Saccadic eye movements in hyperekplexia

Hyperekplexia is an autosomal dominant disorder characterized by excessive startle responses followed by a temporary generalized stiffness. The startle response is generated in the medial bulbopontine reticular formation in the lower brainstem. The pulse generator of horizontal saccadic eye movements is localized in the pontine paramedian reticular formation. Measurements of horizontal visually evoked random saccades, antisaccades, and saccades toward remembered targets were performed in seven patients with familial hyperekplexia and seven health age-matched controls. The peak velocity of all three kinds of saccades was reduced (p < 0.0001) compared with that of controls. Latencies were marginally longer in the patient group (p = 0.0486). Saccadic gains did not differ between patients and controls. The ability to make antisaccades, saccades toward remembered targets, and the ability to suppress reflex saccades are similar in patients and controls. These data suggest that the origin of the excessive startle response is probably more due to a different modulation in the brainstem than to altered cortical influence.

[Startle disease: growing rigid with fear]

Hyperekplexia or startle disease was diagnosed in four patients, a girl of 14 months, two men of 45 and 61 years old, and a woman of 56 years old. This is an autosomal dominant inherited disorder, characterized by excessive startle reactions, notably to auditory stimuli. The four patients belong to a Dutch family in which two forms of the disorder occur. The first one is the major form, in which the startle reaction is followed by a temporary generalized stiffening of the body. These patients experience continuous generalized stiffness from birth to about the second year of life. They fall down frequently. The other is the minor form, characterized by an excessive startle reaction only.

Long latency postural reflexes are under supraspinal dopaminergic control

Scaling of posturally stabilizing long latency (LL) reflexes in tibialis anterior muscles induced by "toe-up" rotational perturbations is abnormal in standing patients with Parkinson's disease. To investigate the contribution of dopaminergic pathways to abnormal scaling, we studied LL reflexes in 22 patients with selective hypodopaminergic syndromes: 10 psychiatric patients taking chronic neuroleptic medication (7 with mild parkinsonism), 8 patients with young-onset Parkinson's disease, and 4 patients with MPTP-induced parkinsonism. Results were compared with those of 10 healthy controls. Stimuli consisted of (a) 10 serial (predictable) perturbations of 4 degrees amplitude, (b) 10 serial (predictable) perturbations of 10 degrees amplitude, and (c) 20 randomly mixed (unpredictable) perturbations of either 4 or 10 degrees amplitude. In normal subjects, LL reflex amplitudes were adapted to match predictable variations in stimulus size, whereas under unpredictable conditions a "default" response emerged that anticipated the 10 degrees perturbation. LL reflex scaling under predictable conditions was intact in patients with neuroleptic-induced parkinsonism and young-onset Parkinson's disease, but the large default LL response under unpredictable conditions was absent. In patients with MPTP-induced parkinsonism, LL reflex scaling was absent during both predictable and unpredictable conditions. We conclude that abnormal scaling of posturally stabilizing LL reflexes is related to decreased supraspinal dopaminergic influence.

Hypokinesia in Parkinson's disease: influence of age, disease severity, and disease duration

The aim of this cross-sectional study was to compare the role of aging in measures reflecting diurnal activity and immobility in 60 parkinsonian patients with predominant features of hypokinesia and rigidity and 100 healthy subjects aged 50 to 98 years. In the patients, we also studied the relation between disease duration and subjective and objective measures of disease severity. Motor activity was recorded during 5 successive days at home with a wrist-worn activity monitor. For each subject, two mean measures reflecting the diurnal activity level and the relative proportion of activity and immobility were calculated. Diurnal measures of activity revealed in both groups a prominent absolute reduction of activity and an increase of the time spent without movement ("immobility") with advancing age. Parkinsonian patients showed significantly lower values for both motor-activity measures than did the healthy subjects. The rate of the age-related decline of both diurnal activity measures in both groups, however, is comparable. Disease duration showed no relation with subjective and objective measures reflecting disease severity. This study shows that if care is taken to control for disease severity, the rate of the age-related decline of measures reflecting diurnal activity and immobility is similar in both groups. The lack of relation between disease duration and subjective and objective measures of disease severity suggests that the rate of progression of Parkinson's disease can be reliably studied only by means of longitudinal studies.

