Transcarpal median motor nerve testing revisited

Transcarpal median motor nerve testing revisited

Society proceedings / Electroencephalography and clinical Neurophysiology 98 (1996) 8P-4OP 114. Root stimulation studies in evaluation of patients wit...

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Society proceedings / Electroencephalography and clinical Neurophysiology 98 (1996) 8P-4OP 114. Root stimulation studies in evaluation of patients with motor neuron disease. - J.A. Hinchey ‘, J.M. Shefner b, M.H. Rosa ‘, D.C. Preston b, E.L. Logigian b and E.M. Raynor a (” Beth Israel Hospital, Boston, MA; b Brigham and Women’s Hospital, Boston, MA) Introduction: Patients with motor neuron disease (MND) are frequently subjected to nerve root stimulation studies to rule out multifocal motor neuropathy with conduction block (MMNCB), although their utility in various forms of MND is unknown. Objective: To assess the utility of root stimulation in distinguishing patients with MND from those ,with MMNCB. Methods: We performed root stimulation (C-8, S-1) in 35 patients using a monopolar needle; 14 MMNCB, 59 MND nerves were studied. MMNCB was diagnosed based on routine motor conduction studies (N - 3 patients). MND patients (N = 32) were subcategorized based on presence or absence of upper motor neuron signs. We calculated percent change in compound muscle action potential amplitude and area between proximal surface and root stimulation sites. Probable conduction block (PCB) was defined as a > 50% drop in amplitude and area across a focal segment. Results: Probable conduction block was found in l/73 nerves. This patient also had distal block and was classified by EMG as MMNCB. He died of MND. In no other MND patient was PCB identified by root stimulation. There was no difference in mean amplitude change across the root segments for the different groups. Conclusion: Root stimulation studies do not typically increase the sensitivity for distinguishing patients with MND from MMNCB. 115. Golseth Young Investigator Honorable Mention Award Winner! Abductor hallucis false motor points: electrophysiologic mapping/cadaver dissection. - D.R. Del Toro and T.A. Park (Medics1 College of Wiionsin, Milwaukee, WI) Introduction: False motor points (FMPs) can occur in foot or hand muscles when there is a compound muscle action potential (CMAP) transition between an initial negative deflection and an initial positive deflection, resulting in an isoelectric segment which increases the CMAP onset latency (OL). Objective: To investigate abductor hallucis (AH) FMPs. Methods: The medial foot (N = 20) was electrophysiologically mapped using a grid of approximately 29 G, sites. The CMAP OL, taken to the initial negativity or positivity, was determined by the EMG instrument (Viking II). Four cadaver feet were dissected to examine muscles, nerves, and motor end-plate regions (EPRs) beneath tbe grid. Results: FMPs, defined as having an additional isoelectric segment (IS-A) which was > 0.5 msec beyond those of adjacent grid sites, were identified in l9/20 feet (mean 2.7 FMPs/subject; IS-A range 0.5-2.3 msec). The flexor hallucis brevis EPR was consistently distal to tbe navicular, the AH EPR was just proximal to the navicular, and the flexor digitorum brevis was inferior and deep to AH, corresponding to the lower half of the grid. Conclusions: This study demomnstratesthat AH FMPs can be identified in virtually all feet, and are likely due to superimposed CMAPs from nearby muscles. 116. Lack of stimulation site specif=ity in palmar transcarpal studies. - T.A. Oswald and J.J. Wertsch (Medical College of Wisconsin, Milwaukee, WI) Introduction: Palmar techniques recommend stimulation in the palmar second interosseous space for the median nerve and in the fourth interosseous space for the ulnar nerve. Objective: The purpose of this study was to examine the specificity of these stimulation sites. Methods: Wrist bar electrodes were used to record simultaneously from tbe median and ulnar nerves: sweep 2 msec/division, bandpass 20 Hz to 2 kHz, temperature > 32% stimulus duration 0.05 msec. Supra-

