Clinical aspects of multifocal or generalized tonic dystonia in reflex sympathetic dystrophy

The authors describe 10 patients with reflex sympathetic dystrophy that progressed to a multifocal or generalized tonic dystonia. The neuropsychologic profile was similar to that of other patients with chronic pain, irrespective of its cause. The distribution pattern of dystonia, the stretch reflex abnormalities, and the worsening of dystonia after tactile and auditory stimuli suggest impairment of interneuronal circuits at the brainstem or spinal level. Antibody titers for glutamic acid decarboxylase, tetanus, and Sjögren antigens were all normal.

The Multiple Tasks Test. Strategies in Parkinson's disease

The clinical balance tests presently used cannot predict falls in Parkinson's disease (PD), perhaps because they probe fairly isolated "components" of postural control. The Multiple Tasks Test (MTT) is a new balance test that simultaneously assesses multiple components of postural control. We investigated whether this MTT can detect postural abnormalities in PD patients. Fifty young controls (mean age 27.6 years), 20 elderly controls (mean age 62.5 years), and 20 PD patients (mean age 61.8 years, mean Hoehn and Yahr stage 2.2) participated. The MTT consisted of eight separate tasks of increasing complexity, which were executed sequentially. These tasks were composed of several motor components (standing up, walking, avoiding obstacles, touching the floor, turning around, and sitting down) and one cognitive component (answering serial questions). Four additional components included carrying an empty or loaded tray, wearing slippery shoes, and reduced illumination. All components within each task had to be performed simultaneously or directly sequentially. Errors were defined as Hesitations (slowed performance) or Blocks (complete cessation), which were scored separately for execution of the motor and cognitive components. Speed of performance was not stressed, but we did measure the time taken to complete all tasks. The complete MTT was performed by all subjects, except for a subgroup of seven patients and seven elderly controls who performed a shortened version, with only three of the eight sequential tasks (simple, intermediate, and most difficult). The number of subjects that produced Hesitations or Blocks for the motor components differed between the three groups [two-way repeated measures MANOVA, F(2.7) = 20.56; P < 0.001], patients making more errors than young and elderly controls. Furthermore, the number of subjects that made motor errors increased as the tasks became more complex [F(2.7) = 6.69; P < 0.001]. This increase differed across the three groups [significant interaction effect; F(2.7) = 3.31; P < 0.001] because particularly patients produced motor errors during the more complex tasks. In both control groups, 62% performed all eight consecutive tasks without errors in the motor components. In contrast, only 8% of the patients completed all tasks without motor errors (log rank test, P < 0.0001). This difference between patients and controls disappeared if the cognitive component was also scored, because more controls made cognitive errors during complex tasks than patients. Controls apparently gave priority to execution of the motor components, which they performed significantly faster than the patients. Both patients and controls made more errors during the shortened MTT, suggesting that learning effects (gain in performance through practice) influenced performance on the complete test. The MTT is a new balance test that clearly discriminates between healthy subjects and PD patients. Unlike controls, PD patients lend less priority to motor tasks over cognitive tasks. In addition, impaired motor learning may partially explain the higher error rate in PD. Future studies must determine if impaired MTT performance can predict actual falls in daily life.

A convenient method to reduce crosstalk in surface EMG. Cobb Award-winning article, 2001

OBJECTIVES

Crosstalk in surface EMG can be reduced by the use of spatial filters. We compared a variety of spatial filters to establish the most effective and the least complex method to reduce crosstalk.

METHODS

Six different spatial filters described in the literature were tested in 8 healthy volunteers. Electrode arrays were placed over the anterior tibial and triceps surae muscles. Selective muscle activation was achieved both by supramaximal nerve stimulation and by maximal voluntary contraction. Selectivity of activation was guaranteed by using intramuscular wire electrodes. Crosstalk was quantified by dividing the amount of EMG activity recorded during pure agonist activation (i.e. the muscle directly under the electrode array) by the EMG activity recorded during pure antagonist activation. This was done for both compound muscle action potentials and voluntary muscle activation. The amount of crosstalk recorded with the different spatial filters was compared with that recorded with a standard bipolar lead.

RESULTS

Crosstalk was most reduced by the "double-differential" (DD) filter, yielding an up to 6-fold improvement of EMG selectivity. We then compared signals recorded with this DD filter with those recorded with the less complex "branched electrode". As expected on theoretical grounds, signals from both filter types were identical.

CONCLUSIONS

Crosstalk is best reduced using a "double-differentiating" recording technique, which can be achieved easily using a branched electrode instead of a standard bipolar lead. This technique can be used with all conventional EMG equipment.

