Cutaneous Silent Period Parameters Research Articles

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

PurposeEarly 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. Methods22 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. ResultsFoot 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. ConclusionsAnalysis 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.

Comparison of cutaneous silent period parameters in patients with primary Sjögren's syndrome with the healthy population and determination of ıts relationship with clinical parameters.

Small fiber neuropathy (SFN) is one of the main neurological manifestations in primary Sjögren's Syndrome (pSS). For the detection of SFN, cutaneous silent period (CSP) measurement is gaining popularity recently due to its non-invasiveness and practical application. Evaluating SFN involvement in patients with pSS using CSP and evaluating its relationship with clinical parameters. Patients with a diagnosis of pSS and healthy volunteers demographically homogeneous with the patient group were included in the study. The CSP responses were recorded over the abductor pollicis brevis muscle. The latency and duration values of the responses were obtained. In patient group, EULAR Sjögren's Syndrome Patient Reported Index (ESSPRI), Hospital Anxiety and Depression Scale (HADS), Short Form-36 (SF-36) questionnaire, Leeds Assessment of Neuropathic Symptoms and Signs (LANSS) and Central Sensitization Inventory (CSI) were applied for the evaluation of symptom severity, mood, quality of life, presence of neuropathic pain and central sensitization, respectively. The mean CSP latency was significantly longer in patient group compared to control group (p < 0.001). Mean CSP duration was also significantly shorter in patient group (p < 0.001). There were no significant differences in CSP parameters according to patients' neuropathic pain or central sensitization profile. There were significant correlations of CSP parameters (latency and duration, respectively) with ESSPRI dryness (ρ = 0.469, p = 0.004; ρ = -0.553, p < 0.001), fatigue (ρ = 0.42, p = 0.011; ρ = -0.505, p = 0.002), pain (ρ = 0.428, p = 0.009; ρ = -0.57, p < 0.001) subscores and mean ESSPRI score (ρ = 0.631, p < 0.001; ρ = -0.749, p < 0.001). When SF-36 subscores and CSP parameters were investigated, a significant correlation was found only between "bodily pain" subscore and CSP duration (ρ = -0.395, p = 0.017). In HADS, LANSS and CSI evaluations, a significant correlation was found only between HADS anxiety score and the CSP duration (ρ = 0.364, p = 0.02). As indicated by CSP measurement, SFN is more prominent in patients with pSS than in the healthy population. It is important to investigate the presence of SFN because of its correlation with the leading symptoms in the clinical spectrum of pSS.

Recording cutaneous silent period parameters in hereditary and acquired neuropathies.

Cutaneous silent period (CSP) is the interruption in muscle activity after painful stimulation of a sensory nerve. The aim of the present study is to assess CSP changes in patients with polyneuropathy (PNP). 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. 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. 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.

AB0494 COMPARISON OF CUTANEOUS SILENT PERIOD PARAMETERS IN PATIENTS WITH PRIMARY SJÖGREN’S SYNDROME WITH THE HEALTHY POPULATION