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maximal amplitude, onset and peak latencies were recorded. Five normal subjects were studied bilaterally. Results: With fourth interosseous space stimulation, there were responses recorded in both electrodes at the wrist mean 44 PV (23-73) over the ulnar nerve and mean 20 PV (5-50) over the median nerve. With second interosseous space, again there were responses recorded in both electrodes: mean 18 PV (5-40) over the ulnar nerve and mean 71 PV (32-137) over the median nerve. Latencies did not appear to be influenced by stimulation site. Conclusion: This study demonstrated a lack of stimulus site specificity during palmar transcarpal studies. There am both anatomic and physiologic possibilities to explain this finding which needs to be considered when transcarpal studies are inconsistent with the rest of the exam. T.A. Oswald, Junior Member Recognition Award. 117. The significance of temporal dispersion in the measurement of compound nerve action potentials. - M.C. Kiernan, I. Mogyores, T.A. Miller and D. Burke (Prince of Wales Medical Research Institute, Sydney, NSW, Australia) As conduction distance increases, there will inevitably be temporal dispersion of compound nerve action potentials, resulting in smaller potentials of longer duration. Objectives: The aim of this study was to quantify the magnitude of changes attributable to temporal dispersion, in both bipolar recordings and their unipolar constituents. Methods: Studies were performed on IO healthy subjects, aged 23-41 years. Compound nerve action potentials of the median nerve were obtained by stimulating supramaximally at sequential sites, advancing 10 mm proximally from the wrist crease. Recordings were made at elbow level using unipolar surface electrodes, with a remote reference, and bipolar electrodes with an interelectrode distance of 40 mm. Results: In referential recordings, amplitude was found to decrease in a linear fashion whether expressed relative to the increase in conduction distance (3.6 %/cm), or to the increase in latency (23.6 %/msec). Similar changes were seen using bipolar recordings. The duration of tbe potential was found to be unreliable in assessing dispersion. Conclusion: There is a substantial amplitude decrease with distance for compound nerve action potentials and this is greater than has been described for muscle action potentials. Study supported by National Health and Medical Research Council of Australia. 118. Transcarpal median motor nerve testing revisited. - HR. Scullin, S.Q. Huang, MA. Harris and P. Scheatzle (MetroHealth Medical Center, Cleveland, OH) Introduction: Midpalm median nerve stimulation is performed to measure compound muscle action potential (CMAP) amplitude and transcarpal conduction velocity (TCCV). However, results may be misleading due to its proximity to the ulnar nerve. Also, the ideal midpalm stimulation site remains controversial. Objective: To identify midpalm stimulation site for most accurate TCCV and CMAP amplitude without significant ulnar contribution. Method: Using tbe Cadwell Excel, the median nerve was stimulated 3 cm proximal to the distal wrist crease and then 8 cm and 6 cm distal to that point in 40 asymptomatic hands. Recording electrodes were placed on the abductor pollicis brevis (APB) and first dorsal interosseous (FDI) simultaneously. Result: Distal latencies were I .% f 0.26 msec at 8 cm and 1.78 f 0.26 msec at 6 cm, while TCCV were 49.7 f 7.3 m/set at 8 cm and 35.5 f 5.2 m/set at 6 cm. An evoked response was elicited from the FDI in 68% of cases at 8 cm and 46% of cases at 6 cm. APB and FDI amplitudes were significantly greater at 8 cm. Conclusion: Median nerve stimulation at 6 cm resulted in erroneously slow TCCV. This may be due to stimulation of the distal branch near tbe motor point, resulting in an erroneously short palmer latency. Stimulation at 8 cm resulted in more accurate TCCV, despite more. common simulta-

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Society proceedings / Elecrroencephulography and clinical Neurophysiology 98 11996) 8P-4OP

neous excitation of the ulnar nerve, and is recommended for clinical practice. Study supported by MetroHealth Medical Center, Department of Physical Medicine and Rehabilitation. 119. Active electrode placement and compound muscle action potential amplitude. - M.B. Bromberg ’ and T. Spiegelbergb (” University of Utah, Salt Lake City, UT; b University of Michigan, Ann Arbor, MI) Introduction: Guidelines for active electrode placement include measured distances and visual estimations. An initial negative deflection indicates proper positioning “over” the motor point. The motor point, however, may cover a large area. Objective: We evaluated compound muscle action potential (CMAP) amplitudes at different electrode positions chosen by a variety of electromyographers. Methods: Eight electromyographers and two technologists placed the active electrode as they wished over 4 muscles on the same subject. Placement sites were marked with invisible ink. Results: Electrode placement and CMAP negative peak amplitude varied with no pattern based on type or level of electromyographic experience. The range of amplitudes expressed as a percentage of the maximal response (lowest value, median value) was: thenar (631, 87%), hypothenar (71%. 86%), extensor digitorum brevis (EDB) (69%, 77%), abductor hallucis (AH) (7.5%. 92%). Correlations of amplitude with rise time were poor (r = 0.02-0.58). Correlations with slope of the negative deflection were better but variable: thenar (r = 0.68, P = 0.03) hypothenar (initial negative wave r = 0.40, P = 0.26, second negative wave r = 0.72, P = 0.021, EDB (r = 0.94, P = O.OOOl),AH (r = 0.42, P = 0.30). Conclusions: CMAP amplitudes were underestimated but median values were reasonable estimates. Visual assessment of waveforms did not reliably predict low amplitudes. When a low amplitude is suspected empiric repositioning of the active electrode is advisable. 120. Distal dorsal ulnar cutaneous nerve conduction technique: normative data. - E.L. DeVos and S.Q. Huang (MetroHealth Medical Center, Case Western Reserve University, Cleveland, OH) Introduction:Dorsal ulnar cutaneous nerve (DUCN) conduction technique stimulating 8 cm proximal to the ulnar styloid is often technically difficult due to ulnar motor nerve interference. Recently, a proposed new technique eliminated such motor contamination by stimulating more distally just volar to the ulnar styloid (Park et al., Muscle Nerve, 1994, 17: 1082). Objective: To confirm the superiority and reliability of and to establish a range of normal values for the distal DUCN conduction technique. Methods: DUCN conduction studies were performed on 60 asymptomatic hands, aged 24-55 years, utilizing an active recording electrode in the fourth web space and stimulating percutaneously 5 cm proximal just volar to the ulnar styloid. Results: Mean peak latency = 1.7f 0.22 msec, mean onset latency = 1.2 f 0.22 msec, mean amplitude = 27 PV (range 4-81 @VI, mean conduction velocity = 41.5 f 7.3 m/set. Conclusions: DUCN conduction response with stimulation just volar to the ulnar styloid is more easily obtained than with more proximal stimulation and produces a clearer response without motor interference. Our data are compatible with published data of DUCN responses obtained with more proximal stimulation. 121. Index finger length and antidromic median nerve sensory conduction. - H.J. Lee ” and H.-K. Kwon b, (” UMD-New Jersey Medical School, Newark, NJ; b Korea University College of Medicine, Seoul, Korea) Latencies and amplitudes on nerve conduction studies are affected by many factors including height. This study describes a possible relation-

