Sensitivity, specificity, and variability of nerve conduction velocity measurements in carpal tunnel syndrome

OBJECTIVE: To explore the diagnostic values of 8 commonly used electrodiagnostic techniques for measuring median nerve conduction velocity (NCV) in carpal tunnel syndrome (CTS). DESIGN: Sensitivity and specificity analyses. SETTING: A hospital-based electrodiagnostic laboratory. PARTICIPANTS: Forty-four normal hands and 136 symptomatic hands. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: (1) Long-segment studies: antidromic wrist-to-digit sensory NCV without subtraction, (2) short-segment studies: transcarpal palm-to-wrist mixed NCV without subtraction, and (3) 2 segment studies: antidromic transcarpal sensory NCV with subtraction (differential calculation from wrist-to-digit and palm-to-digit segments). Both onset and peak latency values were obtained for calculating the NCV. Sensitivity, specificity, and coefficient of variance were calculated for each NCV study. RESULTS: The short-segment, onset latency-based transcarpal mixed NCV yielded the highest sensitivity (75%). CONCLUSIONS: Results from measurement of a single, short-nerve segment tended to be superior to results obtained by either long-segment studies or differential subtraction between 2 segments of the same nerve in the electrodiagnosis of CTS. Explanations for our results are offered from both electrophysiologic and statistical perspectives.     

Differences in sensory conduction velocity between different sensory branches and segments of the median and ulnar nerves

Abnormality of absolute values of median sensory conduction velocities and differences in conduction velocity between median and ulnar nerves are used as criteria for abnormality in the diagnosis of carpal tunnel syndrome. Detailed studies of sensory conduction in various median and ulnar branches and segments indicate that conduction velocities measured and calculated by standard methods are different in the different nerves, segments and branches. In particular, the velocity in the middle digit branch of the median nerve is slower than that in the index, and that in the 3-4 palmar branch is slower than that in the 2-3 palmar branch. Median and ulnar sensory conduction velocities are not well correlated in the same hand in the same individual, so comparison of these nerves for diagnostic purposes is subject to some risk. Palmar and digital conduction velocity in the same nerve may not be identical and the median nerve may have asymptomatic palmar slowing of no clinical significance. The conclusion that abnormality is present must take these factors into account.     

Electrodiagnosis of mild carpal tunnel syndrome

Electrophysiologic tests have been reported to detect mild carpal tunnel syndrome (CTS). Such tests include (i) absolute palmar latency of median wrist segment; (ii) comparison of median and radial distal sensory latencies in digit I; (iii) comparison of median and ulnar distal sensory latencies in digit IV; (iv) comparison of median and ulnar palmar latencies; (v) comparison of median and ulnar sensory potential amplitudes in digits II and V. To clarify the clinical utility of these tests, the parameters of all five tests were determined across four carefully established patient subgroups: group A, controls; group B, CTS referrals with normal nerve conduction studies (NCS) and normal needle electromyography (EMG); group C, CTS referrals with abnormal NCS and normal EMG; group D, CTS referrals with abnormal NCS and abnormal EMG. Special attention was focused on patients in group B who represent the diagnostic dilemma. In group B, tests ii and iii each yielded abnormal results in 44% of hands, while the combination of tests ii and iii yielded abnormal results in 51% of hands.     

Slowed conduction velocity of the median sensory nerve across the carpal tunnel in normal adults