BackgroundNeurological involvement has a great importance in the clinical spectrum of primary Sjögren’s syndrome (pSS) (1). The presence of small fiber neuropathy (SFN), which cannot be detected in routine electrophysiological examinations, causes the peripheral nervous system involvement to be underestimated in the course of the disease and causes pain-related symptoms in patients that cannot be explained by routine examinations (2). Various methods can be used in the detection of SFN, and cutaneous silent period (CSP) measurement is gaining popularity recently due to its non-invasiveness and practical application (3).ObjectivesEvaluating SFN involvement in patients with pSS using CSP and evaluating its relationship with clinical parameters.MethodsPatients with a diagnosis of pSS followed in the rheumatology outpatient clinic and healthy volunteers demographically homogeneous with the patient group were included in the study. The CSP responses were recorded over the abductor pollicis brevis muscle in the upper extremity of all participants. The latency and duration values of the responses were obtained. In patient group, EULAR Sjögren’s Syndrome Patient Reported Index (ESSPRI), Hospital Anxiety and Depression Scale (HADS), Short Form-36 (SF-36) questionnaire, Leeds Assessment of Neuropathic Symptoms and Signs (LANSS) and Central Sensitization Inventory (CSI) were applied for the evaluation of symptom severity, mood, quality of life, presence of neuropathic pain and central sensitization, respectively. Comparison of CSP parameters between patients with pSS and healthy volunteers was determined as the primary outcome measure. The secondary outcome measure was the relationship between CSP parameters and ESSPRI, HADS, SF-36, LANSS and CSI scores.ResultsA total of 36 patients and 36 healthy controls were included in the final analyses. There was no significant difference between the two groups in terms of demographic data. The mean CSP latency was significantly longer in patients with a mean of 78.18 (±7.51) when compared to controls with a mean of 67.91 (±6.41) (95% CI: 6.98- 13.55, p&lt;0.001). Mean CSP duration was also significantly shorter in patients with a mean of 33.40 (±6.93) (95% CI: 9.57 -15.31, p&lt;0.001). There were no significant differences in CSP parameters (latency and duration, respectively) according to patients’ neuropathic pain or central sensitization profile (p&gt;0.05 for all analyses). There were significant correlations of CSP parameters with ESSPRI dryness (r=0.469, p=0.004; r=-0.553, p&lt;0.001), fatigue (r=0.42, p=0.011; r=-0.505, p=0.002), pain (r=0.428, p=0.009; r=-0.57, p&lt;0.001) subscores and mean ESSPRI score (r=0.631, p&lt;0.001; r=-0.749, p&lt;0.001). Significant correlations were not found between CSP parameters and SF-36 scores, other than CSP duration and “pain” subscore (r=-0.395, p=0.017). When the other correlations were investigated there were no significant correlations other than CSP duration and the HADS anxiety score (r=-0.201, p=0.02).ConclusionAs an indicator of CSP measurement, SFN is more common in patients with pSS than in the healthy population. The association with important clinical symptoms of the disease course such as dryness, fatigue, pain and anxiety highlights the importance of detecting small fiber neuropathy.

The effect of vitamin D replacement on spinal inhibitory pathways in women with chronic widespread pain

Vitamin D replacement helps in pain reduction in patients with chronic widespread pain (CWP). But the current literature lack studies that investigate its mechanism. Cutaneous silent period (CSP) is the electrophysiologic analog of the spinal inhibitory pathways and an objective method to document their involvement. This study aims to show if vitamin D replacement has an effect on the spinal inhibitory pathways through CSP parameters. Female patients who have CWP with vitamin D deficiency were included. Patients received an 8-week replacement therapy of vitamin D. Patients’ pain were evaluated using the visual analog scale (VAS) and Leeds assessment of neuropathic symptoms and signs pain scale (LANSS). Quality of life with Nottingham Health Profile (NHP) and CSP parameters were also recorded before and after treatment. A total of 51 patients were included in the final analyses. The mean age of the patients was 44.3 ± 12.7 (minimum 18-maximum 65). Mean symptom duration was 13.1 ± 6.7 (minimum3-maximum 24) months. Patients' mean BMI was 21.6 ± 3.9 (minimum 18.0 maximum 29.1). Patients' median VAS and LANSS scores decreased significantly (p < 0.01) and NHP scores improved significantly in all subsets (p < 0.01). Vitamin D replacement did not significantly change CSP latency and duration (p = 0.06 and p = 0.12).Vitamin D replacement does not seem to work via modifying the spinal inhibitory pathways that are involved in the formation of the cutaneous silent period. This is the first study to objectively investigate the effect of vitamin D replacement on central sensitization mechanisms.

