Stimulation parameters for motor evoked potentials during intraoperative spinal cord monitoring. A systematic review.

OBJECTIVE: The aim of this systematic review was to find the optimal stimulation parameters for muscle recorded transcranial electrical stimulation motor evoked potential (mTc-MEP) and D-wave monitoring during spinal cord monitoring. METHODS: A PRISMA systematic search in Medline and EMBASE and a QUADAS-2 quality evaluation was performed to identify studies that compared stimulation parameters consisting of stimulation location, number of pulses, pulse duration, interstimulus interval, double train (DTS) or recurrent train stimulation (RTS) and intertrain interval (ITI) for performing mTc-MEP and D-wave monitoring. Only studies that used total intravenous anaesthesia (TIVA) were included. RESULTS: Ten studies that compared stimulation parameters for performing mTc-MEP monitoring (stimulation location n = 4, number of pulses n = 2, pulse duration n = 1, interstimulus interval n = 4, DTS n = 1, RTS n = 2, ITI n = 2) were included. No studies compared stimulation parameters (stimulation location and pulse duration) for performing D-wave monitoring. CONCLUSIONS: Few studies examined the optimal stimulation parameters for monitoring mTc-MEPs and no studies were included for D-wave monitoring. There is a need for prospective research to investigate the optimal stimulation parameters for mTc-MEP with the use of TIVA and D-wave monitoring. SIGNIFICANCE: For mTc-MEP monitoring, a table is provided in which the recommended stimulation parameters are stated.

Recommendations of the International Society of Intraoperative Neurophysiology for intraoperative somatosensory evoked potentials.

Intraoperative somatosensory evoked potentials (SEPs) provide dorsal somatosensory system functional and localizing information, and complement motor evoked potentials. Correct application and interpretation require in-depth knowledge of relevant anatomy, electrophysiology, and techniques. It is advisable to facilitate cortical SEPs with total intravenous propofol-opioid or similarly favorable anesthesia. Moreover, SEP optimization is recommended to enhance surgical feedback speed and accuracy by maximizing signal-to-noise ratio (SNR); it consists of selecting highest-SNR peripheral and cortical derivations while omitting low-SNR channels. Confounding factors causing non-surgical SEP reduction should be excluded before issuing a warning. It is advisable to facilitate their identification with peripheral SEP controls and cortical SEP systemic controls whenever possible. Warning criteria should adjust for baseline drift and reproducibility. The recommended adaptive warning criterion is visually obvious amplitude reduction from recent pre-change values and clearly exceeding trial-to-trial variability, particularly when abrupt and focal. Acquisition and interpretation should be done by qualified technical and professional level personnel. Indications for SEP monitoring include intracranial, posterior fossa, and spinal neurosurgery, as well as orthopedic spine, cerebrovascular, and descending aortic surgery. Indications for SEP mapping include sensorimotor cortex and dorsal column midline identification. Future advances could modify current recommendations.

S100B, intraoperative neuromonitoring findings and their relation to clinical outcome in surgically treated intradural spinal lesions.

BACKGROUND: Neurophysiological monitoring (IOM) consisting of somatosensory (SEPs), muscle (MEPs) and spinal motor evoked (D-wave; spinal MEPs) potentials is used to indicate injury related to surgical treatment of intradural and intramedullary lesions. Combining spinal and muscle MEPs reliably predicts long-term motor deficit. If spinal MEPs recording is not possible, additional markers-e.g. S100B, a serum marker for glial injury-may be a helpful adjunct. Thus, serial serum S100B measurements were related to both the intraoperative IOM recordings and the long-term neurological outcome in patients surgically treated for cervical and thoracic intradural lesions. METHODS: In 33 patients (9 men, 24 women, 54 ± 17 years) during intramedullary (8) or intradural (25) cervical or thoracic spinal surgeries significant intraoperative SEP-amplitude decrement >50 % or MEP loss and serial S100B serum concentration (perioperative days 0, 1-3, 5) were related to outcome (>1 year after discharge, grouped into improved and unchanged/altered neurological symptoms). RESULTS: Differences in S100B levels between patients with improved and unchanged/altered neurological outcome were significantly on postoperative days 2 (0.085 ± 0.08 µg/l vs 0.206 ± 0.07 µg/l, p = 0.005) and 3 (0.076 ± 0.03 µg/l vs 0.12 ± 0.05 µg/l, p = 0.007). All patients with permanent altered neurological symptoms developed S100B levels >0.08 µg/l (0.09-0.35 µg/l). Eighty-one percent of patients with improved neurological symptoms presented with S100B levels ≤0.08 µg/l (0.02-0.08 µg/l). Nine out of ten patients (90 %) without changes in EP and S100B had an improved long-term outcome, whereas 9/13 patients (69 %) with changes in EP and S100B had altered neurological symptoms in long-term outcome. CONCLUSION: Intraoperative stable EPs and S100B ≤0.08 µg/l may be used as a marker to predict long-term neurological improvement, whereas EP-changes and elevated S100B levels on the 3rd postoperative day may be useful as a marker to predict long-term neurological alteration. In summary, the combined use of S100B and EPs might be helpful in the prediction of the severity of adverse spinal cord affection following surgery and guidance of patients.

