Cutaneous silent periods – Part 1: Update on physiological mechanisms

Updates to the Physiologic Mechanism, Anatomical Sites, and Diagnostic Utility of the Scratch Collapse Test: A Systematic Review

Background

The scratch collapse test (SCT) has gained popularity as a physical examination technique for diagnosing compression neuropathy. This systematic review aims to assess the reliability of the SCT as a diagnostic tool for compression neuropathy, as well as to propose the underlying physiological mechanisms involved. Specific criteria was developed to broaden the potential anatomical applications of the SCT.

Methods

A literature search was conducted using PubMed, Embase, Scopus, and Google Scholar. Eleven articles meeting predefined inclusion/exclusion criteria were selected for numerical analysis, which yielded sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy values.

Results

In total, 890 patients with carpal tunnel syndrome were reported in 10 studies. The mean (±SD) sensitivity, specificity, PPV, NPV, and accuracy were 0.442 ± 0.272, 0.788 ± 0.163, 0.834 ± 0.143, 0.433 ± 0.297, and 48.8% (range, 31%-82%), respectively. Of the studies that provided interrater reliability (κ), the mean was 0.544 ± 0.441, indicating moderate agreement. A total of 121 patients with cubital tunnel syndrome were reported in three studies, with a mean (±SD) sensitivity and specificity of 0.635 ± 0.367 and 0.945 ± 0.06, respectively. Twenty-four patients with peroneal nerve compression, reported in one study, had sensitivity, specificity, PPV, NPV, and accuracy of 0.77, 0.99, 0.95, 0.92, and 93%, respectively.

Conclusions

Current literature indicates that the SCT can serve as a provocative test to assist in diagnosing compression neuropathy. Nevertheless, the heterogeneity of reported values underscores the necessity for further investigation aimed at enhancing the objectivity of SCT, thus improving interrater reliability and minimizing potential bias.

Differential diagnosis value of sympathetic skin response and cutaneous silent period on early-stage multiple system atrophy and Parkinson disease

PURPOSE

Early differentiation between Parkinson's disease (PD) and Multiple system atrophy (MSA), particularly the parkinsonian subtypes (MSA-P), is challenging due to similar clinical symptoms. We aimed to evaluate Sympathetic skin response (SSR) and Cutaneous silent period (CSP) parameters in patients with MSA-P and PD to identify possible biomarkers that could distinguish the two groups of patients in early stage.

METHODS

22 individuals with early-stage MSA-P, 29 with early-stage PD, and 28 healthy controls were recruited from Guangdong Provincial People's Hospital. Demographic data was collected for all participants. Their SSR and CSP were evaluated using clinical electromyography equipment. Data were compared between different groups. The diagnostic accuracy of SSR and CSP parameters was calculated using the ROC curve. Logistic regression was used to produce an integration model to enhance diagnostic utility.

RESULTS

Foot amplitude, CSP end latency and duration distinguished MSA-P from PD with the area under the curve (AUC) 0.770, 0.806, and 0.776, respectively. Foot and hand SSR amplitude distinguished PD from HC with the AUC 0.871 and 0.768, respectively. Foot SSR amplitude, hand SSR amplitude, and CSP end latency distinguished MSA-P from HC with the AUC 0.964, 0.872, and 0.812, respectively. The combination of SSR and CSP parameters differentiation between MSA-P and PD, PD and HC with the AUC 0.829 and 0.879, respectively.

CONCLUSIONS

Analysis of SSR and CSP parameters showed excellent diagnostic accuracy in discriminating patients with early-stage MSA-P from HC and good diagnostic accuracy in discriminating patients with MSA-P from PD with early stages.

Multiple averaged records to identify Aδ-fibers in sensory nerves

BACKGROUND

Existing methods identify only ≈10 Aδ-fibers in human sensory nerves per recording. This study examines methods to increase the detection of Aδ-fibers.

NEW METHOD

Two to 20 averages of 500 replicate responses to epidermal nerve stimulation are obtained. Pairs of different averages are constructed. Each pair is analyzed with algorithms applied to amplitude and frequency to detect replication of responses to stimulation as "simultaneous similarities in two averages" (SS2AVs) at ≥99.5th percentile of control. In a pair of averages the latencies of amplitude and frequency SS2AVs for the same response to stimulation may differ by ≤0.25 ms. Therefore, Aδ-fibers are identified by the 0.25 ms moving sum of SS2AV latencies of the pairs of averages.

RESULTS

Increasing averages increases pairs of different averages and detection of Aδ-fibers: from 2 to 10 Aδ-fibers with two averages (one pair) to >50 Aδ-fibers with 12-20 averages (66-190 pairs).

COMPARISON WITH EXISTING METHOD(S)

Existing methods identify ≤10 Aδ-fibers in 10 averages/45 pairs with the medians of amplitude and frequency algorithms applied to all 45 pairs. This study identifies Aδ-fibers (i) by applying these algorithms at the 99.5th percentile of control, (ii) to each pair of averages and (iii) by the 0.25 ms sum of algorithm identified events (SS2AVs) in all pairs. These three changes significantly increase the detection of Aδ-fibers, e.g., in 10 averages/45pairs from 10 to 45.

CONCLUSIONS

Three modifications of existing methods can increase the detection of Aδ-fibers to an amount suitable (>50 with ≥12 averages) for statistical comparison of different nerves.

