A clinical, MRI and neurophysiological study of acute transverse myelitis

There is paucity of studies correlating the MRI and evoked potential changes in acute transverse myelitis (ATM). We studied ten patients with ATM (age range 14-57 years; 8 men, 2 women) who were subjected to clinical, MRI and neurophysiological evaluation. The latter included median and tibial somatosensory evoked potentials (SEP), motor evoked potentials (MEP) to upper and lower limbs and concentric needle EMG. The outcome was defined on the basis of three month Barthel Index score. All the patients had pronounced lower limb and three had upper limb weakness. Magnetic resonance imaging scans revealed diffuse to hypointense lesions in T1, which became hyperintense in T2 in all except one patient, who had patchy hyperintense lesions in both T1 and T2 sequences suggesting haemorrhage. The signal changes extended at least three segments above the sensory level. Tibial SEP and central motor conduction time to tibialis anterior (CMCT-TA) were abnormal in nine patients each. Median SEP was normal in all, but CMCT to abductor digiti minimi (CMCT-ADM) was abnormal in four patients. The extent of MRI signal alterations and CMCT-TA correlated with the outcome. Seven patients had a poor outcome, in them MRI changes extended 10 spinal segments or more. In these patients, MEP on lumbar stimulation was either unrecordable or of low amplitude and extensive fibrillations were present in the lower limb muscles. From this study, we conclude that in ATM, extensive MRI changes, unrecordable MEP to lower limbs especially on lumbar stimulation and evidence of denervation in leg muscles seem to predict a poor outcome.     

Somatosensory evoked potential studies in internal capsule and corona radiata infarction

To document the somatosensory evoked potential (SEP) changes in capsular and corona radiata infarction and correlate these with clinical and radiological findings, 15 patients with corona radiata and 16 with internal capsular infarction were studied. The mean age of the patients was 55 years (range 26-80), and 6 of them were female. In the patients with corona radiata infarction, median N9-N20 conduction time was abnormal in 4 cases, which correlated with sensory abnormalities in 1. In 3 of these patients, infarction was located in the anterior two-thirds and in 1 there was total corona radiata infarction. The amplitude of N20 potential on the affected side was reduced in 1 patient. In the capsular infarction group, N9-N20 conduction time was abnormal in 1 patient only who had total involvement of the posterior limb of the internal capsule. The amplitude of N20 was reduced in another patient. There were 4 patients who had abnormal sensory findings, but their SEPs were normal. At 3 months, the SEP changes remained stable in all of the patients who were followed up. The SEP changes did not correlate with changes in sensation or 3-month outcome as assessed by the Barthel index score. The lack of clinicoradiological and SEP correlation may be owing to variation on the organisation of sensory pathways in the corona radiata and internal capsule.     

Predominant involvement of motor fibres in patients with critical illness polyneuropathy

Critical illness polyneuropathy (CIP) is a recognized cause of muscle weakness and failure of weaning from a ventilator. In order to characterize the features of CIP, we have examined 28 consecutive surgical patients with severe sepsis using bedside electrophysiology. Of the 28 patients (median APACHE II score 31), 20 developed moderate to severe CIP, as shown by the presence of moderate to severe denervation activity on resting EMG. The median nerve compound muscle action potential (CMAP) amplitudes were reduced to 3.24 (SEM 0.48) mV, while sensory nerve action potential (SNAP) amplitudes obtained from the same nerve were normal (13.1 (1.9) microV). In approximately 50% of these patients, the reduction in CMAP exceeded 50% of the lower limit of normal. Similar results were obtained from stimulation of the ulnar nerve. We conclude that CIP is a major complication in patients with severe sepsis and prolonged artificial ventilation. It predominantly involves motor fibres and thus markedly interferes with weaning from the ventilator.     

