H reflexes and F waves. Fundamentals, normal and abnormal patterns

Epineural stimulation on distal brachial plexus for functional restoration of the upper limb in a primate study

Restoring upper limb function is critical in individuals with central paralysis, and hand control is a priority in patients with neurological impairments. Functional electrical stimulation with implantable electrodes targeting the peripheral nervous system has the potential to selectively recruit hand muscles and generate multiple functional hand movements. However, the implantation of electrodes in the forearm or elbow areas requires multiple incisions for surgery, and elbow joint movements cannot be performed. In this study, we designed and implanted two epineural cuffs on the median and radial nerves in the distal brachial plexus of a single Japanese macaque (Macaca fuscata) monkey. The cuffs were successfully placed via an axillary approach using a single incision. Electrical stimuli were applied to innervate the contraction patterns of the hand, forearm, and triceps muscles relevant to the median and radial nerves. The evoked potentials of the target muscles electrically stimulated the distal brachial plexus to reliably and selectively innervate the upper limb muscles at the functional group level. Our results demonstrated that the distal brachial plexus can be a useful stimulation site for upper limb muscle contraction and that the axillary approach enables electrode placement to peripheral nerves required for upper limb control.

Spinal Cord Infarction Presenting with Abnormal F Waves

A 42-year-old female presented with acute onset of asymmetric lower extremity weakness, bilateral lower extremity areflexia and sensory loss, and urinary incontinence. Initial investigation with a spine MRI for a spinal cord process was negative, leading to further investigation with nerve conduction studies/electromyography (NCS/EMG). This revealed absent F waves bilaterally in the fibular nerves, and there was only one isolated F wave with decreased amplitude and increased latency in the left tibial nerve and had lack of heterogeneity in the right tibial nerve. Given the early presentation of her symptoms, this led to a working diagnosis of Guillain-Barré Syndrome, which was treated with plasmapheresis without improvement. After plasmapheresis, the diagnosis was revisited, and a repeat spine MRI revealed an extensive lower thoracic and lumbar spinal cord infarction. In this unique scenario, the properties and abnormalities of F waves are discussed and reviewed, along with the influence of acute central nervous system lesions on their configuration.

Short-Term Collagen Nerve Wrapping Facilitates Motor and Sensory Recovery from Nerve Degeneration in a Sciatic Nerve Injury Rat Model

Purpose

This study used a sciatic nerve injury rat model to investigate the short-term effects of a polyglycolic acid (PGA)-collagen tube for nerve injury in continuity.

Materials and Methods

Sixteen female Wistar rats (6-8 weeks) were used, and the left sciatic nerve was crushed with a Sugita aneurysm clip. Sciatic nerve model rats were randomly categorized into two groups (n = 8; control group, n = 8; nerve wrapping group). Then, we measured four sensory thresholds, magnetically stimulated the lumbar region to induce motor-evoked potentials (MEPs), and evaluated the sciatic nerve histopathologically.

Results

In the sensory thresholds, there were significant differences for the main effect in 250 and 2000 Hz stimulation (p = 0.048 and 0.006, respectively). Further, a significant difference was observed with 2000 Hz stimulation at 1 week (p = 0.003). In the heat stimulation, there were significant differences for the main effect in both weeks and groups (p = 0.0002 and 0.0185, respectively). The post-hoc test showed a significant difference between groups only in 2W (p = 0.0283). Three weeks after the surgery, both 2nd and 3rd MEPs waves-related latencies in the nerve wrapping group were significantly shorter than those in the control group (p = 0.0207 and 0.0271, respectively). Histological evaluation of the sciatic nerve revealed considerable differences in the number of axons between the two groups (p = 0.0352).

Conclusion

The short-term PGA-collagen tube nerve wrapping facilitated motor and sensory recovery from nerve degeneration in the sciatic nerve injury rat model.

