Medial thenar recording in normal subjects and carpal tunnel syndrome.
OBJECTIVE
Since little is known about the involvement of median nerve fibres to the medial thenar eminence in CTS, we determine the consistency of a motor response derived from a medial thenar motor (MTM) site. We then compare sensitivity and specificity of this novel site with other nerve conduction parameters in supporting a diagnosis of CTS.


METHODS
The motor responses over the MTM with ulnar and median stimulation were determined in healthy subjects and patients with CTS. Sensitivity and specificity of 4 motor techniques (Abductor Pollicis Brevis (APB) and median MTM latency, 2nd Lumbricales to Interossei latency difference (2-LINT), APB to Adductor Digiti Minimi (ADM) latency difference, median MTM to ulnar MTM latency difference) and the median sensory distal latency in confirming CTS were calculated using the ROC method.


RESULTS
132 hands (68 CTS, 64 controls) were examined. All but one median and ulnar nerve stimulation (both in patients with CTS) resulted in negative MTM compound muscle action potentials. Sensitivity and specificity in diagnosing CTS were 79/97% (APB) 90/98% (median MTM latency), 88/97% (2-LINT), 85/97% (APB to ADM latency difference) and 75/95% (median MTM to ulnar MTM latency difference). Median sensory latency showed 89% sensitivity and 97% specificity.


CONCLUSIONS
Median and ulnar stimulation results in consistent motor responses at the medial thenar site. Median distal motor latency to MTM is frequently abnormal in CTS showing similar sensitivity and specificity to 2-LINT and median distal sensory latency.


CONCLUSIONS
The MTM site shows consistent responses to both median and ulnar stimulation. MTM distal latency can be considered a useful site for supporting a diagnosis of CTS.
Wilder Smith
Einar P V
EP
Neurology, Yong Loo Lin School of Medicine, National University Singapore, Singapore. mdcwse@nus.edu.sg
Chan
Y H
YH
Kannan
T Aravinda
TA
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002349:Carpal Tunnel Syndrome / Q000503:physiopathology*; D003430:Cross-Sectional Studies; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography / Q000379:methods; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000503:physiopathology*; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000503:physiopathology; D009431:Neural Conduction / Q000502:physiology*; D011446:Prospective Studies; D012372:ROC Curve; D011930:Reaction Time / Q000502:physiology; D012680:Sensitivity and Specificity; D014459:Ulnar Nerve / Q000503:physiopathology*