Biomedical subjects
Publications and source records attributed to J G van Dijk.
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.
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.
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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.
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.
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.
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.
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.
In 3 patients, a 72-year-old man, a 62-year-old man and a 73-year-old woman with weakness of respectively the quadriceps femoris, the finger flexors and the pharyngeal muscles, the diagnosis of 'inclusion body myositis' was made. This is a rare, slowly progressive skeletal muscle disorder which is more common in men and after the age of fifty. The activity of serum creatine kinase is often 2-5 times the highest normal value. The electromyogram pattern is myopathic, but can also display neuropathic changes (exclusively). Inclusion body myositis is often misdiagnosed, which can lead to an inappropriate treatment or approach. A frozen muscle biopsy is needed to make cryostat sections for demonstration of myositis with rimmed vacuoles.
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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.
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.
We determined the diagnostic value of the EEG in young children with Angelman syndrome (AS) and Rett syndrome (RS). EEGs, recorded before 5 years of age, of 10 patients with AS, 10 with RS and 10 with mental retardation of other origin were studied blindly by two examiners for the presence of the following items: (A) 4-6 Hz rhythmic activity of over 200 microV; (B) 2-3 Hz frontal activity of 200-500 microV; (C) posterior spikes; (D) triphasic frontal waves; (E) central and/or centro-temporal spike-wave complexes; and (F) other epileptic discharges. Based on these items the EEGs were scored as AS (A-D); RS (E-F); or other. Examiners never made a mistake between AS and RS. One examiner labeled 6 of 10 AS cases correctly, the other 5; 4 (5) were characterized as 'other.' In RS cases 5 were labeled as 'other' by the first examiner and 3 by the second one. We conclude that EEG patterns of AS and RS are sufficiently different to help differentiate between AS and RS at a young age, which has a bearing on genetic counseling.
OBJECTIVE: Restoration of volitional control over elbow flexion has been demonstrated in patients who have undergone intercostal-to-musculocutaneous nerve transfer. We investigated the cortical area involved in the control over elbow flexion after intercostal-to-musculocutaneous nerve transfer. METHODS: Maps of magnetically excitable cortical areas of the affected arms of five patients were compared with maps of their healthy arms and maps of both arms of four healthy control subjects. The intercostal cortical area was also studied, requiring needle electromyography mapping (n = 1). RESULTS: The cortical areas of affected arms were smaller and less excitable than those of healthy arms. The locations of these areas could not be distinguished from that of the normal cortical biceps area but seemed to differ from that of the intercostal cortical area. CONCLUSION: The existence of a biceps-like cortical area related to the reinnervated muscle can be explained in two ways. Interneurons from the original biceps area might excite the cortical neurons controlling the intercostal muscles. Alternatively, corticospinal neurons of the original biceps area may project directly onto spinal intercostal motor neurons. Cerebral plasticity does occur in intercostal-to-musculocutaneous nerve transfers and may be crucial for their clinical success.
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.
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.
We studied the influence of dopaminergic medication on the duration of standing up, static posture and gait in five patients with Parkinson's disease (Hoehn and Yahr stage 1.5 to 3) and four healthy controls, using an optoelectronic camera system. Duration of standing up was prolonged in patients, while static posture and gait were largely unaffected. The prolonged duration of standing up was corrected by dopaminergic medication. These results suggest that an increased duration of standing up is a relatively early and dopa-sensitive abnormality in Parkinson's disease.
BACKGROUND: Patients with hereditary hyperekplexia have excessive startle responses that are accompanied by transient stiffness and also continuous stiffness in infancy. A point of mutation has been identified for the major form of hereditary hyperekplexia in the gene encoding the alpha 1 subunit of the glycine receptor. OBJECTIVE: To measure startle reflexes and autonomic responses in the major form of hereditary hyperekplexia in the original Dutch pedigree. DESIGN: Startle reflexes and autonomic responses were examined by administering 3 series of 20 auditory stimuli at intervals of 10 seconds (90 and 113 dB) and 60 seconds (113 dB). SETTING: The Department of Neurology and Clinical Neurophysiology at the Leiden University Hospital, Leiden, the Netherlands. SUBJECTS: Nine patients with the major form of hyperekplexia and 20 healthy controls. Of the 9 patients, 5 took medication. The patients are part of the Dutch hyperekplexia pedigree. MAIN OUTCOME MEASURES: Startle responses were quantified with latency periods and areas of electromyographic bursts of the orbicular muscle of the eye, sternocleidomastoid and biceps muscles, and the thenar muscles. Autonomic reactions were measured with psychogalvanic responses and beat to beat changes of blood pressure and heart rate. RESULTS: The electromyographic bursts of the 4 muscles occurred in similar order in both patients and controls. The onset of the latency periods in the patient group was significantly (P < .001) prolonged in patients who took medication. Without medication, patients had shorter latency periods of the sternocleidomastoid muscle (P = .003) than controls. The electromyographic burst occurred significantly more often in patients than in controls (P < .001). The areas of the bursts were significantly larger in patients than in controls (P < .001); the degree of habituation was significantly stronger in patients than in controls (P < .001). The amplitude of the psychogalvanic response was increased in hyperekplexia, and the degree of habituation was significantly weaker in patients than in controls. Blood pressure and heart rate did not clearly react in either group. CONCLUSIONS: Motor startle responses are stronger and show more habituation in patients with hereditary hyperekplexia than in controls. The excessive responses include the psychogalvanic response. Increased responses do not necessarily indicate decreased habituation in hyperekplexia.