MR images using the LORETA method and intergroup statistical comparisons were performed using SPM2(R) software. Results: Our main results (in both individual analyses and intergroup comparisons) revealed a reduction in temporal (and more particularly mesiotemporal) sources and, to a lesser extent, frontal sources in TLE patients, compared with controls. Discussion: This reduction may reflect direct, local cortical dysfunction caused by the epileptic focus or more complex interference between epileptic networks and normal attentional pathways. Hum Brain Mapp, 2009. (c) 2008 Wiley-Liss, Inc.

PMID: 19034898 [PubMed - as supplied by publisher]