Abnormal Sensory Nerve Action Potential Research Articles

P.219 Novel clinical phenotype of early-onset amyotrophic lateral sclerosis and frontotemporal dementia with SNCB mutation

The continuum between amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) is well known spectrum of disease and genetic variability in this overlap has been previously reported. We report a novel clinical phenotype of early-onset ALS and FTD with a previously reported <i>SNCB</i> (β synuclein) mutation with Lewi body dementia. 45-year-old woman presented to our department complaining of progressive quadriparesis and dysphagia, which had started with right hemiparesis 4 months ago. She had a history of hypothyroidism but denied neurological family history. Neurologic examination revealed Hoffmann sign positive bilaterally and hyperreflexia of both knees. Nerve conduction study and electromyography showed low complex motor action potentials and widespread denervation in four limbs and thoracic paraspinal muscles without abnormal sensory nerve action potentials. CSF study was unremarkable. Diagnosis of probable ALS was established and riluzole 100mg daily was administered. Three months later, she reported a cognitive decline. In the neuropsychologic assessment battery, her language, memory, and frontal/executive function were below the first percentile for her age with relatively intact attention and visuospatial function. Brain MRI showed bilateral temporal atrophy, especially in the left anterior temporal area. SPECT revealed hypoperfusion in both frontal, temporal, and parietal cortices. Targeted next generation sequencing was conducted for ALS and FTD, and we found heterozygous c.208G>A mutation in <i>SNCB</i>. Despite tremendous research elucidating ALS-FTD, early onset case is rare. With this case, we report a new clinical phenotype of ALS-FTD with <i>SNCB</i> mutation, which has been only reported in few cases of Lewy body dementia and is being investigated recently. This case implies <i>SNCB,</i> which is assumed to contribute to neurodegeneration, can be a new candidate of ALS-FTD, especially in young age.

Variability in electrodiagnostic findings associated with neurogenic thoracic outlet syndrome.

Introduction/AimsNeurogenic thoracic outlet syndrome (NTOS) is a heterogeneous and often disputed entity. An electrodiagnostic pattern of T1 > C8 axon involvement is considered characteristic for the diagnosis of NTOS. However, since the advent of high‐resolution nerve ultrasound (US) imaging, we have encountered several patients with a proven entrapment of the lower brachial plexus who showed a different, variable electrodiagnostic pattern.MethodsIn this retrospective case series, 14 patients with an NTOS diagnosis with a verified source of compression of the lower brachial plexus and abnormal findings on their electrodiagnostic testing were included. Their medical records were reviewed to obtain clinical, imaging, and electrodiagnostic data.ResultsSeven patients showed results consistent with the “classic” T1 axon > C8 pattern of involvement. Less typical findings included equally severe involvement of T1 and C8 axons, more severe C8 involvement, pure motor abnormalities, neurogenic changes on needle electromyography in the flexor carpi radialis and biceps brachii muscles, and one patient with an abnormal sensory nerve action potential (SNAP) amplitude for the median sensory response recorded from the third digit. Patients with atypical findings on electrodiagnostic testing underwent nerve imaging more often compared to patients with classic findings (seven of seven patients vs. five of seven respectively), especially nerve ultrasound.DiscussionWhen there is a clinical suspicion of NTOS, an electrodiagnostic finding other than the classic T1 > C8 pattern of involvement does not rule out the diagnosis. High resolution nerve imaging is valuable to diagnose additional patients with this treatable condition.