Early detection of nerve involvement in presymptomatic TTR mutation carriers: exploring potential markers of disease onset

BACKGROUND

Hereditary transthyretin (ATTRv) amyloidosis is a heterogeneous, progressive, multisystemic disease with a life-threatening course if left untreated. Given the current availability of effective therapies, close follow-up of presymptomatic TTR mutation carriers is essential to recognize disease onset at the earliest sign. In addition to routine techniques, in recent years several novel tools have been proposed, although a consensus on their use has not been reached yet. In this paper, we aimed to evaluate possible markers of neuropathic disease onset intended to discriminate clinically asymptomatic carriers from early symptomatic patients, thus allowing timely treatment initiation.

METHODS

Thirty-eight presymptomatic carriers were enrolled. Clinical and electrophysiological findings at first evaluation and follow-up were collected. All carriers underwent an extensive clinical and instrumental evaluation according to the standard clinical practice. One or more non-routine investigations, whose use in this field is not yet validated (henceforth "unconventional"), were additionally assessed in a subgroup of individuals.

RESULTS

Based on the exclusive use of routine investigations, it was possible to define disease onset in 4/38 carriers during the follow-up. Employing additionally one or more "unconventional" tests, abnormal findings, indicative of a possible "conversion" to symptomatic disease, were detected in further 12 cases. More than half of our study cohort showed findings suggestive of small nerve fiber (SF) involvement at either invasive or non-invasive tests.

CONCLUSIONS

A close, multidisciplinary monitoring of presymptomatic TTR mutation carriers is fundamental, and diagnostic workup should include both routine and "unconventional" tests. Assessment of SF involvement is important also in non-endemic countries.

Segmental motor neuron dysfunction in amyotrophic lateral sclerosis: Insights from H reflex paradigms

INTRODUCTION/AIMS

In amyotrophic lateral sclerosis (ALS), the role of spinal interneurons in ALS is underrecognized. We aimed to investigate pre- and post-synaptic modulation of spinal motor neuron excitability by studying the H reflex, to understand spinal interneuron function in ALS.

METHODS

We evaluated the soleus H reflex, and three different modulation paradigms, to study segmental spinal inhibitory mechanisms. Homonymous recurrent inhibition (H'RI ) was assessed using the paired H reflex technique. Presynaptic inhibition of Ia afferents (H'Pre ) was evaluated using D1 inhibition after stimulation of the common peroneal nerve. We also studied inhibition of the H reflex after cutaneous stimulation of the sural nerve (H'Pos ).

RESULTS

Fifteen ALS patients (median age 57.0 years), with minimal signs of lower motor neuron involvement and good functional status, and a control group of 10 healthy people (median age 57.0 years) were studied. ALS patients showed reduced inhibition, compared to controls, in all paradigms (H'RI 0.35 vs. 0.11, p = .036; H'Pre 1.0 vs. 5.0, p = .001; H'Pos 0.0 vs. 2.5, p = .031). The clinical UMN score was a significant predictor of the amount of recurrent and presynaptic inhibition.

DISCUSSION

Spinal inhibitory mechanisms are impaired in ALS. We argue that hyperreflexia could be associated with dysfunction of spinal inhibitory interneurons. In this case, an interneuronopathy could be deemed a major feature of ALS.

Single motor unit estimation of the cutaneous silent period in ALS

OBJECTIVE

Recent evidence indicated that amyotrophic lateral sclerosis (ALS) also impairs spinal circuits, including those mediating cutaneous silent period (CSP). However, most studies utilised surface electromyography (sEMG), which needs more resolution to pinpoint changes at the single motoneuron level. We aimed to investigate CSP properties using single motor unit discharges in ALS.

METHODS

In mild and severe ALS patients and controls, CSP was recorded in the first dorsal interosseus and analysed using the discharge rate method, which accurately shows the inhibitory postsynaptic potentials (IPSPs) profile.

RESULTS

Our findings confirmed that the CSP latency was prolonged only in severe ALS patients. Moreover, the CSP duration was similar in each group, but late-stage ALS patients tend to have a longer CSP duration. The discharge rate method revealed a significantly longer duration (up to 150 ms) than the duration detected using sEMG. Strikingly, the motoneuron discharge rate - IPSP duration inverse relationship is lost in ALS patients, indicating a possible impairment in the motoneuron integrative properties.

CONCLUSIONS

Our data support previous findings of prolonged latency, presented input-output modifications of motoneurons, and revealed the entire course of the CSP, representing a much stronger inhibitory event than previously thought.

SIGNIFICANCE

Motoneuron integrative property modification assessed by CSP could be a new biomarker for ALS.

Segmental Reflex, Long Latency Reflex, and Mixed Nerve Silent Period in Dystonia

We hypothesized that "long latency reflexes" (LLRs), associated segmental reflex (SR), and mixed nerve silent periods (MnSPs) recorded on the distal upper extremity muscles would behave differently in patients with cervical dystonia and focal hand dystonia. We enrolled patients with cervical dystonia, generalized dystonia, focal hand dystonia, and healthy individuals. We recorded SR, LLRs, and MnSPs. The mean amplitude of SR on the affected side of focal hand dystonia was significantly lower (p = 0.010). The parameters related to LLRs and MnSPs were not different between groups. We suggest, using SR, LLRs, and MnSPs, we could not show an electrophysiological signature specific to dystonia.

Psychophysiological and Neurophysiological Correlates of Dropping Objects from Hands in Carpal Tunnel Syndrome

BACKGROUND

Dropping objects from hands (DOH) is a common symptom of carpal tunnel syndrome (CTS). We evaluated the clinical, neurophysiological, and psychophysiological features of 120 CTS patients to elucidate the DOH pathophysiology. Forty-nine healthy controls were included.