OBJECTIVE: To examine the difference of using onset or peak latency in the segmental conduction study of the median nerve in normal adults without carpal tunnel syndrome. DESIGN: We investigated 60 hands of 30 young healthy adults (15 men and 15 women; mean age, 27.1 yrs; range, 18-36 yrs). We performed the mid-palm segmental conduction study using antidromic and orthodromic techniques in the median sensory nerves of the second and third digits and the onset and peak latencies of the proximal (wrist-palm) and distal (palm-digit) segments were measured. The distoproximal latency ratios were compared between onset and peak latencies and were compared with the ratios of the superficial radial sensory nerve. RESULTS: Distoproximal peak latency ratios in the median and superficial radial sensory nerves were always >1.0 in both the antidromic and orthodromic conduction studies. However, distoproximal onset latency ratios in the median sensory nerve were >1.0 in only 35% and 21.7% of second digits and in only 25% and 11.7% of third digits in orthodromic and antidromic studies, respectively (P < 0.05). The results of distoproximal onset latency ratios in the superficial radial sensory nerve were 93.3% in the orthodromic study and 86.7% in the antidromic study (P < 0.05). CONCLUSION: Prolongation of onset latency across the carpal tunnel during segmental conduction study of the median sensory nerve was common in healthy adults. When comparing proximal and distal segments for diagnosis of carpal tunnel syndrome, using onset latency as a diagnostic variable may cause greater reporting of false positives.     

Electrophysiologic evaluation of local steroid injection in carpal tunnel syndrome

Extensive sensory and motor nerve conduction studies were performed in a series of patients with electrophysiologically proven, idiopathic carpal tunnel syndrome who were treated by a single steroid injection (40 mg of triamcinolone acetonide). Electrophysiologic studies, which included evaluation of median, ulnar, and radial orthodromic sensory action potentials, median and ulnar motor action potentials, and electromyography of two intrinsic muscles of the hand, were done before and at 45 days and six months after the treatment. By the end of the follow-up period, the symptoms had remitted completely in 11 hands (35%), 18 (58%) benefitted from partial relief, and two did not improve. In addition to the relief of symptoms, abnormalities of motor nerve conduction improved in 65% of cases, and abnormalities of sensory nerve conduction improved in 73% of all the individual digital branches of the median nerve examined. Recovery of function of the median nerve continued for a long period, even after the pharmacologic effect of the steroid agent had presumably ceased.     

Carpal tunnel syndrome in patients on long-term hemodialysis

Sixteen cases with carpal tunnel syndrome (CTS) were reported out of 412 patients on long-term hemodialysis due to chronic renal failure. Clinical symptoms included numbness in the area innervated by the median nerve in 100% of symptomatic hands and pain in the wrist and hand in 81%. This pain usually became severer at night and during hemodialysis. Muscle atrophy was noted in 41% of the hands. Nerve conduction studies revealed prolonged distal sensory latency, slowed sensory nerve conduction velocity across the wrist and normal distal motor latency in 18%, prolonged distal motor latency in 51% and no response in motor or sensory stimulation in 31%. Evidence of denervation on electromyography was seen in 36% of the hands. Patients were conservatively treated avoiding daily activities precipitating the condition with volar wrist splint only at night in 18% and in 90% with steroid hormone injection in the carpal tunnel. Median nerve release was performed in 18% of the hands. Amyloid deposit was demonstrated in 3 of 4 operated hands. Although the relation between long-term hemodialysis and the occurrence of the amyloid deposition in the carpal tunnel has not been established, the present data along with other recent reports strongly indicate that amyloid deposit in the carpal tunnel on hemodialysis patients could be one of the most possible cause of CTS.     

腕管综合征46例临床与神经电生理分析

目的：探讨腕管综合征的临床特点和神经电生理检测的诊断价值。方法：回顾性分析46例腕管综合征的临床特征和神经电生理检测结果。结果：46例腕管综合征中76．1％为女性，共有病变71侧，单侧病变21例，双侧病变25例。以桡侧3个半手指为主29侧，5个手指均有症状42侧。临床表现为手指麻木、疼痛，可向肘部和肩部放射。电生理检查正中感觉神经传导速度异常占95．8％，正中运动神经潜伏期延长占67．6％，运动传导速度异常53．5％，拇展短肌呈神经源性损害占31％。结论：腕管综合征以中年女性多见，临床上以手指麻木、疼痛为主要特点，活动和甩手可使症状减轻。神经电生理检测对腕管综合征的诊断与鉴别诊断具有重要价值。     

Effect of Hand Warming on Electrodiagnostic Testing Results and Diagnosis in Patients With Suspected Carpal Tunnel Syndrome

Burnham RS, Burnham TR. Effect of hand warming on electrodiagnostic testing results and diagnosis in patients with suspected carpal tunnel syndrome.