T128. Modulation of exteroceptive electromyographic responses in defensive peripersonal space

Introduction The cutaneous silent period (CSP) is a spinal nociceptive inhibitory reflex, that briefly interrupts voluntary contraction of limb muscles involved in reaching and grasping movements after noxious electrical stimulation of a cutaneous nerve. It is mediated by A-delta afferents. CSPs act in conjunction with flexor withdrawal reflexes to constitute a sophisticated defensive system for protecting a limb from harmful stimuli. CSP is functionally rather than anatomically organized. I1 and I2 components are considered spinal, E2 is regarded transcortical in origin. Defending the body surface from environmental threats requires sensorimotor integration between multimodal sensory afferents and motor planning of defensive movements. Cortical areas involved in this integration are the poly-sensory zone in the precentral gyrus and the ventral intraparietal area. The defensive peri-personal space (DPPS), immediately surrounding the body, was first described in macaque monkeys. Neurophysiological studies of the human DPPS demonstrated larger somatosensory blink reflexes with the stimulated hand located near the face. We investigated the effect of hand position on CSP in DPPS vs. extrapersonal space (EPS). Methods Fifteen healthy volunteers underwent serial CSP testing with the arm resting on an elevated table, elbow flexed, and the hand held either within 5 cm from the nose (NEAR) or away from the body (FAR). Electrical stimuli were applied to either digit 2 or 5 (D2, D5). Sensory thresholds (ST) were established for each subject and digit. EMG recordings were obtained from first dorsal interosseous (FDI) muscle during 20% maximal voluntary contraction, following random stimulation of either D2 or D5 in both NEAR and FAR conditions, with 5, 10, and 15X ST intensity. CSPs were identified by a decrease in mean rectified EMG activity below 80% of prestimulus baseline. CSPs were divided into I1, E2, and I2. Results Following D2 stimulation, CSPs consisted of I1, E2, and I2. With increasing stimulus intensities, CSP duration and I2 duration increased, suppression index (SI) of CSP and I2 decreased, and E2 amplitude decreased progressively, both in DPPS and EPS. E2 amplitude was significantly larger in DPPS vs. EPS, while no other parameter differed between DPPS and EPS. Following D5 stimulation, CSP equaled I2, and there was no clear E2. With increasing stimulus intensities I2 duration increased and SI decreased, both in DPPS and EPS. No parameter differed between DPPS and EPS. Conclusion Concurring with previous literature, E2 was present in FDI only when stimulating homotopic D2 and not heterotopic D5. E2 was larger in DPPS vs. EPS, representing direct neurophysiological evidence of transcortical sensorimotor processing related to DPPS, while inhibitory CSP parameters did not differ between DPPS and EPS, concurring with a spinal organization of its circuitry.

Use of cutaneous silent period parameters as a diagnostic indicator in patients with restless legs syndrome-a study in south Indian population

Objective: The objectives of this study were to investigate cutaneous-silent- period (CSP) parameters- CSP latency and CSP duration in patients with ‘Restless legs Syndrome’ and compare it with that of normal healthy controls. Methods: Thirty patients diagnosed with restless legs syndrome were included in this study. The cutaneous silent period was evoked by electrical stimulation of sural nerve whereby both CSP parameters CSP latency and CSP duration were recorded and analyzed. Results: The mean latencies of CSP among the thirty RLS patients were 101.95±12.12 while the control group showed 96.23± 9.16. There is a statistically significant high average latency in RLS patients (101.95± 12.12) than control group (96.23± 9.16) with p value=0.044. This study also showed the average CSP duration to be high in RLS patients (42.25± 11.12), when compared to the control group – 36.75± 8.35 (p value=0.035). Conclusion: While RLS is a common sensorimotor disorder, the diagnosis of RLS is purely clinical and there are no objective tests for the diagnosis. Unfortunately, the awareness is poor among the lay population, general practitioners and even specialists in the Indian subcontinent. The authors feel that the CSP test can be used as an objective method supporting the diagnosis of RLS. Furthermore, we believe that this paper will help create awareness in addition to encouraging more research in this arena from medical personnel in India.

