Lumbrical and interossei recording in carpal tunnel syndrome

Electrodiagnosis of Common Mononeuropathies: Median, Ulnar, and Fibular (Peroneal) Neuropathies

This article addresses common mononeuropathies seen in the electrodiagnostic laboratory. The most common mononeuropathies-median neuropathy at the wrist (carpal tunnel syndrome), ulnar neuropathy at the elbow, and fibular (peroneal) neuropathy at the fibular head-are reviewed. The causes, clinical presentations, approached to the electrodiagnostic studies (including nerve conduction studies and needle electromyography), and the typical findings are discussed.

A new median motor test: comparison with conventional motor studies in carpal tunnel syndrome

INTRODUCTION

Carpal tunnel syndrome (CTS) is the most commonly operated of entrapment peripheral neuropathies, and its surgical outcome largely depends on the underlying mechanism involved. Early identification of CTS is essential because it is associated with a better prognosis.

AIM

To identify CTS at an earlier stage and hence improve the potential future outcome, the authors propose incorporating a new method of using the second lumbricalis (2L-MC) to register the nerve conduction.

METHODS

We prospectively evaluated 121 of 216 patients with confirmed carpal tunnel syndrome and 49 cases from 25 healthy subjects. According to the accepted criteria of Stevens, we divided our study into two groups of mild CTS and moderate CTS, respectively. Following our proposed method, we stimulated the palm, distal forearm, and elbow and measuring the difference in latency between the second lumbricalis and the second interosseous, in addition to the conventional neurophysiologic assessments.

RESULTS

Seventeen of 109 (15.6%) hands showed a significant difference in latency using 2L-MC within the mild CTS group, while only 4 of 107 (3.7%) within the moderate CTS group remained undiagnosed using this method. In the mild CTS group, motor involvement was only shown to be slightly more sensitive when compared with 2LI-DML.

DISCUSSION

Adding the proposed test to the conventional studies of CTS in our cases presented showed a 14% increased sensitivity in detecting motor dysfunction when compared with conventional studies alone. Therefore, this new 2L-MC study represents a useful technique for assessing early motor involvement in CTS and would only add a few extra minutes to the standard diagnostic procedures. To conclude, we propose that incorporating this study as part of the standard assessment of CTS is given further consideration.

Optimal recording electrode placement in the lumbrical–interossei comparison study

The lumbrical-interossei comparison study is commonly employed in the electrodiagnosis of carpal tunnel syndrome. Placement of the recording electrodes relies on anatomic landmarks as the muscles being recorded cannot be seen or palpated. To determine the optimal active electrode location, 15 controls and 5 patients were studied using a grid of 12 electrodes placed over the lateral palm. Amplitudes, rise-times, and latencies of the responses at each location were measured. The lowest control latency difference was located in the lateral mid-proximal palm (mean 0 ms, upper range of 0.5 ms). This location also had the highest lumbrical amplitude and rise-time. More distal in the palm, the mean latency difference increased to 0.5 ms with an upper range of 0.9 ms. When performing the lumbrical-interossei comparison study, it is essential to place the active recording electrode in the optimal location. Failure to do so will result in an increased number of false-positive studies.

Test of a new technique for the diagnosis of carpal tunnel syndrome

Several new techniques for carpal tunnel syndrome diagnosis have been developed in the last few years. This work tests a technique that compares the distal motor latency of the median nerve to the second lumbrical muscle (2L) with the distal motor latency of the ulnar nerve to the interossei muscle (INT). Results from 40 normal hands give the superior limit of the normal difference (2L-INT) as 0. 26 ms (&xmacr;+3 SD). In 55 hands with different levels of carpal tunnel syndrome, this new technique was more sensitive and accurate than the conventional test which uses the distal motor latency of the median nerve to the abductor pollicis brevis muscle (APB), especially in the less severe cases. With the absence of the compound muscle action potentials of the APB muscle caused by severe thenar atrophy, it is much easier to obtain the potential from the 2L muscle. We concluded that this is a sensitive, simple, rapid, and non-invasive new technique, and therefore, it should be incorporated as part of the routine ENMG procedures for carpal tunnel syndrome diagnosis.

AAEM minimonograph #26: the electrodiagnosis of carpal tunnel syndrome. American Association of Electrodiagnostic Medicine

The electrodiagnosis of carpal tunnel syndrome (CTS) is reviewed, including discussions of old and new techniques of motor and sensory nerve conduction, anomalous innervation, and needle electrode examination. A variety of sensitive nerve conduction studies (NCSs) are available for the evaluation of a patient with suspected CTS. For any particular patient, the NCS method chosen by the clinical neurophysiologist may vary for a number of reasons, including the severity of the deficit and the presence of superimposed conditions.

Lumbrical-interosseous latency comparison in the diagnosis of carpal tunnel syndrome

We examined 66 hands referred with suspected carpal tunnel syndrome (CTS) using the second lumbrical-interosseous distal motor latency difference (2LI-DML) as well as standard tests: Forty-nine cases of CTS were diagnosed by the standard tests, 48 of whom had an abnormal median-ulnar palmar velocity comparison and 48 an abnormal 2LI-DML. The results of these 2 tests were closely correlated. The 2LI-DML supported the diagnosis of CTS in all cases except one, where the result was borderline. In one suspected case the 2LI-DML was the only abnormality. In 9 severe cases no median palmar responses could be obtained but an abnormal 2LI-DML was found. We conclude that the 2LI-DML is as sensitive as the palmar comparison and thus will support the diagnosis of CTS made by standard tests by providing an additional abnormality but that its routine use is unlikely to increase the diagnostic yield. Its value therefore may be in mild cases where the median-ulnar palmar comparison is normal or equivocal and in severe cases where standard test responses are unobtainable. It has also proved useful as a quick and simple screening test for CTS on the asymptomatic side.