Reappraisal of Supraorbital Sensory Nerve Conduction Recordings: Orthodromic and Antidromic Techniques

OBJECTIVE: To establish a supraorbital nerve sensory conduction recording method and assess its usefulness. METHODS: Thirty-one healthy subjects without a history of trauma or neurological disease were recruited. For the orthodromic procedure, the recording electrode was attached immediately superior to the supraorbital notch. The stimulation electrode was placed on points along the hairline which evoked the largest sensory nerve action potentials (SNAPs). The antidromic sensory response was recorded after switching the recording and stimulating electrodes. The measured parameters were onset latency, peak latency, and baseline to peak amplitude of the SNAPs. The electrophysiological parameters of the bilateral supraorbital nerves were compared. We also recruited two patients who had sensory deficits on one side of their foreheads because of laceration injuries. RESULTS: The parameters of orthodromically recorded SNAPs were as follows: onset latency 1.21±0.22 ms (range, 0.9-1.6 ms), peak latency 1.54±0.23 ms (range, 1.2-2.2 ms), and baseline to peak amplitude 4.16±1.92 µV (range, 1.4-10 µV). Those of antidromically recorded SNAPs were onset latency 1.31±0.27 ms (range, 0.8-1.7 ms), peak latency 1.62±0.29 ms (range, 1.3-2.2 ms), and baseline to peak amplitude 4.00±1.89 µV (range, 1.5-9.0 µV). There was no statistical difference in onset latency, peak latency, or baseline to peak amplitude between the responses obtained using the orthodromic and antidromic methods, and the parameters also revealed no statistical difference between the supraorbital nerves on both sides. CONCLUSION: We have successfully recorded supraorbital SNAPs. This conduction technique could be quite useful in evaluating patients with supraorbital nerve lesions.

Anatomical Considerations of Lateral and Medial Antebrachial Cutaneous Nerves

OBJECTIVE: To evaluate the anatomic course of the lateral antebrachial cutaneous nerve (LABCN) and medial antebrachial cutaneous nerve (MABCN) in the forearm. METHOD: We dissected 29 upper extremities of 16 cadavers for LABCN and 20 upper extremities of 15 cadavers for the MABCN. We measured the distance (BT_L) between the biceps tendon (BT) and LABCN on the intercondylar line. The BT is the point at which biceps tendon crosses intercondylar line. The distance (L12) between LABCN and the point of 12 cm distal to BT on the line between BT and radial artery at wrist was measured. The distance (ME_M) between MABCN and medial epicondyle on the intercondylar line was measured. M8 and M10 are the distances between MABCN and the points 8 cm and 10 cm distal to BT on the line from BT to mid-point of flexor carpi radialis and palmaris longus at the wrist respectively. RESULTS: BT_L and L12 were 1.4+/-3.7 mm and 4.4+/-3.7 mm respectively. ME_M, M8 and M10 were 28.6+/-6.9 mm, 18.9+/-8.9 mm and 18.3+/-8.2 mm respectively. The thickness of LABCN and MABCN was 19.1+/-4.9 mm and 13.2+/-4.2 mm respectively. CONCLUSION: The LABCN was emerge just lateral to biceps tendon at the elbow and ran down to radial artery. The anatomic course of MABCN was variable at the elbow and forearm.

Frequency of Carpal Tunnel Syndrome acoording to the Severity of Diabetic Neuropathy