Thenar Muscle Motor Imagery Increases Spinal Motor Neuron Excitability of the Abductor Digiti Minimi Muscle

When a person attempts intended finger movements, unintended finger movement also occur, a phenomenon called “enslaving”. Given that motor imagery (MI) and motor execution (ME) share a common neural foundation, we hypothesized that the enslaving effect on the spinal motor neuron excitability occurs during MI. To investigate this hypothesis, electromyography (EMG) and F-wave analysis were conducted in 11 healthy male volunteers. Initially, the EMG activity of the left abductor digiti minimi (ADM) muscle during isometric opposition pinch movement by the left thumb and index finger at 50% maximal effort was compared with EMG activity during the Rest condition. Next, the F-wave and background EMG recordings were performed under the Rest condition, followed by the MI condition. Specifically, in the Rest condition, subjects maintained relaxation. In the MI condition, they imagined isometric left thenar muscle activity at 50% maximal voluntary contraction (MVC). During ME, ADM muscle activity was confirmed. During the MI condition, both F-wave persistence and the F-wave/M-wave amplitude ratio obtained from the ADM muscle were significantly increased compared with that obtained during the Rest condition. No difference was observed in the background EMG between the Rest and MI conditions. These results suggest that MI of isometric intended finger muscle activity at 50% MVC facilitates spinal motor neuron excitability corresponding to unintended finger muscle. Furthermore, MI may induce similar modulation of spinal motor neuron excitability as actual movement.

Intrafascicular peripheral nerve stimulation produces fine functional hand movements in primates

[Figure: see text].

Mathematical model of patella T-reflex and clinical evaluation with Ashworth scales

Spasticity is one of the major problems that arise in different neurological diseases and seriously affect the quality of human life. Research on the understanding of mechanism of spasticity remains as important as the studies on the spasticity therapy and rehabilitation. In this study, the spasticity mechanism which develops concerning the upper motor neuron lesions is investigated by modelling "Patella tendon reflex triggered patella pendulum". The mathematical model based on the pendulum phenomenon is developed by solving the curve-fitting problem as finding the curve that best fits a set of data points. Electrophysiological and dynamic measurement data were taken from 76 spastic subjects and 20 healthy participants. The mathematical model is determined by the morphological properties of the goniometric variations. The results denote that the mathematical model containing two clinically relevant parameters -frequency component of the damped oscillatory motion defined as "f 0 " with the maximum angle of the reflex defined as "a 0 " ensures to distinguish spasticity from healthy subjects.

A waves in electroneurography: differential diagnosis with other late responses

Neurographic studies are an extension of clinical examination and are performed for the functional assessment of peripheral nerves. The study of motor and sensory conduction velocity and the presence, amplitude, morphology and symmetry of the response to electrical stimulation are crucial for the diagnosis and management of peripheral neuromuscular disorders. Neurography also plays an important role in the search for so-called late responses comprising the F wave, H reflex, axonal response and A wave. By analysing the parameters of each late wave, this paper addresses the pathophysiological features and the most common conditions impairing the physiology of late responses, with a special focus on A waves.

Ultrasound-guided caudal epidural steroid injection in chronic radicular low back pain: short-term electrophysiologic benefits

OBJECTIVE

To assess the short-term efficacy of ultrasound-guided caudal epidural steroid injections (ESIs) in improving pain, and nerve function as measured by electrophysiological testing in chronic radicular low back pain.

METHODS

Patients diagnosed with chronic radicular low back pain were randomized into one of two groups. The injection group (n = 20) underwent a single ultrasound-guided Caudal ESI of 1 ml of 40 mg ml-1 Triamcinolone Acetonide (Kenacort-A), with local anesthetic. The control group (n = 20) underwent a 12-session physiotherapy program. Both groups were evaluated before and 2 weeks after the intervention using visual analog scale for pain and electrophysiological testing comprising peroneal and tibial terminal motor latencies and F-response latencies and chronodispersion.

RESULTS

Both groups showed significant pain reduction on the visual analog scale after the intervention. The injection group showed a significant reduction in F wave chronodispersion post-treatment (<0.01). In the control group, there were no significant differences in F wave parameters pre- and post-treatment (p > 0.05).