METHODS

In the patients, the Boston Carpal Tunnel Questionnaire (BCTQ), the Douleur Neuropathique 4 questions (DN4), and a numeric rating scale for pain (NRS) were evaluated. In patients and controls, we evaluated bilateral median and ulnar motor and sensory nerve conduction studies, cutaneous silent period and cutaneomuscular reflexes (CMR) of the abductor pollicis brevis, cold-detection threshold (CDT) and heat-pain detection threshold (HPT) at the index, little finger, and dorsum of the hand, and vibratory detection threshold at the index and little finger by quantitative sensory testing.

RESULTS

CTS with DOH had higher BCTQ, DN4 and NRS, lower median sensory action potential, longer CMR duration, lower CDT and higher HPT at all tested sites than controls and CTS without DOH. Predictive features for DOH were abnormal CDT and HPT at the right index and dorsum (OR: 3.88, p: 0.03) or at the little finger (OR: 3.27, p: 0.04) and a DN4 higher than 4 (OR: 2.16, p < 0.0001).

CONCLUSIONS

Thermal hypoesthesia in median and extra-median innervated territories and neuropathic pain are predictive of DOH in CTS.

Evaluation of the Cutaneous Silent Period in a Healthy Brazilian Population

PURPOSE

To establish cutaneous silent period (CSP) normative values and investigate the variables that may influence them.

METHODS

We tested 41 healthy subjects. All subjects underwent nerve conduction studies, and we evaluated the CSP in both arms.

RESULTS

Four subjects did not have CSP and were excluded. The analyses were performed in the healthy group composed of 23 women and 14 men, with a mean age of 35 (range, 19-64) years. The CSP median duration was 23.2 milliseconds (ms), with 2 to 98th percentile at 11.3 and 48.7 ms. The median onset latency was 87.9 (range, 72.9-109) ms, and the median end latency was 112 (range, 93.8-138) ms. The CSP onset latency positively correlated with height, whereas CSP end latency and duration were weakly but significantly associated with age. Some measurements of ulnar nerve conduction study also correlated with CSP measures. The interrater coefficients for the primary measures of onset and end latency demonstrates the reproducibility of the method.

CONCLUSIONS

The CSP with the fifth digit stimulation and recording from the abductor digiti minimi muscle is a valid diagnostic tool that can be used in clinical practice.

The cutaneous silent period as a measure of upper motor neuron dysfunction in amyotrophic lateral sclerosis

OBJECTIVES

We investigated the cutaneous silent period (CutSP) as a measure of upper motor neuron (UMN) dysfunction in amyotrophic lateral sclerosis.

METHODS

The onset latency, duration, and amount of EMG suppression of the CutSP were compared with clinical UMN signs in 24 patients with amyotrophic lateral sclerosis (ALS). UMN signs were quantified using a clinical index and transcranial magnetic stimulation (TMS). Central motor conduction time (CMCT), cortical motor threshold and motor evoked potential amplitudes were assessed as measures of UMN dysfunction. CutSP was studied in abductor digit minimi (ADM) and tibialis anterior (TA) EMG recordings following stimulation of the 5th finger and sural nerves respectively. Non-parametric tests and binomial logistic regression were applied to evaluate the data.

RESULTS

CutSP onset latency was increased in ALS patients, compared to healthy controls, both for ADM and TA muscles. In limbs with clinical UMN signs or abnormal TMS findings, the CutSP onset latency was particularly increased. There was a significant positive correlation between CutSP onset latency and the UMN score in both upper and lower limbs. In TA muscles there was also a negative correlation between CutSP onset latency and EMG suppression. The logistic regression model based on CutSP parameters correctly classified more than 70% of the cases regarding the presence of clinical signs of UMN lesion, in both upper and lower limbs. The results were not significant for TMS.

CONCLUSION

We conclude that upper limb CutSP changes associates with UMN lesion in ALS. This neurophysiological measurement merits further investigation in ALS.

[Diabetic neuropathy and diabetic foot syndrome (update 2023)]

These are the guidelines for diagnosis and treatment of diabetic neuropathy and diabetic foot.The position statement summarizes characteristic clinical symptoms and techniques for diagnostic assessment of diabetic neuropathy, including the complex situation of the diabetic foot syndrome. Recommendations for the therapeutic management of diabetic neuropathy, especially for the control of pain in sensorimotor neuropathy, are provided. The needs to prevent and treat diabetic foot syndrome are summarized.

The Silent Period for Small Fiber Sensory Neuropathy Assessment in a Mixed Cohort of Transthyretin-Mediated Amyloidosis

Background: Transthyretin-mediated amyloidosis (ATTR) is a rare multisystemic disease involving the peripheral nervous system and heart. Autonomic and small fiber involvement is one of the hallmarks of ATTR, and many tools have been proposed to assess this aspect. Aim: The aim of this study was to investigate cutaneous and mixed nerve silent periods (CSP and MnSP) as instruments for small fiber assessment. Methods: A total of 21 ATTR patients, 20 healthy controls, and 18 asymptomatic carriers underwent a sensory conduction study from the right sural and non-dominant ulnar nerves. A motor conduction study from the right deep peroneal and non-dominant ulnar nerves, with their F waves, CSPs, and MnSPs, was performed. Results: The amplitudes of the sural and ulnar sensory nerves and of the peroneal and ulnar motor nerves were reduced in ATTR patients compared to the other groups. F waves from the ulnar and peroneal nerves showed no differences between the three groups. The CSP and MnSP latency, but not amplitude, were increased in both the ulnar and peroneal nerves of ATTR patients. Conclusions: ATTR patients showed axonal involvement of large sensory and motor nerve fibers and demyelinating features of small sensory fibers.