Objectives

To evaluate the effects of hand warming on electrodiagnostic (EDX) parameters of carpal tunnel syndrome (CTS). Specifically, to evaluate the type and magnitude of change in EDX values; to determine whether warming can change the EDX diagnosis of CTS and, if so, to determine whether specific EDX tests are more vulnerable to the effects of warming.

Design

Interventional before-after trial.

Setting

Community EDX laboratory.

Participants

Consecutive patients (N=33) referred for EDX evaluation of suspected CTS.

Intervention

Each upper limb was tested at room temperature (average hand temperature, 31.9°C) and retested after 20 minutes of heating pad warming (average hand temperature, 33.5°C).

Main Outcome Measures

Median and ulnar nerve motor and sensory latency, conduction velocity, and amplitude.

Results

Warming resulted in significantly faster transcarpal tunnel sensory and motor conduction (6%–10%), reduced median: ulnar sensory latency to digit 4 difference (23%), and reduced sensory nerve and compound motor action potential amplitude (10% and 13%, respectively). The changes resulted in 15% fewer limbs meeting the EDX conduction velocity criteria of CTS and 9% fewer by median: ulnar sensory latency to digit 4 difference. Waveform amplitudes became abnormally low after warming in 12% of limbs.

Conclusions

Hand warming using a heating pad for 20 minutes increases median nerve transcarpal tunnel conduction velocity and reduces amplitude. These phenomena introduce potential sources of diagnostic error, particularly in borderline cases. Generally, within hand, between nerve, and within nerve comparison techniques are less susceptible to the conduction velocity effects of warming.     

Residual latency: new applications of an old technique

Median and ulnar nerve conduction velocity was studied using residual latency techniques in a control population and in a population with neuropathy. Midpalmar stimulation sites were used to determine the residual latency of the distal short segment. The residual latency index (RLI) was the short segment residual latency divided by the residual latency for the entire terminal nerve segment. While it was 0.61 in the control population, it increased to 0.69 in the patients with ulnar neuropathy distal to the wrist and decreased to 0.36 in patients with neuropathy of the median nerve at the carpal tunnel. In five cases of median neuropathy at the carpal tunnel, muscle biopsy specimens revealed evidence consistent with neuropathic processes. The RLI is an accurate and relevant method of evaluating the sensory and motor conduction of very small nerve segments.     

腕管综合征的电生理分析及与身体质量指数的相关性

目的:探讨88例腕管综合征(CTS)的电生理特点,明确电生理检查的诊断价值。方法:对88例门诊腕管综合征患者行一侧或双侧正中神经、尺神经的分段运动神经传导速度(MCV)和,Ⅰ、Ⅴ、Ⅳ指刺激感觉神经传导速度(SCV)测定,以及拇短展肌针极肌电图检查;计算每一位患者身体质量指数(BMI)及正中神经与尺神经Ⅳ指刺激感觉神经动作电位(SNAP)波幅比值。结果:Ⅰ、Ⅳ指刺激正中神经SNAP潜伏期延长者的百分比分别为59.1%与65.9%;复合肌肉动作电位(CMAP)波幅降低者中拇短展肌肌电图异常者占87.2%;SNAP各参数正常者中有8例(72.7%)出现Ⅳ指刺激正中神经与尺神经波幅比值的异常,各异常参数患者BMI值无显著性差异。结论:神经电生理检查是诊断CTS的理想检测手段。     

