A correlative electrophysiologic study of nerve fiber involvement in carpal tunnel syndrome using current perception thresholds

The Relevance of Collision Tests and Quantitative Sensory Testing in Diagnostics and Postoperative Outcome Prediction in Carpal Tunnel Syndrome

Background

The gold standards for the diagnosis and treatment of carpal tunnel syndrome (CTS) and its outcome are undecided. Using clinical and electrophysiological methods, we tried to establish which fibers achieved full postoperative recovery, and the possibility of using non-standard electrophysiological tests as outcome predictors.

Methods

The study group consisted of 35 patients and controls. The Historical–Objective Scale, standard neurography, conduction velocity distribution tests (CVD), and quantitative sensory testing (QST) were performed before and after CTS surgery.

Results

Clinical improvement was observed on average in 54.3% of the patients, higher in less advanced CTS. All parameters improved significantly after surgery, except for CVD; most remained worse than in the controls. Only QST parameters fully returned to normal limits. Patient age and CTS severity were important in the estimation of the risk of no improvement.

Conclusions

The efficiency of minimally invasive CTS surgery is higher in younger patients with less advanced CTS. Complete recovery was present only in small fibers; larger fibers could most likely be responsible for residual signs. We did not notice any benefits in CTS diagnosis using methods of small fiber assessment. QST seemed to be useful in the diagnosis of residual signs, and in deciding upon possible reoperation.

Current perception threshold testing in chronic ankle instability

BACKGROUND

Damage to sensory input is an underlying pathology of chronic ankle instability (CAI). Therefore, it is necessary to evaluate the sensory function of patients with CAI. The present study quantitatively evaluated sensory nerve function in patients with CAI and healthy controls using current perception threshold (CPT) measurements, as well as the influence of sex, age, and body mass index (BMI) on CPT values and the relations between CPT frequencies.

METHODS

Fifty-nine subjects with CAI and 30 healthy controls participated in this study. CPT values at the anterior talofibular ligament region were recorded on the injured and uninjured sides in CAI patients and on both sides in the healthy control group. Between group differences were compared. The influence of sex, age and BMI on CPT values was evaluated. Correlations between different frequencies were also studied.

RESULTS

There were no significant differences in age, sex, height, weight or BMI between the CAI and healthy control groups. The CPT values did not show a significant difference by sex. The CPT values did not significantly correlate with age or BMI. Compared to the control group, the CAI group had significantly higher CPT values on the injured and uninjured sides under 250-Hz and 5-Hz electrical stimuli; the difference between the groups was significant (p < 0.01), and the effect size were large. No significant difference was observed under 2000-Hz stimuli. There were correlations between CPT values at different frequencies (p < 0.01), especially 250 Hz and 5 Hz.

CONCLUSION

The present study revealed increased sensory thresholds in 250-Hz- and 5-Hz-related sensory nerve fibres in the injured and uninjured ankles of patients with CAI. This increase may indicate dysfunction of A-delta and C fibres. Sex, age and BMI did not significantly impact CPT values. There were correlations between CPT values at different frequencies, especially 250 Hz and 5 Hz.

LEVEL OF EVIDENCE

Level III, case-control study.

A test-retest reliability study of assessing small cutaneous fibers by measuring current perception threshold with pin electrodes

Background

The quantitative measurement of current perception threshold (CPT) has been used as a method to assess the function of nerve fibers in neuropathy diseases. The aim of this study was to assess the test-retest reliability measuring CPT using the circular pin electrodes for assessing the function of cutaneous thin nerve fibers.

Methods

CPT measurement was repeated on two separate days with at least one-week interval in 55 volunteers. Superficial blood flow (SBF) and skin temperature (ST) were measured on the skin in an around area concentric to the circular pin electrodes after the process of finding CPTs. The coefficient of variation (CV) and intra-class correlation coefficient (ICC) were calculated. The correlation between each two of CPT, SBF increment and ST increment was analyzed.

Results

No significant differences were found for CPT, SBF and ST between two sessions. SBF was found to be significantly increased after the process of finding CPT. CPT values of males were found to be higher than females. SBF increment was found to be positively correlated with ST increment. The ICC values for CPT, SBF and ST were 0.595, 0.852 and 0.728, respectively. The CV values for CPT, SBF and ST were 25.53%, 12.59% and 1.94%, respectively.