CONCLUSION

Caudal ESIs were shown to provide short-term improvement of nerve function as evident by improvement in the electrophysiological parameters sensitive to radiculopathy. It was found to be superior to standard physical therapy in this regard.

ADVANCES IN KNOWLEDGE

This work shows a novel electrophysiologic evidence of the short-term efficacy ultrasound-guided caudal ESI.

Reassessment of Split-Leg Signs in Amyotrophic Lateral Sclerosis: Differential Involvement of the Extensor Digitorum Brevis and Abductor Hallucis Muscles

Background: The muscle patterns involved in the “split-leg” syndrome of amyotrophic lateral sclerosis (ALS) remains controversial. We sought to evaluate and reassess the pattern of the extensor digitorum brevis (EDB) and the abductor hallucis (AH) muscles' involvement in split-leg syndrome in ALS.

Methods: We recruited 60 consecutive patients with ALS and 25 healthy controls (HCs). Compound muscle action potentials (CMAPs) and F-waves were recorded over the EDB and AH muscles in all subjects. For comparison, we classified patients into two categories based on the presence or absence of lower limbs symptoms.

Results: The EDB/AH CMAP amplitude ratio was significantly reduced in patients with affected legs (0.33 ± 0.21, P = 0.007), whereas patients with unaffected legs had a ratio similar to that of the HCs. The EDB/AH ratios for the F-wave latencies, mean F-wave amplitude, mean F/M amplitude ratio, and the persistence of the total repeater F-wave shapes (index Freps) of the EDB-AH, were significantly increased in the affected leg group, whereas the EDB/AH ratio for F-wave persistence was significantly reduced. These findings indicated a greater loss of lower motor neurons (LMNs) innervating the EDB and dysfunction of spinal motoneurons innervating the EDB. In the unaffected leg group, the EDB, but not the AH, F-wave latencies, mean and maximal F/M amplitude ratios, and index Freps were significantly altered. Receiver operating characteristic curve analysis suggested that the EDB F-wave latencies, mean F/M amplitude ratios, and index Freqs (area under the curve [AUC] > 0.8) more strongly differentiated patients with ALS from the HCs compared to the EDB/AH CMAP amplitude ratio (AUC = 0.61). Notably, the EDB maximal F-wave latency and index Freqs reliably differentiated patients with unaffected legs (HCs), with AUCs of 0.83 (95% CI 0.76–0.91) and 0.81 (95% CI 0.72–0.89), sensitivities of 76 and 78%, and specificities of 76 and 78%, respectively.

Conclusions: These results suggest preferential EDB compared to AH involvement in the split-leg syndrome of ALS. The EDB maximal F-wave latency and index Freqs robustly differentiated patients with ALS from HCs, which might facilitate an earlier identification of ALS.

Evaluation of Relationship between Extensor Digitorum Communis Hoffmann-reflex Latency and Upper Limb Length and Age

Background:

The aim of this study was to evaluate the relation between normal values of extensor digitorum communis (EDC) Hoffmann-reflex (H-reflex) latency, upper limb length and age in normal participants, and to determine whether there is any regression equation between them.

Materials and Methods:

In this cross-sectional study, 120 upper limbs of 76 normal volunteers (55 limbs of 34 men and 65 limbs of 42 women) were participated in this study. The onset latency of EDC H-reflex was determined with standard electrodiagnostic techniques and was recorded.

Results:

The mean EDC H-reflex latency was 15.89 ± 1.41 ms. There was a positive significant correlation between EDC H-reflex latency and upper limb length (r = 0.749, P < 0.0001) and also arm length (r = 0.758, P < 0.0001), but there was a nonsignificant indirect correlation between age and EDC H-reflex latency (r = −0.111, P = 0.227). The relation between H-reflex and sex was not statistically significant (P = 0.46).

Conclusion:

According to our result, there are good predictive values between upper limb length and arm length for the estimation of normal EDC H-reflex latency.