A central nerve conduction study in hypothyroidism: before and after thyroxine replacement

Employing a Nicolet CA 100 machine, 20 patients of primary hypothyroidism were selected for electrophysiological studies, including somato-sensory evoked potential (SSEP), brainstem auditory evoked potential (BAEP), and visual evoked potential (VEP), to assess the central nerve conduction before and after administration of the thyroid hormone. Before thyroxine replacement therapy, the latencies of N9, N13, and N20 in SSEP showed significant delay, while the central conduction time (CCT) merely had a tendency of prolongation. In BAEP, the peak and interpeak latencies delayed significantly. Additionally, the latency and amplitude of VEP also had significant difference between patients and controls. After thyroxine replacement, the SSEP, BAEP, and VEP studies revealed significant improvement, in correlation with clinical amelioration. In conclusion, the central nerve conduction would be affected in primary hypothyroidism and the improvement was usually the case, reflecting the clinical recovery after appropriate treatment. The electrophysiological study provides an objective method for monitoring the function of central nervous system in hypothyroidism before and after thyroxine treatment.     

Treatment of sudden deafness apropos of 447 cases

Tibial nerve and S1 dermatome somatosensory evoked potentials (SSEPs) were recorded before and after iohexol lumbar myelography in order to evaluate possible neurotoxic effects of this contrast medium. No significant change in SSEP latencies nor amplitudes was noted after iohexol myelography, supporting the low neurotoxic profile of this contrast agent. Results were compared to those of a control group of patients before and after lumbar puncture (LP), without injection of contrast agent. In this group also no significant change in SSEP components was found, indicating that a preceding LP does not affect this electrophysiological examination.     

Effects of birch pollen-specific immunotherapy on apple allergy in birch pollen-hypersensitive patients

Electrophysiological testing remains an important efficacy parameter in clinical neuropathy trials. The quality of nerve conduction studies in reported trials varies greatly, and may be responsible for negative results. We report the utilization of an expert core lab for electrophysiological testing. With the core lab, the variability of repeat testing is comparable to that of a single, excellent laboratory. Motor conduction velocities demonstrated a coefficient of variation of 3% and sensory conduction velocities 4% across 60 study sites. The distal motor evoked potential amplitudes varied by 13% at the ankle, and 10% at the wrist. The sensory potential amplitudes varied by 16% at the ankle, and 11% at the wrist in 60 sites. The overall monitoring rate in all submitted nerve conduction tracings was 36.6%. Our results show that an expert core lab can improve the electrophysiological quality of clinical trial data with the potential to show small changes in nerve conduction velocities and in both motor and sensory potential amplitudes.     

Acoustic neuroma surgery and delayed facial palsy

The Prader-Willi syndrome (PWS) is associated with a tendency to self-injury and a reduced sensitivity to painful stimuli. Somatosensory functions were studied in 5 children aged 11-13 years with PWS. Tactual perception in the hands (stereognosis) was apparently normal in 4 of them. Sensory nerve conduction velocities in the median nerve and latencies for sensory evoked potentials were similar in the PWS subjects and in 10 healthy controls indicating a preserved myelinisation of sensory nerve fibers in PWS. Sensory nerve action potential amplitudes in the PWS group were on an average only 40-50% of normal size (p = 0.03), suggesting a reduced number of normal axons in the median nerve. The results may be relevant for the impaired pain sensitivity in PWS because similar neurographic findings and a low density of peripheral nerve fibers have been reported in patients with hereditary or congenital insensitivity to pain.     

The effects of cortical stimulation, anesthesia and recording site on somatosensory evoked potentials in the rat

The purpose of this study was to standardize the method of spinal cord monitoring with evoked potentials in the rat. Seventeen male Wistar rats were anesthetized with alpha-chloralose and urethane. Somatosensory evoked potential (SEP) and cerebellar evoked potential (CEP) following sciatic nerve stimulation were mapped at different time points after induction of anesthesia. SEP peaks at latencies of 13-18 ms (P13, N18) were localized to an extremely small area over the sensory cortex. In contrasts, a negative peak of the SEP at 11 ms (N11) and the CEP were widely distributed over the cerebral or cerebellar surface. Anesthesia significantly influenced the cortical components of the SEP. In 10 rats, MEP or posterior fossa evoked potential (PFEP) following stimulation of the sensorimotor or cerebellar cortices respectively, were recorded at T9. Stimulation of different points produced little change on the waveforms of the MEP or PFEP. Successive recordings of MEP and SEP revealed that the P13-N18 complex of the SEP was markedly suppressed after MEP recordings were made. In conclusion, this study identified several factors which alter SEP waveforms in the rat including location of recording, anesthesia and sequence with respect to MEP recording. MEP by stimulation of the same sensory cortex as SEP recordings should not be used for concurrent monitoring, since cortical stimulation will change the waveforms of the SEP.     