Conclusions

The reliability of CPT measurement using circular pin electrodes is fair, and need consistence of measurements in longitudinal studies.

Selective activation of small nerve fibers for assessing carpal tunnel syndrome

Carpal tunnel syndrome (CTS) diagnosis could be improved by selectively activating the different types of nerve fibers traversing the carpal tunnel. The objective of this study is to assess the potential of an anodal blocking technique using tripolar surface electrodes for achieving selective fiber activation and evaluating the severity of CTS. Simulations were performed using McNeal's model to determine the stimulating and blocking thresholds for different diameter/conduction velocity groups of nerve fibers. At 9.36 mA stimulus amplitude all nerve fibers from 9 mum to 20 mum were activated. When the current amplitude was increased further, large nerve fibers started getting blocked while small nerve fibers remained active. By gradually increasing the current amplitude small nerve fibers can be selectively activated without the activation of large fibers. The severity of CTS generally progresses from large to small nerve fibers, hence by comparing normal values of amplitude and peak latency of different nerve fiber diameter groups to the CTS affected median nerve recordings of the patient, severity of this syndrome could be detected.

Objective evaluation of the alleviating effects of Goshajinkigan on peripheral neuropathy induced by paclitaxel/carboplatin therapy: A multicenter collaborative study

Paclitaxel/carboplatin chemotherapy for cancer (TC therapy) exhibits neurotoxicity and causes peripheral neuropathy at a high frequency, which is difficult to cope with. In this study, we investigated the efficacy of Goshajinkigan, a traditional Japanese herbal medicine, for TC therapy-induced peripheral neuropathy. The subjects included in our study were patients with ovarian or endometrial cancer who underwent TC therapy and developed peripheral neuropathy. The patients were randomly divided into Group A, comprising of 14 patients (vitamin B12 treatment), and Group B, comprising of 15 patients (vitamin B12 + Goshajinkigan treatment). The observation period was 6 weeks following treatment initiation, and the evaluation items were as follows: i) the current perception threshold (CPT value) of the peripheral nerve, ii) visual analogue scale for numbness, iii) National Cancer Institute Common Terminology Criteria for Adverse Events v3.0 grade of neurotoxicity, and iv) a questionnaire on the subjective symptoms of peripheral neuropathy (functional assessment of cancer therapy-taxane). These were compared between the groups and no significant differences were noted in any item. However, CTCAE grade 3 neurotoxicity developed in 2 patients (14.3%) after 6 weeks of administration in Group A, whereas no neurotoxicity was observed in Group B. When the change in the frequency of abnormal CPT ratio at 6 weeks of administration from that before treatment was compared between the groups, the frequency of abnormal value was significantly lower in Group B than in Group A (p<0.05). This suggests that Goshajinkigan inhibits the progression of peripheral neuropathy.

Power spectral analyses of index finger skin blood perfusion in carpal tunnel syndrome and diabetic polyneuropathy

The main purpose of this study was to investigate the applicability of frequency domain analysis on laser Doppler flowmetry (LDF) data recorded from the index fingers of patients with carpal tunnel syndrome (CTS) and diabetic polyneuropathy (DPN). Patients with numbness of the palm were recruited and grouped according to the results of electrophysiological examinations into 2×2 groups by the existence or nonexistence of CTS and/or DPN. Skin blood perfusion was recorded by LDF in both the neutral position and the maximally flexed position (the Phalen test). S-transformation was utilized to decompose the recorded data into frequency bands, and the relative band power and power dispersion were calculated. Analysis of variance was used to test the effects of DPN, CTS, and the Phalen test results. The results showed that (1) DPN decreased the absolute power and the relative power in some frequency bands in both positions and CTS increased the power dispersion of some frequency bands only during the Phalen test and (2) there was no difference in the LDF results between patients with positive or negative Phalen test results.

