The segmental palmar test in diagnosing carpal tunnel syndrome reassessed

Objective

To test our hypothesis that comparing the sensory nerve conduction velocity of the median nerve across the wrist with that of the forearm is more sensitive than comparing it with that of the palm in the electrodiagnostic confirmation of carpal tunnel syndrome (CTS).

Methods

One hundred and fifty seven consecutive patients with clinically defined CTS were prospectively included and electrophysiologically examined. Antidromic nerve conduction velocities were measured in 3 segments of the median nerve: forearm, wrist, and palm. Differences and ratios in nerve conduction velocities were computed between the forearm and wrist and between the palm and wrist segments.

Results

Comparing the median nerve conduction velocities of the forearm with the wrist segment provides a greater sensitivity (79.6% and 82.8% for the second and third digit, respectively) than comparing the palm with the wrist segment (65.6% and 65.0%). Applying the ratio leads to slightly higher sensitivities for both comparisons.

Conclusions

The modified segmental palmar test is a sensitive, robust and easily applicable method in diagnosing CTS.

Significance

We recommend to use the median nerve sensory conduction velocity in the forearm as a reference in the segmental palmar test instead of that in the palm.     

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

Objective

We investigate electrodiagnostic markers to determine which parameters are the best predictors of spontaneous electromyographic (EMG) activity in carpal tunnel syndrome (CTS).

Methods

We 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.

Results

In 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 ?2.1 mV, 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 (>4.9 mV), 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.

Conclusions

The 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 2.1 mV and the lower normal limit (4.9 mV in the present study).

Significance

Using NCS, electromyographers can predict the presence of spontaneous EMG activity in CTS patients.     

Test-retest reliability of transcarpal sensory NCV method for diagnosis of carpal tunnel syndrome

Background:

Carpal Tunnel Syndrome (CTS) is the most frequent entrapment neuropathy affecting the upper extremity. There are a variety of electrodiagnostic methods available for documenting median neuropathy in CTS. In some studies, determining the sensory NCV across the palm-wrist segment has been introduced as the most sensitive diagnostic procedure for CTS. The aim of this study was to investigate the test-retest reliability of transcarpal median sensory NCV method for the diagnosis of CTS.

Materials and Methods:

Twenty-three patients with clinical symptoms of CTS were tested two times by two different practitioners in one session and again by the first practitioner after one week. Stimulation of the median nerve was performed in the wrist and palm, with a conduction distance maximum of 7 cm, reliabilities of median nerves sensory nerve action potential latencies with stimulation at wrist and palm (W-SNAP, P-SNAP) and its transcarpal NCV were assessed with intraclass correlation coefficient (ICC).

Results:

Comparison of the obtained values, which were done by two practitioners in one session showed ICC of W-SNAP latency, P-SNAP latency and transcarpal NCV of 0.93, 0.88 and 0.87, respectively and values that were done by one practitioner in two sessions with one-week interval showed ICC of 0.60, 0.50 and 0.47, respectively.

Conclusion:

Our findings suggest excellent interpractitioner test-retest reliability of transcarpal median sensory NCV method for diagnosing CTS.     

Frequency-dependent conduction block in ulnar neuropathy localized to the elbow

Objective

To determine whether frequency-dependent conduction block (FDB) occurs in acute ulnar neuropathies localized to the elbow.

Methods

High-frequency nerve stimulation (30 Hz, 20 stimuli) was applied to the ulnar motor nerve above and below the elbow in controls (15) and in patients with short duration (between 2 and 16 weeks) ulnar neuropathy localized to the elbow (10) with evidence of moderate to severe conduction block and slowing.

Results

FDB was not observed in any of the 10 subjects tested. Three of these subjects were seen in follow-up; studies in two of these subjects, during the recovery period, did however demonstrate FDB with a similar pattern to that observed previously in CTS.

Conclusions

This study has demonstrated that the remaining unblocked ulnar motor fibers across the elbow in acute ulnar neuropathy with conduction block, do not demonstrate FDB in response to stimulation at 30 Hz.

Significance

These results suggest that FDB may not occur in the unblocked fibers in ulnar neuropathy despite evidence of conduction slowing. These results differ from previous observations in CTS and imply that demyelinating lesions (conduction block versus slowing) respond differently to high-frequency stimulation.     

