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Neurology India, Vol. 55, No. 4, October-December, 2007, pp. 422 Letter To Editor Variability of the palmar cutaneous branch median nerve sensory nerve action potential with carpal tunnel syndrome Wilder-Smith E. P., Aravinda T. Kannan* Neurology, National University Singapore, 5 Lower Kent Ridge Road, 119074 Singapore,*Neurology Diagnostic Laboratory, National University Hospital, 5 Lower Kent Ridge Road, 119074 Singapore Date of Acceptance: 24-Apr-2007 Code Number: ni07128 Sir, The palmar cutaneous median branch (PCBm) sensory nerve action potential (SNAP) can be useful in investigating hand sensory symptoms. [1],[2] The PCBm SNAP when recorded using an antidromic technique yields two negative peaks followed by the motor potential [Figure 1]a. The first negative peak represents the PCBm SNAP; the second peak a far field potential from transcarpally mediated hand sensory nerve fibers traveling to the thumb. [3] The second peak is a consequence of not being able to selectively stimulate the PCBm. The first and second peak are in close proximity with the first having the appearance of a shoulder sticking out from a hill. It is important to be cognizant of how this shape alters with median nerve entrapment in carpal tunnel syndrome (CTS). [4] When the transcarpal median sensory fibers are solely affected in CTS, this results in the first and second peaks separating out. With increasing pathology of transcarpal fibers [Figure 1]b, the degree of separation increases and in severe CTS can result in a lone SNAP from the PCBm [Figure 1]c. References
Copyright 2007 - Neurology India The following images related to this document are available:Photo images[ni07128f1b.jpg] [ni07128f1c.jpg] [ni07128f1a.jpg] |
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