Current concepts of carpal tunnel syndrome: pathophysiology, treatment, and evaluation

The current concepts of carpal tunnel syndrome (CTS) with respect to its pathophysiology, treatment, and evaluation are discussed. With regard to the pathophysiology of idiopathic CTS, biomechanical studies to determine the kinematics of the flexor tendon, and the median nerve inside the carpal tunnel may provide valuable insights. Different degrees of excursion between the flexor tendons and the median nerve could cause strain and microdamage to the synovial tissue; this has been microscopically observed. A biomechanical approach for elucidating the events that trigger the development of CTS seems interesting; however, there are limitations to its applications. Endoscopic carpal tunnel release (ECTR) is a useful technique for achieving median nerve decompression. However, it is not considered superior to conventional open carpal tunnel release in terms of fast recovery of hand function. Unless the effect of inserting a cannula into the diseased carpal tunnel on the median nerve function is quantitatively elucidated, ECTR will not be regarded as a standard procedure for relieving the median nerve from chronic compression. The treatment of CTS should be evaluated on the basis of patient-oriented questionnaires as well as conventional instruments because these questionnaires have been validated and found to be highly responsive to the treatment. It should be noted that nerve conduction studies exclusively evaluate the function of the median nerve, whereas patient-oriented questionnaires take into account not only the symptoms of CTS but other accompanying pathologies as well, such as flexor tenosynovitis. In Japan, the number of CTS patients is expected to rise; this may be attributed to a general increase in the life-span of the Japanese and increase in the number of diabetic patients. Thus, more efforts should be directed toward elucidating the pathophysiology of so-called idiopathic CTS, so that new treatment strategies can be established for CTS of different pathologies.

Ulnar nerve impairment at the wrist does not contribute to extramedian sensory symptoms in carpal tunnel syndrome

OBJECTIVE

Extramedian spread of sensory symptoms is frequent in carpal tunnel syndrome (CTS) but its mechanisms are unclear. We explored the possible role of subtle ulnar nerve abnormalities in the pathogenesis of extramedian symptoms.

METHODS

We recruited 350 CTS patients. After selection, 143 patients (225 hands) were included. The hand symptoms distribution was graded with a diagram into median (MED) and extramedian (EXTRAMED) pattern. We tested the correlation of ulnar nerve conduction measures with the distribution and the severity of symptoms involving the ulnar territory. The clinical significance of ulnar nerve conduction findings was explored with quantitative sensory testing (QST).

RESULTS

EXTRAMED distribution was found in 38.7% of hands. The ulnar neurographic measures were within normal values. Ulnar nerve sensory measures were significantly better in EXTRAMED vs MED hands and not significantly correlated to ulnar symptoms severity. Ulnar and median nerve sensory measures were significantly correlated. QST showed normal function of ulnar nerve alphabeta-fibers.

CONCLUSIONS

Ulnar nerve sensory abnormalities do not contribute to the spread of sensory symptoms into the ulnar territory.

SIGNIFICANCE

Our data favour the hypothesis that spinal and supraspinal neuroplastic changes may underlie extramedian spread of symptoms in CTS.

Current perception threshold and the HAVS Stockholm sensorineural scale

BACKGROUND

It is important to determine which tests of sensorineural dysfunction identify the neurological damage from hand-arm vibration exposure.

AIMS

To examine the association between the hand-arm vibration syndrome (HAVS) Stockholm sensorineural scale stages and tests of peripheral neurological function including measurement of current perception threshold (CPT) and nerve conduction.

METHODS

All the subjects were men who were assessed for HAVS with a medical and occupational history and physical examination to determine the Stockholm stage, CPT testing at frequencies of 5, 250 and 2000 Hz for the median and ulnar nerves and measurement of nerve conduction carried out in a blinded fashion.

RESULTS

A total of 155 of the 157 recruited subjects agreed to take part in the study, a 99% participation rate. CPT was statistically significantly increased (P < 0.001) in both Stockholm sensorineural Stages 1 and > or =2 in comparison to Stage 0 for every frequency and nerve combination. However, CPT could not discriminate well between Stages 1 and > or =2. There was no association between median or ulnar neuropathy measured by nerve conduction and the Stockholm stages. Polychotomous multinomial logistic regression indicated that the CPT measurements at 2000 Hz, corresponding to damage to large myelinated nerve fibres, were most predictive of both Stockholm Stages 1 and > or =2 in comparison to Stage 0.

CONCLUSIONS

Neuropathy measured by nerve conduction was unrelated to the Stockholm scale stages. CPT was increased above Stage 0 but did not distinguish well between the higher stages of the Stockholm scale.