The latency distribution of motor evoked potentials in patients with multiple sclerosis

Objective

To compare the individual latency distributions of motor evoked potentials (MEP) in patients with multiple sclerosis (MS) to the previously reported results in healthy subjects (Firmin et al., 2011).

Methods

We applied the previously reported method to measure the distribution of MEP latencies to 16 patients with MS. The method is based on transcranial magnetic stimulation and consists of a combination of the triple stimulation technique with a method originally developed to measure conduction velocity distributions in peripheral nerves.

Results

MEP latency distributions in MS typically showed two peaks. The individual MEP latency distributions were significantly wider in patients with MS than in healthy subjects. The mean triple stimulation delay extension at the 75% quantile, a proxy for MEP latency distribution width, was 7.3 ms in healthy subjects and 10.7 ms in patients with MS.

Conclusions

In patients with MS, slow portions of the central motor pathway contribute more to the MEP than in healthy subjects. The bimodal distribution found in healthy subjects is preserved in MS.

Significance

Our method to measure the distribution of MEP latencies is suitable to detect alterations in the relative contribution of corticospinal tract portions with long MEP latencies to motor conduction.     

Ulnar nerve entrapment at wrist associated with carpal tunnel syndrome.

In this study, ulnar nerve entrapments at the wrist were investigated using nerve conduction studies in cases with established diagnosis of carpal tunnel syndrome (CTS). Cases with cervical radiculopathy and polyneuropathy as well as patients with ulnar nerve entrapment at elbow were excluded from the study. Fifty-three cases (46 females, seven males) whose ages ranged between 20 and 72 years (mean: 49.31 +/- 13.78) were evaluated. Among 53 cases, 12 (22.6%) bilateral and 41 (77.3%) unilateral CTS were detected. Totally 65 wrists evaluated and prolongation of median nerve wrist-3rd digit distal sensory latencies (DSL; N: 59; 90.7%) and wrist-abductor pollicis brevis distal motor latencies (N: 48; 73.8%) were seen. In six wrists, diagnoses were established with the detection of an increase in the differences between wrist-4th digit DSL of median and ulnar nerve. This test was used if other test results were in normal limits. Prolongation of ulnar nerve wrist-5th digit DSL were found in 12 wrists (18.4%) in cases with CTS. Among these 12 wrists mild (N: 2), moderate (N: 7) and severe (N: 3) CTS were detected. Ulnar nerve motor conduction studies provided normal results. In conclusion, we are in the opinion that for the detection of associated ulnar nerve wrist entrapments, ulnar nerve conduction studies paying special attention to DSL convey importance in established cases with CTS.     

A study of interpolation method in diagnosis of carpal tunnel syndrome

Context:

The low correlation between the patients’ signs and symptoms of carpal tunnel syndrome (CTS) and results of electrodiagnostic tests makes the diagnosis challenging in mild cases. Interpolation is a mathematical method for finding median nerve conduction velocity (NCV) exactly at carpal tunnel site. Therefore, it may be helpful in diagnosis of CTS in patients with equivocal test results.

Aim:

The aim of this study is to evaluate interpolation method as a CTS diagnostic test.

Settings and Design:

Patients with two or more clinical symptoms and signs of CTS in a median nerve territory with 3.5 ms ≤ distal median sensory latency <4.6 ms from those who came to our electrodiagnostic clinics and also, age matched healthy control subjects were recruited in the study.

Materials and Methods:

Median compound motor action potential and median sensory nerve action potential latencies were measured by a MEDLEC SYNERGY VIASIS electromyography and conduction velocities were calculated by both routine method and interpolation technique.

Statistical Analysis Used:

Chi-square and Student''s t-test were used for comparing group differences. Cut-off points were calculated using receiver operating characteristic curve.

Results:

A sensitivity of 88%, specificity of 67%, positive predictive value (PPV) and negative predictive value (NPV) of 70.8% and 84.7% were obtained for median motor NCV and a sensitivity of 98.3%, specificity of 91.7%, PPV and NPV of 91.9% and 98.2% were obtained for median sensory NCV with interpolation technique.

