Ulnar Somatosensory Evoked Potentials Research Articles

Wednesday, September 26, 2018 9:00 AM – 10:00 AM Best Papers: 5. The significance of upper extremity neuromonitoring changes in patients undergoing thoracolumbar surgery

BACKGROUND CONTEXT Peripheral nerve injuries of the upper extremities in patients undergoing posterior thoracolumbar surgery is a well described, yet preventable complication. Upper extremity (UE) neuromonitoring has been utilized to alert the surgeon of the development of such an injury. PURPOSE The purpose of this study is to investigate the occurrence of upper extremity neuromonitoring changes in patients undergoing thoracolumbar surgery in prone position and to assess the significance of these changes in terms of procedure and patient characteristics, and in preventing postoperative UE neuropathy. STUDY DESIGN/SETTING Pair-matched case-control study (Level III) design, university hospital setting. PATIENT SAMPLE A total of 843 consecutive patients from single institution. OUTCOME MEASURES Presence or absence of postoperative upper extremity neuropathy. METHODS All patients who underwent posterior thoracic, lumbar, or thoracolumbar surgery at a single institution from 2014 to 2016 with neuromonitoring were included in the study. UE neuromonitoring consisted of ulnar somatosensory evoked potentials (SSEPs). Patients with intraoperative ulnar SSEP signal changes were identified and compared with a group of pair-matched patients who did not develop intraoperative ulnar SSEP signal changes. The groups were matched based on the number of vertebral levels undergoing surgery. Data regarding intraoperative attempts to resolve signal changes and outcomes were collected. The two groups were compared to identify the risk factors for the development of UE neuromonitoring changes. RESULTS Between January 2014 and December 2016, 843 patients in our institution underwent thoracic, lumbar or thoracolumbar spine surgeries in prone position with intraoperative bilateral ulnar SSEPs neuromonitoring data available. Of these, 37 patients (4.4%) had intraoperative signal changes in the UE; an equal number of patients without signal changes were also selected. In each group, six patients underwent thoracic, 20 patients underwent lumbar, and 11 patients underwent thoracolumbar procedures. In eight patients (21.6%), there was no resolution of SSEP signal changes despite intraoperative attempts. The two groups were similar with respect to age and co-morbidities including diabetes, ischemic heart disease, and peripheral arterial disease. There was also no significant difference in the mean BMI (p=0.22). The mean duration of the procedures was 324 minutes in the SSEP signal change patients and 260 minutes in the patients who did not experience SSEP signal changes (p=0.03). No patient with UE SSEP changes had a clinically detectable neurologic deficit postoperatively. CONCLUSIONS Upper extremity SSEP signal changes during multilevel posterior thoracolumbar procedures are more likely to occur as the duration of the operation increases. The presence of UE signal changes does not coincide with clinically significant peripheral neuropathies. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.

Causal factors for position-related SSEP changes in spinal surgery.

Somatosensory evoked potentials (SSEPs) are effective in detecting upper extremity positional injuries; however, causal factors for which patient population is most at risk are not well established. To review causal factors for intraoperative SSEP changes due to patient positioning. A case series with retrospective chart analysis was performed. 398 patient charts and intraoperative neurophysiological monitoring data from patients who underwent thoracolumbar and lumbosacral spine surgery were reviewed in a consecutive sequence from 2012 to 2013. Adverse events (AE) with the upper extremity SSEP recordings were compared to the independent variables, sex, positioning, length of procedure, and body habitus. Thoracolumbar and lumbosacral spine surgeries using contemporaneous ulnar and median nerve SSEPs were reviewed. The one-way analysis of variance (ANOVA) test, Chi-square, and independent samples t test were used to determine statistical significance in having an upper extremity SSEP AE to the aforementioned independent variables. The sample consisted of 209 males (52.5%) and 189 females (47.5%) (n=398). AE to the upper extremity SSEP was seen in 44 patients. Sex was found to be statistically significant for isolated ulnar nerve AE (P≤0.001) with males being most at risk (87.5%). AE for isolated median nerve SSEP was statistically significant for supine and prone positions (P=0.043). Length of procedure was statically significant for isolated ulnar nerve SSEP AE (P=0.039). BMI was statistically significant for generalized upper extremity SSEP AE (P=0.016), as well as isolated ulnar SSEP AE (P=0.006), isolated median SSEP AE (P≤0.001) and contemporaneous median and ulnar SSEP AE of the same limb (P≤0.001). Sex, patient positioning, length of procedure, and BMI are determinants for upper extremity neural compromise during thoracolumbar and lumbosacral spine surgeries.