Developing biologically-based assessment tools for physical therapy management of neck pain

SYNOPSIS

Neck pain is a common and episodic condition that is treated using a spectrum of interventions known to be moderately effective but is associated with a significant incidence of chronic pain. Recently, there has been increased focus on defining biological aspects of neck pain. Studies have indicated that neurophysiological, biomechanical, and motor control abnormalities are present and may be useful either in prognosis or classification. We review some of these findings in the context of our own work defining biological markers that may form the basis for clinical tests that can be used for prognosis, classification, or outcome evaluation in patients with neck pain. We have identified abnormalities in neurophysiology using quantitative sensory testing (vibration, touch, and current perception) and response to cold provocation that are related to neck disability. We have identified altered muscle biochemistry by measuring circulating muscle proteins in a lumbar surgery model and are now applying those methods to whiplash injury. We have incorporated capnography into treatment to address central physiological changes present in some patients by monitoring and training CO2 levels. We have developed an innovative new test, the Neck Walk Index, that captures abnormal control of head movement during slow gait as a means of differentiating patients with neck pain from either unaffected controls or individuals with other pathologies. We have used time-varying 3-dimensional joint orientation kinematics to assess deficits in motor control during an upper extremity reach task, the results showing that poor coordination and control of the shoulder girdle leads to shoulder guarding and inconsistencies in elbow joint movement. Despite some promising early results, future research is needed to determine how these measures help clinicians to diagnose, evaluate, and forecast future outcome for patients who present with neck pain.

LEVEL OF EVIDENCE

Diagnosis, level 5.

Electrophysiological responsiveness and quality of life (QuickDASH, CTSI) evaluation of surgically treated carpal tunnel syndrome

BACKGROUND

We evaluated the correlation between Japanese versions of patient-oriented questionnaires and electrophysiological examinations in patients with carpal tunnel syndrome (CTS).

METHODS

A series of 45 patients who were diagnosed with carpal tunnel syndrome and subsequently underwent carpal tunnel release surgery were analyzed. There were 8 men and 37 women with an average age of 64.8 years. They completed the Japanese Society for Surgery of the Hand version of the Carpal Tunnel Syndrome Instrument (CTSI-JSSH), which consisted of a Symptom Severity Score (CTSI-JSSH-SS), Functional Score (CTSI-JSSH-FS), and Japanese Society for Surgery of the Hand version-Quick Disability of Arm, Shoulder, and Hand questionnaire (QuickDASH-JSSH) both preoperatively and 3 months postoperatively. Nerve conduction studies (NCSs) were also performed and included motor distal latency (MDL) and sensory nerve conduction velocity (SCV) measurements. The responsiveness of each instrument was evaluated by calculating the standardized response mean (SRM) and effect size (ES). Correlation coefficients between preoperative and postoperative questionnaire scores and NCS parameters were calculated.

RESULTS

Responsiveness (SRM/ES) was as follows: CTSI-JSSH-SS (-1.06/-1.14), CTSI-JSSH-FS (-0.75/-0.74), Quick-DASH-JSSH (-0.65/-0.62), MDL (-1.45/-1.11), and the neurophysiological stage of the disease (-0.90/-1.42). No significant correlation was observed between the preoperative and postoperative patient-oriented questionnaires and nerve conduction studies (P > 0.05).

CONCLUSIONS

Although NCSs and the Japanese version of patient-oriented questionnaires are highly responsive to treatment, they are not parallel. Multifaceted assessment of CTS treatment is possible by performing both outcome measurements.

A randomized controlled trial of the effects of a combination of static and dynamic magnetic fields on carpal tunnel syndrome

OBJECTIVE

To determine if a physics-based combination of simultaneous static and time-varying dynamic magnetic field stimulation to the wrist 4 hours/day for 2 months can reduce subjective neuropathic pain and influence objective electrophysiologic parameters of patients with carpal tunnel syndrome (CTS).

METHODS

Randomized, double-blinded, placebo-controlled trial of 36 symptomatic hands. Primary endpoints were visual analog scale (VAS) and neuropathic pain scale (NPS) scores at baseline and 2 months and a Patient's Global Impression of Change (PGIC) questionnaire at the end of 2 months. Secondary endpoints were neurologic examination, median nerve distal latencies (compound muscle action potential [CMAP]/sensory nerve action potential [SNAP]), dynamometry, pinch gauge readings, and current perception threshold (CPT) scores. An "active" device was provided gratis at the end of the study, with 15 subjects voluntarily remaining within the open protocol an additional 2-10 months and using the preselected primary and secondary parameters.

