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In normal rat tail nerves the effect of temperature and ischemia on the response to long-term high frequency stimulation (HFS) (143 Hz) was studied. The effect of temperature was studied in two consecutive tests at 14 degrees C and 35 degrees C. Prior to the HFS the peak-to-peak amplitude (PP-amp) of the compound nerve action potential was 139 +/- 20 microV (mean +/- SD) and 127 +/- 37 microV at 35 degrees C and 14 degrees C, respectively (NS). After 15 min of HFS the PP-amp was reduced to 45.3 +/- 20.5% of baseline level at 14 degrees C as compared with 80.8 +/- 10.2% at 35 degrees C (p < 0.001). Applying ischemia to the rat tail, an additional fall of the PP-amp was seen after 15-20 min of HFS at both low (20 Hz) and high (143 Hz) stimulation frequencies. In conclusion, ischemia and cooling result in an impaired ability to transmit high frequency impulses.

We examined occurrence of carpal tunnel syndrome in 48 patients with Down syndrome clinically and electrophysiologically. In the median nerve the distal latency to the abductor pollicis brevis muscle and the distal sensory nerve conduction velocity to digit II and III were recorded. As a control, we examined the ulner nerve. In the median nerve, a distal latency above 4.3 msec and sensory nerve conduction velocity below 50 m/sec were considered indicative of Carpal tunnel syndrome. Twenty seven patients (56%) had normal findings, 13 (27%) had both prolonged distal motor latency and reduced distal sensory nerve conduction velocity, and 8 patients (17%) had one of these signs, a much higher frequency than expected. Results show that prevalence of electrophysiological carpal tunnel syndrome is high in individuals with Down syndrome.

A prevalence study of epilepsy in patients with Down syndrome (n = 85) in three age-groups (14-16 years, 23-29 years, 50-60 years) was conducted in the county of Aarhus, Denmark. Seventy-two patients (85%) participated. An interview and a neurological examination were performed. An EEG was recorded in 50 patients. Twelve patients (17%) had epilepsy. ILAE-1981-classification: two with partial seizures, seven with primary generalized and three with unclassifiable generalized seizures. Two patients with epilepsy had a normal EEG and 13 patients without epilepsy had an abnormal EEG.

The effect of insulin on the response to long-term high-frequency stimulation (HFS = 143 Hz for 20 min) was studied in mixed tail nerves of acute streptozotocin-induced diabetic rats. In consecutive tests, untreated diabetic rats showed a significant decrease in nerve conduction velocity (NCV) and peak-to-peak amplitude (P-Pamp) and the depression of the P-Pamp during HFS was augmented. In contrast, NCV and P-Pamp in the insulin-treated rats were unchanged from the prediabetic state, but the depression of the P-Pamp during HFS reached the same degree as in untreated rats. This implies that although insulin treatment of acute experimental diabetes is able to preserve a normal NCV and P-Pamp in the resting state, it is unable to preserve normal nerve function under stress produced by HFS. Monitoring of the axon membrane functional capacity may have clinical implications in the control of peripheral neuropathies.

The effect of long-term (40 min) high frequency stimulation (143 Hz) of sensory-motor tail nerves was studied in normal and in streptozotocin-diabetic rats. The study comprised a 6-week period, repeating the test at 2-week intervals. In the initial (prediabetic) study, single experiments showed a mild depression of the peak-to-peak amplitude during high frequency stimulation, which reversed completely during a subsequent rest period. In normal rats, the amplitude depression was unchanged in repeated tests over a 6-week period. Diabetic rats showed a greater amplitude depression during high frequency stimulation. The difference was statistically significant after 2 weeks, but showed no further change at subsequent tests. The greater decrease in the amplitude in diabetic rats may reflect a depression of the axon membrane function, which may be the functional correlate to the inhibition of the Na/K ATPase activity in diabetes, described by others. Monitoring of the axon membrane functional capacity may have clinical implications in the control of peripheral neuropathies.

