Cutaneous silent period in syringomyelia

The Role of Neurophysiology in Managing Patients with Chiari Malformations

Chiari malformation type 1 (CM1) includes various congenital anomalies that share ectopia of the cerebellar tonsils lower than the foramen magnum, in some cases associated with syringomyelia or hydrocephalus. CM1 can cause dysfunction of the brainstem, spinal cord, and cranial nerves. This functional alteration of the nervous system can be detected by various modalities of neurophysiological tests, such as brainstem auditory evoked potentials, somatosensory evoked potentials, motor evoked potentials, electromyography and nerve conduction studies of the cranial nerves and spinal roots, as well as brainstem reflexes. The main goal of this study is to review the findings of multimodal neurophysiological examinations in published studies of patients with CM1 and their indication in the diagnosis, treatment, and follow-up of these patients, as well as their utility in intraoperative monitoring.

Cutaneous silent period in myofascial pain syndrome

INTRODUCTION

An increased response to painful stimuli without spontaneous pain suggests a role of central hyperexcitability of pain pathways in the pathogenesis of myofascial pain syndrome (MPS). In this study we aimed to test the hypothesis that spinal pain pathways are affected in MPS. We used cutaneous silent period (CSP) parameters to demonstrate the hyperexcitability of spinal pain pathways in MPS.

METHODS

Twenty-nine patients diagnosed with MPS and 30 healthy volunteers were included in the study. The CSP recordings were performed in the right upper and left lower extremities.

RESULTS

In both upper and lower extremities, patients had prolonged CSP latencies (P = 0.034 and P = 0.049 respectively) and shortened CSP durations (P = 0.009 and P = 0.008, respectively).

DISCUSSION

Delayed and shortened CSP in MPS patients implies dysfunction in the inhibitory mechanism of the spinal/supraspinal pain pathways, suggesting central sensitization in the pathogenesis of MPS and supporting our research hypothesis. Muscle Nerve 57: E24-E28, 2018.

Chiari type I malformation in children

The diagnosis of Chiari type I malformation (CIM) is more and more frequent in clinical practice due to the wide diffusion of magnetic resonance imaging. In many cases, such a diagnosis is made incidentally in asymptomatic patients, as including children investigated for different reasons such as mental development delay or sequelae of brain injury. The large number of affected patients, the presence of asymptomatic subjects, the uncertainties surrounding the pathogenesis of the malformation, and the different options for its surgical treatment make the management of CIM particularly controversial.This paper reports on the state of the art and the recent achievements about CIM aiming at providing further information especially on the pathogenesis, the natural history, and the management of the malformation, which are the most controversial aspects. A historial review introduces and explains the current classification. Furthermore, the main clinical, radiological, and neurophysiological findings of CIM are described to complete the picture of this heterogeneous and complex disease.

Influence of muscle contraction and intensity of stimulation on the cutaneous silent period

We evaluated the influence of stimulus intensity (SI) and the amount of voluntary muscle contraction (VMC) on parameters of the cutaneous silent period (CSP). The CSP was measured in 15 healthy subjects at 20%, 40%, and 60% of maximal VMC and after an electric stimulus of 10, 15, and 20 times the sensory threshold. Average EMG amplitudes prior to stimulus and during the CSP increased with the amount of VMC. The CSP duration increased, and suppression index decreased, with increasing SI. The CSP onset and end latencies seemed to shorten and prolong, respectively, with the increasing SI, although this was not statistically significant. Considering the more meaningful temporal parameters of the CSP and the suppression index, it is not necessary to control the VMC, but it is advisable to control the SI.

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

OBJECTIVE

Small myelinated (A-delta) 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-delta nerve fibers. The aim of this study was to evaluate CSP changes in Type 2 diabetic patients with small fiber neuropathy.

METHODS

Forty-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.

RESULTS

Nerve 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.

CONCLUSION

The 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.

SIGNIFICANCE

An additional CSP evaluation may be considered in cases which nerve conduction studies do not provide sufficient information.

Cutaneous silent periods in the assessment of mild cervical spondylotic myelopathy

STUDY DESIGN

Clinical, neuroradiologic, and neurophysiologic description of 21 patients with compressive cervical spondylotic myelopathy (CCSM).