Clinical uses of H reflexes of upper and lower limb muscles

H reflexes can be recorded from virtually all muscles that have muscle spindles, but reflex reinforcement may be required for the reflex response to be demonstrable. This can allow conduction across proximal nerve segments and most nerve root segments commonly involved by pathology. Stimulus rate is critical in subjects who are at rest. However the reflex attenuation with higher rates is greatly reduced during a background contraction of the test muscle, with only minor changes in latency if any. In addition the contraction ensures that the reflex response occurs in the desired muscle. Reflex latencies should be corrected for height (or limb length) and age. Because the reflex discharge requires a synchronised volley in group Ia afferents, large increases in reflex latency occur rarely with purely sensory lesions. If the H reflex of soleus, quadriceps femoris or flexor carpi radialis is absent at rest but appears during a voluntary contraction at near-normal latency, there is either low central excitability or a predominantly sensory abnormality. With the former H reflexes will be difficult to elicit throughout the body. If H reflexes can be recorded at rest from muscles for which no reflex can normally be demonstrated, there is good evidence for hyperreflexia. In the context of possible ALS, this is an important finding when there is EMG evidence of chronic partial denervation in that muscle.

Median Nerve Conduction in Healthy Nigerians: Normative Data

BACKGROUND

Because of lack of local normative data, electrodiagnostic laboratories in Nigeria apply standard values generated in the USA and Europe to diagnose different median nerve abnormalities.

AIM

To develop normative values for motor and sensory median nerve conduction studies (NCSs) in Nigerian population.

SUBJECTS AND METHODS

In a cross-sectional study design, a total of 200 healthy volunteers were selected after clinical evaluation to exclude systemic or neuromuscular disorders. NCS of the median nerves was conducted on all the healthy volunteers according to a standardized protocol. The data included in the final analysis were amplitude, latency, and nerve conduction velocity. Ethical approval was obtained for the study.

RESULTS

The reference range for median nerve (motor) velocity, distal latency, and amplitude were 49.48-66.92, 1.95-4.52, and 4.3-11.3, respectively. The reference range for median nerve F-wave latency was 44.8-70.5. The reference range for median nerve (sensory) velocity, distal latency, and amplitude were 44.8-70.5, 1.98-4.52, and 16.6-58.4, respectively.

CONCLUSION

Reference values for the nerve conduction parameters of the median (motor and sensory) in the study population were similar to those obtained in the literature.

Low sensitivity of F-wave in the electrodiagnosis of carpal tunnel syndrome

OBJECTIVE

Previous studies showed "F-wave inversion" (F-INV) as a sensitive method in the electrodiagnosis of early stage of carpal tunnel syndrome (CTS). This study aimed at evaluating the sensitivity and specificity of F-wave and nerve conduction velocity (NCV) testing in CTS.

METHODS

We consecutively enrolled 244 cases and 108 controls. F-waves analysis included: Fwave minimum and mean latencies, F-wave persistence and chronodispersion, mean-F/CMAP amplitude ratio, F-INV. Specificity and sensitivity of F-waves parameters were calculated in the whole sample of CTS patients and by grouping the patients according to CTS severity. Multivariate logistic regression was also performed using F-INV as a dependent variable.

RESULTS

In the whole sample the sensitivity of F-mean-INV and of median-ulnar NCV comparative testing was 50.8% and 93.7%, respectively. F-INV sensitivity dropped to 8% in CTS early stage. F-INV could be predicted only by distal motor latency of the median nerve. The sensitivity of all F-wave parameters increased only in the most severe stages of CTS.

CONCLUSIONS

This study does not confirm the electrodiagnostic usefulness of F-INV in early stage of CTS. All F-wave parameters, including F-INV, are much less sensitive than conventional NCV in CTS electrodiagnosis. F-wave does not add further useful information specifically related to CTS.