Upper-limb somatosensory evoked potential monitoring in lumbosacral spine surgery: a prognostic marker for position-related ulnar nerve injury

Background context Somatosensory evoked potential (SSEP) is used to monitor integrity of the brain, spinal cord, and nerve roots during spinal surgery. It records the electrical potentials from the scalp after electrical stimulation of the peripheral nerves of the upper or lower limbs. The standard monitoring modality in lumbosacral spine surgery includes lower-limb SSEP and electromyography (EMG). Upper-limb SSEP monitoring has also been used to detect and prevent brachial plexopathy and peripheral nerve injury in thoracic and lumbosacral spine surgeries. We routinely monitor lower-limb SSEP and EMG in lumbosacral spine procedures at our institution. However, a few patients experienced postoperative numbness and/or pain in their ulnar distribution with uneventful lower-limb SSEP and EMG. Purpose We hypothesized that the postoperative upper extremity paresis in lumbosacral surgeries may result from compression and/or stretch of the brachial plexus and/or ulnar nerve while the patients were in prone position. Using upper-limb SSEP, we investigated whether we observe any significant change in the SSEP, and if so, whether we can prevent or reduce frequency of postoperative upper extremity deficits. Study design/setting In this prospective study, we monitored upper-limb SSEP, in addition to lower-limb SSEP and EMG, in 230 elective, posterior lumbosacral spinal procedures. All operations were performed by a group of four neurosurgeons. Patient sample One hundred and thirty-one female and 99 male with an age range of 28 to 86 years between January 2004 and December 2005 were studied. Outcome measures Amplitude and latency of upper-limb or ulnar SSEP were continuously compared with those of the baseline. A greater than or equal to 50% decrease in SSEPs amplitude and/or a greater than or equal to 10% increase in latency were considered to be significant. Methods After intubation, patients were positioned prone on Jackson or Andrews spinal table. Anesthesia was maintained with inhalant gas (desflurane or sevoflurane) and propofol infusion with and without minimal infusion of narcotics (fentanyl, sufentanyl, or remifentanil). Intraoperative neurophysiologic monitoring of upper-limb or ulnar SSEP was achieved by continuously recording cortical and subcortical responses after alternate stimulation of the ulnar nerve at the wrist. In our institutional protocol, a greater than or equal to 50% decrease in SSEPs amplitude and/or a greater than or equal to 10% increase in latency were considered to be significant to alert the operating surgeons. When significant changes occurred, the surgeon was immediately notified. Also, reevaluation of vital signs, depth of anesthesia, and patient's position, and technical troubleshootings were subsequently followed. Results We observed a greater than or equal to 50% decrease in amplitude of ulnar SSEP in 10 patients without significant changes in lower-limb SSEP (peroneal or posterior tibial nerve SSEP) or EMG during surgery. Eight patients had changes in unilateral limbs, and two patients had changes in bilateral limbs. Two patients with significant changes in unilateral limbs showed changes twice. The mean SSEP amplitude for the 14 changes was 29.2±3.1% (mean±SEM, standard error of mean) of the baseline value at the average surgical time of 60±1.5 minutes. With repositioning of the arms, the amplitudes were immediately restored with the average of 70.2±7.1% (n=14) of the baseline value. The mean amplitude of upper-limb SSEP was 73.4±8.7% (n=12) of the baseline at wound closure. The average surgical time was 154±29.2 minutes per case for the 10 patients. There was no documented postoperative upper extremity paresis in all 230 patients. Conclusions The present study demonstrates that upper-limb SSEP monitoring could detect position-related ulnar neuropathy in 5.2% of the patients undergoing lumbosacral spine surgery.