Relationship Between Cervical Nerve Root Entrapment Due to Cervical 6-7 Foraminal Stenosis and Sensory Nerve Action Potentials in Nerve Conduction Study

Objective To compare the sensory nerve action potentials (SNAPs) between patients with cervical 6-7 foraminal stenosis (FS) and those without. Methods We enrolled patients who underwent a bilateral nerve conduction study (NCS) between January 2016 and December 2017. The FS group (n=35) included patients whose lesion was located at C6-7 FS. The non-FS group (n=75) had no lesions at C6-7 foramen. The amplitudes and latencies of SNAPs on the affected side were compared between the two groups. The proportion of those with abnormal SNAP responses was also evaluated. Results Compared with the non-FS group, the FS group had a significantly lower amplitude (30.5 vs. 40.2 µV; age-adjusted p<0.001) and a longer latency (3.31 vs. 3.17 ms; age-adjusted p=0.001) of the median nerve. Abnormal amplitude was observed in 20.0% of the FS group and 4.0% of the non-FS group (age-adjusted p=0.007), and abnormal latency was observed in 45.7% of the FS group and 26.7% of the non-FS group (age-adjusted p=0.010). The median SNAP ratio between the affected side and the unaffected side was not significantly different between the two groups. Conclusion Patients with C6-7 FS had a lower amplitude and a longer latency of the median nerve than did those without. Abnormal SNAP amplitude and latency were significantly more common in patients with FS. SNAP amplitude may be used as a predictor of cervical FS. Keywords: Electrodiagnosis; Cervical foraminal stenosis; Sensory nerve action potential; Median nerve

Vibratory testing with the 64 Hz Rydel-Seiffer tuning fork and its relation to the sural nerve action potential.

Despite its widespread use, little is known regarding the ability of the semi-quantitative Rydel-Seiffer tuning fork to designate peripheral nerve function. We sought to determine in a large sample of normal and abnormal nerves the relationship between vibration sense and compound sensory nerve action potential (SNAP) parameters recorded in a corresponding innervation area. Vibratory thresholds were determined on a scale of 0 to 8 with a 64 Hz Rydel-Seiffer tuning fork placed on the lateral malleolus of 303 subjects. Sural nerve sensory neurography was employed to derive SNAP parameters, which were related to vibration sense by means of multiple linear regression. ROC curve analysis was performed to determine the classification efficacy of the tuning fork in distinguishing normal from abnormal sural nerve responses. SNAP amplitude was the most significant predictor in the whole subjects group and in the subgroup of subjects with normal SNAPs, whereas conduction velocity played a major role in subjects with abnormal SNAPs. Age was significantly associated with vibration perception, particularly in subjects with normal SNAPs. With an area under the curve of 0.730, vibration sense was a fair classifier for decreased SNAP amplitudes. The optimal vibratory cutoff was 4.2. Age is a major determinant of vibratory test results, highlighting the importance of aging of central and peripheral pathways in mediating vibration sense. Hence, neurophysiological testing cannot be omitted in the context of polyneuropathy work-up, since even at the optimal cutoff threshold, vibratory examination still displays 40% false negative test results.

Sciatic neuropathy with preserved sensory nerve action potentials, a case series

Background: Sciatic neuropathy is differentiated from lumbosacral radiculopathy based on the finding of abnormal sensory nerve action potentials (SNAPs). Cases of sciatic neuropathy with intact SNAPS have not been well described.&#x0D; Methods: A retrospective analysis of 12 patients with sciatic neuropathy in a single institution.&#x0D; Results: We describe 12 patients in whom a sciatic neuropathy was diagnosed based on a combination of history, physical exam, radiological and electrodiagnostic (EDX) findings. Lower extremity SNAPs were found to be within normal range in all patients, although SNAP amplitude asymmetry between both sides was observed in 3. Included patients were young (mean age of 40.3 years) and mostly female (9 patients).&#x0D; Conclusions: Sciatic neuropathy may occur with a relative sparing of sensory fibers. Recognition of this group of patients should help to avoid making a misdiagnosis of lumbosacral radiculopathy.