Clinical and electrophysiological characteristics of symmetric polyneuropathy in a cohort of systemic lupus erythematosus patients

OBJECTIVE

Peripheral neuropathy in systemic lupus erythematosus (SLE) is heterogeneous and its commonest pattern is symmetrical polyneuropathy. The aim of this study was to describe the prevalence, clinical and electrophysiological features, disease associations and effects on function and quality of life of polyneuropathy in SLE patients, defined using combined clinical and electrophysiological diagnostic criteria.

METHODS

Consecutive SLE patients seen at the University of Malaya Medical Centre were included. Patients with medication and other disorders known to cause neuropathy were excluded. Demographic, clinical and laboratory data were obtained using a pre-defined questionnaire. Function and health-related quality of life was assessed using the modified Rankin scale and the SF-36 scores. Nerve conduction studies (NCS) were carried out in both upper and lower limbs. Polyneuropathy was defined as the presence of bilateral clinical symptoms and/or signs and bilateral abnormal NCS parameters.

RESULTS

Of 150 patients, 23 (15.3%) had polyneuropathy. SLE-related polyneuropathy was mainly characterized by sensory symptoms of numbness/tingling and pain with mild signs of absent ankle reflexes and reduced pain sensation. Function was minimally affected and there were no differences in quality of life scores. NCS abnormalities suggested mild length-dependent axonal neuropathy, primarily in the distal lower limbs. Compared to those without polyneuropathy, SLE-related polyneuropathy patients were significantly older but had no other significant demographic or disease associations.

CONCLUSIONS

SLE-related polyneuropathy is a chronic, axonal and predominantly sensory neuropathy, associated with older age. Its underlying pathogenetic mechanisms are unknown, although a possibility could be an increased susceptibility of peripheral nerves in SLE patients to effects of aging.

Recovery of motor neuron excitability after facial nerve impairment in rats

Multiple studies have demonstrated alterations in excitability in the central nervous system after peripheral nerve injury. However, there are few reports on changes in the central nervous system after peripheral facial nerve injury. Our objective was to determine the excitability changes that occur in the facial nucleus after facial nerve impairment. The excitability changes in the facial nucleus were investigated by assessing two types of compound muscle action potentials (M and F waves) in the orbicularis oculi muscles, evoked by electrical stimulation of the zygomatic branch of the facial nerve. In rats, M and F waves were measured in the orbicularis oculi muscles before and every week up to 8 weeks after the application of nerve compression under anesthesia. M and F waves disappeared after nerve compression, only to reappear 2 weeks later, although M-wave amplitude was decreased and the latencies of both waves were delayed. Thereafter, these waves recovered gradually. During the recovery period, the F/M wave amplitude ratio, which is an indicator of facial nucleus excitability, significantly increased on the impaired side but not on the intact side. This increase was most prominent within 3 weeks; thereafter, the ratio gradually decreased and reached the levels recorded before facial nerve impairment by 7 weeks. Facial nerve impairment leads to hyperexcitability of the facial nucleus during the recovery period.

Clinical and electrophysiological features of the 2007 Guillain-Barré syndrome epidemic in northeast China

Guillain-Barré syndrome (GBS) generally presents sporadically. Epidemics of GBS are unusual. We reviewed the medical records of 26 patients hospitalized for GBS during the 2007 GBS epidemic in northeast China. The objective was to determine whether there were clinical and electrophysiological characteristics. All patients had drunk unboiled water, and the illness was preceded by diarrhea in 19 (73%) patients. Only 1 patient had a Campylobacter jejuni infection, whereas 14 (54%) patients exhibited features of acute motor axonal neuropathy (AMAN). The most common electrophysiological findings in early GBS included decreased compound muscle action potential (CMAP) amplitude (62%), abnormal F waves (73%), and abnormal H reflexes (62%). This epidemic of GBS appears to have been associated with consumption of contaminated water. The main subtype was AMAN, which was associated with a longer duration of illness and a worse prognosis. Electrodiagnostic evaluations are helpful for diagnosis in the primary stages of GBS.

H-reflex and motor nerve conduction studies in growth retarded newborn babies

OBJECTIVE

To demonstrate the accelerated postnatal maturation/myelination in growth retarded babies compensating the deficit suffered by them during intrauterine life.