RESULTS

(two months). Of the 31 hands, 25 (13 magnet, 12 sham) had moderate to severe pain (VAS > 4). The VAS and PGIC revealed a nonsignificant pain reduction. NPS analyses (anova) demonstrated a statistically significant reduction of "deep" pain (35% downward arrow vs 12% upward arrow, P = 0.018), NPS Total Composite (decreases of 42% vs 24%, P = 0.042), NPS Total Descriptor Score (NPS 8; 43% vs 24%), and NPS 4 (42% vs 11%). Motor strength, CMAP/SNAP, and CPT scores were not significantly changed. Of the 15 hands with up to 10 months of active PEMF (pulsed electromagnetic fields) exposure, there was objective improvement in nerve conduction (CMAP = 53%, SNAP = 40%, >1 SD), and subjective improvement on examination (40%), pain scores (50%), and PGIC (70%). No detectable changes in motor strength and CPT.

CONCLUSIONS

PEMF exposure in refractory CTS provides statistically significant short- and longterm pain reduction and mild improvement in objective neuronal functions. Neuromodulation appears to influence nociceptive-C and large A-fiber functions, probably through ion/ligand binding.

Increased carrying angle is a risk factor for nontraumatic ulnar neuropathy at the elbow

The literature suggests a possible relationship between carrying angle and nontrauma-related ulnar neuropathy. To confirm that relationship, we asked whether carrying angle is a risk factor in patients with nontrauma-related ulnar neuropathy. We measured the carrying angles of the elbow in 36 patients with a clinically and electrophysiologically confirmed diagnosis of nontraumatic ulnar neuropathy at the elbow and in 50 healthy control subjects. Correlation analysis was performed between carrying angles and parameters of nerve conduction studies, including nerve conduction velocities and amplitudes of muscle and nerve action potentials. The mean carrying angle was greater in the patients than in the control subjects. Females had a greater carrying angle than males. We observed an inverse relationship between carrying angles and motor nerve conduction velocities at cross-elbow segments of the ulnar nerves and with sensory nerve conduction velocities of the distal ulnar nerves. An increased carrying angle of the elbow appears to be an independent risk factor of nontrauma-related ulnar neuropathy.

LEVEL OF EVIDENCE

Level III, diagnostic study. See the Guidelines for Authors for a complete description of levels of evidence.

A practical electrophysiological guide for non-surgical and surgical treatment of carpal tunnel syndrome

In the present study, we illustrate the use of an electrophysiological classification as a guide to the treatment of carpal tunnel syndrome (CTS). A total of 113 CTS patients were assessed with symptom severity scores, hand functional scores and electrophysiological studies. By setting criteria of electrophysiological tests, 179 hands in 113 patients were classified into mild, moderate and severe degrees of CTS. Of these, the 41 hands with severe CTS were referred for surgery. The 58 hands with moderate CTS and 80 hands with mild CTS received conservative treatment. The improvement ratios in the severe group were greater than that in the moderate and mild groups, both at 6 months and at 1 year. Eighteen hands with moderate or mild CTS returned to normal electrophysiology with the conservative treatments. No patient recovered to normal electrophysiology in the severe group. This electrophysiological classification is objective and it may serve as a useful guide for non-surgical and surgical treatment of CTS.

Carpal tunnel syndrome--a comprehensive review

PURPOSE

To provide a comprehensive review of the management of carpal tunnel syndrome.

METHODS AND RESULTS

A systematic literature review is provided of the history, anatomy, pathophysiology, epidemiology, diagnostic criteria, investigative surgical techniques, results and complications for carpal tunnel syndrome.

CONCLUSION

Surgery for carpal tunnel syndrome requires meticulous attention to history-taking, investigation, counseling, training and surgical technique if unsatisfactory results and complications are to be avoided.

The impact of wrist extension provocation on current perception thresholds in patients with carpal tunnel syndrome: a pilot study

PURPOSE

To determine whether current perception threshold (CPT) varied between subjects with and without carpal tunnel syndrome (CTS) and whether positioning in wrist extension (reversed Phalen's test) was provocative.

METHOD

Subjects (n=30) were tested using the Neurometer (Neutron, Inc., Baltimore, MD) at 5, 250, and 2,000 Hz in a rest and reverse Phalen's position. Group and positional differences were analyzed using analysis of variance.

RESULTS

Higher CPT occurred at 2,000 Hz in both rest (p=0.02) and reverse Phalen's position (p=0.01) in CTS subjects. There was also a significant change in CPT in the CTS group following wrist extension, particularly at 2,000 Hz (p<0.05).

