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Frequency‐dependent conduction block in carpal tunnel syndrome
Author(s) -
Watson Bradley V.,
Brown William F.,
Doherty Timothy J.
Publication year - 2006
Publication title -
muscle and nerve
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.025
H-Index - 145
eISSN - 1097-4598
pISSN - 0148-639X
DOI - 10.1002/mus.20513
Subject(s) - carpal tunnel syndrome , median nerve , medicine , stimulation , motor nerve , nerve conduction velocity , entrapment neuropathy , carpal tunnel , wrist , lesion , sensory nerve , sensory system , anatomy , neuroscience , surgery , psychology
Frequency‐dependent conduction block (FDB) across segments of demyelination in response to high‐frequency nerve stimulation has been well demonstrated in animals and has been explored in humans. However, attempts to demonstrate this phenomenon in sensory fibers involved in entrapment neuropathies have been unsuccessful. Therefore, we investigated the effects of high‐frequency nerve stimulation in the median motor nerve in patients with carpal tunnel syndrome (CTS) with moderate to severely increased distal motor terminal latencies (MTL). As a group, the mean decrease in negative peak amplitude (npAmp) during 20 stimuli at 30‐H Z frequency was significantly greater in CTS subjects (−11.3%) than in controls (+7.9%). The degree of FDB was greater when MTL was more prolonged (i.e., −4.9% at 5.0 ms and −25.3% at 9.4 ms) and FDB was more pronounced at higher stimulation frequencies (20 and 30 H Z ). Our results suggest that the safety margin for impulse transmission is impaired in the motor axons of patients with a focal demyelinating lesion. These findings may correlate with the observation of weakness in the absence of conduction block in patients with entrapment neuropathies. Muscle Nerve, 2006