Cutaneous silent period changes in Type 2 diabetes mellitus patients with small fiber neuropathy

ObjectiveSmall myelinated (A-δ) and unmyelinated (C) somatic sensory fibers are initially affected and may be the earliest exhibited sign of neuropathy in glucose dysmetabolism. Cutaneous silent period (CSP) is an inhibitory spinal reflex and its afferents consist of A-δ nerve fibers. The aim of this study was to evaluate CSP changes in Type 2 diabetic patients with small fiber neuropathy.MethodsForty-three patients and 41 healthy volunteers were included. CSP latency and duration, as well as CSP latency difference of the upper and lower extremities, were examined.ResultsNerve conduction studies were within normal limits in both groups. Lower extremity CSP latency was longer (122.1 ± 15.5 vs. 96.4 ± 6.4 ms; p < 0.001), CSP duration was shorter (29.5 ± 8.9 vs. 43.1 ± 5.0 ms; p < 0.001), and latency difference was longer (48.1 ± 12.6 vs. 22.7 ± 3.7; p < 0.001) in patients than controls. The difference was more significant in patients with neuropathic pain. No significant difference existed in upper extremity on CSP evaluation.ConclusionThe CSP evaluation together with nerve conduction study, has been demonstrated to be beneficial and performance of latency difference in addition to CSP latency and duration may be a valuable parameter in electrophysiological assessment of diabetic patients with small fiber neuropathy.SignificanceAn additional CSP evaluation may be considered in cases which nerve conduction studies do not provide sufficient information.     

Motor and somatosensory evoked potentials in Autosomal Dominant Hereditary Spastic Paraparesis (ADHSP) linked to chromosome 2p, SPG4

The aim of our study was to evaluate Motor Evoked Potentials (MEPs) and cortical excitability, using Transcranial Magnetic Stimulation (TMS) as well as short latency Somatosensory Evoked Potentials (SEPs) in Autosomal Dominant Hereditary Spastic Paraparesis (ADHSP) patients. MEPs were recorded from upper and lower limb muscles in 12 patients (7 m and 5f) affected by ADHSP with spastin mutation (SPG4). We measured: (i) motor threshold (MTh); (ii) total motor conduction time (TMCT); (iii) direct and indirect central motor conduction time (d-CMCT and i-CMCT) calculated by subtracting from the cortical latency those obtained on magnetic spinal stimulation (d-PMCT) and via the F-wave method (i-PMCT); (iv) MEP amplitude (MEP/Mmax ratio%) and (v) duration of the cortical silent period (CSP). Latency, amplitude and persistence of the F-wave obtained with electrical nerve stimulation were also considered; H reflex was also tested from lower extremities. SEPs were recorded from spine and scalp sites following median and posterior tibial nerve stimulation; conventional latency and amplitude measurements were performed. In a comparison with the control group, the MTh recording from lower limbs was significantly higher (67.5 +/- 7.7% versus 52.5 +/- 6.9%), MEPs were absent in one case and showed reduced amplitude in the remainders (22.9 +/- 12.6% versus 66.3 +/- 25.9% of M wave); TMCT resulted to be abnormal (36.5 +/- 3.9 ms versus 27.1 +/- 1.4 ms) and d-CMCT as well as i-CMCT were significantly prolonged (23.1 +/- 3.5 ms versus 13.8 +/- 1.3 ms; and 20.1 +/- 3.4 ms versus 10.6 +/- 1.3 ms, respectively). The CSP, which was normal from the hands, was significantly shortened from the legs and correlated with spasticity scoring (Ashworth scale). Cortical SEPs from lower limbs were abnormal in all cases, whereas SEPs by stimulation of median nerves were normal; F-wave parameters from upper limbs showed no abnormalities, whereas an increased persistence was detected from lower limbs; H reflex amplitudes resulted larger compared with controls. Moreover, shortening of the CSP, being correlated with the Ashworth scale, can be considered an electrophysiological marker of spasticity that seems to arise from impairment of the supraspinal or intracortical inhibitory pathways with an additional contribution of increased segmental motor neuron excitability. These data prove the existence of comparable neurophysiological abnormalities in ADHSP with spastin mutation (SPG4) when long ascending and descending pathways are involved.     