METHODS

We studied 16 babies within the first 3 days of birth. These included 6 full term appropriate for gestational age babies (FT AGA) and 10 full term intrauterine growth retarded (FT IUGR). A separate group of 16 babies was examined at 2 months of age. In this group 7 were FT AGA and 9 were FT IUGR at the time of birth. H-reflex latency (HRL), motor nerve conduction velocity (MNCV) and H-reflex excitability (H/M) were measured in the right lower limb. Anthropometric measurements of the babies were also recorded meticulously. All the babies were neurologically normal on clinical evaluation.

RESULT

At birth, MNCV was significantly lower in FT IUGR babies compared to FT AGA babies. However at the age of 2 months the MNCV of both FT AGA and FT IUGR was comparable. Other parameters (HRL and H/M) in the IUGR babies were comparable with normal babies both at birth and 2 months of age. In FT IUGR babies crown-heel length and weight was significantly lower than FT AGA babies both at the time of birth and at 2 months of age.

CONCLUSION AND SIGNIFICANCE

The findings suggest that FT IUGR babies demonstrate accelerated postnatal peripheral neural maturation. At 2 months of age, the motor nerve conduction velocity of these growth retarded babies was comparable to that observed in normal AGA babies of similar age. This provides an insight into the functional aspect of the proven theories of decreased peripheral myelination in FT IUGR babies with subsequent rapid postnatal myelination that renders these babies neurologically equivalent to FT AGA babies despite not achieving comparable anthropometric parameters.

Cortical excitability in Duchenne muscular dystrophy

OBJECTIVE

To investigate the probable cortical excitability changes in DMD by electrophysiological means.

METHODS

Sixteen cases with DMD, 10 age-matched control children (CC) and 10 healthy adult volunteers (AC) were studied with a transcranial magnetic stimulation (TMS) test battery composed of central conduction time, cortical silent period and paired TMS paradigm.

RESULTS

There were no significant differences between DMD and CC groups except for lower amplitude motor responses in DMD cases. These two groups showed a similar pattern of excitability with less short interval intracortical inhibitions and shorter silent period durations as compared to the AC subjects.

CONCLUSIONS

The electrophysiological tests performed in our DMD patients did not reveal abnormalities caused particularly by the disorder.

SIGNIFICANCE

TMS excitability studies performed in DMD boys may not provide findings other than those related to the developmental age.

Criterion validity of the NC-stat automated nerve conduction measurement instrument

The purpose of this study is to assess the criterion validity of peroneal and posterior tibial nerve conduction measurements obtained with the NC-stat system. Sixty patients referred to the Boston VA EMG laboratory were enrolled. Each subject had a full study of the lower extremity performed using traditional EMG equipment prior to obtaining the NC-stat measurements. These included peroneal and posterior tibial distal motor latency (DML), amplitude (AMP) and F-wave latency (FLAT) measurements. Excellent criterion validity was demonstrated for the peroneal and posterior tibial FLATs and the peroneal AMP. Acceptable criterion validity was identified in the peroneal DML and the posterior tibial AMP. The validity of the posterior tibial DML could not be demonstrated. With the exception of the peroneal DML, criterion validity was maintained in a sub-group analysis of the 50% most abnormal parameter values. The comparability of NCS performed with the NC-stat and in traditional settings has been demonstrated for motor studies of the median and ulnar nerves in previous studies. This study shows that the technology used by the NC-stat for studying the peroneal and posterior tibial nerves compares favorably as well with that obtained with traditional EMG equipment used under neurologist supervision.

Placebo controlled utility and feasibility study of the H-reflex and flexor reflex in spastic children treated with intrathecal baclofen

OBJECTIVE

To evaluate feasibility and utility of the soleus H-reflex and tibialis anterior flexor reflex (FR) in identifying spinal cord neuronal response to intrathecal baclofen (ITB) in children with severe spastic cerebral palsy.