Postural reflexes in Parkinson's disease during 'resist' and 'yield' tasks

Postural reflexes in leg muscles appear to be set at a fixed gain in Parkinson's disease. To further investigate gain adaptation, we instructed 16 patients with idiopathic Parkinson's disease (studied during the 'off' phase) and 21 healthy controls to either 'resist' or 'yield' in response to 20 serial 4 degrees toe-up perturbations of a supporting platform on which they were standing. We bilaterally recorded destabilizing medium latency (ML) reflexes from stretched gastrocnemius muscles and corrective long latency (LL) reflexes from shortened tibialis anterior muscles. We also assessed changes in center of foot pressure (CFP) and center of gravity (COG). During the 'resist' condition, patients had increased destabilizing ML reflexes, decreased corrective LL reflexes, increased backward displacement of the COG and increased forward (destabilizing) displacement of the CFP. In addition, the backward (corrective) displacement of CFP between 150 and 250 ms was delayed. During the 'yield' condition, reflex gains were modified in controls: LL reflexes were markedly attenuated, whereas ML reflexes were markedly increased. Although this reflex pattern resembled the 'resist' condition in patients, it was not associated with an increased forward displacement of the CFP, but only with a strongly delayed backward displacement of CFP which started after 150 ms. In patients, ML reflex amplitudes remained unchanged during the 'yield' condition, suggesting a fixed reflex gain. LL reflex amplitudes were reduced in patients but significantly less compared to controls, which again suggests a fixed reflex gain. This 'inflexibility' of postural reflexes was reflected by the CFP which showed much smaller changes between 0 and 250 ms in patients than controls. These results could not be ascribed to a different ability to yield because posterior displacement of the COG was identical in patients and controls during the 'yield' condition. We conclude that (1) patients with Parkinson's disease have abnormal and 'inflexible' postural reflexes, associated with delayed corrective movements about the ankle joint and increased body sway; and (2) the increased forward displacement of the CFP in patients likely reflects high stiffness in ankle muscles because reflex changes in controls only affected the CFP more than 150 ms after the perturbation. The increased muscle stiffness and inflexibility of postural reflexes in Parkinson's disease may contribute to balance impairment in daily life.

Determinants of vibration perception thresholds in IDDM and NIDDM patients

The relative influence of diabetes mellitus-related and physiological factors on vibration perception thresholds was assessed in 353 patients in a hospital-based setting (173 insulin-dependent and 180 non-insulin dependent patients, aged 51.1 +/- 15.9 years) and 80 healthy controls (aged 43.3 +/- 15.2 years) employing a Biothesiometer. Vibration perception thresholds were bilaterally measured at the thumbs, medial malleoli and halluces. Sixty (17.0%) older patients had off-scale thresholds (> 50 V). As no systematic side differences were found, values of contralateral sites were averaged. Considering the effects of age, height, gender and skin temperature in controls, age accounted for 46.7 and 52.2% threshold variance at the ankles and halluces, respectively, while height explained 5.1 and 5.1%, respectively. At the thumbs, only age was of relevance. Age relationships with vibration thresholds in health did not differ from published reports at any site. In the patient group, influences of age, height, gender, skin temperature, years from diagnosis, HbAlc, serum creatinine, drop in systolic blood pressure on standing, and ankle/arm blood pressure indices were assessed for each type of diabetes. For both types, age and height again had relevant effects at the lower extremities as did age and gender at the thumbs. Skin temperature was only marginally significant at the halluces of NIDDM patients. Of the disease-related factors, HbAlc had the strongest effect: for both IDDM and NIDDM higher levels were associated with lower vibration sensitivity. Increasing disease duration led to significantly higher thresholds in IDDM patients.(ABSTRACT TRUNCATED AT 250 WORDS)

CMAP variability as a function of electrode site and size

The site of the recording electrode influences the amplitude of the compound muscle action potential (CMAP) and its variation over a length of nerve. The effects of large electrodes on this source of intraindividual variability were assessed. Right median nerves of 20 healthy subjects were studied, and recordings made at three sites (at 1-cm intervals) using five electrode sizes (0.01, 1, 2, 4, and 10 cm2). Site-induced variability was defined as the standard deviation (SDi) and coefficient of variation (CVi) of the measurements of the three sites. Site induced variability of all parameters (latency, duration, amplitude, area, MNCV, and the percentile changes of duration, amplitude, and area over the forearm) decreased significantly with electrode size. Decreases were most pronounced for amplitude and area: CVi fell from 29% and 30% (0.01-cm2 electrode) to 10% and 8% (10 cm2). It is argued that large electrodes record activity of more motor units than small electrodes, and that their measurement fields overlap to a greater extent. The use of large electrodes is recommended in order to reduce site-induced CMAP variability.