CONCLUSION

A positional effect on sensibility was noted at 2,000 Hz in subjects with CTS. Further evaluation is required to determine the role and optimal test protocols for provocative-sensory testing in diagnosis and outcome assessment of CTS. For CPT these should focus on using the 2,000 Hz frequency.

Age and upper limb tension testing affects current perception thresholds

Current perception threshold (CPT) testing was used to quantitatively measure the sensory response to upper limb tension testing (ULTT). The study addressed the ability of ULTT to tension the intended nerve, and the influence of age on CPT. Normal subjects (n=59) performed a randomized series of CPT tests at 5 and 2,000 Hz in a resting position and in a median-nerve bias position using the Neurometer. Results indicate that ULTT impacts CPT in normal subjects, with greater effects observed in the ulnar nerve (p<0.05) than for median nerve (NS). Age was a significant covariate for CPT (2,000 Hz, p=0.032; 5 Hz, p=0.034), and Pearson correlations indicated a weak but significant correlation of age with CPT. Age had a differential impact on CPT frequencies, suggesting differential impacts on nerve fibers, with a trend towards hypoesthesia at 2,000 Hz (r=0.10 to 0.30) and toward hyperesthesia at 5 Hz (r=-0.16 to -0.28). ULTT causes measurable effects in the sensory threshold of peripheral nerve, which are more pronounced with age; increased touch threshold and decreased pain thresholds can be expected. The specificity of nerve bias elicited by specific ULTT needs further exploration.

Carpal tunnel syndrome

PURPOSE OF REVIEW

Carpal tunnel syndrome, though generally successfully treated by surgical decompression, still results in significant morbidity. The causes remain unclear and there is uncertainty about appropriate investigations for diagnosis and assessment of severity. The best nonsurgical treatment is yet to be fully elucidated. Recent work has begun to cast some light on these uncertainties.

RECENT FINDINGS

The pathology of idiopathic carpal tunnel syndrome is a noninflammatory fibrosis of the subsynovial connective tissue surrounding the flexor tendons. Biochemical studies of surgical specimens suggest that a variety of regulatory molecules may be inducing fibrous and vascular proliferation and that this may be a response to mechanical stresses. Ultrasound imaging has begun to demonstrate its ability to accurately image the carpal canal contents and the diagnostic value of measurements of median nerve cross-sectional area showing expansion of the nerve is becoming established. The sensitivity and specificity of such measurements may be comparable to those of nerve conduction studies, though their prognostic value remains unknown. Nonsurgical treatment with steroid injection may be a more effective treatment than previously recognized, and is under used.

SUMMARY

Suspected carpal tunnel syndrome should be investigated first with nerve conduction studies but consideration should be given to the use of magnetic resonance imaging or ultrasound imaging when diagnostic uncertainty remains, or there is a suspicion of a space occupying lesion in the carpal canal, especially if endoscopic surgery is contemplated. Treatment by local steroid injection should be considered a valid alternative treatment, at least for milder cases.

On the activation threshold of nerve fibers using sinusoidal electrical stimulation

Carpal tunnel syndrome (CTS) diagnosis could be improved by selectively activating different types of nerve fibers traversing the carpal tunnel based on their diameter. The objective of this study was to establish the types of fibers activated by different sinusoidal electrical stimuli. The frequencies selected correspond to those used in an available application known as current perception threshold (CPT). This method has been proposed in the literature to assess the severity of CTS in a patient. CPT operates by varying the amplitude and frequency of stimulating sine wave currents. Subthreshold and supra-threshold responses of nerve fibers were modeled in this study using McNeal's model and Frankanhaeuser-Huxley equations. Simulations were performed in MATLAB to determine the stimulating thresholds for different diameter groups of nerve fibers. The study concluded that large A-beta fibers can be activated alone at the 2000 Hz frequency, the intermediate A-delta fibers can be activated at the 250 Hz frequency in company of A-beta fiber activity, and for fibers with diameter less than 2.5 mum to be activated at the 5 Hz frequency there must be accompanying activity from A-beta and A-delta fibers.

