Optimal recording electrode placement in the lumbrical–interossei comparison study

Measurement of the lumbrical muscle activity of the hand using electromyography supported by the ultrasound imaging technique with string navigation

Although placing surface electrodes on small muscles by palpation is difficult, ultrasound guidance may enable electrode placement on the small muscles. This study aimed to examine whether ultrasound guidance is helpful for placement of electrodes on a small muscle, such as the hand lumbrical muscle. Twelve dominant hands of 12 healthy right-handed adults were included in this study. The first lumbrical muscle belly of the hands was identified using ultrasound guidance with a string navigation technique for placing surface electrodes. This technique was designed to identify the location of the center of the muscle belly under ultrasound imaging using a string. After the electrodes were placed on the muscle belly using this technique, the surface electromyographic signals of the first lumbrical, first dorsal interosseous, and adductor pollicis muscles were recorded. The activity of the lumbrical muscle could be separately measured of the first dorsal interosseous and adductor pollicis muscles. This technique has the potential to enable surface electromyography of small muscles for which placement of surface electrodes by palpation is challenging.

Clinical and electrophysiological evaluation of carpal tunnel syndrome: approach and pitfalls

One of the most common referrals to the electrodiagnostic (EDX) laboratory is to confirm a clinical impression of carpal tunnel syndrome (CTS). The EDX studies are valuable in localizing median nerve abnormalities to the wrist, grading its severity, and excluding other condition that can mimic or coexist with CTS. However, there are many clinical and EDX pitfalls that can lead to misdiagnosis. Careful clinical assessment and attention to technical factors and details of the EDX techniques are fundamental for the quality and accurate interpretation of the study. This review aims to discuss the clinical and the EDX approaches to the diagnosis of CTS with emphasis on the commonly encountered pitfalls.

Efficacy of Optimal Recording Electrode Placement for Median-Lumbrical and Ulnar-Interossei/Lumbrical Distal Latency in the Diagnosis of Carpal Tunnel Syndrome

PURPOSE

This study is to determine the diagnostic utility of optimal recording electrode placement for distal latency comparison of median-second lumbrical and ulnar-interossei/third lumbrical (M2L-UI3L) in carpal tunnel syndrome.

METHODS

Sixty-five hands of control and 75 hands of 62 clinically suspected carpal tunnel syndromes were used for the M2L-UI3L and standard conduction studies. To obtain optimal M2L-UI3L, the recording active electrode (E1) was placed at the midpalm over the third metacarpal bone, whereas the reference electrode (E2) was attached to the palmar digital crease area. Then, median and ulnar nerves were stimulated on the wrist each at 8 cm proximal to E1. M2L-UI3L and standard nerve conduction studies were performed. Sensitivity and specificity of M2L-UI3L were measured in the diagnosis of mild carpal tunnel syndrome.

RESULTS

For statistical analysis, the receiver operating characteristics and Student t-test were used. The area under the receiver operating characteristic curve of M2L-UI3L was 0.993. Diagnostic cutoff value of M2L-UI3L greater than 0.6 milliseconds yields sensitivity of 93% and specificity of 97%. The distal median motor latency to the second lumbrical alone showed the area under the curve of 0.998, and the diagnostic cutoff value greater than 3.4 milliseconds yields sensitivity of 96% and specificity of 100%.

CONCLUSIONS

This technique for M2L-UI3L shows high sensitivity and specificity compared with the previous reports on the diagnosis of carpal tunnel syndrome. Furthermore, the values of median-second lumbrical motor latency alone have higher sensitivity and specificity, comparable with the median sensory conduction study across the wrist segment.