Motoneuron excitability and the F wave

For three motoneuron pools that differ in excitability to Ia inputs [tibialis anterior (TA), abductor pollicis brevis (APB), and soleus], F-wave parameters were measured at rest, during voluntary contraction, and following prolonged vibration. There was an inverse relationship between F-wave chronodispersion and F-wave persistence at rest, and this appeared to be related to the ease of recording the H reflex for the motoneuron pool. During a steady voluntary contraction, overall F-wave activity increased in amplitude but decreased in duration for TA and APB. Following vibration of the test muscle at 50 HZ for 10 min there was a long-lasting depression of the H reflexes of TA and APB, but no significant change in F-wave measurements. These findings are consistent with the view that reflex discharges can prevent F waves in low-threshold motor units, and that chronodispersion is affected by the extent of reflex activity; that is, chronodispersion and related F-wave measurements do not measure motor properties exclusively. The findings also suggest that F waves provide a flawed measure of the excitability of the motoneuron pool.     

Various aspects of F-wave values in a healthy population

Objective: To characterize various aspects of F-wave in a healthy population and establish normative data for future clinical use.Methods: A total of 100 healthy volunteers underwent sensory and motor nerve conduction studies of the ulnar and tibial nerves, including F waves elicited by 32 stimuli.Results: The F-wave measurements (mean±SD for ulnar vs tibial nerve) consisted of persistence (83±19 vs 97±5%), minimum, mean and maximum latencies (26.5±2.1, 28.1±2.2, and 30.4±2.3 vs 47.0±4.1, 49.6±4.4, and 52.5±4.4 ms), minimum, mean and maximum F-wave conduction velocities (FWCV) (55.0±2.7, 60.0±2.3, and 64.0±3.0 vs 49.0±2.9, 52.2±3.1, and 55.5±3.4 m/s), chronodispersion (3.9±0.9 vs 5.5±1.4 ms), mean amplitude (347±152 vs 384±148 μV) and mean duration (8.6±2.9 vs 13.0±4.5 ms). Additional measures, registered by electronic averaging, included latency (27.4±2.3 vs 48.6±4.7 ms), duration (9.6±2.2 vs 16.4±4.2 ms), and amplitude (299±156 vs 208±116 μV).Conclusions: The use of a height nomogram serves well as an acceptable means to adjust F latencies for the limb length. In addition to the commonly used minimal latency, maximal FWCV, and persistence, clinically relevant measures with a narrow variability includes mean and maximal latencies, chronodispersion, and mean duration. In particular, mean latency obtained with 10 stimuli gave accurate results either for group or individual analysis.Significance: The data help establish an adequate manner of recording F-wave latencies in clinical evaluation.     

Spinal motor neuron excitability during the cutaneous silent period

The physiologic mechanisms generating the cutaneous silent period (CSP) remain uncertain. It is not known whether the CSP occurs because of inexcitability of the spinal motor neuron. We, therefore, assessed excitability of the motor neuron during the CSP using F-wave responses. H-reflexes were also elicited during the CSP. Electrical stimulation to the fifth digit produced the CSP in the voluntarily contracting abductor pollicis brevis muscle (APB). Median nerve stimulation at the wrist elicited control F or H responses during isometric APB contraction (condition 1) and in resting muscle (condition 2). Control amplitudes were compared to those elicited in the midst of the CSP. In Condition 1, F-wave amplitudes and frequency during the CSP were unchanged compared with controls. However, F-waves were increased in amplitude and frequency during the CSP (P < 0.001) relative to responses elicited in resting muscle (condition 2). H-reflexes during the CSP were suppressed (P < 0.001) compared with controls elicited during contraction (condition 1), but facilitated relative to the resting state (condition 2) in which no H-reflexes were elicitable. We conclude that spinal motor neurons remain excitable to antidromic volleys at the same time that the corticospinal volley is inhibited to produce the CSP. Moreover, motor neuron excitability appears to be increased during the CSP compared to the relaxed state. © 1995 John Wiley & Sons, Inc.     