Application of electrophysiological measures in degenerative cervical myelopathy

Degenerative cervical myelopathy (DCM) is one of the leading causes of progressive spinal cord dysfunction in the elderly. Early diagnosis and treatment of DCM are essential to avoid permanent disability. The pathophysiology of DCM includes chronic ischemia, destruction of the blood–spinal cord barrier, demyelination, and neuronal apoptosis. Electrophysiological studies including electromyography (EMG), nerve conduction study (NCS), motor evoked potentials (MEPs) and somatosensory evoked potentials (SEPs) are useful in detecting the presymptomatic pathological changes of the spinal cord, and thus supplementing the early clinical and radiographic examinations in the management of DCM. Preoperatively, they are helpful in detecting DCM and ruling out other diseases, assessing the spinal cord compression level and severity, predicting short- and long-term prognosis, and thus deciding the treatment methods. Intra- and postoperatively, they are also useful in monitoring neurological function change during surgeries and disease progression during follow-up rehabilitation. Here, we reviewed articles from 1979 to 2021, and tried to provide a comprehensive, evidence-based review of electrophysiological examinations in DCM. With this review, we aim to equip spinal surgeons with the basic knowledge to diagnosis and treat DCM using ancillary electrophysiological tests.

Recording cutaneous silent period parameters in hereditary and acquired neuropathies

Background Cutaneous silent period (CSP) is the interruption in muscle activity after painful stimulation of a sensory nerve.

Objective The aim of the present study is to assess CSP changes in patients with polyneuropathy (PNP).

Methods The present study was carried out to assess CSP in individuals with diabetes (DM) and Charcot-Marie-Tooth (CMT) disease. The sample comprised 24 individuals with DM, 10 individuals with CMT1 disease, and 10 individuals with CMT2 disease. The control group (CG) consisted of 59 individuals.

Results The mean latencies recorded for the upper limbs in the CG were 79.2 milliseconds (onset latency), 69.3 milliseconds (50% reduction latency), 112.2 milliseconds (end latency), and 33.1 milliseconds (CSP duration). On the other hand, the mean latencies recorded for the lower limbs were 99.0 milliseconds (onset latency), 85.0 milliseconds (50% reduction latency), 136.9 milliseconds (end latency), and 38.2 milliseconds (CSP duration). The mean latencies recorded for the CG were significantly lower than the ones recorded for other groups, both in the upper and lower limbs.

Conclusions Cutaneous silent period values recorded for the CG in the present study were close to the ones reported in studies available in the literature. Abnormal CSP parameters were observed in the group of individuals with PNP. The end latency in the lower limbs helped differentiating the demyelinating subgroup from the axonal one.

Clinical neurophysiology of Parkinson's disease and parkinsonism

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This review is part of the series on the clinical neurophysiology of movement disorders and focuses on Parkinson’s disease and parkinsonism.

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The pathophysiology of cardinal parkinsonian motor symptoms and myoclonus are reviewed.

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The recordings from microelectrode and deep brain stimulation electrodes are reported in detail.

This review is part of the series on the clinical neurophysiology of movement disorders. It focuses on Parkinson’s disease and parkinsonism. The topics covered include the pathophysiology of tremor, rigidity and bradykinesia, balance and gait disturbance and myoclonus in Parkinson’s disease. The use of electroencephalography, electromyography, long latency reflexes, cutaneous silent period, studies of cortical excitability with single and paired transcranial magnetic stimulation, studies of plasticity, intraoperative microelectrode recordings and recording of local field potentials from deep brain stimulation, and electrocorticography are also reviewed. In addition to advancing knowledge of pathophysiology, neurophysiological studies can be useful in refining the diagnosis, localization of surgical targets, and help to develop novel therapies for Parkinson’s disease.

Modulation of motor evoked potentials via the cutaneous silent period within proximal-distal muscles in the upper-limb

A single pulse of high intensity electrical current delivered to the digits of the hand during voluntary contractions produces a period of decreased electromyographic (EMG) activity, known as a cutaneous silent period (CSP) (Caccia G and Violini A, 1973;Inghilleri M et al., 1997;Uncini A et al., 1991). Pairing transcranial magnetic stimulation (TMS) with digit stimulation results in motor evoked potentials (MEPs) with reduced amplitudes in a thenar muscle (Kofler, 2008). It is not known if similar behavior can be observed in more proximal upper-limb muscles. The current study investigated the CSP on several muscles throughout the upper-limb. 14 subjects performed isometric contractions with the following muscles: abductor pollicis brevis (APB), flexor carpi radialis (FCR), extensor carpi radialis (ECR), biceps brachii (BIC), triceps brachii (TRI), anterior deltoid (AD), and posterior deltoid (PD). During the isometric contractions, subjects experienced three different stimulation conditions: electrical stimulation (10x perceptual threshold) of digit II only (CSP), transcranial magnetic stimulation only (TMS), and a pairing of digit II stimulation and TMS (TMS+). The TMS evoked MEP was significantly greater than the TMS+ MEP for APB (p <0.001), FCR (p =0.006), and BIC (p <0.049) muscles. The opposite relationship was seen within the PD (p <0.047) muscle. An ANOVA test of normalized MEP values (TMS+/TMS) showed significant differences in APB vs TRI (p = 0.004) and PD (p = 0.003), and in FCR vs TRI (p = 0.046) and PD (p = 0.037) muscles. The results suggest that the CSP modulates descending drive differentially across upper-limb muscles.