METHODS

During a randomized, double-blind, placebo-controlled dose-escalation test treatment, maximum H amplitude/maximum M amplitude (H/M ratio) and FR parameters were bilaterally recorded at baseline and 2-3 h after intrathecal bolus administration of placebo and increasing doses of baclofen until both an improvement in the individual treatment goal(s) and a one-point reduction on the Ashworth scale were observed.

RESULTS

Electrophysiological data of 14 children were studied. The H-reflex was feasible in 13 children, the FR threshold area in 9 and the FR, elicited with supramaximal stimulation, in only one child. After ITB, the H/M ratio significantly decreased (left: 0.67+/-0.47 to 0.15+/-0.18, P=0.005; right: 0.55+/-0.32 to 0.14+/-0.19, P=0.002) without placebo effect. FR threshold area after ITB, only decreased significantly in children not taking oral baclofen (left: 146+/-53 to 41+/-54 mV ms, P=0.000; right: 156+/-80 to 66+/-48 mV ms, P=0.002).

CONCLUSIONS

This is the first randomized, double-blind, placebo-controlled dose-escalation study in spastic children demonstrating the soleus H-reflex to be a feasible and objective measure to quantify the decreasing motoneuron excitability in response to ITB bolus administration. Only in children not taking oral baclofen, FR threshold area can also be used as an objective outcome measure, yet feasibility is limited.

SIGNIFICANCE

We suggest introducing the H-reflex as the electrophysiological gold standard for the evaluation of the effect of ITB in spastic children.

Spinal motor neuron excitability in newborns following fetal distress: sub-clinical depression revealed by soleus H-reflex

OBJECTIVE

To explore possible spinal cord dysfunction in clinically unaffected newborns emerging from fetal distress, using H-Reflex.

METHODS

This cross-sectional study comprised 48 full-term newborn infants investigated between 8h and 10 days after birth. Twenty-one (21) had fetal distress defined by late-decelerations in fetal heart rate, out of which 11 had also meconium release in utero; 5 passed meconium in utero with normal FHR patterns; and 22 normal controls had uneventful birth. All had normal birth-weight and Apgar scores. All were found normal on neurological examination, except one showing hypotonia following fetal distress. Soleus H-reflex was studied in right lower limb.

RESULTS

Newborns delivered with fetal distress showed significant reduction in H-reflex excitability (H/M ratio) within 2 days of birth. Tests performed closer to the birth event revealed more severe depression. Meconium did not contribute to this effect.

CONCLUSIONS

Fetal distress can lead to transient, subclinical depression of spinal motoneurons in the newborn.

SIGNIFICANCE

This neonatal H-reflex study focuses on excitability of a spinal motoneuron pool rather than conduction parameters (reflecting myelination) available in literature. It reveals excitability changes missed on clinical examination of newborns apparently unaffected by intrapartum hypoxic-ischemic spells. It also draws attention towards spinal cord dysfunction in birth-hypoxia.

Excitability of facial nucleus and related brain-stem reflexes in hemifacial spasm, post-facial palsy synkinesis and facial myokymia

OBJECTIVE

To compare the electrophysiological excitability characteristics of the facial nucleus and related structures in hemifacial spasm (HFS), post-facial palsy synkinesis (PFPS) and facial myokymia (FM).

METHODS

Facial F-waves, blink reflex recoveries and magnetically elicited silent periods (SP) were prospectively studied in 17 HFS, 17 PFPS, 8 FM cases and in 13 controls. Earlier unpublished observations on abnormal impulse transmission in 36 HFS and 29 PFPS cases were also included.

RESULTS

Enhanced F-waves were recorded on the symptomatic side in PFPS and HFS cases with a tendency to be more pronounced in PFPS. HFS and PFPS groups both showed an earlier blink reflex recovery, more prominent in PFPS patients, when stimulated and/or recorded on the symptomatic side. Unelicitable SPs were encountered after 24/39 stimulations in 5 patients with PFPS and rarely in HFS cases. Duration of elicitable SPs did not change remarkably. FM group had similar characteristics as normal controls in the 3 electrophysiological tests. Latencies of the lateral and synkinetic spread responses were significantly prolonged in the earlier PFPS group as compared to HFS. In two-point stimulation, both groups showed a greater latency shift in late responses, again more pronounced in PFPS.