42. The effects of THC on Cutaneous Silent Period

The analgesic effects of cannabinoids are mediated through the activity on the endogenous cannabinoid system. (−)-trans-Δ 9 -tetrahydrocannabinol (THC) is the principal psychoactive constituent of cannabis and it shows a partial agonist activity on cannabinoid receptors, in particular CB1 receptor, mainly expressed by neurons of the central and peripheral nervous system. Several studies demonstrate the effects of THC on pain perception. The aim of this study was to evaluate the effects of THC in 13 healthy volunteers (HV) through the analysis of Cutaneous Silent Period (CSP), a nociceptive spinal inhibitory reflex, considered a defense response, specific for the human upper limbs. CSP parameters have been recorded from the abductor digiti minimi (ADM) before and after an hour from the administration of a cannabis-based preparation. We recorded the same parameters before and after the administration of placebo in the same volunteers. The results showed that the CSP latency and amplitude left unchanged in HV after the drug administration at the dose commonly used to suppress nociceptive reflexes in humans. These differential effects of a narcotic-analgesic drug provide evidence that the Cutaneous Silent Period is not a THC-sensitive nociceptive reflex.

Lengthened Cutaneous Silent Period in Fibromyalgia Suggesting Central Sensitization as a Pathogenesis.

The pathogenesis of fibromyalgia (FM) has not been clearly elucidated, but central sensitization, which plays an important role in the development of neuropathic pain, is considered to be the main mechanism. The cutaneous silent period (CSP), which is a spinal reflex mediated by A-delta cutaneous afferents, is useful for the evaluation of sensorimotor integration at the spinal and supraspinal levels. To understand the pathophysiology of FM, we compared CSP patterns between patients with FM and normal healthy subjects. Twenty-four patients with FM diagnosed in accordance with the 1990 American College of Rheumatology classification system and 24 age- and sex-matched healthy volunteers were recruited. The CSP was measured from the abductor pollicis brevis muscle. Demographic data, number of tender points, and visual analog scale and FM impact questionnaire scores were collected. The measured CSP and clinical parameters of the patient and control groups were compared. In addition, possible correlations between the CSP parameters and the other clinical characteristics were analyzed. Mean CSP latencies did not differ between patients (55.50 ± 10.97 ms) and healthy controls (60.23 ± 11.87 ms; p = 0.158), although the mean CSP duration was significantly longer in patients (73.75 ± 15.67 ms) than in controls (63.50 ± 14.05 ms; p = 0.021). CSP variables did not correlate with any clinical variables. The significantly longer CSP duration in FM patients suggests central dysregulation at the spinal and supraspinal levels, rather than peripheral small fiber dysfunction.

Cutaneous silent period recordings in demyelinating and axonal polyneuropathies

ObjectiveTo investigate the cutaneous silent period (CSP), a spinal inhibitory reflex mainly mediated by A-delta fibres, in demyelinating and axonal polyneuropathy (PNP) and evaluate whether CSP parameters differ between patients with and without neuropathic pain. MethodsEighty-four patients with demyelinating PNP, 178 patients with axonal PNP and 265 controls underwent clinical examination, DN4 questionnaire, standard nerve conduction study, motor-root stimulation and CSP recordings from abductor digiti minimi. We calculated the afferent conduction time of CSP (a-CSP time) with the formula: CSP latency−root motor evoked potential latency. ResultsIn the demyelinating PNP group the a-CSP time was significantly longer; in the axonal PNP group, CSP duration was shorter than the demyelinating group (p=0.010) and controls (p=0.001). CSP parameters were not different between patients with and without neuropathic pain. ConclusionsThe abnormality of a-CSP time in the demyelinating PNP group suggests the crucial role of A-delta fibres in the mechanism of CSP; the shorter CSP duration in the axonal PNP group supports the strong influence of the number of axons on this parameter.Our study suggests that neuropathic pain could be related to pathophysiological mechanisms differing from mere A-delta fibre loss. SignificanceCSP evaluation is effective in detecting A-delta fibre dysfunction in axonal as well as demyelinating PNP.