We report results from 120 (25- to 34-year-old) participants in a neuropathy substudy of subjects with insulin-dependent diabetes mellitus (IDDM) taking part in a cohort follow-up study. Diabetic neuropathy was evaluated by quantitative sensory testing, nerve conduction studies, and clinical examination. Mean quantitative sensory thresholds differed significantly by clinical category of abnormal sensation and ankle reflex activity. Mean sural and peroneal amplitudes and conduction velocities were also significantly lower for subjects classified as having abnormal ankle reflex activity. Modeling potential correlates in logistic analyses showed glycemic control, triglyceride levels, and hypertension status to be independently associated with clinically overt neuropathy. Similar lipid and hemodynamic parameters were associated with abnormality by any single assessment method used to define neuropathy. Although follow-up is needed to resolve the best assessment methods for determining neuropathy, these results suggest that good glycemic control as well as control of blood pressure and lipids is advisible.

We studied the effects of prolonged high-frequency stimulation in normal rat tail nerves. Nerves could conduct impulses at 50 Hz for 5 hours without complete conduction block. However, over time there was a significant decrease in amplitude and increase in latency of the compound nerve action potential (CNAP), which gradually became desynchronized. Changes were influenced by the frequency of stimulation. When stimulating over 30 minutes at 20, 50, 100, and 143 Hz the amplitude decreased to 89%, 79%, 67%, and 65% of baseline values, respectively, whereas the latency was only significantly increased at 100 and 143 Hz. All changes were reversible upon cessation of stimulation. Changes could not be attributed to focal block at the site of stimulation. These changes in the CNAP may reflect functional limitations of the axon membrane which may have pathophysiological implications for the study of neuropathies and focal nerve lesions.

Hemifacial spasm is usually an isolated symptom resulting from facial nerve root compression. Three patients had, in addition, tinnitus, hearing loss, facial sensory loss, diminished gag reflex, dysphagia, and dysarthria. Acoustic reflexes were abnormal, and facial nerve conduction studies showed evidence of ephaptic transmission and ectopic excitation. Brain CT and metrizamide cisternography were normal. Surgical exploration showed compression of cranial nerve roots by posterior inferior cerebellar artery branches. After decompression, symptoms abated, and electrical signs of hemifacial spasm disappeared. Vascular compression of nerve roots in the cerebellopontine recess may cause multiple cranial neuropathy.

Accurate measurements of the vibration amplitude were Fig. 7. Reproducibility of double determinations of the vibratory perception threshold (log V2) in normal persons and uraemic patients. PH=pulp, big toe; MM=medial malleolus. Axes show read values in volts transformed into a log V2 scale. Full and strippled lines indicate mean and 95% confidence limits of expected variation (ref. Table II). Made possible by a piezo-electric transducer (accelerometer). With constant voltage to the vibrator slight compression of the tactor against the skin produced an increase in amplitude, similar to that seen with compression against a rubber diaphragm. Further compression had a variable effect on the vibration amplitude, depending on the nature of the underlying tissue (bone, soft tissue). An exact calibration of the vibration stimulus strength therefore appears impossible, and a comparison of the acuity of vibratory perception is invalidated by the different viscous-elastic protion amplitude and the square of the voltage, as seen for vibrations in air, was also demonstrable between independent measurements of the vibratory perception threshold (VPT) in the two terms. The intra- and interindividual variations in terms of the amplitude and the square of the voltage were of the same order. On a logarithmic scale the reproducibility of VPT was independent of the threshold stimulus strength.

Rhythmic myoclonus in an arm began abruptly following an injury and persisted continuously for six years. Topographical EMG showed abnormal activity confined to muscles innervated by the axillary and radial nerves from the posterior cord of the brachial plexus. Abduction of the arm above horizontal level stopped myoclonus and EMG discharges. EEG was normal. It is suggested that the myoclonus was caused by mechanical irritation of the posterior cord of the brachial plexus.

Pathologic and pathophysiologic findings in hemifacial spasm are reviewed in connection with recent theoretical and experimental studies of ectopic/ephaptic excitation. The intracranial segment of the normal facial nerve is ensheathed by an arachnoid membrane only and shows no fascicular organization. In hemifacial spasm, this segment shows signs of demyelination. Several electrical phenomena relating to ectopic excitation, ephaptic transmission between facial nerve fibers, and autoexcitation can be reproduced in clinical electrophysiologic studies of hemifacial spasm. These abnormalities gradually disappear after facial nerve decompression in the cerebellopontine recess. It is concluded that the normal facial nerve is vulnerable to minor compression, the primary pathophysiologic mechanism in hemifacial spasm is ectopic/ephaptic excitation due to compression and demyelination of the intracranial segment of the facial nerve, and the facial nerve in hemifacial spasm is a useful model for the study of ephaptic transmission, which has provided new information about the resolution of abnormal electrical events after decompression.