Ulnar nerve involvement in carpal tunnel syndrome

This is a retrospective study of the involvement of the ulnar nerve in patients with electrodiagnostic evidence of carpal tunnel syndrome as defined by median sensory nerve action potential (SNAP) greater than 3.6msec at the wrist and/or motor distal latency in excess of 4.3msec. The study included 248 patients, 63 (25%) with unilateral and 185 (75%) with bilateral carpal tunnel syndrome. The electrodiagnostic criteria for ulnar nerve involvement was a SNAP peak latency greater than 3.7msec and/or motor distal latency in excess of 4.2msec. One hundred fourteen patients (46%) had delayed ulnar SNAP peak at the wrist; of these, 100 cases had bilateral ulnar nerve involvement and 14 had unilateral abnormalities. Slowing of the motor nerve conduction velocity for the elbow-wrist segment was noted in 24% and 15% of the study group for the median and ulnar nerves, respectively. An incidental finding was the presence of "double crush syndrome" in 35 patients (14%). The results of this study suggest the frequent association of ulnar nerve involvement at the wrist for sensory fibers and carpal tunnel syndrome.     

Median and radial sensory latencies to digit I as compared with other screening tests in carpal tunnel syndrome

Fifty two patients with suspected carpal tunnel syndrome were evaluated electrodiagnostically by using a variety of screening tests. The criteria of normalcy were as follows: distal median motor latency lower than 4.2 ms, distal median sensory latency wrist-to-third finger at 14 cm higher than 3.2 ms for the onset and than 3.8 ms to the peak, median sensory conduction velocity wrist-to-palm at 7 cm higher than 40 m/s peak-to-peak and difference between median and radial sensory latencies wrist-to-first digit at 11 cm using an intermediate position as site of stimulation and measured peak-to-peak ("bactrian sign") higher than 0.4 ms. Other tests such as median-ulnar comparison using finger 4 were considered less reliable based primarily on the frequent association of carpal tunnel syndrome and Guyon canal entrapment. Carpal tunnel syndrome was confirmed in 49 of 52 suspected cases (94.2%) by at least one abnormal screening test. Bilateral involvement was noted in 65.3% of the cases (32 patients). The "bactrian" (two-hump camels) sign was the single most sensitive test used, being positive in 83.7% of cases. The second most sensitive test was median SNAP (wrist-to-finger) latency and the third, sensory conduction velocity across the carpal tunnel.     

腕尺管综合征肌电图检测分析

目的探讨腕尺管综合征的肌电图表现。方法对13例腕尺管综合征患者行肌电图检测,包括尺神经运动潜伏期、运动波幅、尺神经小指感觉传导速度、感觉波幅等,与其健侧对照比较,评估肌电图表现差异。结果腕尺管综合征患者其患侧肌电图与健侧比较,尺神经运动潜伏期延长(P<0.01),运动波幅缩小(P<0.01),尺神经小指感觉传导速度减慢(P<0.01)、感觉波幅缩小(P<0.01),小指展肌、第Ⅰ骨间肌肌电图也出现静息状态及重收缩状态的改变。结论腕尺管综合征患者存在肌电图的多项改变,早期检测对于其诊断及其治疗具有重要意义。     

Median nerve conduction study through the carpal tunnel using segmental nerve length measured by ultrasonographic and conventional tape methods

Rha D-W, Im SH, Kim S-K, Chang WH, Kim KJ, Lee SC. Median nerve conduction study through the carpal tunnel using segmental nerve length measured by ultrasonographic and conventional tape methods.

Objective

(1) To determine whether a 5-cm segment includes the entire anatomic carpal tunnel in live subjects, and to compare surface, ultrasonographic, and direct measures of the median nerve length in human cadavers. (2) To investigate the actual difference of sensory conduction velocities between the conventional tape method and the ultrasonographic method.

Design

Cross-sectional study.

Setting

University rehabilitation hospital.

Participants

Healthy volunteers (N=40; 20 men, 20 women).

Interventions

Not applicable.

Main Outcome Measures

Onset latencies at the palm and wrist, nerve conduction velocity (NCV) in nerve conduction study (NCS), median nerve length measured by ultrasound and tape method.

Results

A real-time ultrasonographic study revealed that a 5-cm segment included the entire carpal tunnel. In the cadaveric study, the median nerve length measured by ultrasound was closer to the actual nerve length than the conventional surface length. The median nerve length in the wrist-to-palm segment measured by ultrasound was shorter than the surface distance. The sensory NCV using the nerve length measured by ultrasound was slower than that using the surface distance (P<.05).