P627: Is precautionary neurophysiological monitoring useful for beta-thalassemia patients?

P627: Is precautionary neurophysiological monitoring useful for beta-thalassemia patients?

78. Cutaneous silent period recordings in demyelinating and axonal polyneuropathies

Cutaneous silent period (CSP) is a pause in voluntary muscle contraction following painful cutaneous nerve stimulation which allows to study small-myelinated fibres. We investigated CSP in patients with demyelinating and axonal polyneuropathy (PNP) and explored correlation between CSP changes and neuropathic pain. Eighty demyelinating PNP patients, 178 axonal PNP patients and 265 controls underwent clinical (neurological examination, DN4-Questionnaire) and electrophysiological (motor root conduction time, compound muscle action potentials, sensory nerve action potentials and CSPs of the ulnar nerve) investigations. In the demyelinating PNP group, all electrophysiological latencies were longer with respect to the axonal PNP group and the controls ( p = 0.0001); axonal PNP group had shorter CSP duration with respect to the controls ( p = 0.0001). Axonal PNP patients suffered from painful sensations more than the demyelinating PNP patients ( p = 0.02) but CSP parameters were not different among painful and painless patients. Our findings confirm in a large number of patients that CSP evaluation is effective to study small-fibres dysfunction in both axonal and demyelinating PNP. The lack of correlation between shortened CSP duration and presence of neuropathic pain could suggest that neuropathic pain primarily arises, rather than from altered peripheral signals, from changes in spinal cord plasticity.

A neurophysiological approach to the complex organisation of the spine: F-wave duration and the cutaneous silent period in restless legs syndrome

Objective It is generally accepted that F-wave duration (FWD) and the cutaneous silent period (CSP) are influenced by diminished central inhibition. The aim of this study was to diagnose patients of restless legs syndrome (RLS) with the help of FWD and/or CSP parameters. Methods In all, 24 patients with primary RLS were compared with 31 age- and sex-matched controls. The participants were evaluated based on nerve conduction study (NCS), F-wave parameters (minimum, maximum and mean latency; chronodispersion, persistence and duration; and the ratio of the mean FWD to compound muscle action potential (CMAP) duration), CSP (latency, duration and the ratio of lower-extremity (LE) to upper-extremity (UE) duration that is, silent period ratio (SPR)), the expiration to inspiration ratio (E/I) and sympathetic skin response (SSR). Results There were not any significant differences in NCS, E/I or SSR between the patients and controls. However, FWD was prolonged ( P < 0.0001 for UE and LE) and FWD/CMAP duration was increased in upper and lower extremities ( P < 0.001 for UE and P < 0.0001 for LE). Further, CSP latencies in UE ( P = 0.030) and LE ( P < 0.001) were prolonged, and CSP duration and SPR were significantly reduced in the patient group ( P < 0.0001). Conclusions As both NCS and autonomic test results were in the normal range, abnormalities in FWD and CSP parameters were attributed to the dysfunction of different interneuron groups in the spine. Significance The use of FWD and CSP could aid in the diagnosis of RLS patients in whom conventional electrophysiological procedures are ineffective.

Utility of the cutaneous silent period in the evaluation of carpal tunnel syndrome

This study investigates the utility of the cutaneous silent period (CuSP) in evaluating patients with carpal tunnel syndrome (CTS). The authors measured the CuSP from the abductor pollicis brevis muscle in 135 hands of patients with idiopathic CTS and 30 hands of age- and gender-matched controls. The patient group was further divided into subgroups according to the Canterbury scale. The differences in parameters between the patient subgroups and control group were analysed. A predetermined analysis looked at the possible correlation between the CuSP and symptom severity as measured by the Boston-Questionnaire. The mean CuSP latencies in the patient group (72.4+/-16.1 ms) was significantly longer than the control group (64.6+/-13.4 ms; P=0.014), although there was no difference in the duration of the CuSP between groups. The duration and latency of the CuSP correlated to a higher severity on the Canterbury scale (r=0.273, P<0.001 and r=-0.164, P=0.036, respectively). However, the CuSP parameters did not correlate with the Boston-Questionnaire scores. Although patients with CTS had significantly prolonged CuSP latency, the CuSP did not correlate with the clinical symptoms scale. The CuSP is a useful ancillary test to evaluate Adelta fibre function; however, it is not a reliable tool to quantify clinical severity.