Intra-operative subcortical electrical stimulation: a comparison of two methods.

OBJECTIVE: For intra-operative subcortical electrical stimulation of the corticospinal tract, two techniques - originally described for cortical stimulation - have evolved: the 50-Hz-stimulation first described by Penfield in 1937 and the high-frequency multipulse train stimulation technique first described by Taniguchi in 1993. Motor thresholds of both methods in combination with a bipolar and monopolar stimulation technique and their reliability for eliciting motor evoked potentials (MEPs) were studied. METHODS: Data were obtained in 20 patients (50±17 years; 10 females) undergoing tumour resection under general anaesthesia. Both 50-Hz-stimulation of 1-s duration and a multipulse stimulation (5 pulses interstimulus interval 4 ms, 0.5-Hz repetition rate) were applied with a bipolar probe (1.5-mm ball tip, 8-mm interelectrode distance) and a monopolar probe (1.5-mm-diameter tip). MEPs were recorded in muscles contralateral to the stimulated hemisphere. Comparison of different stimulation modalities was performed at the site where monopolar multipulse stimulation technique elicited MEPs with the lowest stimulation intensity (constant current monophasic cathodal stimulation, individual pulse width 0.5 ms, max. 25 mA). RESULTS: MEPs were elicited by monopolar multipulse stimulation with an intensity of 8±3.9 mA (21/21 stimulation sites); monopolar 50-Hz stimulation with 12±5.4 mA (18/21 stimulation sites); bipolar multipulse stimulation with 14±8.1 mA (12/21 stimulation sites) and bipolar 50-Hz stimulation with 15±6.3 mA (11/21 stimulation sites). CONCLUSIONS: Stimulation intensities for eliciting MEPs are significantly lowest for the monopolar multipulse stimulation (p<0.025). Monopolar compared to bipolar stimulation resulted in eliciting MEPs in a higher number of tested patients (Fisher's p<0.0001). SIGNIFICANCE: Subcortical stimulation with a monopolar probe and a multipulse stimulation is most efficient for the purpose of identifying the corticospinal tract. This is explained by the more radiant electric field properties of the monopolar probe compared to the bipolar probe.

Significance of serial S100b and NSE serum measurements in surgically treated patients with spondylotic cervical myelopathy.

BACKGROUND: Predicting functional outcome following surgery performed for spinal cord compression is still a considerable problem. Recent observations, though, strongly suggest that with serial measurements of serum S100b, this might be possible in patients with subacute spinal cord compression. The aim of this study was to examine whether this potential significance of S100b applies as well to patients with spondylotic cervical myelopathy. A further purpose was to assess the value of NSE in this regard, another biochemical marker widely used to monitor cerebral lesions. METHODS: Fifty-one patients were included in this prospective study. Outcome was considered as favourable in case of neurological improvement with preservation or retrieval of walking ability, whereas non-improvement without restoration of gait function was regarded as unfavourable. The preoperative levels of S100b and NSE were correlated with the degree of paresis, duration of symptoms, and presence of intramedullary high signal intensities on MRI. The postoperative values of both markers were correlated with outcome. FINDINGS: The preoperative levels of S100b were neither correlated with degree or duration of paresis nor with outcome. In case of an uncomplicated course the postoperative levels of S100b were also not correlated with outcome. In complicated courses with acute postoperative deterioration normal values on the 3rd day after the event were associated with a favourable outcome, whereas one patient with unfavourable outcome showed a persistent pathological increase. The serum levels of NSE were not correlated with clinical parameters or with outcome in any of the cases. CONCLUSIONS: Serial S100b serum measurements do not permit prediction of functional outcome in patients with spondylotic cervical myelopathy in case of an uncomplicated postoperative course. In complicated courses with postoperative deterioration, such measurements reflect postoperative events with possibly prognostic relevance. NSE does not have any significance in these patients with chronic lesions of the spinal cord.

[Perioperative lesions of the corticospinal tract. Etiology, neuroradiological features and clinical outcome]. / Perioperative Läsionen des Tractus corticospinalis. Atiologie, neuroradiologische Befunde und klinischer Verlauf.