Conclusions

The 5-cm segment test included the entire carpal tunnel and might be advantageous in the diagnosis of carpal tunnel syndrome (CTS), especially for early lesions. We expect that ultrasonographic measurement of nerve length might raise the sensitivity of NCSs for the diagnosis of CTS.     

正中神经压迫试验对腕管综合征神经传导速度的影响

目的比较正中神经压迫试验对腕管综合征（carpal tunnel syndrome,CTS）患者正中神经传导速度的影响。方法设置CTS组和对照组两个组别,共29例受试者纳入研究。CTS组为14例CTS患者,对照组为15例健康受试者。神经传导速度测定包括正中神经和尺神经的感觉传导末端潜伏期（distal sensory latency,DSL）、感觉神经动作电位（sensory nerve action potential,SNAP）、跨腕关节感觉传导速度（sensory conduction velocity,SCV）、运动传导末端潜伏期（distal motor latency,DML）及复合肌肉动作电位（compound muscle action potential,CMAP）。先测感觉传导,再测运动传导。正中神经压迫试验5min后再次测量上述指标。结果正中神经压迫试验前后电生理检查考虑诊断CTS分别为22侧和24侧。压迫正中神经后,CTS组正中神经DSL较压迫前显著延长（P〈0.05）。CTS组尺神经和对照组正中神经及尺神经的各参数在压迫前后均无显著改变（P〉0.05）。与对照组相比,在压迫试验前后CTS组的正中神经DSL和DML均明显延长（P〈0.05）,尺神经DSL和DML均无显著改变（P〉0.05）。结论正中神经压迫试验5min能使CTS患者正中神经的感觉传导末端潜伏时明显延长,有助于提高神经传导测定对早期CTS的诊断率。     

Physiological Localization by Sensory and Motor Inching Studies and Structural Abnormalities Detected by Ultrasonographic Changes in Carpal Tunnel Syndrome

ObjectiveTo study mild to moderate carpal tunnel syndrome (CTS), compare median nerve entrapment sites detected by electrophysiological inching studies with ultrasonographic abnormalities of cross-sectional area (CSA), and correlate focal points of conduction delays detected by sensory and motor inching recorded from the third digit and second lumbrical muscle.DesignAnalytic cross-sectional study.SettingDepartment of Rehabilitation Medicine, King Chulalongkorn Memorial Hospital, Bangkok, Thailand.ParticipantsHands from 10 participants without CTS (n=15) and hands with mild to moderate CTS from 29 participants (n=40) were selected by convenience sampling (N=55).InterventionsNot applicable.Main Outcome MeasuresCorrelation of electrophysiological entrapment site localization by inching study with anatomic entrapment site detected by ultrasound (US).ResultsIn all 40 hands tested, a sharply localized latency was found to increase across a 1-cm segment, most commonly 2-3 cm distal to the distal wrist crease for both sensory and motor studies, showing a good match between the 2 with Pearson correlation coefficient value (r=0.72). US revealed a narrowing CSA of the median nerve at 1-2 cm distal to the distal wrist crease.ConclusionsThis study showed a high correlation for focal point conduction delay detected by sensory and motor nerve conduction study. Recording from the second lumbricalis facilitated motor inching along the straight course of the nerve instead of the arcuate recurrent branch innervating the abductor pollicis brevis, the muscle traditionally used. US examination also revealed a localized narrowing of the median nerve CSA at 1-2 cm distal to the distal wrist crease, a possible site for anatomic entrapment. The most enlarged CSA was seen at the distal wrist crease, a level corresponding to the inlet of the carpal tunnel.     