The effect of a prepulse stimulus on the EMG rebound following the cutaneous silent period

The cutaneous silent period (CSP) is a spinal inhibitory reflex mediated by Adelta fibres. The postinhibitory rebound of electromyographic (EMG) activity following the CSP has been mainly attributed to resynchronization of motoneurons, but the possibility of startle reflex activity contributing to the EMG burst has also been suggested. Several types of reflexes may be suppressed by a preceding weak stimulus--a phenomenon called prepulse inhibition (PPI). Our aim was to study whether PPI would diminish the EMG rebound, thereby providing further evidence for excitatory reflex activity contained within the postinhibitory EMG rebound following the CSP. Ten healthy subjects underwent CSP testing following noxious digit II stimulation in two conditions, with and without a prepulse applied to digit III. Rectified surface EMG recordings were obtained from right orbicularis oculi, sternocleidomastoid and thenar muscles of the dominant hand during thumb abduction with 25% of maximum force. The area of the EMG rebound and the EMG reflex responses in orbicularis oculi and sternocleidomastoid were significantly smaller in recordings where a prepulse stimulus was applied 100 ms before the stimulus as compared to control responses without prepulse. CSP onset and end latency, CSP duration, and the degree of EMG suppression were not influenced. Prepulses significantly reduced subjective discomfort as based on visual analog scale scores. Inhibition of the EMG rebound by prepulse stimulation supports the hypothesis that the excitatory EMG activity following the CSP contains not only resynchronization of motoneuronal firing, but also an excitatory reflex component. The most probable type of reflex seems to be a somatosensory startle reflex, a defence reaction which is generated in structures located in the caudal brainstem following an unexpected intense stimulus. Reduction of the discomfort associated with high-intensity electrical fingertip stimulation by a prepulse without affecting CSP parameters underlines the utility of PPI in the context of CSP testing.

Ipsi- and contralateral exteroceptive EMG modulation in uni- and bilaterally activated thenar muscles

Objective The cutaneous silent period (CSP) is a spinal inhibitory reflex mediated by A-δ fibers. The exact underlying neural pathway, however, is unknown. This study was undertaken to investigate whether the neural circuitry mediating CSPs is wired unilaterally or whether there is evidence of influence from or upon the contralateral side. Methods Fifteen healthy subjects underwent bilateral CSP testing following unilateral nociceptive digit II stimulation. Surface electromyographic (EMG) recordings were obtained bilaterally from thenar muscles following unilateral recurrent nociceptive digit II stimulation while activating the ipsilateral or the contralateral or both thenar muscles against resistance. Results Nociceptive digit II stimulation evoked consistent CSPs in ipsilateral thenar muscles during voluntary contraction, while there was no consistent influence on EMG activity in contralateral thenar muscles at rest. Furthermore, nociceptive digit II stimulation did neither consistently affect EMG activity in ipsilateral thenar muscles at rest nor in contralateral thenar muscles during voluntary contraction. Finally, there was no significant difference between any CSP parameters obtained during unilateral versus bilateral muscle contraction. Occasional late excitatory EMG activity in relaxed or contracted thenar muscles resembled startle reflexes, which seem to contribute to the post-inhibition EMG-rebound. Conclusions The present findings are consistent with unilateral wiring of the spinal circuitry mediating CSPs. Significance The essential lack of a crossed inhibitory influence of nociceptive digit II stimulation underscores the utility of CSP testing in the assessment of the A-δ fiber system in healthy subjects and patients with various pathologies.

