Parthasarathy D. Thirumala

Microvascular Decompression for Hemifacial Spasm: Evaluating Outcome Prognosticators Including the Value of Intraoperative Lateral Spread Response Monitoring and Clinical Characteristics in 293 Patients

Hemifacial spasm is a socially disabling condition that manifests as intermittent involuntary twitching of the eyelid and progresses to muscle contractions of the entire hemiface. Patients receiving microvascular decompression of the facial nerve demonstrate an abnormal lateral spread response (LSR) in peripheral branches during facial electromyography. The authors retrospectively evaluate the prognostic value of preoperative clinical characteristics and the efficacy of intraoperative monitoring in predicting short- and long-term relief after microvascular decompression for hemifacial spasm. Microvascular decompression was performed in 293 patients with hemifacial spasm, and LSR was recorded during intraoperative facial electromyography monitoring. In 259 (87.7%) of the 293 patients, the LSR was attainable. Patient outcome was evaluated on the basis of whether the LSR disappeared or persisted after decompression. The mean follow-up period was 54.5 months (range, 9–102 months). A total of 88.0% of patients experienced immediate postoperative relief of spasm; 90.8% had relief at discharge, and 92.3% had relief at follow-up. Preoperative facial weakness and platysmal spasm correlated with persistent postoperative spasm, with similar trends at follow-up. In 207 patients, the LSR disappeared intraoperatively after decompression (group I), and in the remaining 52 patients, the LSR persisted intraoperatively despite decompression (group II). There was a significant difference in spasm relief between both groups within 24 hours of surgery (94.7% vs. 67.3%) (P < 0.0001) and at discharge (94.2% vs. 76.9%) (P = 0.001), but not at follow-up (93.3% vs. 94.4%) (P = 1.000). Multivariate logistic regression analysis demonstrated independent predictability of residual LSR for present spasm within 24 hours of surgery and at discharge but not at follow-up. Facial electromyography monitoring of the LSR during microvascular decompression is an effective tool in ensuring a complete decompression with long-lasting effects. Although LSR results predict short-term outcomes, long-term outcomes are not as reliant on LSR activity.

Diagnostic Value of Somatosensory Evoked Potential Changes During Carotid Endarterectomy: A Systematic Review and Meta-analysis

IMPORTANCE Perioperative stroke is a persistent complication of carotid endarterectomy (CEA) for patients with symptomatic carotid stenosis (CS). OBJECTIVE To evaluate whether changes in somatosensory evoked potential (SSEP) during CEA are diagnostic of perioperative stroke in patients with symptomatic CS. DESIGN, SETTING, AND PARTICIPANTS We searched PubMed and the World Science Database for reference lists of retrieved studies and/or experiments on SSEP use in postoperative outcomes following CEA in patients with symptomatic CS from January 1, 1950, through January 1, 2013. We independently screened all titles and abstracts to identify studies that met the inclusion criteria and extracted relevant articles in a uniform manner. Inclusion criteria included randomized clinical trials, prospective studies, or retrospective cohort reviews; population of symptomatic CS; use of intraoperative SSEP monitoring during CEA; immediate postoperative assessment and/or as long as a 3-month follow-up; a total sample size of 50 or more patients; studies with adult humans 18 years or older; and studies published in English. MAIN OUTCOME AND MEASURE Whether intraoperative SSEP changes were diagnostic of perioperative stroke indicated by postoperative neurological examination. RESULTS Four-hundred sixty-four articles were retrieved, and 15 prospective and retrospective cohort studies were included in the data analysis. A 4557-patient cohort composed the total sample population for all the studies, 3899 of whom had symptomatic CS. A change in SSEP exhibited a strong pooled mean specificity of 91% (95% CI, 86-94) but a weaker pooled mean sensitivity of 58% (95% CI, 49-68). A pooled diagnostic odds ratio for individual studies of patients with neurological deficit with changes in SSEPs was 14.39 (95% CI, 8.34-24.82), indicating that the odds of observing an SSEP change among those with neurologic deficits were 14 times higher than in individuals without neurologic deficit. CONCLUSIONS AND RELEVANCE Intraoperative SSEP is a highly specific test in predicting neurological outcome following CEA. Patients with perioperative neurological deficits are 14 times more likely to have had changes in SSEPs during the procedure. The use of SSEPs to design prevention strategies is valuable in reducing perioperative cerebral infarctions during CEA.

