Ann Rehabil Med.  2016 Feb;40(1):50-55. 10.5535/arm.2016.40.1.50.

Diagnostic Value of the Second Lumbrical-Interosseous Distal Motor Latency Comparison Test in Severe Carpal Tunnel Syndrome

• Lee S
• Kim D
• Cho HM
• Nam HS
• Park DS

• KMID: 2155165
• DOI: http://doi.org/10.5535/arm.2016.40.1.50

Abstract

OBJECTIVE
To examine the usefulness of the second lumbrical-interosseous (2L-INT) distal motor latency (DML) comparison test in localizing median neuropathy to the wrist in patients with absent median sensory and motor response in routine nerve conduction studies.
METHODS
Electrodiagnostic results from 1,705 hands of patients with carpal tunnel syndrome (CTS) symptoms were reviewed retrospectively. All subjects were evaluated using routine nerve conduction studies: median sensory conduction recorded from digits 1 to 4, motor conduction from the abductor pollicis brevis muscle, and the 2L-INT DML comparison test.
RESULTS
Four hundred and one hands from a total of 1,705 were classified as having severe CTS. Among the severe CTS group, 56 hands (14.0%) showed absent median sensory and motor response in a routine nerve conduction study, and, of those hands, 42 (75.0%) showed an abnormal 2L-INT response.
CONCLUSION
The 2L-INT DML comparison test proved to be a valuable electrodiagnostic technique in localizing median mononeuropathy at the wrist, even in the most severe CTS patients.

Keyword

Carpal tunnel syndrome; Nerve conduction; Second lumbrical-interosseous distal motor latency comparison test

MeSH Terms

Carpal Tunnel Syndrome*
Hand
Humans
Median Neuropathy
Mononeuropathies
Neural Conduction
Retrospective Studies
Wrist

Figure

• 

  Fig. 1 Recording and stimulation site of 2L (A) and INT (B). 'A' is active electrode, 'R' reference electrode, and 'G' ground electrode. 2L, second lumbrical; INT, interosseous.

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  Fig. 2 The second lumbrical-interosseous distal motor latency comparison test showing (A) normal latency difference (0.2 ms) and (B) prolonged latency difference (2.1 ms).

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  Fig. 3 Flowchart defining the extremely severe group. The whole experimental group was first classified according to Padua's neurophysiologic staging of CTS. Among the severe CTS group (401 hands), the extremely severe group was sorted by those whose median SNAP and CMAP were absent (56 hands). Forty-two hands in the extremely severe group showed abnormal 2L-INT DML comparison and 14 hands showed no response in 2L. CTS, carpal tunnel syndrome; SNAP, sensory nerve action potential; CMAP, compound muscle action potential; 2L, second lumbrical; INT, interosseous; DML, distal motor latency.

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