Conclusions:

Median motor interpolation method is a good technique, but it has less sensitivity and specificity than median sensory interpolation method.Key Words: Carpal tunnel syndrome, electrodiagnosis, interpolation, nerve conduction velocity     

Sensitivity of three median-to-ulnar comparative tests in diagnosis of mild carpal tunnel syndrome

We studied 193 hands of 113 patients referred for typical carpal tunnel syndrome (CTS). Ninety-five (49%) hands had normal median distal motor latency (≤4.2 ms) and normal or borderline sensory conduction velocity from digit 2 stimulation (≥45 m/s). In these cases we performed three median to ulnar comparative tests: (1) difference between median and ulnar distal motor latencies recorded from the second lumbrical and interossei muscles (2L-INT); (2) difference between median and ulnar sensory latencies from digit 4 stimulation (D4M-D4U); and (3) difference between median and ulnar mixed nerve latencies from palmar stimulation (PM-PU). The 2L-INT difference was ≥0.6 ms in 10% of hands. PM-PU and D4M-D4U were ≥0.5 ms in 56% and 77% of hands, respectively. The greater sensitivity of D4M-D4U might be explained by the funicular topography and consequent greater susceptibility to compression of the cutaneous fibers from the third interspace which, at the distal carpal tunnel, are clumped superficially in the anteroulnar portion of the median nerve just beneath the transverse ligament. © 1993 John Wiley & Sons, Inc.     

Diagnostic specificity of sensory and motor nerve conduction variables in early detection of carpal tunnel syndrome

Summary In the carpal tunnel syndrome (CTS) sensory nerve conduction is more sensitive than motor conduction. However, 8%–25% of the sensory distal latencies in symptomatic hands may still be normal. A systematic study was made of the median, ulnar and radial orthodromic nerve conduction velocities (SNCV) stimulating each of the fingers separately. Four SNCVs from the median nerve, two SNCVs from the ulnar nerve and one from the radial nerve were obtained, and the ratio of the median to radial SNCV and the ratios of the median and ulnar SNCVs were estimated. The significance of these parameters in the diagnosis of the CTS was studied, and a rapid technique for the screening of nerve entrapment in the initial stages of the disease is proposed. Three hundred and seventy-five symptomatic hands were examined. Seventy-five hands showed normal distal latency, in which cases, however, the SNCV of the ring finger was always outside the normal range, while the SNCVs of the thumb, index and middle fingers were abnormal in 64%, 80% and 92% of cases respectively. The amplitudes of the sensory responses were the least sensitive of the parameters studied. Our results suggest that a study of the median nerve digital branch to the ring finger may be of value in providing an easily performed and rapid technique for screening an early median nerve entrapment at the wrist.     

Lumbrical and interossei recording in carpal tunnel syndrome.

Median motor studies are commonly "normal" in mild carpal tunnel syndrome (CTS). This reflects either the sparing of motor compared to sensory fibers, or the inability of conventional studies to detect an abnormality. A novel approach to demonstrate early motor fiber involvement in CTS is the placement of the same active electrode lateral to the third metacarpal, allowing recording from the second lumbrical or the deeper interossei, when stimulating the median or ulnar nerves at the wrist, respectively. We compared the difference between these latencies in 51 normal control hands to 107 consecutive patient hands referred with symptoms and signs suggestive of CTS, who were subsequently proven to have electrophysiologic CTS by standard nerve conduction criteria. A prolonged lumbrical-interossei latency difference (> 0.4 ms) was found to be a sensitive indicator of CTS in all patient groups. It was also helpful in patients with coexistent polyneuropathy, where localization at the wrist was otherwise difficult.     

Electrophysiological index of acoustic temporal regularity violation in the middle latency range

Objective

Acoustic violations in temporal regularity have been traditionally indexed by mismatch negativity (MMN). However, recent studies have demonstrated that humans can detect auditory changes in physical sound features, such as frequency, location and intensity, in the first 50 ms after sound onset. Our aim was to examine if temporal regularity violations could be detected in the middle latency range.

Methods

We used an oddball paradigm with 290 ms as standard stimulus onset asynchrony (SOA) and 200 ms as deviant SOA. We also employed a control paradigm that comprised of seven SOAs including 200 and 290 ms, in order to control for differences due to refractoriness.