Alternative Options for Complex, Recurrent Pain States Using Cannabinoids, Psilocybin, and Ketamine: A Narrative Review of Clinical Evidence

With emerging information about the potential for morbidity and reduced life expectancy with long-term use of opioids, it is logical to evaluate nonopioid analgesic treatments to manage pain states. Combinations of drugs can provide additive and/or synergistic effects that can benefit the management of pain states. In this regard, tetrahydrocannabinol (THC) and cannabidiol (CBD) modulate nociceptive signals and have been studied for chronic pain treatment. Psilocybin, commonly known as “magic mushrooms”, works at the serotonin receptor, 5-HT_2A. Psilocybin has been found in current studies to help with migraines since it has a tryptamine structure and works similarly to triptans. Psilocybin also has the potential for use in chronic pain treatment. However, the studies that have looked at alternative plant-based medications such as THC, CBD, and psilocybin have been small in terms of their sample size and may not consider the demographic or genetic differences in the population because of their small sample sizes. At present, it is unclear whether the effects reported in these studies translate to the general population or even are significant. In summary, additional studies are warranted to evaluate chronic pain management with alternative and combinations of medications in the treatment of chronic pain.

Excitatory and inhibitory responses to cervical root magnetic stimulation in healthy subjects

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We studied excitatory and inhibitory responses to cervical root magnetic stimulation.

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CRMS elicited direct and reflex responses in hand muscles.

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CRMS is painless and well tolerated and, therefore, applicable to clinical studies.

Objectives

To characterize direct and reflex hand muscle responses to cervical root magnetic stimulation (CRMS) in healthy volunteers during sustained voluntary contraction.

Methods

In 18 healthy volunteers, we recorded from the first dorsal interosseous (FDI) muscle the responses to CRMS of progressively increasing intensity and level of muscle contraction. The compound muscle action potential (CMAP) and the silent period (SP) were compared to those obtained with plexus, midarm and wrist stimulation. Additionally, in a smaller number of subjects, we obtained the peristimulus time histogram (psth) of single motor unit firing in the FDI, examined the effects of vibration and recorded the modulation of sustained EMG activity in muscles of the lower limbs.

Results

Increasing CRMS intensity led to larger CMAP with no relevant changes in SP1 or SP2, except for lower amplitude of the burst interrupting the silent period (BISP). Increasing the level of muscle contraction led to reduced CMAP, shorter SP duration and increased BISP amplitude. The psth analysis showed the underlying changes in the motor unit firing frequency that corresponded to the changes seen in the CMAP and the SP with surface recordings. Progressively distal stimulation led to CMAPs of shorter latency and increased amplitude, SPs of longer latency and shorter duration, and a BISP of longer latency. Vibration led to reduction of the SP. CRMS induced SPs in muscles of the lower limb.

Conclusions

CRMS induces excitatory and inhibitory responses in hand muscles, fitting with the expected behavior of mixed nerve stimulation at very proximal sites.

Significance

Characterization of the effects of CRMS on hand muscles is of physiological and potentially clinical applicability, as it is a painless and reliable procedure.

Cutaneous silent period in ulnar neuropathy at the elbow

INTRODUCTION/AIMS

The cutaneous silent period (CSP) reflects the function of A-delta sensory fibers. There are few studies on CSP in nerve entrapment syndromes. This study aims to evaluate the neurophysiological abnormalities of small-diameter sensory fibers in ulnar neuropathy at the elbow (UNE) by means of CSP.

METHODS

We consecutively evaluated UNE patients at one electrodiagnostic laboratory. The CSP was obtained upon stimulating the fifth (D5) and third digits, recording from the first dorsal interosseous (FDI) and abductor pollicis brevis (APB) muscles.

RESULTS

We enrolled 37 UNE patients (mean age 55.4 ± 11.2 y) and 30 controls (mean age 51.2 ± 11.1 y). The combinations of the D5-APB and D5-FDI mean onset latencies of CSP were significantly more prolonged in patients (83.7 ± 6.8 and 84.5 ± 8 ms, respectively) than in controls (78.2 ± 8.1 and 79.4 ± 7.6 ms, respectively). The D5-FDI duration of CSP was shorter in patients (52.2 ± 8.3 ms) than in controls (55.8 ± 7 ms). The mean of the onset latencies of D5-FDI and D5-APB was related to the clinical severity (P = .013 and .0025, respectively). D5-APB and D5-FDI onset latencies were more prolonged and the duration was shorter in the UNE group with absent ulnar sensory nerve action potentials (SNAPs) and axonal motor damage than in patients with preserved SNAPs and with demyelinating damage.

DISCUSSION

CSP was able to demonstrate abnormalities of small-diameter myelinated sensory fibers. This damage was directly related to UNE severity and to axonal damage of motor fibers. Absence of a sensory large-diameter fiber response did not exclude preserved residual small fiber conduction.

Electrophysiological findings in patients with restless legs syndrome

BACKGROUND

Restless legs syndrome (RLS) manifests as an urge to move the body to relieve the discomfortable sensations, primarily when resting, sitting, laying down, or sleeping. Diagnosis of RLS relies on clinical criteria, and the immobilization test was the only instrumental tool with equivocal results.

OBJECTIVES

To assess different electrophysiological findings in patients with RLS, and compare the diagnostic values of these parameters in the diagnosis of RLS.

METHODS

30 patients with primary RLS and 30 controls who were matched for age and gender were studied. Participant's demographics, laboratory findings, and electrophysiological test, namely nerve conduction studies (NCS), cutaneous silent period (CSP), H reflex and sympathetic skin response (SSR), F-wave latency, amplitude, F-wave duration (FWD), and the ratio between FWD and duration of the corresponding compound muscle action potential (FWD/CMAPD) were analyzed.