Influence of recording site on CMAP amplitude on its variation over a length of nerve

The distinctions between blocking, abnormal temporal dispersion, and normal conduction require delineation of the normal change in amplitude of the compound muscle action potential (CMAP) over a length of nerve. Effects of the recording site on CMAP amplitude and on its variation were studied in median and ulnar nerves of 13 healthy subjects. CMAPs were recorded from three sites: halfway along the muscles and 1 cm distal and proximal. Elbow-wrist amplitude percentages (CMAP%) were calculated. CMAP amplitudes varied considerably between sites and subjects. Amplitudes were maximal at the middle site in only 16 of 26 nerves. The site of maximal amplitude could not be identified on the basis of thumb anatomy. CMAP% was not related to CMAP amplitude, and differed by up to 32% between adjacent sites. CMAP formation involves spatial factors (electrode site, limb position, and limb anatomy), temporal factors (dispersion), and their interaction, explaining why CMAP% can exceed 100%. The site of the recording electrode affects CMAP amplitude and CMAP% to clinically relevant degrees. Standardization of the recording site may improve reliability of CMAP% studies.

Clinically silent dysfunction of dorsal columns and dorsal spinocerebellar tracts in hereditary spastic paraparesis

Hereditary spastic paraparesis (HSP) is a neurodegenerative disorder, of which progressive spastic paraparesis is the clinical hallmark. Given the neuropathological evidence of degeneration of pyramidal tracts, dorsal columns, and dorsal spinocerebellar tracts, it is surprising that sensory symptoms are so indistinct compared to motor symptoms. We investigated the involvement of peripheral conduction and spinal proprioceptive pathways by nerve conduction studies, somatosensory evoked potentials of the median and tibial nerves, and quantitative assessment of the vibration perception thresholds of the hands and feet respectively in 32 patients suffering from HSP and healthy control groups. We did not find peripheral conduction abnormalities in HSP patients. Log-transformed vibration perception thresholds of the feet were abnormal in 13/32 HSP patients and in 0/64 controls (p < 0.00001), while tibial nerve somatosensory evoked potentials were abnormal in 20/32 patients and in 1/17 controls (p = 0.00001). The values for the upper extremities were within normal limits for nearly all subjects. In the HSP group, the neurophysiological disturbances did not correlate significantly with duration or severity of the disease, when age was controlled for, except for median nerve SSEP latency, which was affected by severity (p = 0.0072). We conclude that neurophysiological methods detected proprioceptive, subclinical abnormalities in several HSP patients, which may reflect degeneration of the dorsal columns, and/or dorsal spinocerebellar tracts. Since we found no correlation with several disease variables, the fact that not all HSP patients displayed these abnormalities may be caused by anatomical variations in proprioceptive pathways, rather than by phenotypical heterogeneity.

Altered attentional processing of background stimuli in Gilles de la Tourette syndrome: a study in auditory event-related potentials evoked in an oddball paradigm

In 24 adults and 29 children both with Gilles de la Tourette syndrome and in 24 control adults and 17 control children we studied auditory event-related potentials (ERP's) evoked in 2 different oddball paradigms: a passive listening paradigm (PLP) in which subjects had only to attend tones (260 standards, 40 deviants), followed by an active discrimination paradigm (ADP) in which subjects had to press a microswitch in response to the deviant tones. In the adult Tourette patients the PLP disclosed between 200-300 msec at all derivations (Fz, Cz, Pz, C3, C4, P3, P4) a significantly more negative activity than in the controls. In the Tourette children such a result was only found at Fz. In the ADP the differences between both adult groups disappeared, but the curves of the control children became now significantly more positive than those of the Tourette ones except at C3 and P3. Between 200-300 msec the curves of all 4 groups were significantly less negative in the ADP than in the PLP. This decrease in negativity was significantly larger in the adult Tourette patients than in the adult controls, but in the children groups the reverse occurred. It is hypothesized that the differences in amplitude between patients and controls and between both paradigms are due to differences in amplitude of an endogenous negative component overlapping the exogenous N100-N200 standard curve. Based on this hypothesis the results could suggest that one of the problems in Tourette syndrome is an increased attention to non-relevant stimuli.