Effect of corn silage supplementation on intake and milk production in cows grazing grass pasture

We studied the changes of frontal and parietal somatosensory evoked potentials (SEPs) in the awake state versus different stages of sleep in 10 normal adult subjects. Frontal and parietal SEP components were affected differentially as sleep stages progressed. In general, the amplitudes of frontal components, notably P22, were increased in sleep, whereas the amplitudes of parietal components were decreased in sleep. A sensitive waveform change from the awake state to sleep was present in the frontal response, where a subtle notched negativity, termed "N40," was present only in the awake state and quickly dissipated in all stages of sleep, including stage 1. The amplitude changes from the awake state to stage 3/4 sleep were neither linear nor parallel among SEP components. The most discordant changes occurred in stage 3/4. The amplitudes for the frontal N18-P22-N30 complex and parietal N20-P26-N32 complex increased from stage 2 to stage 3/4, while those for frontal N30-fP40 and parietal N32-pP40 decreased. In contrast to these divergent amplitude changes, the latencies of all components except P14 and frontal N18 showed progressive prolongation from the awake state to slow-wave sleep. The SEP waveforms and latencies in REM sleep approximated those in the awake state, although amplitudes for frontal peaks still remained slightly higher and amplitudes for parietal peaks slightly lower. We postulate that interactions of excitatory and inhibitory phenomena are responsible for the component-dependent and sleep-stage-dependent amplitude enhancement or depression in sleep.     

Peripheral nervous system involvement in human and experimental chronic American trypanosomiasis

An electrophysiological and histological study of the muscle and the peripheral nervous system (PNS) was carried out in chronic human American trypanosomiasis (Chagas' disease) and in an experimental Chagas' disease (Chd) mouse model. Altogether 995 patients with chronic Chd and 261 mice, experimentally infected with RA and CA-I parasite strains, were investigated. Results were compared with matched controls. Techniques employed in humans were: clinical assessment, conventional electromyography (EMG), estimated number of motor units, motor and sensory nerve conduction velocities, repetitive nerve stimulation and muscle and sural nerve biopsies. In mice conventional EMG, sciatic nerve conduction time, sciatic nerve action potential amplitude, in vitro miniature end-plate potentials (MEPPs) and end-plate potentials (EPPs) recordings, muscle, nerve and spinal cord histology and identification of cell phenotypes within the inflammatory infiltrates were the employed procedures. Out of 511 patients submitted to clinical examination, 52 disclosed signs and symptoms of mixed peripheral neuropathy. By employing electrophysiological techniques, it could be shown that about 30% of the investigated patients had one or more of the following features: diminished interference pattern, most of the remainder motor unit potentials being (MUPs) polyphasic; reduced number of functional motor units in the thenar, hypothenar, soleus and/or edb muscles; slow sensory and motor nerve conduction velocities; low sensory action potential amplitude and impairement of neuromuscular transmission. In mice, MUPs duration and amplitude were increased at later stages of the infection, nerve conduction was slow, nerve action potentials were of low amplitude, mepps were of low amplitude and double epps were frequently found. Muscle histology in humans with chronic Chd showed type I and type II grouping, atrophic angular fibers and targetoid muscle fibers. In mice perivascular mononuclear cells infiltrates, small round fibers, muscle fibers necrosis, atrophic angular fibers, type II muscle fibers grouping and grouped muscle fibers atrophy were found. Sural nerve samples showed segmental and paranodal demyelination and axonal loss. The same features were observed in mice nerves, also in this model mononuclear cells infiltrates at the nerve, dorsal root ganglia and meninges surrounding the spinal cord were observed. Muscle and nervous tissues infiltrates were mainly composed of T lymphocytes with predominance of CD8 or CD4 subsets according to the parasites strain employed for infecting the animals. These findings suggest that the skeletal muscle and the PNS may be involved in chronic American trypanosomiasis.     