Somatosensory-evoked potential monitoring during instrumented scoliosis corrective procedures: validity revisited

BACKGROUND Intraoperative monitoring (IOM) using somatosensory-evoked potentials (SSEPs) plays an important role in reducing iatrogenic neurologic deficits during corrective pediatric idiopathic procedures for scoliosis. However, for unknown reasons, recent reports have cited that the sensitivity of SSEPs to detect neurologic deficits has decreased, in some to be less than 50%. This current trend, which is coincident with the addition of transcranial motor-evoked potentials, is surprising given that SSEPs are robust, reproducible responses that were previously shown to have sensitivity and specificity of >90%. PURPOSE Our primary aim was to assess whether SSEPs alone can detect impending neurologic deficits with similar sensitivity and specificity as originally reported. Our secondary aim was to estimate the potential predictive value of adding transcranial motor-evoked potentials to SSEP monitoring in idiopathic scoliosis procedures. DESIGN This was a retrospective review to analyze the efficacy of SSEP monitoring in the group of pediatric instrumented scoliosis fusion cases. PATIENT SAMPLE We retrospectively reviewed all consecutive cases of patients who underwent idiopathic scoliosis surgery between 1999 and 2009 at Childrens Hospital of Pittsburgh. We identified 477 patients who had the surgery with SSEP monitoring alone. Exclusion criteria included any patients with neuromuscular disorders or unreliable SSEP monitoring. Patients who had incomplete neurophysiology data or incomplete postoperative records were also excluded. OUTCOME MEASURES Major outcomes measured were clinically significant postoperative sensory or motor deficits, as well as significant intraoperative SSEP changes. METHODS Continuous interleaved upper- and lower-extremity SSEPs were obtained throughout the duration of all procedures. We considered a persistent 50% reduction in primary somatosensory cortical amplitude or a prolongation of response latency by >10% from baseline to be significant. Persistent changes represent significant deviation in SSEP amplitude or latency in more than two consecutive averaged trials. Patients were classified into one of four categories with respect to SSEP monitoring: true positive, false positive, true negative, and false negative. The sensitivity, specificity, positive predictive value, and negative predictive value were then calculated accordingly. RESULTS Our review of 477 idiopathic scoliosis surgeries monitored using SSEPs alone revealed a new deficit rate of 0.63% with no cases of permanent injury. Sensitivity = 95.0%, specificity = 99.8%, positive predictive value = 95%, negative predictive value = 99.8%. Using evidence-based epidemiologic measures, we calculated that the number needed to treat was 1,587 patients for one intervention to be performed that would have been missed by SSEP monitoring alone. In addition, the number needed to harm, which represents the increase in false positives with the addition of transcranial electrical motor-evoked potentials, was 200. CONCLUSION SSEP monitoring alone during idiopathic scoliosis continues to be a highly reliable method for the detection and prevention of iatrogenic injury. Our results confirm the high sensitivity and specificity of SSEP monitoring alone published in earlier literature. As such, we suggest the continued use of SSEP alone in idiopathic scoliosis surgeries. At this time we do not believe there are sufficient data to support the addition of MEP monitoring, although more studies and revised criteria for the use of MEP may provide added value for its use in the future.

Hearing outcomes following microvascular decompression for hemifacial spasm

PURPOSE Facial nerve microvascular decompression (MVD) for hemifacial spasm (HFS) provides relief to most patients. Due to the proximity of the cochlear and facial nerves, hearing loss is a potential MVD complication, however, there is a wide range in the reported incidence of hearing loss (HL) in the literature. In order to better understand the HL incidence in our MVD population, we utilized the combination of speech discrimination scores (SDS) and air and bone pure tone threshold averages (PTA) to identify patients with no hearing change, sensorineural hearing loss, or conductive hearing loss. We also assessed the predictive value of patient-reported hearing deficits on the ultimate audiometric diagnosis of hearing loss. METHODS One hundred and fifty one patients underwent facial nerve MVD at the University of Pittsburgh Medical Center between January 2000 and December 2007. Peri-operative audiometric data, including changes in air and bone pure tone thresholds and speech discrimination scores, were analyzed retrospectively. Criteria from the 1995 American Academy of Otolaryngology Committee on Hearing and Equilibrium consensus were used to analyze post-operative hearing loss. Patient-reported hearing disturbances obtained in the immediate post-operative period were compared to seven-day post-operative conductive and sensorineural HL status. RESULTS Non-functional, non-serviceable HL (Class D) occurred in 6.6% of patients, while 10.6% developed cumulative non-functional HL (Class C and D). Twenty-nine patients (18.7%) exhibited conductive HL. While patient-reported complaints were predictive of Class C/D HL (<0.0001) with a 56.3% sensitivity and 92.6% specificity, patient-reported complaints were not strongly associated with conductive HL status (p = 0.369) with 17.2% sensitivity and 88.5% specificity. CONCLUSIONS Perioperative hearing evaluations, in conjunction with careful scrutiny of patient complaints and air-bone pure tone testing enables the physician to more precisely quote complication rates and rapidly distinguish potentially reversible conductive hearing pathologies from permanent sensorineural disorders.