Neurophysiological evidence of increased cortical reactivity in migraine

Cortical reactivity in migraine can be studied with evoked potentials. The majority of the evidence shows increased reactivity in migraine, which may be due to abnormal inhibition. At present, the techniques are not useful for diagnosis. Discrepancies between reports may be due to fluctuations in reactivity over time. Documenting this changing reactivity requires refinement of analysis techniques.

Clinical and para-clinical tests in the routine examination of headache patients

Para-clinical examinations in the diagnosis and treatment control of headache patients vary considerably between clinics and headache centers. Among the neurological societies in Europe there has been a consensus that some common procedures and recommendations should be created. In the Fall of 1998, the European Federation of Neurological Societies (EFNS) commissioned a Task Force on Neurophysiological Tests and Imaging Procedures in Headache Patients. Members of the Task Force are the present authors and we have reviewed the literature on 1) neurophysiological tests (EEG and evoked potentials), 2) autonomic nervous system and clinical tests and 3) imaging and cerebrovascular tests (X-ray, CT, MR, fMRI, PET, SPECT and transcranial Doppler). The literature was carefully evaluated with respect to validity and strength of the data. The task was to reach conclusions about each technique in the form of guidelines for clinical use. Finally, selected areas for future research will be outlined. The extensive review and the guidelines will be published by the EFNS during 2000.

Narcolepsy: clinical features, new pathophysiologic insights, and future perspectives

Narcolepsy is characterized by excessive daytime sleepiness and abnormal manifestations of rapid eye movement sleep such as cataplexy. The authors review the clinical features of narcolepsy, including epidemiology, symptoms, diagnosis, and treatment, in detail. Recent findings show that a loss of hypocretin-producing neurons lies at the root of the signs and symptoms of narcolepsy. The authors review the current state of knowledge on hypocretin anatomy, physiology, and function with special emphasis on the research regarding the hypocretin deficiency in narcolepsy, which may also explain associated features of the disorder, such as obesity. Lastly, they discuss some future perspectives for research into the pathophysiology of sleep/wake disorders, and the potential impact of the established hypocretin deficiency on the diagnosis and treatment of narcolepsy.

Long-term results of anterior anal sphincter repair for fecal incontinence due to obstetric injury / with invited commentaries

AIMS

This study is to report short- and long-term results of anterior sphincter repair for fecal incontinence due to obstetric injury and factors predicting an unsuccessful outcome.

METHODS

Thirty-nine consecutive patients, mean age 51 years (range 29-74), who underwent anterior sphincter repair for fecal incontinence due to obstetric injury were investigated. Duration of symptoms ranged from 9 months to 34 years. All patients underwent an anterior overlapping sphincter muscle reconstruction and in most cases a puborectal muscle plasty.

RESULTS

Three months after surgery 77% of the patients had regained continence (Parks score of 1 or 2), at 9 months 67% were continent and after 12 months or more (mean, range 12-114) only 62%. Patients with prolonged pudendal latency (>2.2 ms) did significantly worse than patients without it (p < 0.05). Patients who had had lateral episiotomy during labor had significantly better outcome than those without it (p < 0.05).

CONCLUSION

The outcome of anterior sphincter repair deteriorates with time after surgery. Assessment should be done at least 1 year after surgery to evaluate the final results of anterior sphincter repair. Prolonged pudendal latency predicts a poor outcome of anterior sphincter repair, and a prior lateral episiotomy is possibly a good prognostic factor.

What is the best way to assess focal slowing of the ulnar nerve?

OBJECTIVE

The study assessed the influence of the length of the across elbow (AE) segment of the ulnar nerve on the true and false positive rates of velocity measurements of the AE segment. Using a short AE length will increase effects of the measurement error (ME), and using a long distance will 'dilute' the slowing due to the focal lesion; it is not known which length is optimal to detect focal slowing.

METHODS

A simulation was performed to assess diagnostic yield for AE lengths of 50, 100 and 150 mm, taking into account ME, variation in true velocity, and severity of the lesion. ME of latencies and distances were first determined in a healthy subject.

RESULTS

ME proved lower than in a published study. Diagnostic yield was consistently better for an AE length of 50 mm than for 100 or 150 mm. The optimum length is therefore near 50 mm. Yield increased with severity of the lesion, smaller ME, and when interindividual variation in true velocity was small. Judging AE on its own had a slightly better yield than comparing AE velocity to forearm velocity, except for populations with a larger than normal spread in true conduction variability.