RESULTS

None of the patients showed altered NCS data. FWD of upper (12.37 ± 2.77 ms) and lower limb (21.71 ± 5.24 ms) were significantly longer in patients. Also, FWD/CMAP duration of the upper (1.03 ± 0.2) and lower limb (2.02 ± 0.55) was longer in patients. Likewise, they exhibited delayed CSP latency from TA (110.62 ± 13.73 ms) and APB (77.35 ± 12.16 ms) whereas the CSP duration from TA and APB was decreased (37.36 ± 11.59 ms; 42.55 ± 7.97 ms, respectively). The SSR latency was not different, and right-sided H reflex amplitude (5.07 ± 3.98 mV) and H/M ratio (0.65 ± 1.81) were significantly increased in the patient group.

CONCLUSION

The data suggest that there may be a dysfunction of the inhibitory/excitatory circuits at a spinal level; and no pathology in the peripheral nerves. The unilateral difference of H reflex amplitude and H/M ratio may suggest asymmetrical central inhibitory dysfunction. Further prospective studies with larger cohorts are now needed to evaluate the pathophysiology of RLS with different neurophysiological assessment tools.

Exploring the effect of capsaicin-induced central sensitization on the upper limb nociceptive withdrawal reflex threshold

The nociceptive withdrawal reflex (NWR) threshold is commonly employed in the lower limb to assess clinical and experimentally induced pain. However, no studies to date have investigated changes in spinal nociception in the upper limb, via the NWR threshold, following experimentally induced central sensitization (CS). We tested the hypothesis that experimentally induced CS of the C5-C6 spinal segment significantly reduces NWR thresholds in muscles of the upper limb. Upper limb NWR thresholds from 20 young, healthy adults were assessed by applying noxious electrical stimuli to the right index finger and recording muscle activity from the biceps brachii (BI), triceps brachii (TRI), flexor carpi ulnaris (WF), and extensor carpi radialis longus (WE) muscles via surface electromyography. Topical cream (either 0.075% capsaicin, or control) was applied to the C5-C6 dermatome of the lateral forearm (50 cm²). NWR thresholds were compared at baseline, and four 10-min intervals after topical application. WF muscle NWR thresholds were significantly reduced in the capsaicin session compared to control, while TRI muscle NWR thresholds were significantly reduced 40 min after capsaicin application only (p < 0.05). There were no significant differences for BI or WE muscle NWR thresholds. We observed poor to moderate test-retest reliability for all upper limb NWR thresholds, a key contributor to the selective reduction in NWR thresholds among muscles. Accordingly, while our findings demonstrate some comparability to previously reported lower limb NWR studies, we concurrently report limitations of the upper limb NWR technique. Further exploration of optimal parameters for upper limb NWR acquisition is needed.

Effects of Medications and Subthalamic Nucleus-Deep Brain Stimulation on the Cutaneous Silent Period in Patients With Parkinson's Disease

OBJECTIVES

We sought to evaluate whether the cutaneous silent period (CSP) could be an electrophysiological indicator reflective of the effects of therapy for Parkinson's disease (PD), including anti-PD medications or deep brain stimulation (DBS).

MATERIAL AND METHODS

We recorded the CSP in 43 patients with PD prior to and following the administration of medication during a pre-DBS evaluation (30 cases) and the "on" and "off" states of subthalamic nucleus DBS (13 cases). The CSP was elicited from the abductor pollicis brevis muscle by an electrical stimulation of the index finger that was 2, 4, and 15 times stronger than the sensory threshold (ST). We measured changes in latencies, including the onset, duration, and end of CSP, and waveform scores from 0 to 3. The correlation between the CSP score and unified PD rating score part III (UPDRS-III) also was assessed.

RESULTS

The onset latency and duration of CSP were significantly different between high (15ST) and low-strength stimulations (2ST and 4ST). However, there were no significant latency changes (onset, duration, end of CSP) before and after receiving medication, or during the on and off state of the DBS. Anti-PD medications substantially increased the CSP waveform score only in the 4ST state. However, the waveform score significantly increased in all stimuli states during the DBS-on state. Both medication and the DBS-on state decreased the UPDRS-III. Nevertheless, there was no statistically significant correlation between the UPDRS-III and CSP waveform scores.

CONCLUSION

Different onset latencies and the duration of CSP between low- and high-strength stimuli support the hypotheses proposing two different reflex pathways. Despite being independent from the UPDRS-III, the CSP may be an electrophysiological indicator reflective of the changes in inhibitory activity to the spinal α-motoneuron in response to anti-PD medications and DBS.

The cutaneous silent period in motor neuron disease

OBJECTIVE

To investigate the cutaneous silent period (CSP) by measuring its onset latency, duration and amount signal suppression in patients with motor neuron disease (MND) grouped according to the intensity of upper motor neuron involvement (UMN), and to test the effect of contralateral hand contraction.

METHODS

Painful stimulation was applied at the V finger, and contraction recorded from the abductor digiti minimi (ADM) muscle (baseline condition). Afterwards, CSP was studied during strong contralateral ADM contraction (test condition). 10-15 consecutive traces were recorded for each condition, signals were rectified, averaged, and analyzed offline.

RESULTS

46 patients were investigated, 15 with progressive muscular atrophy (PMA), 16 with typical amyotrophic lateral sclerosis (ALS), 15 with primary lateral sclerosis/predominant UMN-ALS (PLS+UMN-ALS), and 28 controls. In the baseline condition, all MND groups showed delayed onset latencies (p = 0.001). There was no significant difference in the CSP duration. Suppression was lower in the PLS + UMN-ALS group (p = 0.004). In the control group, contralateral contraction did not change CSP, but onset latency shortened significantly in the PMA group.