Electrical brain activity in preterm infants at risk for intracranial hemorrhage

We studied the effect of preterm birth on electroencephalographic background activity in 20 infants < 32 weeks' gestation. Six infants developed periventricular-intraventricular hemorrhage during the study period. Four-channel 24-h cassette recordings were obtained on day 1, 3-5 and 7-9. For each of the 24-h recordings, the percentage of the time showing stage I (continuous activity), stage II (mixed activity) and stage III (discontinuous activity) epochs was calculated. In infants without periventricular-intraventricular hemorrhage, a positive linear relationship between gestational age and continuous activity and a negative linear relationship between gestational age and discontinuous activity existed in the first day recordings; in infants with periventricular-intraventricular hemorrhage, such relationships were not found. To determine if the changes in continuous and discontinuous activities during the first week of extrauterine life were different from the expected changes during a corresponding time in utero, we calculated the expected amounts of stage I and III changes for each infant. The actual changes were not significantly different from the expected values in both study groups. However, during the onset and/or extension of periventricular-intraventricular hemorrhage, depression of the electroencephalographic background activity was found.

Medium latency stretch reflexes in young-onset Parkinson's disease and MPTP-induced parkinsonism

It is still unclear why components of the phasic stretch reflex are increased in Parkinson's disease (PD). To study the role of aging, we assessed medium latency (ML) stretch reflexes in 19 Parkinson patients (8 with young-onset PD, 11 with late-onset PD) and 23 normal subjects (10 young, 13 old). To assess the contribution of supraspinal dopaminergic influences, we also studied 5 young parkinsonian patients with a selective central dopamine deficiency induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). ML responses were recorded from the medial gastrocnemius muscle which was stretched by 4 degrees toe-up rotations of a platform upon which subjects were standing. ML responses were significantly enhanced in late-onset patients compared with older controls. In contrast, ML responses did not differ between young-onset patients and young controls. This observation could be attributed to the significantly different influence of age on ML-amplitudes in patients and controls. Thus, ML-amplitudes declined with age in controls, whereas they increased with age in PD possibly because older patients were more severely affected than younger patients. Thus, the difference between young-onset and late-onset PD seems to be related to the opposite effects of increasing age and disease severity in patients and controls. ML-amplitudes did not differ between patients with MPTP-induced parkinsonism, patients with young-onset PD and controls, suggesting that supraspinal dopaminergic systems are not critically involved in control of ML responses. This result also indicates that the severity effect in PD may be related to disruption of non-dopaminergic pathways which occurs in late-onset, but not young-onset patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of supine blood pressure on interpretation of standing up test in 500 patients with diabetes mellitus

The relationship between fall in blood pressure (BP) on standing and supine BP before standing up was studied in 75 healthy controls and in 500 patients with diabetes mellitus (DM) using conventional BP measurements. The influences of physiological (sex, age, height) and DM-related factors (type, duration, HbA1c-level, use of insulin, oral antidiabetic and anti-hypertensive medication) on BP-fall were assessed. The effects of using a fixed abnormality threshold and a new supine BP-related abnormality definition on interpretation of the test were determined. Highly significant relationships of BP-fall with supine BP were found in control and DM subjects. Slopes did not differ between these groups. Slopes for systolic BP-fall were steeper in type 1 than in type 2 DM patients. A forward stepwise regression procedure revealed that supine BP (explaining 24% of variance) and HbA1c (explaining 1%) had significant influences on systolic BP-fall. Diastolic supine BP explained 14% of diastolic BP-fall, age 3%, and sex 2%. Only supine BP was thus of practical relevance in explaining BP-fall. Taking supine BP into consideration affected test results: of 74 subjects with an abnormal conventional systolic BP-fall, 10 (13.5%) had been misclassified according to the new method, and 4 additional patients had been misclassified as normal. Classification changes were much larger for diastolic BP-fall (63% of conventionally abnormal results were reclassified as normal), but the range of diastolic BP is smaller than for systolic BP, meaning that the measurement error interferes with its clinical utility.(ABSTRACT TRUNCATED AT 250 WORDS)

Auditory information processing in sleep: habituation to repetitive stimuli

Habituation to evoked responses is obvious in waking but still controversial in sleep. Single-response analysis proves short-term habituation of auditory evoked potentials in stage 2 NREM sleep. The data are discussed referring to the two-system hypothesis of sensory processing in sleep and to DC instability and sleep maintenance mechanisms in stage 2 NREM. It is suggested that information processing might continue in sleep.