BACKGROUND: The neurosurgical resection of mass lesions in the vicinity of the corticospinal tract (CST) may induce a postoperative impairment of motor function. The etiology and localisation of lesions causing postoperative motor deterioration were analysed by preoperative and postoperative magnetic resonance imaging (MRI). PATIENTS AND METHODS: In 32 patients with mass lesions near the CST and intraoperative deterioration of the motor-evoked potentials, preoperative and postoperative MRI was performed and evaluated for new lesions along the CST. These lesions were classified into edema, infarction and haemorrhage. All patients were examined for perioperative central motor function. RESULTS: New lesions along the CST were found in 19 of the 32 patients. Postoperatively new or deteriorated motor function was found in 13 of these 19 patients (edemas: 4 out of 6, haemorrhages: 4 out of 7; infarctions: 5 out of 6). Of the 13 patients without new MRI lesion along the CST one had a new motor deficit. CONCLUSION: The postoperative MRI in patients with mass lesions near the CST and postoperative central motor deterioration sensitively showed the etiology and localisation of the lesion. Apart from being due to infarctions and haemorrhages, a larger number of postoperative motor impairments may be caused by edema.

Laser Doppler imaging for intraoperative human brain mapping.

The identification and accurate location of centers of brain activity are vital both in neuro-surgery and brain research. This study aimed to provide a non-invasive, non-contact, accurate, rapid and user-friendly means of producing functional images intraoperatively. To this end a full field Laser Doppler imager was developed and integrated within the surgical microscope and perfusion images of the cortical surface were acquired during awake surgery whilst the patient performed a predetermined task. The regions of brain activity showed a clear signal (10-20% with respect to the baseline) related to the stimulation protocol which lead to intraoperative functional brain maps of strong statistical significance and which correlate well with the preoperative fMRI and intraoperative cortical electro-stimulation. These initial results achieved with a prototype device and wavelet based regressor analysis (the hemodynamic response function being derived from MRI applications) demonstrate the feasibility of LDI as an appropriate technique for intraoperative functional brain imaging.

Transcranial and direct cortical stimulation for motor evoked potential monitoring in intracerebral aneurysm surgery.

STUDY AIM: To analyse the parallel use of transcranial electrical stimulation (TES) and direct cortical stimulation (DCS) for eliciting muscle motor evoked potentials (MMEPs) in intracranial aneurysm surgery; to correlate permanent or transient TES- and/or DCS-MMEP changes with surgical maneuvers and clinical motor outcome. PATIENTS AND METHODS: TES and DCS were intraoperatively performed in 108 patients (51.5+/-14.7 years); MMEPs were obtained in muscles belonging to the vascular territory of interest. Monopolar, anodal stimulation was achieved with a train of five stimuli consisting of an individual pulse width of 0.5ms, an interstimulus interval of 4ms, a train repetition rate of 0.5-2Hz, and maximum stimulation intensities up to 200mA (TES) versus 25mA (DCS). RESULTS: In 95/108 (88%) patients, no changes in MMEPs occurred and none of these patients suffered a permanent severe motor deficit. In 14/108 (12%) patients, we observed nine (64%) temporary changes, four (29%) permanent deteriorations and one (7%) permanent MMEP loss. Out of 14 MMEP changes, nine (64%) occurred with TES, compared to 13 (93%) with DCS (Fishers'p=0.165). Parallel changes in TES- and DCS-MMEPs occurred in 8/14 patients (57%), in which case a permanent loss was always followed by a permanent severe motor deficit. Sixty-seven percent of all permanent changes occurred with DCS-MMEPs, compared to 33% with TES-MMEPs (p=0.567, NS). DISCUSSION AND CONCLUSIONS: In aneurysm surgery, provided that close-to-motor-threshold stimulation and the most focal stimulating electrode montage are used, TES- and DCS-MMEPs do not differ in their capacity to detect an impending lesion of the motor cortex or its efferent pathways. TES stimulation can cause significant muscular contraction during surgery, potentially disrupting the operating surgeon. DCS maintains the singular advantage of stimulating a very focal and superficial motor cortex stimulation that does not result in patient movement.

Tranylcypromine abuse associated with an isolated thrombocytopenia.

The authors report a case of a 35-year-old woman with a known history of alcohol abuse, who developed a tranylcypromine abuse with up to 600 mg tranylcypromine daily. She developed a severe thrombocytopenia and secondly a delirious withdrawal syndrome. MAOI causing thrombocytopenia is reviewed and the prescription of tranylcypromine to patients with previous substance abuse is discussed.

Spinal and supraspinal mechanisms contribute to the silent period in the contracting soleus muscle after transcranial magnetic stimulation of human motor cortex.

In the voluntarily activated muscle, transcranial magnetic stimulation (TMS) of motor cortex produces subsequently to the motor evoked potential (MEP) a silent period (SP) in the electromyogram. We studied the time course of soleus motoneuron (MN) pool excitability after conditioning TMS by Hoffmann reflex (HR) testing, to determine whether inaccessibility of MNs after corticospinal input contributes to the SP. Coincidently with the early part of the SP, and only in the contracting soleus, MN depression was obtained that covaried with the degree of preinnervation, and with the size of the preceding MN discharge. However, MN excitability recovered significantly prior to the end of the SP. It is concluded that in the contracting soleus spinal mechanisms (most likely Renshaw inhibition and MN afterhyperpolarization) contribute to the early part of the SP, while the late part of the SP is supraspinal (probably cortical) in origin.