CONCLUSIONS

CSP onset latency is delayed in all investigated groups of MND, including in PMA, indicating subclinical UMN involvement. Changes in CSP can indicate UMN lesion in MND.

SIGNIFICANCE

CSP should be explored to identify UMN involvement in MND.

Slowly conducting potentials in human sensory nerves

BACKGROUND

In clinical practice, small myelinated sensory fibers, Aδ-fibers, conveying mainly pain and temperature sensations, cannot be examined with available nerve conduction study techniques. Currently, these fibers can only be examined with experimental or very specialized and not commonly available nerve conduction techniques, or only indirectly with cerebral evoked potentials.

NEW METHOD

This study uses equipment and methods available in clinical neurophysiology laboratories to record from human sensory nerves ≥1000 averaged responses to focal, non-painful stimuli applied by a special electrode to epidermal nerves. The averaged responses to odd numbered stimuli are compared to the averaged responses to even numbered stimuli. An algorithm identifies potentials common in both averages. The 99^th and 99.9^th percentiles for this algorithm are obtained from control records without stimulation and applied to records with stimulation to identify potentials resulting from stimulation of intraepidermal nerves.

RESULTS

The algorithm identifies numerous negative and positive potentials as being different from controls at the 99th and 99.9^th percentile levels. The conduction velocities of the potentials range from of 1.3-29.9 m/s and are compatible with conduction velocities of Aδ-fibers.

COMPARISON WITH EXISTING METHOD(S)

No existing methods.

CONCLUSIONS

The stimulation, recording and data analysis methods used in this study can be applied in the clinical EMG laboratory to identify Aδ-fibers in human sensory nerves.

Cannabinoids in multiple sclerosis: A neurophysiological analysis

OBJECTIVES

To investigate the action of cannabinoids on spasticity and pain in secondary progressive multiple sclerosis, by means of neurophysiological indexes.

MATERIAL AND METHODS

We assessed 15 patients with progressive MS (11 females) using clinical scales for spasticity and pain, as well as neurophysiological variables (H/M ratio, cutaneous silent period or CSP). Testing occurred before (T0) and during (T1) a standard treatment with an oral spray containing delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD). Neurophysiological measures at T0 were compared with those of 14 healthy controls of similar age and sex (HC). We then compared the patient results at the two time points (T1 vs T0).

RESULTS

At T0, neurophysiological variables did not differ significantly between patients and controls. At T1, spasticity and pain scores improved, as detected by the Modified Ashworth Scale or MAS (P = .001), 9-Hole Peg Test or 9HPT (P = .018), numeric rating scale for spasticity or NRS (P = .001), and visual analogue scale for pain or VAS (P = .005). At the same time, the CSP was significantly prolonged (P = .001).

CONCLUSIONS

The THC-CBD spray improved spasticity and pain in secondary progressive MS patients. The spray prolonged CSP duration, which appears a promising tool for assessing and monitoring the analgesic effects of THC-CBD in MS.

Cutaneous silent period in patients with spinal muscular atrophy type 2 and type 3

OBJECTIVE

The aim of this study was to examine cutaneous silent periods (CSPs) in spinal muscular atrophy (SMA) type 2 and type 3 patients.

METHODS

Fourteen patients with SMA and 14 healthy subjects were included. CSPs were recorded from thenar muscles after painful stimulation of the index finger during slight thumb abduction. CSP parameters (including onset latency, duration, index of suppression, long-loop reflex, and post-inhibitory rebound activity) were measured. All parameters were compared between SMA patients and healthy subjects using the Mann-Whitney U test. We then correlated CSP parameters to Hammersmith Functional Motor Scale Expanded (HFMSE) scores in SMA patients by Spearman-rho testing.

RESULTS

No CSP parameter except E3% (i.e., the post-inhibitory rebound activity relative to pre-stimulus baseline) differed significantly between SMA patients and healthy subjects. E3% was significantly smaller in patients than healthy individuals. HFMSE scores of SMA patients correlated negatively with CSP duration and positively with E3%.

DISCUSSION

Smaller E3%, correlating with longer CSP duration, in SMA patients with more severe clinical findings and therefore more marked motoneuron loss suggests that the E3 component following the CSP is directly affected by motoneuron loss.

Modulation of the cutaneous and cortical silent period in response to local menthol application

In this study, we investigated the effects of menthol application on the cortical and cutaneous silent period (CSP/cutSP). Both the cutSP and CSP were assessed while participants (n = 11, young adults) exerted a light contraction with the right thumb. In the 1st block of trials, SPs were measured after the application of a Neutral gel (Aloe Vera) to the dorsal aspect of the hand. In the 2nd block, the same measures were repeated following a Menthol gel (4%) application. Subjective ratings of cooling sensations were obtained for each block. The Neutral gel was consistently perceived as slightly cool by participants, wheres the Menthol gel elicited sensations from cool to very cold. Paired t-tests showed no difference in the cutSP duration between the two conditions, whereas a significant increase in the CSP was detected with the Menthol condition. No correlation was found between changes in the CSP and those of the cutSP. These results highlight the difference between the cutSP and the CSP, as inhibitory phenomena, and point to a cortical contribution to the soothing effects associated with topical menthol applications.

Modulation of the excitatory phase following the cutaneous silent period by vibration

INTRODUCTION

The post-inhibition excitatory phase (E3) of the cutaneous silent period (CSP) is attributed to the resynchronization of motoneuron activity following the inhibitory period but there is also evidence that a somatosensory startle reflex may contribute to this phase. We hypothesized that the startle reflex component contained in E3 will decrease during vibration.