OBJECTIVE: To investigate the frequency of carpal tunnel syndrome (CTS) according to the severity of diabetic polyneuropathy. METHOD: Electrophysiologic study was performed in 456 patients (male 222, female 233, average age 58) with diabetes mellitus. Electrophysiologically diagnosed diabetic neuropathy was classified as suspected, probable or definite. CTS was also diagnosed both in cases with and without underlying diabetic peripheral neuropathy. The ANOVA test was used for statistical analysis. RESULTS: Out of 456 diabetic patients, 228 patients were diagnosed as diabetic peripheral neuropathy. The patients with diabetic neuropathy consisted of 107 cases (23.5%) of sus pected group, 95 cases (20.8%) of probable group and 26 cases (5.7%) of definite group. The frequencies of concomitant CTS were 49 cases (21.5%) in 228 diabetic patients without diabetic polyneuropathy, 31 cases (29%) in suspected group and 30 cases (31.6%) in probable group. These were statistically significant. However, only one case showed concomitant CTS in 26 cases of definite group. CONCLUSION: The frequency of CTS was higher in probable group compared to suspected group. However the frequency decreased in definite group because there is a difficulty in the differential diagnosis of two disease in the cases of advanced peripheral neuropathy.

Abductor Digiti Minimi and First Dorsal Interosseous Recordings for the Localization of Ulnar Neuropathy at the Elbow

OBJECTIVE: To compare abductor digiti minimi (ADM) recording with first dorsal interosseous (FDI) recording for the localization of ulnar neuropathy at the elbow. METHOD: The subjects were consisted of 28 patients of ulnar neuropathy at the elbow. The subjects were divided into 3 groups: focal demyelination; focal demyelination and axonal degeneration; axonal degeneration. Compound muscle action potentials were recorded from both ADM and FDI muscles and ulnar nerve was stimulated at the wrist, 2 cm distal and 8 cm proximal to the medial epicondyle. Focal demyelination were analyzed into conduction block and/or conduction slowing. RESULTS: Conduction block was observed in 13 out of 28 patients (46%) with FDI recording and 11 out of the 28 patients (39%) with ADM recording. Conduction block was found solely with FDI recording in 3 patients, whereas 1 patient showed conduction block with ADM recording only. Concomitant segmental motor conduction slowing was observed in 11 out of 13 patients with FDI recording and in 6 out of 11 patients with ADM recording. CONCLUSION: Measurements to the FDI had a higher yield of abnormality than the ADM. In some patients, only one recording muscle showed abnormal findings. Therefore, it may be useful to record from both muscles to localize ulnar neuropathy at the elbow.

Antidromic and Orthodromic Sensory Conduction of Ring Finger in Carpal Tunnel Syndrome

For the diagnosis of carpal tunnel syndrome (CTS), a sensory conduction study of median nerve is the most sensitive parameter, by either antidromic or orthodromic recording. Many different sensory recordings have been developed to detect the mild or early cases of carpal tunnel syndrome. A comparison of the median and ulnar sensory responses using the 4th digit either orthodromically or antidromically has been one of the methods. However, a simultaneous comparison of both antidromic and orthodromic methods on the 4th digit has not been documented. For the comparison between the median and the ulnar sensory nerve conduction of the 4th digit recorded antidromically or orthodromically, conduction studies of the median and ulnar sensory nerves were performed using standard methods in normal populations as well as in patients with carpal tunnel syndrome. We studied 31 CTS patients (46 hands) with mean age of 54 years old (range, 25~70). Also, 51 subjects (102 hands) with mean age of 48 years old were studied as control. The difference of antidromic latencies between the median and the ulnar nerves was less than or equal to 0.4 msec in the control subjects and greater than or equal to 0.5 msec in the patients with carpal tunnel syndrome. The difference of orthodromic latencies was less than or equal to 0.5 msec in the control subjects and greater than or equal to 0.5 msec in the patients with carpal tunnel syndrome. By the antidromic and orthodromic methods, the mean difference between latencies of the median or ulnar nerve was not statistically significant. However the amplitude of median or ulnar nerve was 2 times larger by the antidromic method than by the orthodromic. We concluded that the latency difference of 0.5 msec or greater between the median and ulnar nerve sensory conductions from the 4th digit would be valuable for the diagnosis of CTS. The antidromic methods with larger amplitude may be more technically convenient to determine CTS than the orthodromic methods.