Vascular factors and neuropathy in lower limb of diabetic patients

Asymmetric clinical presentation in some patients with diabetic polyneuropathy may result from the different vascular environments in both lower limbs. The aim of the study is to determine the association of neuropathy with vascular factors in each lower limb of diabetic patients. A total of 102 patients (204 lower limbs) given a diagnosis of diabetic polyneuropathy were enrolled. The primary end points are sensory nerve action potential (SNAP) amplitude and conduction velocity (CV) of the sural nerve and independent variables are vascular and nonvascular factors. Vascular factors include mean arterial pressure and pulse pressure at the ankle, ankle-brachial index, and arterial stiffness assessed by pulse wave velocity. Nonvascular factors include age, gender, height, body weight, body mass index, total cholesterol, and hemoglobin A1C. Age, hemoglobin A1C, and ankle pulse pressure were inversely correlated with SNAP amplitude of the sural nerve, while no factors were correlated with CV of the sural nerve. Increased arterial stiffness was significant in the limbs group with abnormal SNAP amplitude of the sural nerve, while increased height was significant in the limbs group with abnormal CV of the sural nerve. Vascular factors were more significantly associated with decreased SNAP amplitude rather than decreased CV of the sural nerve in the nerve conduction study of diabetic patients.

Diagnostic Accuracy of Sensory Clinical Findings of the Hand Dorsum and of Neurography of the Dorsal Ulnar Cutaneous Nerve in Ulnar Neuropathy at the Elbow

ObjectiveThe main objective is to investigate the diagnostic accuracy and the relation of touch sensation and subjective sensory symptoms in the medial aspect of the hand dorsum, and neurography of the dorsal ulnar cutaneous nerve (DUCN) in ulnar neuropathy at the elbow (UNE). Secondary objective is to report the electrophysiological occurrence of anatomical variant of sensory innervation of the medial aspect of the hand dorsum from superficial radial nerve (SRN). DesignProspective, cohort study. SettingElectromyography laboratory. ParticipantsConsecutive participants (N=282), those with UNE (n=81) and those without UNE (n=201), were enrolled. InterventionsNot applicable. Main Outcome MeasuresAccuracy and agreement between sensory clinical findings of the medial hand dorsum and neurography of DUCN in UNE diagnosis. ResultsDUCN neurographic and sensory findings had high specificity and relatively low sensitivity. Normal or abnormal sensory nerve action potential (SNAP) of DUCN matched with normal or abnormal touch sensation of the medial aspect of hand dorsum. Abnormal DUCN SNAP was related to the clinical severity of UNE and to the axonal damage of the ulnar nerve. Anatomical variant of the innervation of hand dorsum from SRN was demonstrated in 31 of 564 hands (6.2%) belonging to 26 of 282 participants (9.2%). If the variant was present, DUCN SNAP of the same side was more frequently absent or of low amplitude. ConclusionsThe utility of DUCN neurography and sensory findings of the medial aspect of the dorsum of the hand is limited in the diagnosis of UNE. However, if DUCN SNAP is absent or low in amplitude, it is advisable to check the presence of the anatomical variant of the innervation of the medial aspect of the hand dorsum from SRN.

Predictive value for weakness and 1-year mortality of screening electrophysiology tests in the ICU.

Muscle weakness in long-stay ICU patients contributes to 1-year mortality. Whether electrophysiological screening is an alternative diagnostic tool in unconscious/uncooperative patients remains unknown. We aimed to determine the diagnostic properties of abnormal compound muscle action potential (CMAP), sensory nerve action potential (SNAP), and spontaneous electrical activity (SEA) for Medical Research Council (MRC)-defined weakness and their predictive value for 1-year mortality. Data were prospectively collected during the EPaNIC trial (ClinicalTrials.gov: NCT00512122). First, sensitivity, specificity, positive (PPV) and negative predictive values (NPV) of abnormal CMAP, SNAP, and SEA for weakness were determined. Subsequently, association between 1-year mortality and abnormal findings on electrophysiological screening was assessed by univariate and multivariate analyses correcting for weakness and other risk factors and the prediction model involved only a development phase. A total of 730 patients were electrophysiologically screened of whom 432 were tested for weakness. On day 8, normal CMAP excluded weakness with a high NPV (80.5 %). By day 15, abnormal SNAP and the presence of SEA had a high PPV (91.7 and 80.0 %, respectively). Only a reduced CMAP on day 8 was associated with higher 1-year mortality [35.6 vs 15.2 % (p < 0.001)]. This association remained significant after correction for weakness and other risk factors [OR 2.463 (95 % CI 1.113-5.452), p = 0.026]. Also among conscious/cooperative patients without weakness, reduced CMAP was independently associated with a higher likelihood of death occurring during 1 year [HR 2.818 (95 % CI 1.074-7.391), p = 0.035]. The diagnostic properties of electrophysiological screening vary over time. Abnormal CMAP documented early during critical illness carries information about longer-term outcome, which should be further investigated mechanistically.