Results

In the middle latency range, temporal regularity violations led to enhanced Pa and Nb responses, which behaved differently to the corresponding SOAs in the control condition. In the long latency range, temporal regularity violations led to similar behaviours in both oddball and control paradigms.

Conclusions

These findings suggest that with a fast presentation rate, human brains are capable to detect temporal regularity violations in the middle latency range.

Significance

Together with previous studies that found early change detection responses, the current study emphasises that the human brain can encode simple regularity violation as early as approximately 50 ms post-stimulus onset.     

Comparison of high-resolution sonography and electrophysiology in the diagnosis of carpal tunnel syndrome

Background:

The diagnostic accuracy of high-resolution ultrasonography (HRUS) in comparison to electro-diagnostic testing (EDX) in carpal tunnel syndrome (CTS) is debatable.

Objective:

The aim of this study was to compare the diagnostic accuracy of HRUS with EDX in patients with various grades of CTS and CTS associated with peripheral neuropathy (CTS + PNP).

Materials and Methods:

A prospective cohort of 57 patients with possible CTS was studied along with matched controls. The cross-sectional area (CSA) of the median nerve at the inlet of carpal tunnel was assessed by a sonologist blinded to the clinical and EDX data. Palm wrist distal sensory latency difference (PWDSLD), second lumbrical-interosseus distal motor latency difference (2LIDMLD) and CSA were compared in patients with different grades of severity of CTS and CTS+PNP.

Results:

Total 92 hands of 57 patients met the clinical criteria for CTS. Mean CSA at the inlet of carpal tunnel was 0.11 ± 0.0275 cm². It had the sensitivity, specificity, positive predictive value and negative predictive values of 76.43%, 72.72%, 89.47% and 68%, respectively (P < 0.0001). Overall, HRUS had good correlation with PWDSLD and 2LIDMLD electro-diagnostic studies in all grades of CTS and CTS + PNP.

Conclusion:

HRUS can be used as a complementary screening tool to EDX. However, EDX has been found to be more sensitive and specific in mild CTS.     

Modulation of spinal reflex by assisted locomotion in humans with chronic complete spinal cord injury

Objective

In healthy subjects, spinal reflexes (SR) evoked by non-noxious tibial nerve stimulation consist of an early (60–120 ms latency) and an occasional late-appearing (120–450 ms latency) component in the ipsilateral tibialis anterior. In chronic (>1 year) complete spinal cord injured (cSCI) subjects early components are small or lacking while late components are dominant. Here we report on the modulation of SR by assisted locomotion in healthy and chronic motor cSCI subjects.

Methods

SR was evoked by tibial nerve stimulation at the terminal stance phase during assisted locomotion and was compared to SR recorded during upright stance.

Results

In chronic cSCI subjects only a late SR component was consistently present during upright stance. However during assisted locomotion, an early SR component appeared, while amplitude of the late SR component became small. In contrast, in healthy subjects the early SR component dominated in all conditions, but a small late component appeared during assisted locomotion.

Conclusion

A more balanced activity of early and late SR components occurred in both subject groups if an appropriate proprioceptive input was provided.

Significance

Early and late SR components are assumed to reflect the activity of separate neuronal circuits, which are associated with the locomotor circuitry possibly by shaping the pattern.     

Changes in Dermatomal Somatosensory Evoked Potentials according to Stimulation Intensity and Severity of Carpal Tunnel Syndrome

Objective

To investigate the change of latency of cervical dermatomal somatosensory evoked potential (DSEP) according to stimulation intensity (SI) and severity of carpal tunnel syndrome (CTS).

Methods

Stimulation sites were the C6, C7, and C8 dermatomal areas. Two stimulation intensities 1.5×sensory threshold (ST) and 2.5×ST were used on both normal and CTS patients.

Results

In moderate CTS, the latencies of C6 and C7 DSEP during 1.5×ST SI and those of C7 DSEP during 2.5×ST SI were significantly delayed compared with the values of normal subjects. Significant correlation between the latency of C7 DSEP of 2.5×ST stimulation and the median sensory nerve conduction velocity was observed.

Conclusion

We suggest that these data can aid in the diagnosis of cervical sensory radiculopathy using low stimulation intensity and of those who have cervical sensory radiculopathy combined with CTS patients.     