Serial Electrodiagnostic Evaluation after Carpal Tunnel Release

OBJECTIVE: Patients with carpal tunnel syndrome are often refered for electrophysiologic evaluation of postoperative residual symptoms. We performed this prospective study to assess changes of the electrophysiological parameters after carpal tunnel release. METHOD: Fifty-four hands of 29 patients with electrodiagnostically confirmed carpal tunnel syndrome underwent surgical release of the transverse carpal ligament. Serial electrophysiological evaluation of the median nerve performed at 2 weeks, and 1, 3, 6 months after surgery in all patients. All the tests were performed by one electromyographer using Dantec Counterpoint machine. Median motor and sensory responses were obtained from abductor pollicis brevis and 3rd digit respectively. Repeated measure ANOVA test was done to observe the changes in each parameter on serial examination. RESULTS: The median motor latency (ML), motor amplitude (MA), sensory latency (SL) and sensory amplitude (SA) were as follows: preoperative ML (6.1 0.2 ms), MA (7.3 0.5 mV), SL (5.1 0.2 ms), SA (6.8 1.0 uV); postoperative week 2, ML (5.5 0.2 ms), MA (6.9 0.5 mV), SL (4.5 0.2 ms), SA (11.4 1.3 uV); postoperative month 1, ML (5.1 0.2 ms), MA (7.1 0.5 mV), SL (4.1 0.2 ms), SA (13.0 1.3 uV); month 3, ML (4.6 0.1 ms), MA (7.2 0.1 mV), SL (3.8 0.2 ms), SA (15.4 1.4 uV); month 6, ML (4.6 0.2 ms), MA (7.4 0.5 mV), SL (3.5 0.1 ms), SA (16.5 1.4 uV). CONCLUSION: Improvement was gradually seen up to the postoperative 3 months. However, the least amount of improvement was observed in the postoperative 3 to 6 month period.

Neurofibromatous Polyneuropathy

Peripheral neuropathy constitutes a rare clinical manifestation in the neurofibromatosis. Eleven cases of peripheral neuropathy associated with the neurofibromatosis have been reported. We report a sensorymotor peripheral neuropathy in 2 cases of neurofibromatosis.

Variations in Motor Nerve Conduction Latency According to Different Recording Electrodes

OBJECTIVE: To explore the effects of different recording electrodes on motor nerve conduction latencies. METHOD: Median motor conduction study was performed in 10 healthy subjects. Motor conduction latency was determined by placing different recording electrodes (surface disc, monopolar needle and concentric needle) at the motor point of the left abductor pollicis brevis muscle, and reference electrodes on the proximal interphalangeal joint of the thumb. Motor nerve conduction recording was performed by using a surface disc, monopolar needle, and concentric needle. For the intramuscular recordings, needles were inserted both superficially and deep. The stimulus electrodes were secured 8 cm proximal to the recording electrodes, and the same intensity was applied throughout the tests. RESULTS: Deep intramuscular monopolar and concentric needle electrodes recorded the shorter latencies, 3.0+/-0.4 ms and 3.0+/-0.3 ms, respectively. Superficial concentric needle electrode recorded the longest latency of 3.4+/-0.3 ms. Motor nerve conduction latencies using a surface disc and superficial monopolar electrode were 3.2+/-0.3 ms and 3.2+/-0.3 ms, respectively. CONCLUSION: We conclude that the distal motor nerve conduction latency is variable depending on the type of recording electrodes.