Referral of patients with polyneuropathy by the family physician: influence of type of symptoms but not of age

OBJECTIVE: To investigate the influence of the age of the patient and the nature of a polyneuropathy on the referral behaviour of general practitioners (GPs). DESIGN: Written questionnaire sent to GPs regarding paper case records of polyneuropathy. SETTING: University Hospital Utrecht, the Netherlands. METHODS: 1590 GPs were asked about their differential diagnosis regarding a paper case record of a patient with polyneuropathy. There were six case records, differing in age (53, 64 and 73 years) and nature of the disease (sensory or sensorimotor polyneuropathy). The GPs were divided into six groups with similar demographic characteristics and type of practice. To avoid focus on polyneuropathy, all GPs also received questions about three other neurological cases (amaurosis fugax, radicular syndrome and vasovagal collapse). RESULTS: The mean response of the questionnaire was 54% (n = 844). Most GPs diagnosed the polyneuropathy (analysis of variance; p < 0.0001). The age of the patient did not influence the diagnosis nor the referral behaviour. At least 73% of the patients with a sensory and 81% of the patients with a sensorimotor polyneuropathy were referred to neurologists for further investigations (chi(2)-test; p < 0.05). CONCLUSION: At least 73% of the GPs referred a patient with polyneuropathy to a neurologist; patients with muscle weakness were referred more often than patients with only sensory disturbances. Referral was not influenced by the age of the patient.     

Correlations between clinical deficits, motor and sensory evoked potentials and radiologic aspects of MRI in malformative syringomyelia. 27 Cases

Twenty-seven patients (15 males, 12 females, age range: 16-66 years) were admitted for malformative syringomyelia diagnosed on MRI with measures of syrinx extending and transverse diameter. Posterior tibial somatosensory evoked potentials (PT SEP), median (M SEP), trigeminal (V3 SEP), brain stem auditory evoked potentials (BEAP), cortical and cervical motor evoked potentials (MEP) were correlated with clinical and radiological findings. SEP abnormalities were not correlated with the duration of symptoms. PT SEP proved to be more sensitive than M SEP. MEP abnormalities were very frequent (87% of the cases), even without clinical motor deficits. Trigeminal SEP were more sensitive than BEAP which were not related to the presence of associated cranio-vertebral abnormalities. We found no significative relationship between clinical and radiological results. Moreover, there was a positive relationship between electrophysiological and radiological results: abnormal trigeminal SEP were detected in 85% of the patients with high cervical syringomyelia. In all cases, trigeminal SEP and MEP should be done in association with M and PT SEP as both of them detect subclinical evidence of spinal cord dysfunction in syringomyelia.     

Neurophysiological assessment of children with obstetric brachial plexus palsy]

INTRODUCTION: The objectives of the neurophysiological evaluation of infants with brachial plexus palsy are to determine the time of occurrence of the lesion, to locate the lesion and to determine its course. METHODS AND CONCLUSIONS: These objectives are achieved by studying affected upper extremity muscles by needle electromiography (EMG) and affected nerves by motor and sensory conduction studies. EMG is performed in the first week of life in those patients with brachial plexus palsy of unknown etiology to determine the age of the lesion for medico-legal reasons. EMG is performed before surgery for tendon transfer in the selected muscles to assure that they are normal. EMG and motor and sensory conduction studies are performed at the age of 3 and 6 months in infants with less than 4 muscle weakness to determine candidates for surgical exploration. Motor and sensory nerve conduction studies are performed intraoperative to determine the functional status of the affected axons and the best surgical procedure (neurotization, neurolysis and/or neuroma resection and homologous nerve graft).     

A case of cortical reflex positive-negative myoclonus--electrophysiological study

An 11-year-old girl who had the positive-negative myoclonus and the history of the generalized tonic clonic seizure was electrophysiologically studied. She had no siblings with either myoclonus or epilepsy, and her intellectual level was normal. She had no other neurological deficits including ataxia, pyramidal and extrapyramidal signs. Surface EMG showed a brief increase in the EMG activity followed by the silent period associated with positive and negative myoclonus during sustained wrist extension. Giant SEP and C reflex (38.6 ms) following electric stimulation of the median nerve at the wrist were obtained in the resting condition and the silent period (about 180 ms) following C reflex was obtained during voluntary contraction. Jerk-locked back averaging of the EEG time-locked to the onset of the myoclonic discharge recorded from the right biceps muscle showed a cortical spike at the left central region preceding the myoclonus onset by 12.6 ms. The latency of C reflex in this case was very short compared with that of previously reported cortical reflex myoclonus. The estimated cortical delay between the arrival of the somatosensory volley and the motor cortex discharge responsible for the C reflex was -1.0 ms and this value was shorter than that in patients with typical cortical reflex myoclonus (mean 3.7 +/- 1.1 ms). Conditioning stimuli (C) of the right median nerve at the wrist started to facilitate the amplitude of the motor evoked potential recorded from the right abductor pollicis brevis muscle after magnetic test stimuli (T) of the left motor cortex at 20 ms of the C-T interval. This C-T interval was shorter than that (24.6 +/- 1.6 ms) in patients with the typical cortical myoclonus. These electrophysiological findings suggested the shorter reflex pathway of the cortical reflex myoclonus in this case than in typical cortical reflex myoclonus. We speculated that the myoclonus was based upon the direct sensory projection from the thalamus to the motor cortex in this case.     