Effect of previous botulinum neurotoxin treatment on microvascular decompression for hemifacial spasm

OBJECT The objective of this study was to investigate the clinical characteristics, intraoperative findings, complications, and outcomes after the first microvascular decompression (MVD) in patients with and without previous botulinum neurotoxin treatment for hemifacial spasm (HFS). METHODS The authors analyzed 246 MVDs performed at the University of Pittsburgh Medical Center between January 1, 2000, and December 31, 2007. One hundred and seventy-six patients with HFS underwent botulinum neurotoxin injection treatment prior to first MVD (Group I), and 70 patients underwent their first MVD without previous botulinum neurotoxin treatment (Group II). Clinical outcome data were obtained immediately after the operation, at discharge, and at follow-up. Follow-up data were collected from 177 patients with a minimum follow-up period of 9 months (mean 54.48 ± 27.84 months). RESULTS In 246 patients, 89.4% experienced immediate postoperative relief of spasm, 91.1% experienced relief at discharge, and 92.7% experienced relief at follow-up. There was no significant difference in outcomes and complications between Group I and Group II (p > 0.05). Preoperatively, patients in Group I had higher rates of facial weakness, tinnitus, tonus, and platysmal involvement as compared with Group II (p < 0.05). The posterior inferior cerebellar artery and vertebral artery were intraoperatively identified as the offending vessels in cases of vasculature compression in a significantly greater number of patients in Group II compared with Group I (p = 0.008 and p = 0.005, respectively, for each vessel). The lateral spread response (LSR) disappeared in 60.48% of the patients in Group I as compared with 74.19% in Group II (p > 0.05). No significant differences in complications were noted between the 2 groups. CONCLUSIONS Microvascular decompression is an effective and safe procedure for patients with HFS previously treated using botulinum neurotoxin. Intraoperative monitoring with LSR is an effective tool for evaluating adequate decompression.

Incidence of high-frequency hearing loss after microvascular decompression for hemifacial spasm

OBJECT The primary aim of this study was to evaluate the incidence and discuss the pathogenesis of high-frequency hearing loss (HFHL) after microvascular decompression (MVD) for hemifacial spasm (HFS). METHODS Preoperative and postoperative audiogram data and brainstem auditory evoked potentials (BAEPs) from 94 patients who underwent MVD for HFS were analyzed. Pure tone audiometry at 0.25-2 kHz, 4 kHz, and 8 kHz was calculated for all individuals pre- and postoperatively ipsilateral and contralaterally. Intraoperative neurophysiological data were reviewed independently. An HFHL was defined as a change in pure tone audiometry of more than 10 dB at frequencies of 4 and 8 kHz. RESULTS The incidence of HFHL was 50.00% and 25.53% ipsilateral and contralateral to the side of surgery, respectively. The incidence of HFHL adjusted for conductive and nonserviceable hearing loss was 26.6% ipsilaterally. The incidence of HFHL at 4 and 8 kHz on the ipsilateral side was 37.23% and 45.74%, respectively, and it was 10.64% and 25.53%, respectively, on the contralateral side. Maximal change in interpeak latency Waves I-V compared with baseline was the only variable significantly different between groups (p < 0.05). Sex, age, and side did not increase the risk of HFHL. Stepwise logistic regression analysis did not find any changes in intraoperative BAEPs to increase the risk of HFHL. CONCLUSIONS High-frequency hearing loss occurs in a significant number of patients following MVD surgery for HFS. Drill-induced noise and transient loss of CSF during surgery may impair hearing in the high-frequency ranges on both the ipsilateral and contralateral sides, with the ipsilateral side being more affected. Changes in intraoperative BAEPs during MVD for HFS were not useful in predicting HFHL. Follow-up studies and repeat audiological examinations may be helpful in evaluating the time course and prognosis of HFHL. Prospective studies focusing on decreasing intraoperative noise exposure, as well as auditory shielding devices, will establish causation and allow the team to intervene appropriately to decrease the risk of HFHL.

