Subpial spinal evoked potentials in patients undergoing junctional dorsal root entry zone coagulation for pain relief

Abstract

Seven patients with complete avulsion of the brachial plexus underwent junctional coagulation lesions of the dorsal root entry zone (DREZ) for relief of intractable pain in the paralyzed arm. Intra-operative monitoring by recording spinal cord somatosensory evoked potentials (SEP) resulting from tibial nerve stimulation was done using subpial recording electrodes situated dorsal to the posterior median sulcus at the C4 and T2 segment. SEP on the normal side showed an initial positive wave and two negative waves followed by a group of high frequency waves of relatively high amplitude which continued into high frequency, low amplitude potentials. The conduction velocity of the fastest spinal evoked potential components were, on average, 86 m/s. Recordings from the side of avulsion revealed a steep positive potential of high amplitude which appeared in five patients prior to the creation of the DREZ lesion. This effect was assumed to be secondary to spinal cord damage caused by avulsion. During the DREZ coagulation the SEP from the unaffected side did not change. On the side of DREZ coagulation the velocity of the fastest fibres decreased. Four patients reported sensory deficits after the operation, which were transient in three. In one of these patients, the first two negative potentials disappeared. In the fourth patient, who had permanent sensory deficits, the positive steep potential appeared after generation of the lesion. Our results point to the usefulness of the subpial SEPs monitoring during microneuro-surgical procedures on the spinal cord to provide further insight into evoked electrical activity of the normal and injured spinal cord, and to minimize post-operative neurological morbidity.

Dorsal Root Entry Zone Lesioning for Brachial Plexus Avulsion: A Comprehensive Literature Review

“…The post-BPA spinal cord is often profoundly scarred, distorted and atrophic at levels of root avulsion, 53,64,68,70 greatly hampering identification of the PLS, the chief DREZ landmark. Uncertainty can be reduced in several ways: 1) visualisation of ipsilateral non-avulsed rootlet entry points above and below affected spinal segments to facilitate the interpolation of an imaginary line spanning the pathological DREZ segments, which may require caudal and/or rostral extension of the laminectomy;…”

“…Generic complications associated with spinal neurosurgery also apply to DREZ lesioning, including cerebrospinal fluid leak, 17,37 subdural haematoma, 10 extradural haematoma, 17,64 meningitis, 32 wound infection or dehiscence, 32,37 and infrequently death. 11,36,38,40,54 New or changed pain character 7,9,38,45,50,60,64,68,69 Gait ataxia 7,11,58,68 From myocardial infarction 11,54,58 Dys-or hypoaesthesia of ipsilateral lower limb 6,8,12,19,45,59,69,70 From gastrointestinal bleeding 38 Proprioceptive deficit in ipsilateral lower limb 12,15,36 CSF leak or fistula 7,19,37,40,45 Paraesthesia or dysaesthesia of ipsilateral limbs 9,19,…”

Evoked Spinal Cord Potentials

“…All components of the SCPs activated by descending volleys were decreased or disappeared in recordings from the lesioned level, as expected. Thus, intraoperative recording of the SCPs during DREZL might also be beneficial for monitoring spinal cord injury, and also for studying human spinal cord function (Nashold et al, 1985;Prestor et al, 1989;Fujioka et al, 1992).…”

Treatment of pain following traumatic lesions of the brachial plexus

“…eine genauere Kontrolle der Temperatur an der Elektrodenspitze bei der Koagulation und vor allem Benutzung feinerer Elektroden, die eine festdefinierte, umgeschriebene Läsion erzeugen können, sind die Komplikationen in der letzten Zeit deutlich gesenkt worden [11,12,18,28]. eine genauere Kontrolle der Temperatur an der Elektrodenspitze bei der Koagulation und vor allem Benutzung feinerer Elektroden, die eine festdefinierte, umgeschriebene Läsion erzeugen können, sind die Komplikationen in der letzten Zeit deutlich gesenkt worden [11,12,18,28].…”