Miller-Fisher syndrome: electrophysiological serial study of five patients

OBJECTIVE: The object of the present study is to show the spectrum of neurophysiological findings during clinical course of Miller Fisher syndrome (MFS), avoiding the controversy over a combined central and peripheral pathology. PATIENTS AND METHODS: We report five patients with a syndrome of ophthalmoplegia, ataxia and areflexia. A similar episode had been suffered previously by 2 of these patients, 14 and 13 years before. In one of them the second episode evolved to a typical Guillain-Barré syndrome (GBS). Motor and sensory conduction velocity of upper and lower limbs, F waves, blink-reflex and somatosensory evoked potentials were recorded in all cases. Needle electromyography in four and brainstem evoked potentials in three of them and the jaw-reflex in another one. RESULTS: In all patients there was a markedly reduced amplitude of the distal sensory evoked response, and no signs of denervation in the EMG. The other results were variable both interindividually and intraindividually. The severity of abnormalities was also different between different patients. The clinical recovery was always accompanied by a improvement of neurophysiological parameters. CONCLUSIONS: The electrophysiological findings in MFS can be variable but they appear always related with the clinical symptomatology. We report for the first time a case in whom the jaw-reflex was abnormal whereas the blink-reflex was normal.     

Alcohol-related acute axonal polyneuropathy: a differential diagnosis of Guillain-Barré syndrome

BACKGROUND: Chronic axonal polyneuropathy is a well-known clinical sequela of excessive alcohol consumption; however, acute axonal polyneuropathy related to alcohol abuse is less well recognized. OBJECTIVE: To describe alcohol-related acute axonal polyneuropathy in 5 chronic alcoholics who developed ascending flaccid tetraparesis and areflexia within 14 days. METHODS: Case series with clinical, laboratory, electrophysiological, and, in 1 patient, biopsy data. RESULTS: All 5 patients consumed a daily average of 250 g of alcohol, and 4 had lost a substantial amount of weight recently. Additional clinical features included painful paresthesia, myalgia, and glove and stocking-type sensory loss. Repeated cerebrospinal fluid examinations failed to show the marked increase of protein concentration with normal cell count typical of Guillain-Barré syndrome, although the protein level was mildly elevated in 1 patient. Blood laboratory findings were consistent with longstanding alcohol abuse. Compound muscle and sensory nerve action potentials were absent or reduced, while conduction velocities were normal or mildly reduced. Three to 4 weeks after onset, needle electromyography displayed moderate to severe fibrillations and positive sharp waves in addition to normal motor unit potentials, indicating an acute axonal polyneuropathy; this was confirmed by sural nerve biopsy in 1 patient. CONCLUSIONS: Excluding other factors, we assume that in these patients the combination of alcohol abuse and malnutrition caused severe acute axonal polyneuropathy. Its distinction from Guillain-Barré syndrome is important because treatment requires balanced diet, vitamin supplementation, and abstinence from alcohol, while immunotherapy may not be indicated.     