OBJECTIVE

To describe the utility of cutaneous silent periods (CSPs) for functional evaluation of mild CCSM.

SUMMARY OF BACKGROUND DATA

Electroneurography, electromyography, and somatosensory and motor evoked potentials (SEPs, MEPs) are routinely used for comprehensive functional neurophysiological evaluation of CCSM. CSPs have been reported in various intramedullary spinal cord lesions, however, they have not been systematically studied in mild CCSM.

METHODS

We investigated 21 patients with multilevel CCSM as documented by magnetic resonance imaging. We recorded CSPs in thenar muscles after noxious digit II stimulation and compared them with median and tibial nerve SEPs and MEPs obtained from abductor digiti minimi and tibialis anterior muscles. Electroneurography and electromyography were obtained in affected myotomes.

RESULTS

CSP onset and end latencies were delayed, and CSP duration was shortened, in CCSM patients. CSP abnormalities were present in 17 patients of whom all, but 1 presented with intramedullary magnetic resonance imaging hyperintensity. All 11 limbs affected by hypalgesia and thermhypesthesia had abnormal CSPs, whereas no spinothalamic deficit was noted in any limb with normal CSPs. CSP onset latency was inversely correlated with JOA score and N13 amplitude, and was positively correlated with central motor conduction time to abductor digiti minimi. CSP duration was inversely correlated with central motor conduction time to tibialis anterior. Electromyographic abnormalities were found in 7 patients.

CONCLUSION

We confirm the value of neurophysiological evaluation of CCSM. MEPs were more frequently abnormal than SEPs. CSP abnormalities were almost equally sensitive as upper limb MEPs, and were highly associated with spinothalamic dysfunction. The high correlation of CSP abnormalities with corticospinal tract dysfunction suggests supraspinal influence on CSPs. Our findings corroborate the utility of CSP testing in the comprehensive assessment of intramedullary spinal cord dysfunction in CCSM.

A new concept in the electrophysiological evaluation of syringomyelia

Object

The current neurophysiological assessment of syringomyelia is inadequate. Early-stage syringomyelia is anatomically predisposed to affect decussating spinothalamic fibers that convey pain and sensation primarily. Silent periods have been proven to be a sensitive tool for detecting alterations in this pathway.

Methods

Thirty-seven patients with syringomyelia were included in this prospective study. Routine electrophysiological measurements were applied including somatosensory evoked potential (SSEP) and motor evoked potential (MEP) recordings for all extremities. The silent periods were recorded from the pollicis brevis muscle, and electrical stimuli were applied to the ipsilateral digiti II. To establish baseline values, the authors had 28 healthy controls undergo monitoring. Sensitivity and specificity values were statistically evaluated according to the main clinical symptoms (paresis, dissociative syndrome, and pain).

Results

All control individuals had normal silent periods in voluntarily activated muscle. In syringomyelia patients, the affected limb showed pathological silent periods with all symptoms (sensitivity 30–50%). Pain was the most specific symptom (90%), despite SSEP and MEP values that were within the normal range.

Conclusions

Silent period testing is a sensitive neurophysiological technique and an invaluable tool for preoperative assessment of syringomyelia. Silent periods are associated with early dysfunction of thin myelinated spinothalamic tract fibers, even when routine electrophysiological measurements still reveal normal values. Conduction abnormalities that selectively abolish the silent periods can distinguish between hydromyelia (a physiologically dilated central canal) and space-occupying syringomyelia.

Influence of the corticospinal tract on the cutaneous silent period: a study in patients with pyramidal syndrome

The cutaneous silent period (CSP) is a brief transient suppression of the voluntary muscle contraction that follows a noxious cutaneous nerve stimulation. In this study we investigated the influence of the corticospinal tract on this spinal inhibitory reflex. In patients with pyramidal syndrome and in a group of healthy subjects we delivered painful electrical finger stimulation during sustained contraction of the ipsilateral abductor digiti minimi muscle. The CSP latency and duration and the background electromyographic (EMG) activity were measured and compared between-groups. The compound motor action potential amplitude and F-wave latency were also measured after electrical stimulation of the ulnar nerve at the wrist. The CSP latency was significantly longer in patients than in healthy subjects. None of the other variables differed in patients and healthy subjects. Our findings suggest that corticospinal projections influence the CSP latency probably by modulating the balance of excitability in the underlying circuits.