The safety of a blood lead concentration of 70 microgram/100 ml as a hygienic border value with regard to development of lead neuropathy was tested in 95 employees, who had been exposed occupationally to lead for more than 9 years. The blood lead concentration was slightly above the border value in nine subjects, while the erythrocyte-Zn-protoporphyrin concentration was significantly elevated in 81 subjects, indicating an abnormal accumulation of metabolically active lead. None of the group showed clinical evidence of peripheral neuropathy, and the vibratory perception thresholds as well as motor conduction data from the median, radial, and common peroneal nerves were normal, as compared with an age-matched control group of 21 non-exposed normal subjects. The amplitude ratio between proximally and distally evoked muscle action potentials was normal in all lead-exposed subjects. These findings suggest that lead-exposed subjects are well protected against peripheral lead neuropathy, when blood lead levels are kept below the hygienic border value.

The natural history of diabetic neuropathy and its risk factors are not well understood, apart from the recognition that prevalence increases with duration and, in many studies, degree of glycemia. The role of potential risk factors was therefore evaluated in a cross-sectional analysis from the baseline examination of the Pittsburgh Epidemiology of Diabetes Complications Study. We present results from the first 400 subjects seen at baseline examination. Neuropathy was determined by a trained internist with a standardized examination and was defined as the presence of at least two of three criteria: abnormal sensory or motor signs, symptoms consistent with neuropathy, and decreased tendon reflexes. The prevalence of neuropathy in this cohort was 34% (18%, 18-29 yr old, 58% greater than or equal to 30 yr old) with no difference by sex. By focusing on subjects greater than or equal to 18 yr old, all significant univariate variables (e.g., duration, glycosylated hemoglobin [HbA1]) were analyzed in 3 multiple logistic regression models: all subjects greater than or equal to 18 yr old and separating the same subjects into two groups based on age (18-29 and greater than or equal to 30 yr). Duration, HbA1, smoking status, and high-density lipoprotein cholesterol were found to be associated with neuropathy in the models for the greater than or equal to 18-yr-old group and the greater than or equal to 30-yr-old group. In the 18- to 29-yr-old group, duration, HbA1, and hypertension status were found to be significantly associated with neuropathy.(ABSTRACT TRUNCATED AT 250 WORDS)

We report two unusual features of a 37-year-old man with palatal myoclonus. Although the rhythmic palatal contractions of this disorder are usually incessant, he was able to voluntarily suppress them for minutes. During periods of suppression, specific voluntary actions using the left side of his body, but not the right, reliably elicited single contractions. Various stimuli to the left side of his body, but not the right, also produced single contractions. Stimulation of trigeminal nerve branches evoked palatal electromyographic discharge after 55 ms. Microsurgical vascular decompression of posterior fossa neural structures led to improvement of several of the patient's symptoms and signs.

The blink reflex was examined in 62 patients with hemifacial spasm. The latency and amplitude of the early (R-1) component of the orbicularis oculi response were increased as compared with the contralateral, unaffected side and controls, p less than 0.001. On the affected side, all patients showed a synkinetic response in the mental muscle, and after-activity and late-activity was observed after the reflex response. These findings indicate lateral spread of impulses to other fibers in the facial nerve (ephaptic transmission) and autoexcitation of fibers. The increased latency indicates a slowing of the nerve conduction in the facial nerve, in keeping with pathologic findings of focal demyelination.

We studied 62 patients with hemifacial spasm to test the presence of ephaptic transmission and ectopic excitation. The zygomatic and mandibular branches of the facial nerve were stimulated separately, recording simultaneously from the orbicularis oculi and mental muscles. Antidromic impulses were transmitted bidirectionally between the two branches. Transmission took place in a fraction of slow conducting motor nerve fibers. After-activity and late-activity were recorded as single potentials or trains, suggesting autoexcitation of fibers. The interspike frequency was 250 to 350 Hz. Hyperventilation produced synchronous clonic-tonic activity, suggesting ectopic excitation caused by hypocalcemia. Ectopic excitation and ephaptic transmission are important pathophysiologic factors in hemifacial spasm.