Influence of limb temperature on cutaneous silent periods

ObjectiveThe cutaneous silent period (CSP) is a spinal inhibitory reflex mediated by small-diameter afferents (A-delta fibers) and large-diameter efferents (alpha motoneurons). The effect of limb temperature on CSPs has so far not been assessed.MethodsIn 27 healthy volunteers (11 males; age 22–58 years) we recorded median nerve motor and sensory action potentials, median nerve F-wave and CSPs induced by noxious digit II stimulation in thenar muscles in a baseline condition at room temperature, and after randomly submersing the forearm in 42 °C warm or 15 °C cold water for 20 min each.ResultsIn cold limbs, distal and proximal motor and sensory latencies as well as F-wave latencies were prolonged. Motor and sensory nerve conduction velocities were reduced. Compound motor and sensory nerve action potential amplitudes did not differ significantly from baseline. CSP onset and end latencies were more delayed than distal and proximal median nerve motor and sensory latencies, whereas CSP duration was not affected. In warm limbs, opposite but smaller changes were seen in nerve conduction studies and CSPs.ConclusionThe observed CSP shift “en bloc” towards longer latencies without affecting CSP duration during limb cooling concurs with slower conduction velocity in both afferent and efferent fibers. Disparate conduction slowing in afferents and efferents, however, suggests that nociceptive EMG suppression is mediated by fibers of different size in the afferent than in the efferent arm, indirectly supporting the contribution of A-delta fibers as the main afferent input.SignificanceLimb temperature should be taken into account when testing CSPs in the clinical setting, as different limb temperatures affect CSP latencies more than large-diameter fiber conduction function.     

Sleep-related movement disorders and growing pains: differences in daytime and bedtime behavior in 2–6 year old children with cleft palate

BackgroundBehavioural difficulties are common in children with sleep disorders. However, up to now no study has investigated the association between sleep-related movement disorders (SRMD) and behavior in children with craniofacial cleft. The aim of this study was to assess the frequency and impact of SRMD and growing pains in daytime/bedtime behavior in young children with cleft palate.MethodsCross-sectional survey study of sleep and behavior in 2.0–6.9 year old children with cleft palate. Parents completed the Pediatric Sleep Questionnaire, which queries reports of periodic limb movements (PLMS), restless leg syndrome (RLS), growing pains, daytime sleepiness, sleep latency/duration, and the Conners' Early Childhood Questionnaire which asks about behavioral difficulties.ResultsAmong 71 children with cleft palate (52.1% boys) 14.1 % screened positive for PLMS, 8.5% reported RLS and 9.9% growing pains. Children who screened positive for PLMS and RLS were more likely to report sleepiness (PLMS 40% vs. 4.9%, p = 0.001; RLS 33.3% vs. 7.7%, p = 0.04) and long sleep latency (PLMS 80% vs. 32.8%, p = 0.005; RLS 100% vs. 33.8%, p = 0.002) compared to those who did not endorse the respective sleep problems. Children who reported PLMS had a higher T-score for emotional (58.2 ± 7.6 vs. 50.7 ± 8.4, p = 0.01) and somatic symptoms (66.2 ± 15.2 vs. 49.9 ± 9.5, p = 0.0001). Sleepiness was associated to an increased frequency of externalizing, psychiatric and somatic problems. While children with long sleep latency reported more emotional and somatic symptoms, and those with reduced sleep duration more internalizing difficulties.ConclusionsParents of young children with cleft palate reported frequently PLMS, RLS and growing pains. Daytime/bedtime behavior varies depending on the presence of SRMD. Sleepiness and sleep variables might play a role on behavioural problems in children with cleft and SRMD symptoms.     

Alterations in excitatory and inhibitory brainstem interneuronal circuits in fibromyalgia: Evidence of brainstem dysfunction