Diagnostic accuracy of EEG changes during carotid endarterectomy in predicting perioperative strokes

The 30 day stroke rate following carotid endarterectomy (CEA) ranges between 2-6%. Such periprocedural strokes are associated with a three-fold increased risk of mortality. Our primary aim was to determine the diagnostic accuracy of electroencephalogram (EEG) in predicting perioperative strokes through meta-analysis of existing literature. An extensive search for relevant literature was undertaken using PubMed and Web of Science databases. Studies were included after screening using predetermined criteria. Data was extracted and analyzed. Summary sensitivity, specificity and diagnostic odds ratio were obtained. Subgroup analysis of studies using eight or more EEG channels was done. Perioperative stroke rate for the cohort of 8765 patients was 1.75%. Pooled sensitivity and specificity of EEG changes in predicting these strokes were 52% (95% confidence interval [CI], 43-61%) and 84% (95% CI, 81-86%) respectively. Summary estimates of the subgroup were similar. The diagnostic odds ratio was 5.85 (95% CI, 3.71-9.22). For the observed stroke rate, the positive likelihood ratio was 3.25 while the negative predictive value was 98.99%. According to these results, patients with perioperative strokes have six times greater odds of experiencing an intraoperative change in EEG during CEA. EEG monitoring was found to be highly specific in predicting perioperative strokes after CEA.

American Clinical Neurophysiology Society Guideline 2: Guidelines for Standard Electrode Position Nomenclature

This revision to the EEG Guidelines is an update incorporating current electroencephalography technology and practice and was previously published as Guideline 5. While the 10-10 system of electrode position nomenclature has been accepted internationally for almost two decades, it has not been used universally. The reasons for this and clinical scenarios when the 10-10 system provides additional localizing information are discussed in this revision. In addition, situations in which AF1/2, AF5/6, PO1/2 and PO5/6 electrode positions may be utilized for EEG recording are discussed.

American Clinical Neurophysiology Society Guideline 3: A Proposal for Standard Montages to Be Used in Clinical EEG

This revision to the EEG Guidelines is an update incorporating current electroencephalography technology and practice and was previously published as Guideline 6. A discussion of methodology for the appropriate selection of reference electrodes is added. In addition, montages are added to assist with localization of abnormal activity in mesial frontal and anterior temporal regions.

Reduction in high-frequency hearing loss following technical modifications to microvascular decompression for hemifacial spasm

OBJECT Microvascular decompression is a safe and effective procedure to treat hemifacial spasm, but the operation poses some risk to the patients hearing. While severe sensorineural hearing loss across all frequencies occurs at a low rate in experienced hands, a recent study suggests that as many as one-half of patients who undergo this procedure may experience ipsilateral high-frequency hearing loss (HFHL), and as many as one-quarter may experience contralateral HFHL. While it has been suggested that drill-related noise may account for this finding, this study was designed to examine the effect of a number of techniques designed to protect the vestibulocochlear nerve from operative manipulation on the incidence of HFHL. METHODS Pure-tone audiometry was performed both preoperatively and postoperatively on 67 patients who underwent microvascular decompression for hemifacial spasm during the study period. A change of greater than 10 dB at either 4 kHz or 8 kHz was considered to be HFHL. Additionally, the authors analyzed intraoperative brainstem auditory evoked potentials from this patient cohort. RESULTS The incidence of ipsilateral HFHL in this cohort was 7.4%, while the incidence of contralateral HFHL was 4.5%. One patient (1.5%; also included in the HFHL group) experienced an ipsilateral nonserviceable hearing loss. CONCLUSIONS The reduced incidence of HFHL in this study suggests that technical modifications including performing the procedure without the use of fixed retraction may greatly reduce, but not eliminate, the occurrence of HFHL following microvascular decompression for hemifacial spasm.