Neuromuscular transmission and the staircase phenomenon in the adductor pollicis muscle were studied in six patients with myasthenia gravis before and 24 hours after single plasma exchanges given in short series over one to four weeks. An improvement in neuromuscular transmission was observed in all patients but one within 24 hours, suggesting that an immunological block of receptor sites is reversible or that acetylcholine receptors are rapidly resynthesized. In addition to a neuromuscular transmission defect, two of the patients also showed evidence of impaired excitation-contraction coupling with a negative staircase phenomenon and reduced posttetanic twitch potentiation. This condition became normal after plasma exchange, which may indicate that a reversible immunological impairment of the sarcoplasmic reticulum was present. Improvement lasted up to several months. The anti-acetylcholine receptor antibody titers were lowered in response to single plasma exchanges, but actual titer levels showed poor correlation with clinical and electrophysiological changes.

In 1979 Wiechers and Johnson described ten patients with diffuse abnormal insertional activity on EMG examination in the absence of neuromuscular disease. We present a family group with identical findings. The propositus is a 53-year-old woman who presented with back pain. EMG studies revealed trains of positive sharp waves with needle movement in all muscles studied. Nerve conduction studies, radiographs, and laboratory studies were all unremarkable. We recruited eight additional family members who underwent a screening EMG of five muscles. Four patients had trains of positive sharp waves present in all five muscles. To our knowledge, this is the first report confirming the findings of Wiechers and Johnson. We concur with them that the abnormality appears to be genetically transmitted in an autosomal dominant pattern. Although without clinical significance, it is important for electromyographers to be aware of this entity so as not to mistakenly ascribe serious neuromuscular disease to these patients.

The prevalence of lead induced subjective symptoms was evaluated by a standardised questionnaire in a group of 96 workers employed between nine and 45 years in a secondary lead smelting works. A control group of 96 non-lead exposed subjects, matched for age and sex, were chosen from the Glostrup population study. Blood lead concentrations were in excess of 60 micrograms/100 ml in about 30% of the lead workers. Zinc protoporphyrin levels were found to be higher than 500 mumol/Hb in nearly 18% of the lead workers. The prevalence of fatigue, headache, sleep disturbance, and digestive symptoms (constipation and colic) were not higher in the lead exposed group. The body weight showed no significant difference in the two groups. Nervousness was four times more frequent in the control group. The results indicate that subjective symptoms are useless as indicators of incipient lead poisoning.

We studied 59 patients with hemifacial spasm before decompression of the facial nerve in the cerebellopontine angle. Fifty-three patients were reexamined 1 week later, and 30 patients after 2 to 8 months. Within 1 week, ephaptic transmission disappeared in 23% and changed from bidirectional to unidirectional in 45%. After-discharges disappeared in 64% and were mild in 34%. Synkinesis after supraorbital nerve stimulation disappeared in 53%, and the blink reflex amplitude became normal. After 2 to 8 months, ephaptic transmission was abolished in 73% and unidirectional in 17%. After-discharges and synkinesis disappeared in 90%, and the latency of the blink reflex decreased. It is concluded that decompression stops ectopic/ ephaptic excitation due to decrease in the interstitial resistance, and enables remyelination.

Absolute thresholds for sensation of a 100-Hz mechanical sine-wave stimulus applied with an electromagnetic vibrator were measured on eight stimulus points in the glabrous skin of the human hand in normal subjects and in patients with verified, circumscribed unilateral suprathalamic lesions of the hemispheres. In both groups, the threshold on the hypothenar eminence was lower than the threshold on the third digit, which in turn had a lower threshold than the fifth digit. For each locus of stimulation, there was a rectilinear regression of threshold with age. Women had lower thresholds than men. The spatial distribution of the thresholds might suggest that Pacinian corpuscles are the receptors activated by threshold stimulation. Unilateral suprathalamic lesions of the hemisphere did not cause any elevation of vibratory thresholds.