ship between the length of the 2nd digit and the antidromic median nerve sensory conduction. Recording ring electrodes were placed on the 2nd digit with a 4 cm separation. The stimulating cathode was placed 14 cm proximal to the active electrode. Skin temperature was maintained at 33°C or above. Second digit lengths were measured from the midpoint of the proximal digital crease to the tinger tip. Finger circumferences were also measured. Onset latencies and amplitudes from baseline to negative peak were measured in 30 nerves in 30 normal adult subjects, aged 25-67 years (mean 38). A positive linear correlation was found between the finger length and onset latency (r = 0.58, P = O.ooO8). Inverse correlations were found between the amplitude and fmger length (r = 0.51, P = 0.004). and circumference (r = 0.40, P = 0.03). Failure to consider the 2nd digit length when interpreting the results of antidromic median nerve sensory conduction may result in a decrease in diagnostic sensitivity. 122. Semiquantification of fibrillation with intramuscular temperature reduction. - H.J. Lee ‘, H.-K. Kwon b and M.-O. Kii ’ (” UMD-New Jersey Medical School, Newark, NJ; b Korea University College of Medicine, Seoul, Korea) It is well known that the quantity of fibrillation potentials (FP) decreases with drop in the intramuscular temperature.. We describe the semiquantitative measurement of FP and positive waves (PW) with intramuscular temperature changes in an experimental animal (rat, Sprague-Dawley). Using intraperitoneal sodium pentobarbital, the right sciatic nerve of 4 rats was surgically isolated. A 1 cm segment was excised after tying the proximal and distal ends of the nerve segment. A concentric needle and thermometer needle probe were inserted 1 cm apart into the posterior tibia1 muscles 3-4 days after nerve injury. Before and during cooling the muscles with ice, FP and PW were measured and electronically stored for later analysis. Visually recognizable potentials (30 PV or above) in each stored tracing with temperature changes (range, 3PC to 15°C) were counted. A positive linear correlation was found between the temperature changes and the quantity of denervation activities. The recording of denervation activities (FP and PW) completely ceased at approximately 20°C below baseline temperature. In this study, we have successfully semiquantified denervation activities in a wide range of intramuscular temperature reduction. 123. Chronic fatigue syndrome patients demonstrate abnormalities of autonomic nervous system function. - J.A. Cohen’, D.L. Hamilos b, J. Gershtenson b and T.F. Jones b (” University of Colorado/Kaiser, Denver, CO; b National Jewish Hospital, Denver, CO) Introduction: Chronic fatigue syndrome (CFS) is poorly understood. CFS patients can complain of autonomic disturbances (syncope). An explanation is depression. Therefore, we studied the autonomic nervous system CANS) function in CFS, major depression and control subjects. Objective: We evaluated ANS in 3 groups: CFS ( 12 females, 3 males; aged 39.5 f 5.9), major depression (11 females, I male; aged 42.1 + 3.6) and normal control subjects (12 females; aged 45.1 f 6.0). Methods: CFS subjects were selected based on Centers for Disease Control criteria. Group measurements were compared by Student’s t test using the Tukey-Kramer test. Heart rate (HR) and blood pressure were recorded continuously, recumbent and 30 and 120 set after being tilted to 80” from horizontal. Skin sympathetic response (SSR) was measured at the hand and foot. Results: CFS but not depressed subjects demonstrated a greater mean increase in HR after tilting for 30 set and 120 set than control subjects. The mean latency of the foot SSR in CFS subjects (foot: 2.25 set) was significantly slower than control subjects (foot: 1.50 see) or depressed subjects (foot: I .5 1 set).