METHODS

Sixteen healthy individuals were included in the study. CSP was recorded from slightly contracted right thenar muscles after painful index finger stimulation, before, during, and immediately after vibration. The values of the percentage change of E3 relative to pre-stimulus baseline (E3%) were compared before, during, and after vibration for each individual.

RESULTS

There was a reduction in E3% during vibration and the values returned to normal immediately after vibration (153.1 ± 43.5%, 115.2 ± 30.2%, 154.9 ± 68.2%, respectively; p = 0.030).

DISCUSSION

E3 is reduced during vibration in healthy individuals, presumably due to suppression of a reflex component, which is superimposed upon the known resynchronization of motoneurons.

How can neurophysiological studies help with movement disorders characterization in clinical practice? A review

BACKGROUND

Neurophysiological studies are ancillary tools to better understand the features and nature of movement disorders. Electromyography (EMG), together with electroencephalography (EEG) and accelerometer, can be used to evaluate a hypo and hyperkinetic spectrum of movements. Specific techniques can be applied to better characterize the phenomenology, help distinguish functional from organic origin and assess the most probable site of the movement generator in the nervous system.

OBJECTIVE

We intend to provide an update for clinicians on helpful neurophysiological tools to assess movement disorders in clinical practice.

METHODS

Non-systematic review of the literature published up to June 2019.

RESULTS

A diversity of protocols was found and described. These include EMG analyses to define dystonia, myoclonus, myokymia, myorhythmia, and painful legs moving toes pattern; EMG in combination with accelerometer to study tremor; and EEG-EMG to study myoclonus. Also, indirect measures of cortical and brainstem excitability help to describe and diagnose abnormal physiology in Parkinson's disease, atypical parkinsonism, dystonia, and myoclonus.

CONCLUSION

These studies can be helpful for the diagnosis and are usually underutilized in neurological practice.

Exteroceptive suppression of voluntary activity in thenar muscles by cutaneous stimulation: How many trials should be averaged?

OBJECTIVE

To determine a minimum number of trials that preserve input-output (I-O) properties of duration and magnitude of exteroceptive EMG suppression (eEMGs).

PATIENTS AND METHODS

eEMGs was recorded in 16 healthy subjects from thenar muscles following index finger stimulation at 2.5, 5, 10, and 20 times sensory threshold (xST). Individual trials were rectified and incrementally averaged in blocks of 5, 10, 20, 30, 40, 50, and 60. To determine if the block size affects I-O properties, the goodness of curve fit parameter R² for each block was compared to R² of the global function across all blocks combined.

RESULTS

eEMGs was found in all subjects at 10xST and 20xST (100%, respectively) but less often at 5xST (63-75%) and 2.5xST (25-56%). A quadratic function best described both duration and magnitude of eEMGs. The quadratic R² did not significantly differ between any individual block function (5-60) and the global function (eEMGs duration 0.647-0.704 vs 0.679; magnitude 0.525-0.602 vs 0.560, respectively).

CONCLUSIONS

Averaging 5 trials consistently shows eEMGs at and above 10xST. I-O properties of eEMGs do not differ whether 5 or up to 60 trials are averaged. Clinical studies of eEMGs in thenar muscles are possible with as few as 5 trials averaged.

Reversible cutaneous silent period abnormalities in vitamin B12 deficiency: A case report

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Polyneuropathy is a frequent neurological manifestation of B12 hypovitaminosis.

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Thin-myelinated A-delta fibers may be affected in B12 hypovitaminosis.

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CSP testing is a useful diagnostic tool for A-delta fiber function in B12 deficiency.

Objectives

Vitamin B12 deficiency is common in adult and elderly patients and is often underdiagnosed because of its polymorphous manifestations. Neurological symptoms of this condition include subacute combined degeneration and polyneuropathy, with possible affection of thin-myelinated A-delta fibers. Cutaneous silent periods (CSPs) may serve to test small-diameter fiber function non-invasively, using routine electrodiagnostic equipment, but to the best of our knowledge have not been studied so far in vitamin B12 deficiency.

Methods

We report a 49-year-old male patient suffering from B12 hypovitaminosis due to autoantibodies against gastric parietal cells, who underwent neurophysiological investigation to confirm clinically suspected polyneuropathy during the first month of intramuscular vitamin B12 supplementation. We performed standard electroneurography, needle electromyography in tibialis anterior muscle, quantitative sensory testing, and cutaneous silent periods six months after symptom onset and repeated the electrodiagnostic study 21 months later, after intramuscular vitamin B12 supplementation.

Results

Standard electroneurography demonstrated axonal sensory polyneuropathy. Needle electromyography (EMG) in tibialis anterior muscle was unremarkable. Cutaneous silent periods in tibialis anterior muscle after noxious electrical sural nerve stimulation were delayed, with incomplete EMG suppression concurring with dysfunction of thin-myelinated A-delta fibers. Quantitative sensory testing revealed altered cold and warm perception thresholds in both upper limbs, but normal values in both lower limbs. A follow-up electrodiagnostic study after 21 months intramuscular vitamin B12 supplementation revealed improvement of all neurophysiological findings, including normalization of cutaneous silent periods.

Conclusions

Thin-myelinated A-delta fibers may be affected in B12 hypovitaminosis and may show recovery after intramuscular vitamin B12 supplementation. CSP may serve to diagnose small fiber affection in this medical condition and to monitor their recovery after vitamin supplementation.

Significance

CSP testing represents a useful, non-invasive, rapidly available diagnostic and follow-up tool in vitamin B12 deficiency.