How to Deal with the Latency of Unobtainable Responses in the Statistical Analysis

OBJECTIVE: To evaluate the usability of near-nerve needle recording techniques in cases of unrecordable sensory nerve action potentials (SNAPs) with a surface electrode and to determine a proper alternative value of the missing latencies. METHOD: Twenty six hands of 23 patients with a carpal tunnel syndrome (CTS) and an unobtainable median SNAP by surface electrode were evaluated by the near-nerve needle recording of median SNAPs. Using the nerve conduction data of 113 patients with CTS, we have established 3 alternative values: maximal, 95 percentile and predictive latencies. The alternative values were compared with the mean onset latencies by the near-nerve needle recordings of median SNAPs. RESULTS: Median SNAPs were obtainable in the 22 out of 26 hands by the near-nerve recording technique. The mean onset latency was 5.51+/-0.36 ms. The alternative values from 113 patients with CTS were as follows: maximum latency, 6.9 ms; 95 percentile latency, 5.6 ms; and predictive latency, 5.52 ms (Y = 0.123x X 5.52491; Y, onset latency; X, amplitude; r2=0.564; p=0.00). The Predictive latency was nearest to the mean onset latency. CONCLUSION: To minimize the selection bias and statistical errors, the near nerve recording techniques proved to be a valuable method in cases of unrecordable SNAPs with surface electrode. For compensation of missing data, a proper alternative value can be obtained by the predictive latency calculated from a linear regression.

The Relationship between Clinical and Electrodiagnostic Findings in Carpal Tunnel Syndrome

OBJECTIVE: Carpal tunnel syndrome (CTS), a common entrapment neuropathy of the median nerve at the wrist, can be diagnosed clinically and electrophysiologically and treated successfully. The purpose of this study was to determine an association between clinical findings and the electrodiagnostic severity of this syndrome. METHOD: Medical records of 313 patients with CTS which was confirmed based on clinical and electrophysiological findings were reviewed. Clinical symptoms and signs (thenar atrophy, sensory change, positive Tinel sign and Phalen test) and electrodiagnostic values were recorded. CTS severity was determined according to the modified Stevens' criteria. The relationship between electrodiagnostic severity and clinical findings was investigated and statistically analyzed using the ANOVA and chi square tests. RESULTS: The median motor and sensory latencies became prolonged and amplitudes decreased with worsening electrophysiological severity of CTS, and the differences between severity groups were statistically significant. The frequency of symptoms and signs obtained was significantly greater in the more severe CTS groups. CONCLUSION: A positive correlation exists between the frequency of clinical findings and electrophysiological severity of CTS.

Clinical Pictures of Stroke Patients

OBJECTIVE: The present study evaluated the characteristics and natural history of stroke patients. METHOD: Seven hundred and sixty seven consecutive patients admitted through acute care facility were reviewed. All medical records including age, case fatality, risk factors and radiological findings including CT or MRI were reviewed. To investigate the activities of daily living (ADL) of stroke patients, follow-up study was done in 303 patients through telephone interview or direct contact. Stroke was subdivided into cerebral infarct, intracerebral hemorrhage (ICH) and subarachnoid hemorrhage (SAH). RESULTS: The proportion of stroke subtypes were infarct (45.9%), ICH (34.7%) and SAH (19.4%). The recurrence rate of stroke was higher in the infarct patient. Higher percentage of fatality was noted in the SAH patient. Higher incidence of hemorrhage was still observed compared to western country. Hypertension is the major risk factors for all stroke subtypes. But among hypertensive individuals, only 29% patients controlled the hypertension. Fifty-eight percent of stroke patients regained independent ADL. CONCLUSION: The result of this study shows the clinical pictures of stroke patients. Further research was needed to investigate the trends of stroke and control of risk factors and attention must be paid to the patients who is dependent in ADL.

Posterior Cutaneous Nerve of Arm Conduction Study in Healthy Adults: Reference Value

OBJECTIVE: To establish the posterior cutaneous nerve of arm (PCNA) conduction technique and set up the reference values. METHOD: A PCNA conduction study was performed in 80 nerves of 40 neurologically healthy adult subjects with a mean age of 38 years (range, 20 to 56). Dantec Counterpoint MK2 machine was used. The recording bar electrodes were placed 10 cm distal to the axillary fold on a line connecting the posterior axillary fold and the olecranon. Supramaximal stimulation was applied to the axilla posterior to the brachial artery. Onset latency, baseline to peak amplitude and negative spike duration of sensory nerve action potentials were obtained. Skin temperature was measured in the posterior arm and maintained at 34 degrees C or above. RESULTS: Compound sensory action potential for the PCNA was recordable in all the subjects. The results were as follows: onset latency, 1.7+/-0.1 msec; baseline to peak amplitude, 4.6+/-1.4 microvolt; negative spike duration, 1.1+/-0.2 msec. CONCLUSION: PCNA response is readily obtainable. This study may help to assess the pain or paresthesia in the posterior aspect of the arm, although more studies are required for clinical application.