CONCLUSIONS

The best balance between effects of ME and 'dilution' to detect focal nerve slowing is obtained at nerve lengths of about 50 mm. The need to incorporate all possible compression sites necessitates the use of a suboptimal length of about 80 mm.

Repetitive nerve stimulation: effects of recording site and the nature of 'pseudofacilitation'

OBJECTIVES

To describe changes in the waveform of the compound muscle action potential (CMAP) during repetitive nerve stimulation for various recording sites.

METHODS

Responses to trains of 10 stimuli given at 0.1, 1, 3, 5, 10 and 30 Hz to the ulnar nerve were recorded simultaneously from 8 hand sites in 15 healthy subjects. Percentile changes of amplitude, duration and area of both negative and positive phases were analyzed.

RESULTS

Duration consistently decreased during the trains. At 30 Hz, the mean amplitude of the negative phase increased on 5 sites but decreased on 3. Area consistently decreased, but least for hypothenar sites. Repeated stimulation causes an alteration in the waveform of the CMAP that consists of 4 elements: (1) shorter duration; (2) changed amplitude of the negative phase (up or down); (3) merging of bifid peaks; (4) changes were more pronounced for positive than negative phases.

CONCLUSIONS

As the term 'pseudofacilitation' implies an increase in amplitude, it is often not appropriate. Increased muscle fiber conduction velocity can explain most of the waveform alterations. Movement and shortening of muscles may play additional roles. Consequences for diagnostic yield await a comparison with disease groups.

'Rules of conduct': some practical guidelines for testing motor-nerve conduction

The testing of nerve conduction using electromyography (EMG) is a frequently used diagnostic method for the identification of various neuropathies. The present article illustrates a variety of conditions on the basis of clinical data, and suggests how one can obtain the best results by observing a few simple rules.

Effects of startle and laughter in cataplectic subjects: a neurophysiological study between attacks

OBJECTIVES

Cataplexy, when unequivocally present together with excessive daytime sleepiness, is diagnostic for narcolepsy. Unfortunately, it is difficult to induce cataplexy during consultation. In this study we tried to assess presumed subclinical expressions of cataplexy using neurophysiological tests.

METHODS

In this controlled explorative study, we studied 14 patients with a clear history of cataplexy and 12 matched controls using standard H-reflex, H/M ratios, audiospinal reflex, H-reflexes modulated by emotions and startle reflexes.

RESULTS

H-reflexes were attenuated during laughter in patients as well as controls. Startle reflexes were increased in patients. Audiospinal reflexes were not influenced.

CONCLUSIONS

The patterns found add relevant knowledge concerning pathophysiological mechanisms and involved brain areas in cataplexy, and may reflect subclinical expressions of cataplexy. The presumed specificity of the abolishment of H-reflexes during cataplectic attacks is questioned by our findings. The exaggerated startle reflex is in line with recent findings concerning involved brain areas in narcolepsy.

Repeatability of the intensity dependence of cortical auditory evoked potentials in the assessment of cortical information processing

Data on repeatability and optimal settings are needed when studying the influence of drugs on the intensity dependence of auditory evoked cortical potentials (IDAP). IDAP was recorded at intervals of 1, 2, and 24 h at two centers in 22 healthy volunteers. Settings were modified to compare fixed versus randomly varied stimulus repetition rate, as well as 30 Hz and 100 Hz low pass filters. Repeatability was assessed for different intervals and different settings. Group means did not differ between centers, the 2-h or 24-h retest, or when using different settings. We observed an order effect for the 1 h retest. Fixed repetition rate and the 30 Hz filter improved repeatability with still high intraindividual variability. IDAP group means can be compared between centers for retest intervals of 2 h and 24 h and different settings. Variability is too large to compare individuals.

Auditory evoked potentials in the assessment of central nervous system effects of antimigraine drugs

Because the "intensity dependence" of cortical auditory evoked potentials (IDAP) is under serotonergic control, it can be used to assess central antimigraine effects of 5HT1B/1D agonists. We measured IDAP before and 2 h after naratriptan (5 mg, n = 19) and zolmitriptan (5 mg, n = 19) in healthy volunteers. IDAP was expressed as the amplitude-stimulus intensity function ("ASF slope"). Naratriptan tended to increase ASF slope (mean difference 0.23 +/- 0.62 microV/10 dB, p = 0.06) while zolmitriptan (0.08 +/- 0.95 microV/10 dB, p = 0.35) did not. We assessed the suitability of IDAP for measuring central antimigraine drug effects using repeatability data (see companion paper). We calculated the trade-off between the size of the expected drug effects (ASF slope difference) and the necessary sample size. Because of poor repeatability 36 to 80 subjects are required to detect ASF slope changes in the 0.25-0.5 microV/10 dB range. These data can be used to design trials using IDAP.