Effects of carpal tunnel syndrome on adaptation of multi-digit forces to object texture

Objective

The ability to adapt digit forces to object properties requires both anticipatory and feedback-driven control mechanisms which can be disrupted in individuals with a compromised sensorimotor system. Carpal tunnel syndrome (CTS) is a median nerve compression neuropathy affecting sensory and motor function in a subset of digits in the hand. Our objective was to examine how CTS patients coordinate anticipatory and feedback-driven control for multi-digit grip force adaptation.

Methods

We asked CTS patients and healthy controls to grasp, lift, and hold an object with different textures.

Results

CTS patients effectively adapted their digit forces to changes in object texture, but produced excessive grip forces. CTS patients also produced larger peak force rate profiles with fewer modulations of normal force prior to lift onset than did controls and continued to increase grip force throughout the lift whereas forces were set at lift onset for the controls.

Conclusions

These findings suggest that CTS patients use less online sensory feedback for fine-tuning their grip forces, relying more on anticipatory control than do healthy controls.

Significance

These characteristics in force adaptation in CTS patients indicate impaired sensorimotor control which leads to excessive grip forces with the potential to further exacerbate their median nerve compression.     

Reproducibility of contact heat evoked potentials (CHEPs) over a 6 months interval

Objective

Contact heat evoked potentials (CHEPs) mediated by primary afferent Aδ-fibers can be recorded at the vertex. CHEPs are reduced in small fibre neuropathy and considered as a noninvasive measure of small fibre function. As long-term stability of CHEPs has not been examined, it is presently not clear if CHEPs may also be useful for following the course of small fibre neuropathy.

Methods

Here, we analyzed CHEPs from 60 healthy subjects recorded at two occasions separated by 6 months.

Results

There was a systematic shift towards larger amplitudes (from 40.2 ± 13.8 μV to 53.3 ± 17.5 μV, p < 0.001) and towards shorter latencies (from 425.0 ± 28.8 ms to 387.2 ± 30.3 ms, p < 0.001) after six months, while CHEP areas were more constant over time.

Conclusions

The present results show that systematic changes of CHEP amplitudes and latencies may occur over time. Possible reasons include seasonal differences in skin conductivity for heat and psychological effects.

Significance

CHEP areas seem to be more stable over time than amplitudes or latencies, however, it remains to be determined if CHEP areas differentiate between subjects with lesions of the nociceptive system and healthy controls as reliably as CHEP amplitudes.     

Median-ulnar nerve communications: electrophysiological demonstration of motor and sensory fibre cross-over

Summary In a 33-year-old female with carpal tunnel syndrome the presence of anomalous communications between median and ulnar nerves was electrophysiologically demonstrated in the forearm. Motor latencies from proximal and distal stimulation sites along the median nerve fibres to the abductor pollicis brevis were identical. Proximal latency increased after procaine infiltration of the ulnar nerve at the wrist. Normal latency to the abductor digiti minimi was obtained on stimulation of the median nerve at the elbow. Along the sensory fibres of the median nerve orthodromic conduction velocity was markedly slowed from digit III to the wrist and normal from the wrist to the elbow. On supramaximal stimulation of digit III a sensory response was also recorded from the ulnar nerve at the wrist. On stimulation of digit V a sensory potential was recorded from the median nerve at the elbow. This appears to be the first electrophysiological demonstration of an anomaly involving both the motor and sensory fibres of both the median and the ulnar nerves.

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Zusammenfassung Bei einer 33-jährigen Patientin mit einem Carpaltunnelsyndrom wurde das Vorhandensein einer abnormen Verbindung zwischen N. medianus und N. ulnaris am Vorderarm elektrophysiologisch nachgewiesen. Die motorische Latenzzeit vom Medianusstamm zum M. abductor pollicis brevis waren von proximalen und distalen Reizorten aus identisch. Die proximale Latenz nahm nach Procaine-Infiltration des Ulnarnerven am Handgelenk zu. Eine normale Latenz zum M. abductor digiti minimi wurde nach Stimulation des N. medianus am Ellbogen nachgewiesen.Die sensible orthodrome Leitgeschwindigkeit am Medianus war bei Reizung des Mittelfingers und Ableitung vom Handgelenk hochgradig verlangsamt, jedoch normal vom Handgelenk zum Ellbogen. Bei supramaximaler Reizung des Mittelfingers wurde auch vom Ulnarnerven am Handgelenk eine sensorische Antwort erzeugt. Bei Reizung des Kleinfingers wurde ein sensorisches Potential vom N. medianus am Ellenbogen abgeleitet.Unseres Wissens ist dies der erste Fall, in welchem elektrophysiologisch eine Anomalie sowohl der motorischen wie der sensiblen Fasern von Median- und Ulnarnerven nachgewiesen wurde.