Quantitative Motor Unit Analysis in Patients with Post-Polio Syndrome

OBJECTIVE: To investigate the clinical feature and quantitative electromyographic (QEMG) findings in the patients with post-polio syndrome (PPS). METHOD: Eleven patients who had clinical evidences of antecedent poliomyelitis were evaluated with standardized clinical history, physical examination and QEMG study. If a patient had fulfilled provisional criteria for PPS, he was regarded as PPS and six patients had fulfilled the criteria. Other patients were treated as control group with stable poliomyelitis. Manual muscle testing and needle EMG study including quantitative motor unit analysis was performed at the tibialis anterior and vastus medialis muscles. The existence of abnormal spontaneous activity and parameters of quantitative motor unit analysis, mean duration and amplitude of motor unit action potentials (MUAPs), were compared between PPS and control groups. The correlation between the muscle strength and parameters of QEMG was investigated. RESULTS: Abnormal spontaneous activities were noted in 4 out of 11 patients (36.4%) and three of these 4 patients were PPS. Mean duration and amplitude of MUAPs of tibialis anterior and vastus medialis muscles were not different significantly between the PPS and stable poliomyelitis group (p>0.05). The parameters of MUAPs were poorly correlated with muscle strength. CONCLUSION: Distribution of abnormal spontaneous activities and parameters of QEMG study were not different in PPS and stable poliomyelitis patients. QEMG study may not have additional benefit in differentiating PPS from stable poliomyelitis.

Electronic Filter Setting Effects on Parameters of Nerve Conduction Studies

OBJECTIVE: To investigate the influence of electronic filter setting change on the parameters of motor and sensory nerve conduction studies. METHOD: Median motor and sensory nerve conduction studies were performed in 25 neurologically healthy adult subjects with a mean age of 29 years (range, 20~50). Compound muscle action potentials (CMAPs) and sensory nerve action potentials (SNAPs) were recorded after fixing the low frequency filter cutoff value of 1 Hz, 10 Hz, 100 Hz and 300 Hz and by changing high frequency filter cutoff level from 10 KHz to 0.5 KHz. Onset and peak latency, amplitude of CMAPs and SNAPs were measured and the area of CMAPs were also recorded. Dantec Counterpoint MK2 machine was used. Skin temperature was maintained at 34degrees C or above. RESULTS: As the high frequency filter was changed from 10 KHz to 0.5 KHz, the mean amplitude of SNAPs and CMAPs decreased by 33.5%, 3.3%, respectively. Onset and peak latency prolonged significantly below the high frequency filter level of 2 KHz (p0.01). CONCLUSION: Significant alterations in parameters of CMAPs and SNAPs were produced by modification of filter setting. Optimum filter setting is recommended in nerve conduction study and filter parameters must remain constant when determining normal values and when performing serial studies on patients.

Comparison of Sensory Nerve Action Potential Parameters Using Different Recording Electrodes

