136 DOI: 10.5152/NSN.2019.11499 Research Article Cauda equina sensory conduction time in normal adult humans Ayşen Süzen Ekinci 1 , Ayçin Yıldız Tabakoğlu 2 , Aycan Oto 3 , Fikret Bademkıran 3 , Cumhur Ertekin 3 1 Clinic of Neurophysiology, İzmir Katip Çelebi University Atatürk Training and Research Hospital, İzmir, Turkey 2 Clinic of Neurophysiology, Bursa Şevket Yılmaz Training and Research Hospital, Bursa, Turkey 3 Division of Clinical Neurophysiology, Ege University School of Medicine, İzmir, Turkey Corresponding Author: Ayşen Süzen Ekinci E-mail: asuzenekinci@gmail.com Submitted: 4 July 2018 Accepted: 15 June 2019 You may cite this article as: Süzen Ekinci A, Tabakoğlu AY, Oto A, Bademkıran F, Ertekin C. Cauda equina sensory conduction time in normal adult humans. Neurol Sci Neurophysiol 2019; 36(3): 136-40. This study has been orally presented in the 31 st National Clinical Neurophysiology EEG-EMG Congress, 9 April 2015, Antalya, Turkey. Abstract Objective: The clinical usefulness of the cauda equina motor conduction time (CE-MCT) is well established either by magnetic or electrical stimulation of the lumbar roots at the lumbar spine levels. However, the cauda equina sensory conduction time (CE- SCT) is not studied systematically in human adults. Methods: Lumbar laminar electrical stimulation from the level of theL1 and L5 vertebrae was applied using needle electrodes. The smallest M-responses obtained from both soleus muscles were considered as the motor threshold for the L1and L5 motor root levels. Afterwards, with the needles in the same place, the connection cables were removed from the stimulation channel and replaced to the recording channel, then the sensory program of the electromyograph was selected. The posterior tibial nevre was excited with superfcia lbipolar electrodes from the popliteal fossa, and after a very slight muscle twitch was observed the intensity was reduced slightly. Therefore, the pure sensory fbers were stimulated. Cauda equina sensory action potentials were recorded and averaged at the laminar levels of L1 and L5 in the spine. Twenty adult normal controls were studied. Results: The monopolar recordings of cauda equina sensory responses at the L1 and L5 laminar levels were measured from their frst positive peaks and the CE-SCT was found as 1.9±0.4 msec (mean ± SD) and ranged from 1.0 to 2.8 msec. Conclusion: The method of CE-SCT recording and calculation is very easy to use and applicable in all normal adult subjects. Themean CE-SCT value is similar to those found for CE-MTC. Keywords: Cauda equina, laminar stimulation, lumbosacral roots, sensory and motor conduction INTRODUCTION Cauda equina motor conduction time (CE-MCT) has been investigated using percutaneous magnetic coil stimu- lation at the dorsolumbar spine levels (1, 2). CE-MCT from L1 to L5 levelshas provided an alternative method in the evaluation of the lumbar motor root in lumbosacral root and motor nerve fber disorders (2-7). However, there are some disavantages of using magnetic stimulation even stronger than Magnetic Augmented Translumbosacral Stimulation-coil stimulation (7). One of the disadvantages of magnetic stimulation in measuring the CE-MCT is that it is impossible to obtain supramaximal compound muscle action potential at the most proximal cauda equina, which prevents us from judging whether there is a conduction block within the cauda equina (7). Another disad- vantage of magnetic stimulation at the lumbar level is the large size coil and high cost (6). In such circumstances, using a needle electrode could be a choice for stimulation of the cauda equina (8-10). However, previous reports have stimulated only one level of the lumbar spine and were not help fulin obtaining information about L1-L5 CE-MCT. When laminar electrical stimulation is performed at the posterior lamina of the spine from two diferent levels, such as L1 and L5, muscle recordings are obtained from the anterior tibial and/or soleus unilaterally or bilaterally; such methods could give us the values of motor conduction time along with the cauda equina. It has been found that this kind of method was more reliable to measure the CE-MCT