     

Lumbrical-interossei motor studies localize ulnar neuropathy at the wrist

Ulnar nerve entrapment at the wrist (UNW) is uncommon and often difficult to localize electrophysiologically. The difference between the motor latencies to the median-innervated second lumbrical (2L) and ulnar-innervated palmar interosseous (PI) (Diff 2L-PI) has been shown to be of localizing value in patients with median neuropathy at the wrist. In the last year, we evaluated 2 patients with clinically definite ulnar neuropathy at the wrist. We performed motor studies to the 2L-PI on the 2 patients and 12 disease controls with ulnar neuropathy at the elbow as follows: Using the same electrodes to record both the 2L and PI, the median and ulnar nerves were each stimulated supramaximally above the wrist using identical distances. In the disease control subjects, the Diff 2L-PI was essentially the same as normal controls (mean [0.13], range [(−0.3)−0.4]). In both patients with UNW, the Diff 2L-PI clearly supported the routine electrophysiological studies in localizing the lesion (ulnar latencies were 1.1 and 1.8 ms longer than the median latencies). We conclude that the lumbrical-interosseous latency difference is useful in localizing ulnar nerve entrapment to the wrist. © 1996 John Wiley & Sons, Inc.     

A neurophysiological grading scale for carpal tunnel syndrome

Different ways of expressing the severity of carpal tunnel syndrome (CTS) are found in the existing literature and in clinical records. This paper documents the distribution of patients on a scale based upon the nerve conduction study findings, which are largely independent of the exact normal values used in any given laboratory and demonstrate a highly significant linear relationship between the neurophysiological grading and a numerical score derived from the clinical history. Patients with more characteristic stories of CTS generally have higher neurophysiological grades. The scale is as follows: normal (grade 0); very mild (grade 1), CTS demonstrable only with most sensitive tests; mild (grade 2), sensory nerve conduction velocity slow on finger/wrist measurement, normal terminal motor latency; moderate (grade 3), sensory potential preserved with motor slowing, distal motor latency to abductor pollicis brevis (APB) < 6.5 ms; severe (grade 4), sensory potentials absent but motor response preserved, distal motor latency to APB < 6. 5 ms; very severe (grade 5), terminal latency to APB > 6.5 ms; extremely severe (grade 6), sensory and motor potentials effectively unrecordable (surface motor potential from APB < 0.2 mV amplitude).     

Reduced functional connectivity in visual evoked potentials in children with autism spectrum disorder

Objective

An analysis of EEG synchrony between homologous early visual areas tested the hypothesis that interhemispheric functional connectivity during visual stimulation is reduced in children with autism compared to controls.

Methods

EEG power and coherence within and between two homologous regions of the occipital cortex were measured during long latency flash visual evoked potentials. Measures were compared between two groups of children (5.5–8.5 years), one with autism spectrum disorders and the other with typical development.

Results

In and below the theta band, interhemispheric synchrony was reduced in autistic subjects compared to typical controls by as much as 50%. Above the theta band interhemispheric synchrony in autistic children became indistinguishable from what would occur for uncorrelated cortical activity. Interhemispheric synchrony in autistic subjects was decreased in spite of bilaterally increased power. Wavelet power showed autistic children had a more rapid initial response to stimulation, a slower recovery, and more modulation at longer latencies.

Conclusions

Results suggest that the sensory cortices of autistic children are hypersensitive to stimulation with concurrent diminished functional connectivity between hemispheres.

Significance

Simultaneously increased intrahemispheric power and decreased interhemispheric synchronization of elemental visual information suggests either that power increases cause poor interhemispheric connectivity or that processes, such as thalamocortical regulation, impact power and coherence independently.