[Gammahydroxybutyrate must remain available for patients with narcolepsy]

There is growing public concern about the use of gamma-hydroxybutyrate (GHB) as a party drug. This justified concern about misuse, however, should not lead to prohibition of the drug as it is efficacious in narcolepsy.

Weak with laughter

We found a marked reduction of H-reflex amplitude during laughter, suggesting that motor inhibition may underlie the feeling of being "weak with laughter". This effect may have a role in cataplexy, which is preferentially elicited by laughter.

Pathophysiology of chorea and bradykinesia in Huntington's disease

This article reviews the neurophysiological abnormalities described in Huntington's disease. Among the typical features of choreic movements are variable and random patterns of electromyographic (EMG) activity, including cocontraction of agonist and antagonist muscles. Studies of premotor potentials show that choreic movements are not preceded by a Bereitschaftspotential, therefore demonstrating that choreic movement is involuntary. Early cortical median-nerve somatosensory-evoked potentials have reduced amplitudes and the reduction correlates with reduced glucose consumption in the caudate nucleus. Long-latency stretch reflexes evoked in the small hand muscles are depressed. These findings may reflect failed thalamocortical relay of sensory information. In Huntington's disease, the R2 response of the blink reflex has prolonged latencies, diminished amplitudes, and greater habituation than normal. These abnormalities correlate with the severity of chorea in the face. Patients with Huntington's disease perform simple voluntary movements more slowly than normal subjects and with an abnormal triphasic EMG pattern. Bradykinesia is also present during their performance of simultaneous and sequential movements. Eye movements show abnormalities similar to those seen in arm movements. In Huntington's disease, arm movement execution is associated with reduced PET activation of cortical frontal areas. Studies using transcranial magnetic stimulation show that patients with Huntington's disease have normal corticospinal conduction but some patients have a prolonged cortical silent period. Bradykinesia results from degeneration of the basal ganglia output to the supplementary motor areas concerned with the initiation and maintenance of sequential movements. The coexisting hyperkinetic and hypokinetic movement disorders in patients with Huntington's disease probably reflect the involvement of direct and indirect pathways in the basal ganglia-thalamus-cortical motor circuit.

CMAP amplitude cartography of muscles innervated by the median, ulnar, peroneal, and tibial nerves

The spatial and temporal distribution of compound muscle action potential (CMAP) amplitudes was mapped using 1 x 1-cm grids over thenar, hypothenar, dorsal foot, and foot sole muscles (seven maps each). The high-amplitude zone (HAZ, area where amplitudes were over 80% of the maximum amplitude) denoted susceptibility to changes in recording site. Thenar maps had one peak (spatially and temporally) with a HAZ of 3.5 +/- 2.3 cm2. Hypothenar maps had two peaks (spatially and temporally) with a HAZ of 7.7 +/- 3.6 cm2. Dorsal foot maps had one temporal peak, which could be split up spatially; the HAZ was smallest, at 1.7 +/- 1.7 cm2. Foot sole muscles had one peak (spatially and temporally), with the largest HAZ at 18.4 +/- 6.1 cm2. Wave-form differences were ascribed to differences in muscle anatomy, architecture, and variability. These explain differences in amplitude reproducibility between nerves and the differing effect that increasing electrode size has on reproducibility.

Are automatic postural responses in patients with Parkinson's disease abnormal due to their stooped posture?