Role of Spinal Inhibitory Mechanisms in Whiplash Injuries

Whiplash injury, commonly encountered in road traffic accidents, is a major cause of morbidity. Its pathophysiology is not well understood, and diagnosis remains clinical. Imaging and electrophysiological methods have not provided objective diagnostic evidence. Availability of a sensitive and specific diagnostic method would be of high clinical interest. We studied 20 consecutive patients with chronic whiplash injury. Despite persistent symptoms, most had minimal neurological findings. Cutaneous silent period (CSP), a nociceptive spinal inhibitory electromyographic reflex, showed 90% sensitivity and 90% specificity for its diagnosis. In contrast, only two patients (10%) had abnormal transcranial magnetic stimulation findings, and another two (10%) showed abnormal electromyography. Magnetic resonance imaging (MRI) showed cervical cord abnormalities in only two of 20 (10%) patients. None of the patients had abnormal somatosensory evoked potential studies. Our findings suggest that neurological dysfunction of whiplash may occur at several possible spinal cord localities in the CSP functional pathway. The use of this simple, quick, and sensitive method is advocated in the diagnostic work up of whiplash injury.

Cutaneous silent periods in the evaluation of cord compression in cervical spondylosis

OBJECTIVE

The clinical diagnosis of cervical spondylotic myelopathy (CSM) may be challenging in patients with cervical spondylosis (CS). Routine nerve conduction studies (NCS) may not evaluate cord compression adequately.

METHODS

We obtained cutaneous silent periods (CSP) in 26 consecutive patients presenting with clinical features of CS, in comparison with 30 normal controls. The results were also compared with transcranial magnetic stimulation (TMS) findings, and magnetic resonance imaging of the cervical cord as the gold standard.

RESULTS

CSP findings showed similarly high sensitivity of up to 96% with TMS in evaluating cervical cord dysfunction.

CONCLUSION

In specific clinical settings, CSP is of value for the diagnosis of CSM in CS. CSP measurement is advocated as a simple and rapid diagnostic adjunct to NCS in evaluating CS patients with possible cord compromise.

Cutaneous silent period in human immunodeficiency virus-related peripheral neuropathy

The aim of this work was first to determine whether the cutaneous silent period (CSP), a marker of small-nerve-fibre function, was altered in human immunodeficiency virus (HIV)-positive subjects with predominantly sensory symmetrical polyneuropathy and, second, to assess whether such alterations were predictive of an impairment in the largest calibre sensory and motor nerve fibres of the upper limb (UL) peripheral nerves. CSP was assessed in three groups of subjects: healthy control subjects, HIV-positive subjects with peripheral neuropathy (PN) of the lower limbs, and HIV-positive patients with clinical and neurophysiological involvement of the four limbs. CSP study showed a significant increase of the latency compared to the controls both in HIV-positive cases with no impairment in the UL (p=0.006) and in patients with four-limb neuropathy (p=0.002). CSP study in HIV-positive patients with mild lower limb distal sensory polyneuropathy can detect an early involvement of the UL peripheral nerves. CSP latency increase could therefore be addressed as the first sign of PN spreading to the UL.

Cutaneous silent periods in intramedullary spinal cord lesions

OBJECTIVE

The neurophysiological assessment of intramedullary spinal cord lesions has been unsatisfactory. Previous studies in patients with syringomyelia suggest that testing of cutaneous silent periods (CSPs) may be useful to assess centromedullary lesions.

METHODS

The authors studied nine patients with intramedullary spinal cord lesions of different etiologies. Eight patients with cervical lesions presented with hypalgesia, hypothermesthesia, or pain in at least one upper extremity; five of them had also upper limb weakness or sensory impairment. One patient with a thoracic lesion had normal upper limb function. The authors recorded CSPs in abductor pollicis brevis muscle following digit II and digit V stimulation. Somatosensory evoked potentials (SEPs) were obtained following median and tibial nerve stimulation. Motor evoked potentials (MEPs) were obtained in biceps brachii, abductor digiti minimi and tibialis anterior muscles following transcranial magnetic or electrical stimulation.