Comparative diagnostic sensitivities of orthodromic or antidromic sensory inching test in mild carpal tunnel syndrome

OBJECTIVES: To compare the reliability, sensitivity, and specificity of the "inching test" (IT) or "centimetric test," performed orthodromically (OIT) and antidromically (AIT). METHODS: Incremental palmar study of the sensory fibers of the median nerve was evaluated over 10cm across the wrist in 20 patients with mild carpal tunnel syndrome (CTS) and in 20 controls. Mild CTS was defined as clinical features of CTS with normal electrophysiologic findings by standard methods. The CTS patients were preselected with abnormal orthodromic median-ulnar latency difference of the fourth digit (mean .66+/-.21ms; nl < .40ms). RESULTS: In controls, the mean conduction delay per centimeter (CD/cm) was .192ms for OIT and .191ms for AIT; the mean maximum conduction delay per centimeter (MCD/cm) was .250+/-.032ms for OIT and .344+/-.10ms for AIT. MCD/cm was located inside the carpal tunnel in 85% of patients (OIT) versus 80% for AIT. No MCD/cm was greater than .32ms (OIT) or .60ms (AIT). With corresponding pathologic thresholds of .36ms (mean + 3.4 standard deviation [SD]) for OIT and .64ms (mean + 2.6 SD) for AIT, IT was abnormal in 20 patients (100%) with OIT compared with only 4 patients (20%) with AIT. CONCLUSIONS: The orthodromic method was superior to the antidromic method in controls and in patients (chi2 = 23; p = 1.8 x 10(-6)). These findings suggest that orthodromic IT should be used when standard electrodiagnostic tests fail to reveal median nerve sensory abnormality in persons with mild CTS.     

腕管综合征和肘管综合征的超声影像学研究

目的探讨超声在腕管综合征和肘管综合征中的诊断价值。方法80例健康者为对照组,临床疑诊27例腕管综合征和32例肘管综合征患者,超声测量其正中神经、尺神经的前后径、左右径及横截面积,同时测定神经传导速度。结果腕管综合征和肘管综合征组正中神经、尺神经的前后径、左右径及横截面积均大于对照组（P〈0．01）,腕管综合征和肘管综合征组的病变神经横截面积均与运动传导速度呈负相关（r分别为-0．76、-0．80）。结论超声可为腕管综合征和肘管综合征的诊断提供影像学依据,并对其治疗及疗效评价有重要价值。     

80例腕管综合征患者的神经电生理测定

目的：观察神经电生理检测对腕管综合征(CTS)的诊断敏感性。方法：80例临床提示为CTS或不能除外CTS的患者进行神经电生理测定并进行回顾性分析。结果：80例116侧正中神经复合肌肉动作电位末端运动潜伏期和波幅、肘至腕的运动传导速度、指至腕部的感觉传导速度及感觉神经动作电位波幅等5项指标检测异常率分别为75．0％、19．8％、9．5％、88．8％及37．9％；45例65侧拇指正中／桡浅神经潜伏期差(MRLD)及环指正中／尺神经潜伏期差(MULD)检测异常率95．4％。结论：正中神经拇指至腕段的感觉传导速度测定是诊断CTS的敏感指标，采用MRLD及MULD测定，诊断敏感性更高。     

Second lumbrical muscle recordings improve localization in severe carpal tunnel syndrome

OBJECTIVE: To determine how often the second lumbrical motor potential is present when the abductor pollicis brevis (APB) motor potential is absent in severe carpal tunnel syndrome (CTS). DESIGN: Prospective study of consecutive patients with severe CTS and an absent motor potential from the APB. SETTING: Single-center public hospital-based electromyography lab. PARTICIPANTS: Patients with a clinical diagnosis of CTS who had an absent median sensory response and an absent median motor response to APB on routine nerve conduction testing. Twenty-two hands of 19 patients were examined. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURE: Presence and distal latency of motor potential to the second lumbrical. RESULTS: The second lumbrical potential was present in 17 hands (77%). The distal motor latency to the second lumbrical was prolonged in all (mean, 9.1ms; normative value, <4.1ms). CONCLUSIONS: Second lumbrical recordings improve localization in many patients with severe CTS when routine median sensory and motor conduction studies produce no potentials.