Antidromic sensory nerve conduction study of the digital branches of the medial plantar nerve: A novel method to detect early diabetic sensory axonal polyneuropathy

Distal sensory neuropathy is the most common form of diabetic neuropathy. We developed a novel antidromic technique for assessment of distal nerve function for early diagnosis of diabetic neuropathy. Diabetic and control groups underwent standard and more distal sensory nerve conduction studies (NCS); sensory nerve action potentials (SNAPs) of the proper digital branches of the medial plantar nerve were recorded with our method after stimulation at the sole and recording from digits I and II. Comparison between controls and diabetics showed a statistically significant difference in mean SNAP amplitudes for all nerves tested. A higher percentage of abnormal SNAPs was obtained with our technique than with either conventional or more distal NCS in all patients. As compared with clinical evaluation and other NCS, our antidromic stimulation was the most sensitive method to detect abnormal sensory nerve conduction in symptomatic and asymptomatic diabetic patients.

Which nerve conduction parameters can predict spontaneous electromyographic activity in carpal tunnel syndrome?

ObjectiveWe investigate electrodiagnostic markers to determine which parameters are the best predictors of spontaneous electromyographic (EMG) activity in carpal tunnel syndrome (CTS). MethodsWe enrolled 229 patients with clinically proven and nerve conduction study (NCS)-proven CTS, as well as 100 normal control subjects. All subjects were evaluated using electrodiagnostic techniques, including median distal sensory latencies (DSLs), sensory nerve action potentials (SNAPs), distal motor latencies (DMLs), compound muscle action potentials (CMAPs), forearm median nerve conduction velocities (FMCVs) and wrist–palm motor conduction velocities (W–P MCVs). All CTS patients underwent EMG examination of the abductor pollicis brevis (APB) muscle, and the presence or absence of spontaneous EMG activities was recorded. Normal limits were determined by calculating the means±2 standard deviations from the control data. Associations between parameters from the NCS and EMG findings were investigated. ResultsIn patients with clinically diagnosed CTS, abnormal median CMAP amplitudes were the best predictors of spontaneous activity during EMG examination (p<0.001; OR 36.58; 95% CI 15.85–84.43). If the median CMAP amplitude was ⩽2.1mV, the rate of occurrence of spontaneous EMG activity was >95% (positive predictive rate >95%). If the median CMAP amplitude was higher than the normal limit (>4.9mV), the rate of no spontaneous EMG activity was >94% (negative predictive rate >94%). An abnormal SNAP amplitude was the second best predictor of spontaneous EMG activity (p<0.001; OR 4.13; 95% CI 2.16–7.90), and an abnormal FMCV was the third best predictor (p=0.01; OR 2.10; 95% CI 1.20–3.67). No other nerve conduction parameters had significant power to predict spontaneous activity upon EMG examination. ConclusionsThe CMAP amplitudes of the APB are the most powerful predictors of the occurrence of spontaneous EMG activity. Low CMAP amplitudes are strongly associated with spontaneous activity, whereas high CMAP amplitude are less associated with spontaneous activity, implying that needle EMG examination should be recommended for the detection of spontaneous activity in those CTS patients whose NCS reveals CMAP amplitudes between 2.1mV and the lower normal limit (4.9mV in the present study). SignificanceUsing NCS, electromyographers can predict the presence of spontaneous EMG activity in CTS patients.

