Sensory extension of the musculocutaneous nerve (lateral antebrachial cutaneous branch, LACB) is injured seperately in rare and its clinical usability has been ignored at most. One original case is reported here. Twentysix year-old male visited EMG laboratory, complaining the paresthesia, numbness and hyperalgesia on left lateral antebrachial area after electrical burn on left Erb's point and near bicipital tenomuscular junction of the elbow. His sensory conduction of left musculocutaneous nerve (MCN) was not responsive and its somatosensory evoked potential was weak (much low amplitude) but relatively spared initial peak latency, and other nerve conductions including musculocutaneous motor nerve were within normal limit. In follow-up study 7 month later, symptoms on left forearm, were normalized nearly but no specific change in the peripheral conduction was seen in left LACB. Only one change in electrodiagnostic study was visible in somatosensory evoked potential (SEP) of left LACB. Amplitudes in left LACB SEP became higher and more prominant by still low. It was concluded that the sensory extension of left musculoctaneous nerve was injured isolatedly in condition of intact motor nerve innervating brachial muscles an its injury was severe axonotmesis combined with secondary demyelination near bicipital tenomuscular junction of the elbow by electric burn. Sensory branch of MCN arising from C5 and C6 roots innervate C6 dermatomal area and we tried its SEP, not reported until now, and present its clinical usability. And so we think that sensory branch of MCN may be useful in cervical radiculopathy and brachial plexopathy because of the benefits that its SEP is possible to check the sensory root of C6 and/or C5 and its peripheral conduction study is easer, more accurate and not discomfortable than motor. Sensory branch of the musculocutaneous nerve may be more available clinically than its present utility.