OBJECTIVE: To investigate the influence of five different recording electrodes on the various parameters of sensory nerve action potentials (SNAPs). METHOD: Median sensory nerve conduction study was performed in 50 normal subjects using different five types of recording electrodes-disc electrode, ring electrode, bar electrode and two kinds of felt-tip bar electrodes (type 1 and 2). The interelectrode distances between active and reference electrodes were set at 4 cm for the disc and ring electrodes. The bar electrode, felt-tip electrodes type 1 and 2 were fixed at interelectrode distances of 3 cm, 3.7 cm and 2.3 cm, respectively. Onset and peak latency, onset to peak amplitude, peak to peak amplitude and duration of negative spike of SNAPs were measured. These parameters were compared using ANOVA test. RESULTS: Onset and peak latencies of SNAPs recorded from five different electrodes were not different (p>0.05). Onset to peak and peak to peak amplitudes of SNAPs recorded from felt-tip type 2 electrode were significantly reduced compared to other electrodes (p<0.05). Onset to peak amplitude of SNAPs was also reduced when the ring electrode was used (p<0.05). The negative spike durations of SNAPs recorded from felt-tip type 2 and bar electrodes were shorter than other electrodes recording (p<0.05). CONCLUSION: Onset and peak latencies of SNAPs were not affected by the types of electrodes used. Shortening of interelectrode distance may be a main cause of reduction of peak to peak amplitude and negative spike duration of SNAPs.

Follow-up Study of Carpal Tunnel Syndrome with Conduction Block: Comparison between Operative and Non-operative Management

OBJECTIVE: To compare the degree of improvement of conduction block in carpal tunnel syndrome (CTS) between the patients who received operation and those who received conservative treatment. METHOD: Subjects included 33 hands of 27 CTS patients who received operation (operation group) and 20 hands of 17 patients who were managed conservatively (non-operation group). Median antidromic sensory responses were recorded with wrist and palm stimulation. The criterion for conduction block was more than 50% drop of baseline to negative peak amplitude of sensory nerve action potential with wrist stimulation compared to palm stimulation. The degree of conduction block was measured before and aftertreatment, and the improvement of conduction block was compared between the two groups. RESULTS: The degrees of conduction block were 59.9+/-14.3% in operation group and 60.5+/-14.5% in the non-operation group at initial evaluation. The improvements of conduction block were 32.1+/-15.1% (5~58.9%) in operation group and 7.8+/-19.8% (-27.3~36.7%) in non-operation group after treatment and the difference was statistically significant. CONCLUSION: The results suggest that operative treatment may be useful even in patients with carpal tunnel syndrome with conduction block.

Skin Temperature Mapping in Upper and Lower Extremities

The role of skin temperature is very important in clinical neurophysiology but has often been neglected. In nerve conduction studies, lower normal temperature affects slower conduction velocities and increased nerve (sensory or mixed) action potential amplitudes. To determine the normal skin temperature in various parts of upper and lower extremities within close approximation of the nerve passages, the temperature was measured using Physitemp Model BAT-12 (Accuracy 0.1oC, Clifton, New Jersey, U.S.A.). Fifty-three neurophysiologically healthy adults (Age range, 22-77 years old) were tested : upper extremity, 20 (male, 7 ; female, 13) ; lower extremity, 33 (male, 11 ; female, 22). The total points of skin temperature measurement were 21 : upper extremity, 10 ; lower extremity, 11. The skin temperature for the upper and lower extremities was 34.6+/-0.9 degrees C (range, 32.6-36.7degrees C) and 33.4+/-1.1degrees C (range, 28.1-35.7degrees C), respectively. Although it is frequently time consuming, monitoring normal skin temperature will result in greater electrodiagnostic accuracy.

Dorsal Ulnar Cutaneous Nerve Conduction Study in Entrapment Ulnar Neuropathy at the Elbow