Dermatomal and mixed nerve somatosensory evoked potentials in the diagnosis of neurogenic thoracic outlet syndrome

To evaluate the diagnostic utility of dermatomal and mixed nerve somatosensory evoked potentials (SEPs) in patients with thoracic outlet syndrome (TOS) and to compare their value with routine electrodiagnostic methods, we studied a group of 44 patients with neurogenic TOS and 30 healthy controls. In addition to bilateral median and ulnar SEPs, evoked potentials were recorded after stimulation of C6 and C8 dermatomes from the first and fifth digits, respectively. The patients were classified into 3 groups according to the nature of their clinical condition. The abnormality rate for both ulnar and C8 dermatomal SEPs was 100% in a small group of patients with severe neurological signs like atrophy. In groups of patients with lesser degrees of neurogenic damage, abnormality rates for ulnar and C8 dermatomal SEPs on affected limb(s) were 67 and 50%, respectively. Same abnormality rates were 25 and 18% in patients with only subjective symptoms. In patients with objective neurological signs, the major increase in sensitivity was with electromyography (EMG). Abnormalities of routine nerve conduction studies and F-wave latency were observed in patients with severe neurogenic damage. We concluded that the most useful tests in the diagnosis of neurogenic TOS are needle EMG and ulnar SEPs.

Traumatic cervical spinal cord injury: Relation between somatosensory evoked potentials, neurological deficit, and hand function

Objective: Median and ulnar somatosensory evoked potentials (SEP) in the assessment of cervical spinal cord injury (SCI) in relation to the outcome of hand function. Design: Cohort analytical study. Setting: Spinal cord injury center, university hospital. Patients: Consecutively sampled, 23 acute and 46 chronic tetraplegics. Main Outcome Measures: (1) Median and ulnar SEP recordings graded in 5 categories, from normal to absent; (2) clinical examination of algesia/aesthesia in dermatomes C5/6 and C8/Th1 graded in categories of normal, impaired, and loss of sensation; (3) clinical examination of hand function graded in 4 categories, from active to inactive hand function. Results: Pathological median and ulnar SEP were found in 46% and 76% of patients, respectively. A differentiation between upper (C3–C6) and lower (C6/C7-Th1) cervical SCI was possible by comparing the SEP N20 latencies (but not amplitudes) of both nerves (Mann-Whitney U test, p < .01). In follow-up examinations over 6 months the N20 amplitude increased significantly (ANCOVA, p < .001), while the N20 latency did not change. By both ulnar SEP recordings and assessment of the sensory deficit in dermatome C8/Th1 the outcome of hand function, ie, the development of active or inactive hand function, could be predicted (Mann-Whitney U test, p < .01). Conclusion: Median and ulnar SEP are valuable to indicate the level of injury, the degree of sensory impairment and to predict the outcome of hand function even in unconscious patients. They can improve the diagnostic assessment of cervical SCI.

Somatosensory evoked potentials: lack of value for diagnosis of thoracic outlet syndrome.

Twenty patients with thoracic outlet syndrome (TOS) seen at the Mayo Clinic between October 1984 and November 1985 were studied prospectively with routine nerve conduction studies, concentric needle examination, and bilateral median and ulnar somatosensory evoked potentials (SEPs). Results of nerve conduction studies and needle examination were abnormal in 30% of the patients, one patient having a reduced ulnar sensory nerve action potential amplitude and five others having neurogenic motor unit potential changes in the hand muscles. Ulnar SEPs were abnormal in three patients (15%), and median SEPs were abnormal in one patient, who also had abnormalities in ulnar SEPs. In patients with TOS, routine nerve conduction studies and needle examination were the most helpful electrophysiologic studies in excluding more common conditions. The routine use of ulnar SEPs in the evaluation of patients with TOS is probably not worthwhile.

The value of ulnar somatosensory evoked potentials (SEPs) in cervical myelopathy

In 57 patients with clinical signs and surgical documentation of compressive myelopathy, ulnar nerve somatosensory evoked potentials (SEPs) were more sensitive (with 74% abnormal) than either median or tibial nerve SEPs. The most frequent abnormalities were reduced or absent neck evoked responses and prolonged central conduction time. All subjects who had an SEP abnormality were identified by combined tibial and ulnar SEPs. Median nerve SEP added no additional information. Normal ulnar and tibial nerve SEPs were also able to exclude major cord damage in patients with cervical radiculopathy but little evidence of myelopathy.