Elsevier

Clinical Neurophysiology

Volume 110, Issue 8, 1 August 1999, Pages 1471-1474
Clinical Neurophysiology

Exclusive electrophysiological motor involvement in carpal tunnel syndrome

https://doi.org/10.1016/S1388-2457(99)00071-1Get rights and content

Abstract

Objective: To define the frequency of exclusive electrophysiological motor involvement in carpal tunnel syndrome (CTS).

Methods: We reviewed the electrophysiological studies of 2727 consecutive hands with typical symptoms and signs of CTS and at least one abnormal test of the following: median distal motor latency (DML), digit two sensory conduction velocity (D2-SCV), segmental D2-SCV from wrist to palm, median-ulnar sensory latency difference from ring finger stimulation.

Results: Thirty-one hands (1.2%) had prolonged median DML (>4.4 ms) with normal SCV (>48 m/s). In 17 of 31 hands, segmental D2-SCV from wrist to palm or median-ulnar latency difference from ring finger stimulation were also performed with normal results in 8 hands, demonstrating a true exclusive electrophysiological motor involvement.

Conclusions: In CTS, exclusive electrophysiological involvement of median motor fibers is rare. It may be related to preferential compression of the intraneural motor fascicles clumped superficially in the most volar-radial nerve quadrant or, more probably, to the fact that the recurrent thenar branch may exit the carpal tunnel through a separate ligamentous tunnel within the transverse carpal ligament where it may be preferentially or selectively compressed.

Introduction

Median nerve entrapment in the wrist to palm segment produces a clinical condition known as carpal tunnel syndrome (CTS) which is the most common entrapment neuropathy (Stevens, 1987). It is generally accepted that median sensory conductions are more sensitive than motor conductions in the electrodiagnosis of CTS (Stevens, 1987, AAEM, 1993). There are 3 studies, employing segmentary techniques, which show that motor conduction velocity may be selectively effected in CTS and that segmental motor conduction may be even more frequently abnormal than sensory conduction (Kimura, 1979, White et al., 1988, Di Guglielmo et al., 1997). However, motor segmental studies have a number of pitfalls and technical problems, and have been considered unreliable and time consuming (Ross and Kimura, 1995).

The aim of this study is to investigate the frequency of exclusive electrophysiological motor involvement in a large population of hands with CTS.

Section snippets

Materials and methods

We reviewed the EMG reports (including history and pertinent neurological examination) of the studies performed in an 8 year period for all patients with signs and symptoms characteristic of CTS and with at least one abnormal electrophysiological test of the following: prolonged distal motor latency (DML), abnormal digit two median sensory conduction velocity (D2-SCV), abnormal median to ulnar sensory comparative test, or abnormal wrist to palm sensory segmentary test.

For median DML recording,

Results

In the 8 year period considered, there were 2727 consecutive hands with typical symptoms and signs of CTS and at least one abnormal electrophysiological test. Thirty-one hands (1.2%) presented prolonged distal motor latency (>4.4 ms) and normal sensory conduction velocities (>48 m/s) either recorded orthodromically (16 hands) or antidromically (15 hands) (Table 1). Fig. 1 reports the most significant example. In 11 of these 31 hands, we also performed a segmental SCV from wrist to palm which

Discussion

It is generally stated that sensory nerve testing is more sensitive than motor nerve testing in CTS (Stevens, 1987, AAEM, 1993). Using the inching technique, it has been found that motor conductions across the wrist may be selectively affected (Kimura, 1979) and even more sensitive than inching of sensory fibers (White et al., 1988). However, inching of motor fibers of the median nerve is technically difficult because of a lack of consistent latency changes in the sequential 1 cm steps and the

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