OBJECTIVE: To evaluate the electrophysiologic findings of the dorsal ulnar cutaneous nerve (DUCN) in ulnar neuropathy at the elbow and to correlate the sensory nerve action potential (SNAP) amplitude of DUCN to those of ulnar compound muscle action potential (CMAP) and SNAP. METHOD: The subjects were 39 patients diagnosed as ulnar neuropathy at the elbow. Electrophysiologic classification consisted of 3 groups: conduction block (CB); conduction block and axonal degeneration (CBAD); axonal degeneration (AD). Findings of DUCN conduction study were evaluated according to the electrophysiologic classification. The amplitude of DUCN was correlated to those of CMAP and SNAP. RESULTS: The DUCN conduction study was normal in all cases of CB (4 cases), but was abnormal in 21 cases of CBAD (23 cases) and in 10 cases of AD (12 cases). Even in the cases with AD, 4 cases showed normal DUCN potentials. Correlations of DUCN to ulnar SNAP and CMAP were r=0.48, (p<0.01) and r=0.33, (p<0.05), respectively. CONCLUSION: Findings of DUCN may be related to the fascicular involvement of the ulnar nerve at the elbow. Although it is possible for the DUCN to be spared in ulnar neuropathy at the elbow, electrophysiologic measurement of the DUCN response remains useful, but only in those cases where it is abnormal, which suggests the lesion to be at a more proximal site.

Median and Ulnar Sensory Nerve Conduction Study in Five Digits

OBJECTIVE: To establish the reference values of the sensory conduction for all the digits in the hand, conduction studies were performed using the standard technique. METHOD: One hundred hands of fifty neurologically healthy adults with mean age of 45 years (range, 23~69) were tested. Depending on ages, the 50 adults were devided into three groups: group 1, 20~45 years old; group 2, 46~60 years old; group 3, 61~ years old. Antidromic sensory nerve conduction techniques using a fixed distance were performed. The onset latency and baseline to peak amplitude of the sensory nerve action potentials (SNAPs) were measured. During the test, the skin temperature of the hand was maintained at 34 degrees C or above. These variables from SNAPs were compared according to age, gender, side, and recording digits. RESULTS: Comparison of the median and ulnar SNAPs between age groups revealed longer onset latency and smaller amplitude in the elderly group. The amplitude of SNAPs was larger in females than in males and the left side than the right side. Comparison of the latencies and amplitudes between the second and third digits showed no significant difference statistically. Also, the latencies and amplitudes of the median and ulnar nerves recorded from the fourth digits showed no significant difference statistically. CONCLUSION: Based on these results, the reference values for sensory conductions from all the digits were obtained. These values would be helpful in evaluation of CTS or unspecified finger pain or upper extremity neuropathy.

Conduction Block in Carpal Tunnel Syndrome

OBJECTIVE: To demonstrate a conduction block of the median nerve at the flexor retinaculum (FR) in carpal tunnel syndrome (CTS), comparison of potentials obtained with stimulation of median nerve at the wrist and the palm may be required. METHOD: To determine the severity and incidence of conduction block in patients with CTS, seventy hands of neurologically healthy adults (mean age, 48 years) as control, and seventy hands of patients with CTS (mean age, 51 years) were tested. We performed median motor and middle finger recorded antidromic sensory conduction study with stimulation of the wrist and palm of a distance of 5 cm. The negative peak spike duration and baseline to peak amplitude of the compound muscle action potential (CMAP), and sensory nerve action potential (SNAP) with wrist and palm stimulations were measured. From these values, the wrist to palm duration ratio and amplitude ratio were obtained. RESULTS: The criteria of median motor nerve conduction block were a wrist to palm amplitude ratio of less than 0.7 and a wrist to palm duration ratio of less than 1.13. The criteria of median sensory conduction block were a wrist to palm amplitude ratio of less than 0.61 and a wrist to palm duration ratio of less than 1.33. In the patient group, 10 hands (14.3%) showed motor conduction block and 12 hands (17.1%) showed sensory conduction block and 3 hands (4.3%) showed both. The wrist to palm amplitude ratios of CMAP and SNAP in the patient showing conduction block were 0.6+/-0.1, and 0.4+/-0.2, respectively. There was no correlation between palm CMAP or SNAP amplitude and respective wrist to palm ratios. CONCLUSION: Comparison of the amplitude and duration of CMAP or SNAP obtained with stimulation of both wrist and palm may be able to differentiate between conduction block and axonal degeneration. These values may be useful in planning treatment and predicting outcome.