ObjectivePatients with fibromyalgia syndrome (FMS) perceive stimuli differently and show altered cortical sensory representation maps following peripheral stimulation. Altered sensory gating may play a causal role.MethodsBlink reflex, blink reflex excitability recovery, and prepulse inhibition of the blink reflex – representing brainstem excitability – were assessed in 10 female patients with FMS and 26 female healthy controls.ResultsUnconditioned blink reflex characteristics (R1 latency and amplitude, R2 and R2c latency and area-under-the-curve) did not differ significantly between patients and controls. Blink reflex excitability recovery was enhanced in patients versus controls at all intervals tested. Prepulses significantly suppressed R2 area and increased R2 latency in patients and controls. However, R2 area suppression was significantly less in patients than in controls (patients: to 80.0 ± 28.9%, controls: to 47.8 ± 21.7%). The general pattern of corresponding changes in R2c was similar.ConclusionsBlink reflex is normal, whereas blink reflex excitability recovery is enhanced and blink reflex prepulse inhibition is reduced in patients with FMS, suggesting functional changes at the brainstem level in FMS.SignificanceReduced blink reflex prepulse inhibition concurs with altered sensory gating in patients with FMS.     

Effect of pramipexole on cutaneous-silent-period parameters in patients with restless legs syndrome

Objective

The aim of this study was to investigate cutaneous-silent-period (CSP) parameters in patients with restless legs syndrome (RLS) and examine the effects of treatment on CSP which, to our knowledge, have not been investigated till date.

Methods

A total of 25 patients with RLS and 25 healthy volunteers were studied. CSP latency and duration in the upper and lower extremities were examined in the two groups. In RLS patients, the variables were examined before and after pramipexole treatment.

Results

Lower-extremity CSP latency was longer (106.22 ± 11.69 ms vs. 91.67 ± 8.53 ms; p < 0.001) and CSP duration was shorter (35.50 ± 10.91 ms vs. 49.47 ± 6.43 ms; p < 0.001) in patients, compared with controls. In the patient group, CSP durations in the upper (40.88 ± 7.95 ms vs. 46.84 ± 10.22 ms; p = 0.006) and lower extremities (35.50 ± 10.91 ms vs. 44.91 ± 6.43 ms; p = 0.005) were prolonged after treatment, compared with pre-treatment values.

Conclusions

Small-fibre neuropathy may exist in RLS. In addition, we suggest that pramipexole may regulate cortical and spinal inhibitory mechanisms.

Significance

The use of CSP may aid in the diagnosis of RLS and may be used as a measure of treatment effectiveness.     

Reflex studies and MRI in the restless legs syndrome

Brainstem and spinal pathways of untreated patients with idiopathic restless legs syndrome (RLS) were examined using magnetic resonance imaging (MRI), blink reflex, first and second exteroceptive suppression (ES1, ES2) of temporalis muscle, and H reflex. MRI of 25 patients elicited no structural lesions beyond age-related atrophy or white matter lesions on proton density- and T2-weighted coronal and axial images. All patients showed a normal latency of the soleus H reflex (mean·SD latency=31.22·2.81 ms) and the H/M ratio was 48·17%. The duration and onset latency of the direct and indirect blink reflex responses were normal in all patients compared with those of controls (p>0.5). There was no significant difference in ES1 and ES2 latencies or duration between patients and controls (p>0.5). These results suggest that the etiology of RLS symptoms does not involve structural lesions.     

Noninvasive Vagus Nerve Stimulation: A New Therapeutic Approach for Pharmacoresistant Restless Legs Syndrome

AimsThis work aimed to study the effect of noninvasive vagus nerve stimulation on severe restless legs syndrome (RLS) resistant to pharmacotherapy.Materials and MethodsPatients with severe pharmacoresistant RLS were recruited from a tertiary care sleep center. Intervention was one-hour weekly sessions of transauricular vagus nerve stimulation (tVNS) in the left cymba concha, for eight weeks. The primary outcome measure was the score on the International Restless Legs Rating Scale (IRLS); secondary outcome measures were quality of life (Restless Legs Syndrome Quality of Life scale [RLSQOL]), mood disorders using the Hospital Anxiety and Depression scale subscale for depression (HADD) and Hospital Anxiety and Depression scale subscale for anxiety (HADA), and objective sleep latency, sleep duration, efficiency, and leg movement time measured by actigraphy.ResultsFifteen patients, 53% male, aged mean 62.7 ± 12.3 years with severe RLS, reduced quality of life, and symptoms of anxiety and depression, were included. The IRLS improved from baseline to session eight: IRLS 31.9 ± 2.9 vs 24.6 ± 5.9 p = 0.0003. Of these participants, 27% (4/15) had a total response with a decrease below an IRLS score of 20; 40% (6/15) a partial response with an improvement in the IRLS > 5 but an IRLS above 20; and 33% (5/15) were nonresponders. After tVNS, quality of life improved (RLSQOL 49.3 ± 18.1 vs 80.0 ± 19.6 p = 0.0005), as did anxiety (HADA 8.9 ± 5.4 vs 6.2 ± 5.0 p = 0.001) and depression (HADD 5.2 ± 4.5 vs 4.0 ± 4.0 p = 0.01). No significant change was found in actigraphic outcome measures.ConclusionsIn this pilot study, tVNS improved the symptoms of RLS in 66% of participants (10/15) with severe pharmacoresistant RLS, with concomitant improvements in quality of life and mood. Randomized controlled trials evaluating therapeutic efficacy of tVNS in RLS are needed to confirm these promising findings.     