Neural mechanisms of the corneal blinking reflex in cats

Neural mechanisms of the blinking reflex elicited by corneal stimulation were analyzed with electrophysiological techniques in the encéphale isolé cat. (1) Mechanical and electrical stimulation elicited two successive responses of the electromyogram of the orbicularis oculi. Neuromuscular unit studies revealed that the same unit was excited twice and that the latencies of both responses corresponded well with the two EMG responses. (2) The late response was easily affected by anoxia and pentobarbital administration, and was also abolished with the slow-wave sleep stage. (3) Both responses were abolished by ipsilateral transection between the inferior colliculus and genu of the facial nerve. (4) Compared with the latencies of the EMG, the sum of the conduction times through the sensory trigeminal nucleus and the facial nucleus corresponded with the latency of the early response. The sum of the conduction times through the reticular formation, added to the former reflex arc, corresponded to the latency of the late response. (5) The reflex pathway of the early response is consistent with a three-neuron arc passing through the sensory trigeminal nucleus and the facial nucleus. The late response may employ a multisynaptic arc passing through the brain stem medial reticular formation between the sensory trigeminal nucleus and the facial nucleus.     

Male and female mice differ for baseline and nicotine-induced event related potentials.

The usage patterns and biological effects of cigarette smoking differ significantly among men and women. This study seeks to clarify the interaction that exists between nicotine and biological gender by investigating changes in brain electrical activity after acute nicotine treatment. The P20, N40, and P80 components of the auditory evoked potential were examined in male and female C57BL/6J mice using a paired-stimulus gating paradigm. Consistent with previously published data, acute nicotine resulted in increased gating of the P20 but a decrease in that of N40. Nicotine also resulted in a lengthening of P20 latency but a decrease in that of N40 and P80. The P80 latencies of male and female subjects were differentially affected by nicotine, as males appeared to be more sensitive to its shortening effect. Males and females also exhibited differences in N40 and P80 amplitudes, both of which were smaller in males. The effects of gender on auditory evoked potential amplitude suggest dimorphic signaling in the N40 and P80 generators. Whether this electrophysiological sexual dimorphism has functional consequences for sensory or cognitive abilities requires additional research. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of anesthetics on somatosensory evoked potentials by median nerve stimulation in human--analyses after single administration in volunteers

In the present study, effects of midazolam, thiopental sodium, propofol, and nitrous oxide upon SEP in a clinically used dose were investigated on 24 male volunteers. In addition, antagonistic actions of flumazenil and naloxone against effects of midazolam and nitrous oxide, respectively, on SEP were studied. Midazolam had no effect on latencies of N 20 and P 25, but increased latency of P 45 and attenuated P 100 amplitude. Flumazenil reversed these effects of midazolam of P 45 latency and P 100 amplitude to their control values. While thiopental sodium and propofol suppressed P 100 amplitude, they had no effect on N 20, P 25, P 45 latencies. Nitrous oxide elongated latencies of N 20, P 25, P 45 and decreased P 100 amplitude. Naloxone reversed the effects of nitrous oxide on N 20 and P 25 latencies without affecting increased P 45 latency and attenuated P 100 amplitude. These results suggest that midazolam might have an analgesic action of suppressing cortical sensory neurons, whereas thiopental sodium and propofol have no effect on neurons in the primary sensory cortex. The finding that naloxone antagonized the increased latencies of N 20 and P 25 by nitrous oxide could be explained by the analgesic action of nitrous oxide that could be mediated by opioid receptors. The results also indicate that electrical activities of the cortical neurons in the associated area are more susceptible to psychotropic agents than those in the primary sensory cortex. The effects of anesthetics on SEP appear to reflect their characteristics of functioning mechanisms on cortical neurons. Analysis of SEP is, therefore, useful for the assessment of the mechanism and the acting site of anesthetics in the sensory cortex.     

Peripheral neuropathy in scleroderma

The diagnostic relevance of recording motor evoked potentials (MEPs) after electrical stimulation of the cervical region, as compared with conventional needle electromyography (EMG), was evaluated in 26 patients with brachial plexus (BP) damage of different aetiology, severity and topography. MEP abnormalities (absence or latency increase) were observed in at least one muscle of all the patients, with a global incidence of 61.5% of the muscles examined. Neurogenic EMG signs were present in all but one patient with an incidence of 62.2% of the muscles examined. Combining the two methods, the global incidence of abnormalities rose to 69.9%. MEP abnormalities were consistent with the clinical topography and severity of BP lesions and were fairly parallel with EMG findings. Recording MEPs after percutaneous electrical stimulation of the cervical region may be regarded as a rapid, non-invasive method for quantitative electrophysiological assessment of BP damage.