RESULTS

CSP abnormalities were found in all patients with cervical lesions, but not in the patient with a thoracic lesion. Cortical median nerve SEPs had normal latencies in all patients, while tibial nerve SEPs, upper limb MEPs, and lower limb MEPs were delayed in five patients each. In one patient, abnormal CSP were the only neurophysiological finding. CSP abnormalities were associated with hypalgesia and hypothermesthesia in 95% of the studies.

CONCLUSION

Upper extremity CSP testing is a sensitive neurophysiological technique for the assessment of cervical intramedullary lesions. In particular, abnormal CSPs are highly associated with spinothalamic dysfunction.

Cutaneous silent periods

The cutaneous silent period (CSP) refers to the brief interruption in voluntary contraction that follows strong electrical stimulation of a cutaneous nerve. The CSP is a protective reflex that is mediated by spinal inhibitory circuits and is reinforced in part by parallel modulation of the motor cortex. This review summarizes current understanding of the afferents and circuits that are responsible for producing CSPs; the utility of the CSP for investigating peripheral and central nervous system disorders; and the relationship between the CSP, other cutaneous reflexes, and peripheral silent periods.

Cutaneous silent periods in patients with Fabry disease

We assessed the cutaneous silent period (CSP) in 24 patients with Fabry disease with small-fiber sensory neuropathy and 12 normal subjects to test the hypothesis that small-diameter afferents are responsible for producing the CSP. Sensory nerve conduction studies and quantitative sensory testing for cold and vibration detection thresholds were also measured. Overall, Fabry patients had impaired thermal, but not vibration, detection thresholds, with greatest impairment in the feet. In the upper extremity, CSP latencies, duration, and suppression of electromyographic activity (EMG) did not differ. In the lower extremity, patients had reduced suppression of EMG during the CSP compared to normal controls. CSP durations exhibited a bimodal distribution in patients, including a subset of seven patients with durations shorter than all controls. This subset had profound loss of thermal sensation in the feet, but this was also true of some patients who had normal CSPs. Patients with shortened CSPs had modestly elevated vibration thresholds and reduced sensory potentials in comparison to patients with normal CSPs. Reduced CSPs in Fabry patients are associated with, but not entirely explained by, the severity of small-fiber neuropathy as measured by quantitative sensory testing. The possibility that large-diameter fibers provide a minor contribution to producing the CSP should be considered.

Cortical motor neuron excitability during cutaneous silent period

OBJECTIVE

To investigate cortical motor neuron excitability during cutaneous silent period (CSP), motor evoked potentials (MEPs) from abductor pollicis brevis following transcranial magnetic stimulation (TCM) were recorded with and without a conditioning of ipsilateral painful digital nerve electric stimulation.

METHODS

MEPs following TCM were recorded with and without a conditioning stimulation at an interstimulus interval (ISI) from 0 ms to 100ms in 6 controls and four patients who had reduced pain sensation in unilateral upper limbs associated with cervical syringomyelia. In addition MEPs and evoked spinal cord potentials (ESCPs) from cervical epidural space following TCM with and without a conditioning stimulation were recorded in four patients with thoracic myelopathy.

RESULTS

MEP amplitude was clearly attenuated by a conditioning stimulation at an ISI from 40 ms to 80 ms in controls (statistically significant at 60 ms). In patients with cervical syringomyelia, MEP amplitude was attenuated by a conditioning stimulation in asymptomatic hands similarly in controls but that was unchanged by a conditioning stimulation in the symptomatic hand with reduced pain sensation. In patients with thoracic myelopathy MEP amplitude was attenuated by conditioning stimulation similarly in controls, but ESCP amplitude was unchanged.

CONCLUSIONS

We demonstrated that noxious cutaneous nerve stimulation suppressed spinal motor neurons but cortical motor neuron excitability was unchanged during CSP. In clinical practice, measurement of MEP suppression after noxious cutaneous nerve stimulation may provide useful information in patients with damaged pain related nerve fibers.