Group I nonreciprocal inhibition in primary restless legs syndrome

Electrophysiological investigations of restless legs syndrome (RLS) have found spinal circuits impinging on motoneurones. We evaluated the H reflex threshold, latency, the Hmax/Mmax ratio, and the short latency autogenic inhibition in 7 patients with RLS and 10 age‐matched controls by testing the excitability changes in soleus H reflex Ib interneuron function. A significant reduction in Ib inhibition at 4 (P = 0.043), 5 (P = 0.007), and 6 ms (P = 0.001) of H reflex conditioning interstimulus interval was found in RLS patients. Data support the hypothesis that altered group I nonreciprocal inhibition is implicated in enhancing the spinal circuitry excitability of RLS, and are consistent with the view of an abnormal supraspinal drive to spinal interneurons in RLS. © 2007 Movement Disorder Society     

Higher nocturnal systolic blood pressure in patients with restless legs syndrome compared with patients with insomnia

BackgroundThere is evidence linking restless legs syndrome (RLS) with increased blood pressure (BP), but the mechanism of this relation remains unclear. Is the BP increased due to some features of RLS or to deterioration of sleep caused by RLS? This study compared values of nocturnal BP in patients with RLS and patients with insomnia. If increased BP in RLS is a consequence of disordered sleep, then it should be similar to increased BP in insomnia.MethodsPolysomnographic recordings of patients admitted to a sleep center with RLS or insomnia were analyzed. Demographic and clinical data, objective sleep parameters, and nocturnal BP were compared.ResultsRecordings of 35 patients with RLS and 33 patients with insomnia were analyzed. The groups did not significantly differ in terms of demographic traits or prevalence of other comorbidities. Patients with RLS had significantly higher systolic BP during the night (122.4 ± 13.8 vs 116.3 ± 13.4; p = 0.03) and during sleep (121.4 ± 13.3 vs 115.7 ± 13.3; p = 0.04). The only significant difference in sleep architecture was an increased number of periodic limb movements in sleep (PLMS) and PLMS with arousal in the RLS group (25.5 ± 24.6 vs 13.9 ± 22.7; p = 0.02 and 4.7 ± 5.4 vs 2.1 ± 3.4; p = 0.01).ConclusionOur results suggest that patients with RLS have higher nocturnal BP than patients with insomnia, and that increased PLMS is related to the increase in BP.     

Do tone duration changes that elicit the mismatch negativity also affect the preceding middle latency responses?

The human brain can automatically detect sound changes. Previous studies have reported that rare sounds presented within a sequence of repetitive sounds elicit the mismatch negativity (MMN) in the absence of attention in the latency range of 100–250 ms. On the other hand, a previous study discovered that occasional changes in sound location enhance the middle latency response (MLR) elicited in the latency range of 10–50 ms. Several studies have reported an increase in the amplitude of the MLR within the frame of oddball paradigms such as frequency and location changes. However, few studies have been conducted on paradigms employing a duration change. The purpose of the present study was to examine whether the peak amplitudes of the MLR components are enhanced by a change in duration. Twenty healthy Japanese men (age: 23.9 ± 2.9 years) participated in the present study. We used an oddball paradigm that contained standard stimuli with a duration of 10 ms and deviant stimuli with a duration of 5 ms. The peak amplitudes of the MLR for the deviant stimuli were then compared with those for the standard stimuli. No changes were observed in the peak amplitude of the MLR resulting from a duration change, whereas a definite MMN was elicited. The amplitude of the MLR was increased within the frame of oddball paradigms such as frequency and location changes. By contrast, the amplitude of the MLR was not changed within the duration change oddball paradigm that elicited the MMN.     