CONCLUSIONS

PFPS and HFS cases had similar enhanced excitability patterns at the facial nucleus and related brain-stem structures, more marked on the symptomatic side and more obvious in the PFPS group. Findings elicited in the FM group were thought to be caused by asynchronous hyperactivity of facial motoneurons.

SIGNIFICANCE

In this comparative electrophysiological study, similar excitability patterns were found in HFS and PFPS groups, albeit with different intensities.

F-waves: neurophysiology and clinical value

This review deals with F responses, which are late responses obtained by supramaximal stimulation of virtually all the motor and mixed peripheral nerves. They are recorded over a muscle innervated by the stimulated nerve. The first description of F-waves was published in the fifties. Their neurophysiological mechanisms have been abundantly discussed in the literature leading to a current consensus, whereby F-waves are considered as antidromic responses produced by a pool of motoneurons activated by peripheral nerve stimulation. In the first part of this review, the neurophysiological mechanisms of F-waves as well as the distinction between these and H reflexes are described from a historical point of view. Other late responses are intentionally not reported; nevertheless A-waves are discussed since they are frequently ill-described in a number of conditions. Stimulation and recording procedures as well as F-wave parameters analysis are detailed, with emphasis on measures most useful for clinical purposes. A rigorous F-wave recording method is mandatory for reliable and meaningful analyses. Physiological factors, which influence F-waves such as ageing, drugs and sleep, must be known and their effects discussed. Also, as maturation is an important factor in clinical neurophysiology, data on F-wave ontogenesis are reviewed and discussed. Finally, the different F-wave alterations described so far in the literature, in either peripheral or central disorders, are listed and commented. It is emphasised that F-waves are particularly useful for the diagnosis of polyneuropathies at a very early stage and for the diagnosis of proximal nerve lesions. F-wave recording is indeed one of the rare methods in routine examination allowing at the same time the functional assessment of motor fibres on their proximal segment, and contributing to the evaluation of motoneuronal excitability.

Effect of Vim thalamic DBS in Parkinson’s disease on F wave duration

F waves were recorded from abductor hallucis muscle in eight Parkinsonian patients with deep brain stimulation (DBS) electrodes surgically implanted in their Vim thalamic nucleus in two conditions of DBS ON and OFF. Patients with relatively anteriorly located electrodes exhibited a significant reduction in F wave duration and also in the UPDRS rigidity score of the corresponding foot when the DBS was ON. In contrast, patients with relatively posteriorly located electrodes exhibited no significant difference in F wave duration in the two DBS ON and OFF conditions. The rigidity UPDRS score in the corresponding foot diminished very little in the latter group. Both groups had great improvement in their tremor at rest UPDRS score in that foot when the DBS was ON. Vim surgery is generally accepted to affect tremor mechanisms. However, surgical intervention in anterior parts of Vim has been reported to affect rigidity mechanisms. This correspondence of these two symptoms of rigidity and tremor with the two locations of anterior and relatively posterior Vim may indicate the contribution of mechanisms of rigidity, but not tremor, in enhancement of F wave duration and hyper excitability of spinal motoneuron.

Electrodiagnostic testing in neuromuscular disorders

For the past approximately six decades, electrodiagnostic testing orelectrodiagnosis (EDX) has played an increasingly important role in the clinical evaluation of patients who have neuromuscular disorders. This in part is because of a greater understanding of the pathophysiology of these disorders. Also of importance is the development of the techniques themselves, beginning with basic needle electromyography (EMG) and electroneurography (or nerve conduction studies) (NCS) in the 1940s. Today the clinician has a larger menu of testing options, including somatosensory evoked potentials,quantitative EMG, single fiber EMG, and autonomic testing. The advent of computers has added speed and accuracy to testing