Interfascicular neurolysis of the ulnar nerve at the elbow was performed in nine consecutive patients with moderate to severe ulnar palsy. Sensory and motor conduction velocities were determined before and up to six times after the operation, and a follow-up period of three years or more in all but two patients. None of the patients recovered after the operation, and all developed severe and sometimes persistent paraesthesiae. Electrophysiologically there was no evidence of improvement immediately following the operation. On the contrary in some patients there were changes suggesting deterioration. At the final investigation most electrophysiological parameters were still abnormal. The only significant change was an increase in the amplitude of sensory action potentials at the wrist and just below the elbow. Only one patient showed a more synchronised sensory potential after operation. It is our conclusion that interfascicular neurolysis of the ulnar nerve should be abandoned.

Sensory potentials recorded at two to four sites along the median nerve during ischemia in normal subjects were analyzed with respect to the effects of conduction distance and duration of ischemia. Latency increased rectilinearly with the squared duration of ischemia in minutes, and the rate of the latency increase along the nerve was a power of the preischemic latency, a measure of conduction distance. This finding indicates a temporospatial slowing of sensory conduction velocity of ischemic nerves. Calculated latencies fitted with measured values within +/- 0.2 msec in 95% of 385 recordings. The compound potential amplitude decreased exponentially with the concomitant increase in temporal dispersion, which was the major cause for the decrease in amplitude during the first 20 minutes of ischemia. The nerve conduction pattern during ischemia may serve as a model for biochemical axon membrane dysfunction, a possible factor in the pathogenesis of toxic-metabolic neuropathies.

We studied three patients with paramyotonia congenita and three with myotonia congenita. At room temperature myotonic bursts in the EMG were similar in the two disorders. After repetitive maximal contractions, patients with paramyotonia showed decreasing recruitment pattern and increasing after-activity, while myotonia patients showed unchanged recruitment pattern, and after-activity tended to decrease, but these differences were not consistent. However, immersion of the hand in ice water for 10 minutes caused unambiguous differences: In paramyotonia, the myotonic discharges disappeared and the muscles went into stiff, electrically silent, contracture; in myotonia patients, the myotonic activity increased and muscle contraction patterns remained normal.

The need for a standardized and valid means of assessing diabetic neuropathy has been increasingly recognized. To identify potential components of such an assessment, interobserver variation (neurologist and internist) of a standard neurologic examination and the comparability of this examination with vibratory and thermal sensitivity testing was studied. The study population comprised the first 100 participants in a neuropathy substudy of 25- to 34-yr-old subjects with insulin-dependent diabetes mellitus taking part in a cohort follow-up study. Symptoms of dysesthesias, paresthesias, and burning, aching, or stabbing pain revealed good interobserver agreement. Signs of neuropathy, more prevalent in the great toe than index finger, showed poor interobserver agreement for vibration, but fair interobserver agreement for touch and pinprick. Mean quantitative sensory thresholds differed significantly by clinical category of abnormal vibratory and pinprick sensations. Threshold testing showed twice the prevalence of abnormality compared with clinical examination. It is concluded that components of the clinical examination can be identified that, along with quantitative sensory-threshold testing, may provide a satisfactory core assessment for use both in epidemiologic studies and incorporation into more in-depth protocols required for clinical research and practice. The clinical relevance of the greater prevalence of abnormalities on threshold testing will be established by long-term follow-up.

Sensory thresholds for vibrations and electrical shocks and the sensory nerve conduction velocity (median nerve) were measured during 30 minutes of induced limb ischaemia in 10 normal subjects and 15 patients with chronic hepatic failure. Sensory action potentials were recorded simultaneously at the wrist and elbow. Seven patients (group A) had a normal perception time for vibrations. As in normal subjects, the potential amplitude decreased from the onset of ischaemia, more pronounced at the elbow than at the wrist, and the conduction velocity became reduced more rapidly in the wrist-elbow than the first digit-wrist segment, indicating impulse propagation with decrement. Eight patients (group B) had a markedly prolonged perception time for vibrations. The reduction of potential amplitude and conduction velocity was considerably delayed, and the impulse propagation showed no evidence of decrement for 20-25 minutes of ischaemia. A rise of the threshold for electrical shocks was absent or very delayed. As in the two other groups, the rise was abrupt and occurred at the moment when the potential below the occluding cuff (elbow) was extinct. In both groups of patients there was an increasing temporal dispersion of action potentials and in patient group A a desynchronization of the late phase of the potential took place early in the course of ischaemia. Differences between groups A and B could not be predicted from the pre-ischaemic nerve conduction data.