Abnormal automatic postural responses are thought to contribute to balance impairment in Parkinson's disease. However, because postural responses are modifiable by stance, we have speculated that some postural abnormalities in patients with Parkinson's disease are secondary to their stooped stance. We have studied this assumption by assessing automatic postural responses in 30 healthy subjects who were instructed either to stand upright or to assume a typical parkinsonian posture. During both conditions, subjects received 20 serial 4 degrees 'toe-up' rotational perturbations from a supporting forceplate. We recorded short-latency (SL) and medium-latency (ML) responses from stretched gastrocnemius muscles and long-latency (LL) responses from shortened tibialis anterior muscles. We also assessed changes in the center of foot pressure (CFP) and the center of gravity (COG). The results were qualitatively compared to a previously described group of patients with Parkinson's disease who, under these circumstances, typically have large ML responses, small LL responses and insufficient voluntary postural corrections, accompanied by a slow rate of backward CFP displacement and an increased posterior COG displacement. The stooped posture resulted in unloading of medial gastrocnemius muscles and loading of tibialis anterior muscles. Onset latencies of stretch responses in gastrocnemius muscles were delayed in stooped subjects, but the onset of LL responses was markedly reduced. Amplitudes of both ML and LL responses were reduced in stooped subjects. Prestimulus COG and, to a lesser extent, CFP were shifted forwards in stooped subjects. Posterior COG displacement and the rate of backward CFP displacement were diminished in stooped subjects. Voluntary postural corrections were unchanged while standing stooped. These results indicate that some postural abnormalities of patients with Parkinson's disease (most notably the reduced LL responses) can be reproduced in healthy subjects mimicking a stooped parkinsonian posture. Other postural abnormalities (most notably the increased ML responses and insufficient voluntary responses) did not appear in stooped controls and may contribute to balance impairment in Parkinson's disease.

Influence of electrode site and size on variability of magnetic evoked potentials

Successive magnetic evoked potentials (MEPs) concern varying motor neurons. We investigated whether this MEP-specific source of variability depends on electrode site and size. Amplitude variability (standard deviation) was largest over the center of the hypothenar muscles. Latencies were longer at distal and proximal sites than at the center site. Large electrodes (10 cm2) did not decrease this source of amplitude variability compared with EEG electrodes, in contrast to other sources of variability.

Changing central nervous system control following intercostal nerve transfer

OBJECT

The goal of this study was to find which central nervous system (CNS) pathways are involved in volitional control over reinnervated biceps or pectoral muscles.

METHODS

Intercostal nerves (ICNs) were coapted to the musculocutaneous nerve (MCN) or the medial pectoral nerve (MPN) in 23 patients with root avulsions of the brachial plexus to restore biceps or pectoral muscle function. The facilitatory effects of respiration and voluntary contraction on cortical motor-evoked potentials of biceps or pectoral muscles were used to study CNS control over the reinnervated muscles. The time course of the facilitatory effect of respiration and voluntary contraction differed significantly. In the end stage of nerve regeneration, the facilitatory effect of voluntary contraction was significantly larger than that of respiration, indicating that the CNS control network over the muscle comes to resemble that of the recipient nerve (MCN or MPN) rather than that of the donor nerve (ICN).

CONCLUSIONS

The strengthening of previously subthreshold synaptic connections in a CNS network connecting ICN to MCN or MPN neurons may underlie changing excitability.

Acquired slow-channel syndrome: a form of myasthenia gravis with prolonged open time of the acetylcholine receptor channel

A 32-year-old female presented with a 2-year history of fluctuating generalized weakness including extraocular, bulbar, and limb muscles, suggesting myasthenia gravis, but with poor response to pyridostigmine and unusual electromyographic findings. After rest, power increased on repeated maximal contractions, followed by progressive weakness. There were decremental responses at low-frequency stimulation, but incremental responses at high frequencies, and single stimuli evoked repetitive compound muscle action potentials. Plasmapheresis was ineffective. In a conventional assay, antibodies against acetylcholine receptors (AChRs) were borderline. However, in an assay using cells expressing mainly adult-type human AChRs, the patient's serum was positive. Thymectomy revealed a hyperplastic thymus. An intercostal muscle specimen revealed small miniature end-plate potentials, 0.22+/-0.02 mV instead of 0.56+/-0.05 mV in controls. The number of 125I-alpha-bungarotoxin binding sites was normal. The decay time constant of end-plate potentials was increased from 5.3+/-0.6 msec in controls to 23+/-3.6 msec in the patient. Ultrastructurally, there was no destruction of the end plate. Transfer of the patient's plasma to mice in vivo produced similar physiological changes in their diaphragms. We conclude that the patient has an immune-mediated disorder, in which an antibody specific to the adult form of the AChRs alters the channel properties, reducing total current and slowing the closure. We propose the name "acquired slow-channel syndrome" for this variant of myasthenia gravis.

Prolonged coma and severely attenuated EEG after a single seizure

A 63-year-old woman presented with a comatose state after a fall. Results of cranial computed tomography (CT) and magnetic resonance imaging (MRI) scans were normal. An EEG recorded 5 h after admission was very severely attenuated and slowed. Consciousness and EEG were improved the next day. No cause was detected initially. After sleep deprivation, the patient had a generalized seizure followed by a similar coma and EEG. Even a single seizure may cause a prolonged coma with a very severely attenuated and slowed EEG.