Exercise following immobility increases lower motor neuron excitability: F-wave and H-reflex studies

ObjectivesThe excitability of lower motor neurons can be explored non-invasively by several neurophysiological techniques, e.g., F-wave and H-reflex studies after a period of immobility and then after subsequent exercise. The aim of this study is to investigate the impact of exercise and high frequency repetitive nerve stimulation (RNS) following changes induced by 75 min of immobility.MethodsWe studied 10 healthy subjects following 75 min lower limb immobility, then randomized to RNS or cycling on different days. The neurophysiological studies of M-response, F-wave latency, F/M amplitude ratio and persistence; H-reflex threshold and latency, H/M amplitude ratio, and homosynaptic depression were performed at baseline, after immobility and immediately following the intervention, using stimulation of posterior tibial and peroneal nerves.ResultsAfter immobility F-wave latencies were delayed and homosynaptic depression at 2 Hz was increased (p < 0.025). RNS had no effect, but cycling exercise reduced H-reflex latencies (p = 0.025) and decreased homosynaptic depression at 2 Hz.DiscussionOur findings suggest that both proprioceptive stimulation and supraspinal pathways modulate intraspinal physiological changes after immobility. These observations suggest that specific exercise protocols may be useful in managing patients recovering from periods of immobility.     

Reliability of phrenic nerve conduction study: In healthy controls and in patients with primary lateral sclerosis

ObjectivePhrenic nerve conduction study is a marker of hypoventilation in amyotrophic lateral sclerosis. We aimed to evaluate its intra-rater reliability in healthy subjects and in a cohort of Primary Lateral Sclerosis (PLS) patients.MethodsEighteen healthy subjects and 16 PLS patients were included. All subjects underwent three phrenic nerve conduction evaluations (time interval: 1 week for healthy controls; 1 year for PLS patients). We analyzed intra-rater reliability for five parameters of the diaphragmatic motor response: latency; negative-peak duration, area and amplitude; peak-to-peak amplitude.ResultsHealthy subjects showed excellent inter-test reliability for most parameters (coefficients of variation <10%). In PLS patients coefficients of variation resulted <10% for latency and peak-to-peak amplitude, <20% for remaining parameters. Inter-test reliability was excellent for latency and peak-to-peak amplitude [intra-class correlation coefficient (ICC) > 0.9] and good for negative-peak amplitude and area (ICC 0.75 ≥ 0.9); duration was not reliable (ICC = 0.383). Negative peak and peak-to-peak amplitude had the least random error (respectively ±0.136 mV and ± 0.177 mV). All parameters showed homoscedasticity (R2 < 0.1).ConclusionsIntra-rater reliability is high for phrenic nerve study, especially for latency, peak-to-peak and negative-peak amplitude.SignificancePhrenic nerve conduction study is a reliable method to monitor respiratory function.     

The cutaneous silent period is mediated by spinal inhibitory reflex

High-intensity cutaneous stimuli inhibit tonically firing motor neurons resulting in a silent period (CSP) in EMG activity. To determine the central nervous system (CNS) circuitry of this inhibitory reflex, soleus H reflexes evoked by tibial nerve stimuli were conditioned by high-intensity sural stimuli in 5 normal men and 5 men with complete, traumatic cervical myelopathy. The sural-tibial interstimulus interval (ISI) was varied between 0 and 200 ms. In normals, the CSP in the tonically contracted soleus muscle began 90-100 ms after sural stimuli and had a duration of 60-80 ms. In the relaxed soleus, the conditioned soleus H-reflex amplitude was correspondingly reduced at ISIs of 60-120 ms. In patients, conditioned H-reflex amplitude was also reduced over the same ISI range, but the degree of inhibition was significantly less than in normals. These data support the hypothesis that the CSP is mediated by a spinal inhibitory reflex that is subject to supraspinal descending control.     