Variability of the main sequence

PURPOSE

This study investigated the relationship between amplitude and peak velocity of saccadic eye movements (the so-called main sequence) and the intra-individual variability of the main sequence.

METHODS

Saccadic amplitudes and peak velocities were measured twice in 58 healthy subjects with an infrared reflection technique.

RESULTS

Considerable intra-individual variability was found between the first and second recordings.

CONCLUSIONS

Intra-individual variability of saccadic peak velocity affects the interpretation of changes in repeated recordings of peak velocities, such as before and after medication is administered. Furthermore, considerable intra-individual variability decreases the probability that statistically significant differences between patients and control subjects can be detected, especially when groups are small. Calculating the intraclass correlation coefficient allows the number of subjects in comparative studies to be determined.

Sleep, excessive daytime sleepiness and fatigue in Parkinson's disease

The objective of this questionnaire-based survey was to evaluate the prevalence and causes of sleep disturbances in 90 nondepressive patients with Parkinson's disease (PD) and 71 age-matched healthy subjects. We also assessed the prevalence and characteristics of excessive daytime sleepiness (both groups) and excessive fatigue (PD patients). A high prevalence of sleep disturbances in PD patients was found; this is to a large extent probably the result of aging. As compared with controls, patients had a more severely disturbed sleep maintenance because of nycturia, pain, stiffness, and problems with turning in bed. The prevalence of excessive dreaming is similar in both groups, but altered dream experiences almost exclusively occurred in PD. Patients rated themselves more often to be morning-types than controls. This finding may account for the reported adaptation effects in experimental settings and the reduced REM latency in PD patients. The prevalence of daytime sleepiness was similar in both groups. Excessive daytime sleepiness showed a clear diurnal pattern with a peak in the early afternoon. As for excessive fatigue, the majority of the patients did not report a preferential time for this symptom. Our findings further argue against an association of fatigue with any circadian factor, and instead suggest a relationship with the motor deficits of PD.

Autonomic nervous system dysfunction in Parkinson's disease: relationships with age, medication, duration, and severity

Heart rate variability at rest, during deep breathing, or standing up and with the Valsalva manoeuvre did not differ significantly between 67 patients with idiopathic Parkinson's disease (PD) and 31 healthy age matched controls. Blood pressure (BP) responses to standing up and sustained handgrip revealed diminished autonomic function in the PD group. In a preliminary analysis of the PD group older age, anti-Parkinson medication and higher Hoehn and Yahr (HY) stages were each associated with poor autonomic responsiveness. Disease duration was only related to the systolic BP fall on standing up. Multiple stepwise regression analysis showed that older age explained most of the variance of heart rate variability (up to 36%), and the only significant PD related factor was the use of medication, which explained less than 7%. The HY stage accounted for 12.7% of the variance in the standing up BP test, and the use of medication explained 10.6% of the variance of the systolic BP change in the sustained hand grip test. The unmedicated PD subgroup (n = 33), who had mild disease of short duration, showed no evidence of autonomic dysfunction. Cardiovascular autonomic dysfunction in PD is mild, mainly affects blood pressure responses, and occurs only in advanced cases.

Quantitative assessment of parkinsonian patients by continuous wrist activity monitoring

The aim of this study was to examine the quantitative relationship between activity monitor measures and clinical scores of patients with Parkinson disease (PD). Motor activity was recorded continuously for 5 to 6 days at home with a wrist-worn activity monitor in 69 PD patients and 59 healthy controls. Clinical scores of the patients, age, and sex were submitted to multiple regression analysis to examine the quantitative relationship with measures reflecting the activity level and the proportion of activity and immobility over time. The patients' age, sex, and scores representing hypokinesia and rigidity and resting tremor explained approximately 50% of the variance of the motor activity measures. All motor activity measures declined with age; the rate of decline was similar for the patients and controls. Sex emerged as a predictor of the motor activity measures in the patients only. Male patients with PD showed significantly lower values for all motor activity measures than female patients and controls. Our results show that activity monitoring can be used as an objective quantitative assessment in PD.