Conduction velocity distribution estimation using the collision technique for assessing carpal tunnel syndrome

A technique for selectively activating nerve fibers based on their diameter using the collision technique and evaluating nerve integrity using a conduction velocity distribution (CVD) estimator is discussed in this paper. This study is aimed at improving current diagnostic techniques used for assessing carpal tunnel syndrome (CTS). Current nerve conduction studies are influenced by the activity of the largest fibers active at the moment of recording and it is not possible to selectively analyze the functioning of smaller nerve fibers. According to the literature, the severity of CTS progresses from large nerve fibers to small nerve fibers. Therefore, the current study is an attempt to selectively evaluate nerve fibers based on their diameter and hence detect the severity of CTS in a patient more effectively.

The value of ultrasonographic measurement in carpal tunnel syndrome in patients with negative electrodiagnostic tests

The diagnosis of carpal tunnel syndrome (CTS) is mainly based on clinical findings and electrodiagnostic tests (EDT). However, EDT results do not support clinical findings in some cases. It has been recently suggested that ultrasonography (US) can be used to diagnose CTS. In this study, we aimed to investigate whether US has a diagnostic value for CTS in patients with negative EDT findings or not. EDT was performed on 319 wrists with clinical CTS findings in electrophysiology laboratory. Median and ulnar nerve conduction velocities were measured in all cases and electromyography was performed in patient with tenar atrophy and having suspicion involvement of brachial plexus as EDT. Fifty-nine wrists with negative EDT (study group) and 30 wrists from 15 healthy individuals (control group) were examined using US. The mean of cross-sectional areas (CSAs) measurements were found 8.83+/-3.05 mm2 by tracing method (TM) and 8.51+/-3.13 mm2 by ellipsoid formula (EF) in study group, and 7.63+/-1.52 mm2 by TM and 7.66+/-1.42 mm2 by EF in control group. The differences between study group and control group according to both TM and EF were significant (t-test p=0.0079, p=0.0460, respectively). In study group, CSAs were larger than 10.5 mm2 in 18 (30.51%) and 16 (27.12%) wrists according to TM and EF findings, respectively, and in only one wrist (3.33%) in control group by both TM and EF. The differences of ultrasonographic CTS numbers between study group and control group were significant (p=0.0024 by TM, p=0.0086 by EF). We confirmed the usefulness of quantitative US assessment in the diagnosis of CTS in the patients with negative EDT findings. If EDT findings are inadequate to confirm the CTS in the patients with clinical CTS, US studies may be helpful to diagnose.

Selective activation of primary afferent fibers evaluated by sine-wave electrical stimulation

Transcutaneous sine-wave stimuli at frequencies of 2000, 250 and 5 Hz (Neurometer) are thought to selectively activate Aβ, Aδ and C afferent fibers, respectively. However, there are few reports to test the selectivity of these stimuli at the cellular level. In the present study, we analyzed action potentials (APs) generated by sine-wave stimuli applied to the dorsal root in acutely isolated rat dorsal root ganglion (DRG) preparations using intracellular recordings. We also measured excitatory synaptic responses evoked by transcutaneous stimuli in substantia gelatinosa (SG) neurons of the spinal dorsal horn, which receive inputs predominantly from C and Aδ fibers, using in vivo patch-clamp recordings. In behavioral studies, escape or vocalization behavior of rats was observed with both 250 and 5 Hz stimuli at intensity of ~0.8 mA (T5/ T250), whereas with 2000 Hz stimulation, much higher intensity (2.14 mA, T2000) was required. In DRG neurons, APs were generated at T5/T250 by 2000 Hz stimulation in Aβ, by 250 Hz stimulation both in Aβ and Aδ, and by 5 Hz stimulation in all three classes of DRG neurons. However, the AP frequencies elicited in Aβ and Aδ by 5 Hz stimulation were much less than those reported previously in physiological condition. With in vivo experiments large amplitude of EPSCs in SG neurons were elicited by 250 and 5 Hz stimuli at T5/ T250. These results suggest that 2000 Hz stimulation excites selectively Aβ fibers and 5 Hz stimulation activates noxious transmission mediated mainly through C fibers. Although 250 Hz stimulation activates both Aδ and Aβ fibers, tactile sensation would not be perceived when painful sensation is produced at the same time. Therefore, 250 Hz was effective stimulus frequency for activation of Aδ fibers initiating noxious sensation. Thus, the transcutaneous sine-wave stimulation can be applied to evaluate functional changes of sensory transmission by comparing thresholds with the three stimulus frequencies.