Interside comparison of cutaneous silent periods in thenar muscles of healthy male and female subjects

Objective: The cutaneous silent period (CSP) is a spinal inhibitory reflex mediated by A-δ fibers. To date, no data are available about normal interside differences. Methods: Twenty healthy subjects underwent comparison of CSPs in the dominant and non-dominant hand. Surface electromyographic (EMG) recordings were obtained from thenar muscles on either side following ipsilateral recurrent nociceptive digit II stimulation. Results: Group average CSP onset and end latency, CSP duration, and the magnitude of EMG suppression were not significantly different between both sides. Regression analysis revealed powerful correlations between individual CSP parameters of dominant and non-dominant hands. Calculated upper normal limits of maximum interside differences were 17% for CSP onset latency, 14% for CSP end latency, 22% for CSP duration, and 45% for the index of suppression. CSP parameters in right-handed subjects did not differ significantly from those in left-handed subjects. Female subjects tended to have shorter CSP onset latencies, longer CSP duration, and a smaller index of suppression, resulting in a larger overall suppression. Conclusions: CSPs prove to be robust nociceptive cutaneomuscular reflexes with little side-to-side difference. Significance: The presented normative values of interside differences enable a more thorough comparison with patient data in various conditions.

Interside comparison of cutaneous silent periods in thenar muscles of healthy male and female subjects

Objective: The cutaneous silent period (CSP) is a spinal inhibitory reflex mediated by A-δ fibers. To date, no data are available about normal interside differences. Methods: Twenty healthy subjects underwent comparison of CSPs in the dominant and non-dominant hand. Surface electromyographic (EMG) recordings were obtained from thenar muscles on either side following ipsilateral recurrent nociceptive digit II stimulation. Results: Group average CSP onset and end latency, CSP duration, and the magnitude of EMG suppression were not significantly different between both sides. Regression analysis revealed powerful correlations between individual CSP parameters of dominant and non-dominant hands. Calculated upper normal limits of maximum interside differences were 17% for CSP onset latency, 14% for CSP end latency, 22% for CSP duration, and 45% for the index of suppression. CSP parameters in right-handed subjects did not differ significantly from those in left-handed subjects. Female subjects tended to have shorter CSP onset latencies, longer CSP duration, and a smaller index of suppression, resulting in a larger overall suppression. Conclusions: CSPs prove to be robust nociceptive cutaneomuscular reflexes with little side-to-side difference. Significance: The presented normative values of interside differences enable a more thorough comparison with patient data in various conditions.

Cutaneous afferents mediating the cutaneous silent period in the upper limbs: evidences for a role of low-threshold sensory fibres

Objectives: To evaluate the contribution of the low-threshold afferents to the production of the cutaneous silent period (CSP) in the upper limbs. Methods: The CSP was studied in 10 healthy adults and 4 patients with Friedreich's ataxia. The following neurophysiological aspects were studied: (a) relationship between sensory threshold (ST), sensory action potential (SAP) amplitude and CSP parameters; (b) habituation and recovery cycle of the CSP at different stimulus intensities (2×ST and 8×ST); (c) pattern of responses in distal and proximal muscles at different stimulus intensities (2×ST and 8×ST). Results: (a) The CSP occurred at low intensities (1×ST and 2×ST) and increased abruptly between 3.5×ST and 4×ST (corresponding to the pain threshold). The SAP amplitude was saturated before CSP saturation. In the patients with Friedreich's ataxia, the CSP appeared only at higher stimulus intensities (6×ST–8×ST). (b) The CSP evoked at 2×ST showed a fast habituation and slow recovery cycle whereas the opposite behaviour was found at 8×ST. (c) Low-threshold stimuli induced an inhibitory response restricted to the distal muscles. High-intensity stimulation produced an electromyographic suppression, significantly increasing from proximal to distal muscles. Conclusions: Our findings support the notion that low-threshold afferents participate in the production of the CSP in the upper limbs. The different afferents may activate different central neural networks with separate functional significance.