Practical approach to electrodiagnosis of the carpal tunnel syndrome: A review

Despite being the most common entrapment neuropathy and the most common reason for referral to the electromyography (EMG) laboratory, the diagnosis of carpal tunnel syndrome (CTS) continues to be challenging due to a large number of electrodiagnostic (EDX) tests available. We present a flowchart and propose a practical approach to the diagnosis of CTS using the available literature and the American Association of Neuromuscular and Electrodiagnostic Medicine (AANEM) guidelines and the Practice Parameter for Electrodiagnostic Studies in Carpal Tunnel Syndrome.

Second lumbrical and mixed nerve segmental conduction studies in carpal tunnel syndrome

OBJECTIVES

We report the findings of 20 patients with carpal tunnel syndrome (CTS) who had segmental motor studies to the second lumbrical (2L) and mixed nerve action potential (MNAP) across the carpal tunnel.

METHODS

This was a prospective study of 20 patients randomly selected who had clinical and electrophysiologic evidence of CTS using standard techniques. Six CTS patients had studies pre- and post-surgical release.

RESULTS

Mean 2L motor amplitude reduction across the carpal tunnel was 55.19% ± 6.6% in patients (controls = 15.9% ± 9.4%). Mean motor velocity across the carpal tunnel was 23.4 ± 7.05 m/s versus 46.45 ± 6 m/s in controls. Mean reduction of the MNAP amplitudes was 79.0% ± 23% versus 20% ± 15% in controls. The mean MNAP velocity was 12.3 ± 13.1 m/s versus 48.35 ± 5.18 m/s in controls. The 6 surgical cases showed improvement in amplitude reduction and velocity at 2-6 months consistent with preoperative severity.

CONCLUSIONS

These studies show that segmental conduction studies to the 2L and MNAP can demonstrate conduction block that improves with decompression.

Carpal tunnel syndrome in the elderly: nerve conduction parameters

OBJECTIVE: To establish nerve conduction parameters for carpal tunnel syndrome (CTS) electrodiagnosis in the elderly. METHOD: Thirty healthy subjects (65-86 years), 9 male and 21 female, were studied. Routine median and ulnar sensory and motor nerve conduction studies, median mixed palmar latency, comparative latency techniques median to ulnar (sensory, mixed and motor lumbrical-interossei), median to radial (sensory), and combined sensory index (CSI) were performed in both hands. RESULTS: The upper limits of normality (97.5%) were: median sensory distal latency 3.80 ms (14 cm); median motor distal latency 4.30 ms (8 cm); median palmar latency 2.45 ms (8 cm); lumbrical-interossei latency difference 0.60 ms (8 cm); comparative median to radial 0.95 ms (10 cm); comparative median to ulnar 0.95 ms (14 cm); comparative palmar median to ulnar 0.50 ms (8 cm); and CSI 2.20 ms. Sensory and mixed latencies were measured at peak. CONCLUSION: Our results establish new nerve conduction parameters for mild CTS electrodiagnosis in the elderly and will be helpful to reduce the number of false positive cases in this age.

Contribution of reference electrode to the compound muscle action potential

In compound muscle action potential (CMAP) recording, the contribution by the reference electrode is considered to be much smaller than that of the active electrode. We tested this assumption by making quantitative measurements of the signals recorded individually by the active and reference electrodes. In the thenar (median nerve) and extensor digitorum brevis (peroneal nerve) muscles, the reference electrode did contribute less. In the hypothenar muscle (ulnar nerve), however, the signals recorded by active and reference electrodes were of similar amplitude. In tibial nerve conduction studies (NCS), the CMAP from the abductor hallucis (AH) muscle was recorded mainly by the reference electrode; the large-amplitude signal recorded by the reference electrode is attributed to volume-conducted activity from other muscles stimulated during the study. The onset latency of the potential recorded by the active and reference electrodes was similar despite significantly different distances from the stimulating site. Hence, the merits of using anatomic landmarks for defining the distal stimulation site are assessed. When the reference electrode makes a large contribution, the CMAP amplitude may not decrease commensurate with any wasting of the muscle under the active recording electrode, and the need to use another muscle for recording the CMAP for that nerve should be considered.