Effect of ischemia and cooling on the response to high frequency stimulation in rat tail nerves.

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.

Occurrence of carpal tunnel syndrome among slaughterhouse workers.

OBJECTIVES: The aim of this study was to examine the risk of carpal tunnel syndrome (CTS) among workers with daily occupational exposure to high-force and high-velocity manual work. METHODS: The study was carried out retrospectively among a cohort of 1591 workers employed at a slaughterhouse or at a chemical factory; 1141 persons (71.7%) participated. Workers not doing tasks in slaughtering or meat processing constituted the reference group. Exposure assessments were made for 46 different tasks in slaughtering and meat processing from video-based observations at the workplace. CTS was diagnosed if there were current symptoms typical of CTS in combination with positive neurophysiological signs of CTS or if the subject had previously been operated on for CTS. RESULTS: Altogether 1.6% of the reference group, 5.1% of the nondeboning slaughterhouse workers [prevalence ratio (PR) 3.23, 95% confidence interval (95% CI) 1.3-7.99] and 7.8% of the deboning slaughterhouse workers (PR 4.91, 95% CI 2.03-11.81) had CTS. Increased risk estimates persisted after adjustment for other potential risk factors by logistic regression. The prevalence of CTS in the dominant hand was equally increased in both groups of slaughterhouse workers (but only statistically significant for the workers in deboning tasks), while the prevalence of CTS in the nondominant hand was significantly increased only among the slaughterhouse workers in deboning tasks. CONCLUSIONS: This study supports the hypothesis that daily high-velocity and high-force manual work is a risk factor for CTS.

Prevalence of carpal tunnel syndrome among individuals with Down syndrome.

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.

Epilepsy in Down syndrome--prevalence in three age groups.

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.

Inability of insulin to maintain normal nerve function during high-frequency stimulation in diabetic rat tail nerves.

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.

Reduced capability of transmitting high frequency impulses in tail nerves of diabetic rats.

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.

Measuring subclinical neuropathy: does it relate to clinical neuropathy? Pittsburgh epidemiology of diabetes complications study-V.

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.

Limits of normal nerve function during high-frequency stimulation.

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.

Epidemiological correlates of diabetic neuropathy. Report from Pittsburgh Epidemiology of Diabetes Complications Study.

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)

Measuring diabetic neuropathy. Assessment and comparison of clinical examination and quantitative sensory testing.

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.

Syndrome of diffuse abnormal insertional activity: case report and family study.

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.

Electrophysiology of the facial nerve in hemifacial spasm: ectopic/ephaptic excitation.

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.

Brachial plexus myoclonus.

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.

Vascular compression, hemifacial spasm, and multiple cranial neuropathy.

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.

Palatal myoclonus. Reflex activation of contractions.

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.

Pathophysiology of hemifacial spasm: III. Effects of facial nerve decompression.

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.

Pathophysiology of hemifacial spasm: II. Lateral spread of the supraorbital nerve reflex.

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.

Pathophysiology of hemifacial spasm: I. Ephaptic transmission and ectopic excitation.

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.