Terminal latency abnormality in amyotrophic lateral sclerosis without split hand syndrome

Amyotrophic lateral sclerosis (ALS) has a peculiar involvement pattern; clinically it is known as split hand syndrome and electrophysiologically shows abnormalities in the abductor pollicis brevis (APB)/abductor digiti minimi (ADM) ratio. The aim of this study was to find a significant electrophysiological parameter in upper limb onset ALS patients with normal APB/ADM ratio when compared to cervical spondylotic amyotrophy (CSA) and healthy controls. We retrospectively reviewed the electrophysiological results of 47 upper limb onset ALS and 42 CSA cases; 20 healthy individuals were included as controls. We included ALS and CSA patients with normal ADM/APB ratio (≥0.6, and ≤1.7), and the parameters of electrophysiological study were compared. The electrophysiological parameters of statistical significance among ALS, CSA and normal controls were: amplitude of median and ulnar nerves, the terminal latency of median nerve, F-wave latency of median and ulnar nerves, terminal latency ratio of ulnar/median nerves, and F-wave latency ratio of ulnar/median nerves (p < 0.05). Among these parameters, the terminal latency ratio of ulnar/median nerve and terminal latency of median nerve in ALS were significantly different with both of CSA and normal control (p < 0.006). The abnormality in the terminal latency of the median nerve can be partly explained by the distal motor axonal dysfunction due to sodium and potassium channel abnormalities. The hypothesis of distal axonopathy is known to play an important role in the pathogenesis of ALS causing a significant prolongation of the terminal latency in the median nerve and the ulnar/median nerve ratio.     

Amyotrophic lateral sclerosis weakens spinal recurrent inhibition and post-activation depression

ObjectivesAmyotrophic lateral sclerosis (ALS) disrupts motoneurons that control movement and some vital functions, however, exact details of the neuronal circuits involved in ALS have yet to be fully endorsed. To contribute to our understanding of the responsible neuronal circuits, we aimed to investigate the spinal recurrent inhibition (RI) and post-activation depression (P-AD) in ALS patients.MethodsIn two groups of ALS patients, i.e. lumbar-affected (clinical signs in leg muscles) and nonlumbar-affected (clinical signs in arms or bulbar region but not in the legs), RI and P-AD on the soleus muscle were investigated using single motor units and amplitude changes of H-reflex in surface electromyography, respectively. The data were compared with healthy subjects.ResultsCompared to controls, P-AD of H-reflex was reduced severely in lumbar-affected patients and reduced to a certain degree in nonlumbar-affected patients. Similarly, a significant reduction in the duration of RI on firing motoneurons was found in lumbar-affected patients (11.5 ± 2.6 ms) but not in nonlumbar-affected patients (29.7 ± 12.4 ms, P < 0.0001) compared to controls (30.8 ± 7.2 ms, P < 0.0001).ConclusionThe current study revealed that spinal inhibitory circuits are impaired in ALS.SignificanceThese findings may provide insight for proposing new therapeutic approaches and following disease progression in humans.     

Age-related characteristics and normative values of F waves in healthy infants

ObjectiveTo establish age-related characteristics and normative values of F waves in healthy Chinese infants.MethodsWe studied median, ulnar and tibial nerves on one side distally in 229 healthy Chinese infants (108 males) ranging from 1 to 12 months old.ResultsMinimal F-wave latencies (Fmin) showed a strong negative correlation to the age for median, ulnar and tibial nerves (P < 0.01) but no correlation to the height. Statistical analyses revealed a significant (P < 0.01) decrease of Fmin during the second month of life and no change (P > 0.05) thereafter. Dividing the infants into 1 month old (Group 1) and 2–12 months old (Group 2), normal values (Mean ± SD ms) of Fmin for tibial, median and ulnar nerves consisted of 23.38 ± 1.68, 17.19 ± 0.95 and 16.47 ± 1.06 for Group 1 and 21.42 ± 1.25, 14.50 ± 1.15 and 14.52 ± 0.90 for Group 2.ConclusionF-wave latencies shorten in the 2nd month of life and change little thereafter when age-related maturation counters the concomitant growth of the nerve length.SignificanceF waves can assess infantile neuropathies as a reliable measure, complementing the technically difficult conventional nerve conduction study in short limbs.