THE MECHANISMS OF MOTOR AND SENSORY NERVE DYSFUNCTION AFTER CHRONIC ARSENIC EXPOSURE IN RATS

Background and Aims: Tens of millions of people are exposed to arsenic contaminated drinking water all over the world, including residents in Argentina, Bangladesh, Chile, China, Mongolia, Taiwan, etc. Previous studies have shown that chronic arsenic exposure could cause various cancers, skin diseases, neurological diseases, cardiovascular diseases and cerebrovascular diseases. Recent epidemiologic studies from Bangladesh showed that chronic arsenic exposure was associated with abnormal sensory nerve action potentials. We therefore set up an animal model to explore the mechanisms of neuropathy caused by chronic arsenic exposure. Methods: We treated spontaneous hypertensive-prone rats with drinking water containing 133 μg/ml of arsenic (experimental group) for 40 consecutive weeks and compared them to a blank control group. At the end of exposure, we assessed motor functions by observing spontaneous locomotor behaviors (including motion distance and motion velocity) in the open field and monitored the sensory function by measuring the pain stimulation latency during the hot plate test. The enzymatic Na(+)/K(+)-AT Pase activity of sciatic nerve was determined by a colorimetric assay, and the pathological changes and severity of neuropathy were be examined by hematoxylin-eosin stain. The possible mechanisms affecting heat shock protein 70 (HSP70) and C-reactive protein (CRP) on nerves were studied by immunohistochemistry. The arsenic levels of the whole blood and the sciatic nerve were measured using Inductively Coupled Plasma Mass Spectrometry and correlated with the toxic effects on the peripheral nerve. Results: After arsenic exposure, the hot stimulation latencies prolonged statistically significantly in arsenic exposure rats (37.60±1.77 vs. 5.60±1.50 seconds, p&lt;0.05). The motor functions in terms of motion distance, velocity and spontaneous locomotion did not decrease significantly. The Na+/K+-ATPase and CRP activities of the sciatic nerve were inhibited, but the HSP70 activity was enhanced. Conclusions: Chronic arsenic exposure could affect sensory nerve functions probably via enhancing HSP70 and inhibiting Na+/K+-ATPase and CRP activities.

Fatigue and abnormal neuromuscular transmission in Kennedy's disease

We describe a patient with Kennedy's disease (X-linked bulbospinal neuronopathy) who experienced leg muscle fatigue with long-distance running. The patient also reported muscle twitching involving the face and extremities and long-standing muscle cramps. Aside from mild facial and tongue weakness (and fasciculations), his examination was normal, including completely preserved muscle strength in the extremities. Electrodiagnostic evaluation revealed evidence for a chronic motor axonopathy/neuronopathy and abnormal sensory nerve action potentials. In addition, repetitive nerve stimulation studies were normal, but neuromuscular jitter tested in the same muscle was markedly abnormal. The normal clinical strength and repetitive nerve stimulation studies in a muscle showing markedly increased neuromuscular jitter suggested a mechanism for this patient's symptoms of muscle fatigue, related to failure of neuromuscular transmission at a critical number of endplates during extremes of physical activity.

Sensory Nerve Action Potential Abnormalities in Neuralgic Amyotrophy: A Report of 18 Cases

To report patients with neuralgic amyotrophy (NA) and abnormal sensory nerve action potentials (SNAP). A retrospective study of NA cases diagnosed in electrodiagnostic evaluation during a 5-year period found 18 patients with 23 abnormal SNAP. Clinical and neurophysiological records were reviewed. NA was diagnosed according to clinical features and disease course. Radiologic and laboratory investigations were conducted to rule out other disorders. The 23 individual sensory nerve lesions were 8 median, 5 radial, 4 ulnar, and 6 lateral antebrachial nerves. Our findings suggest that clinical and electrodiagnostic sensory involvement in NA is not uncommon and may be a prominent feature. They confirm that the most typical pattern of NA is mononeuritis or mononeuritis multiplex, and that the frequent lack of sensory deficit is because the lesions usually affect pure motor proximal or distal nerves.