OBJECTIVE: The purpose of this study was to obtain an analyzable wave of the antidromic facial nerve response (ADFNR) without interference of the compound muscle action potential (CMAP) at the outpatient clinic setting. BACKGROUND: To evaluate intratemporal facial nerve function with the ADFNR, it is necessary to analyze the waveform of propagating nerve impulses in the temporal bone. However, this small nerve response is easily disturbed by the CMAP, which is simultaneously evoked by electrical stimulation. METHODS: The ADFNR was recorded at the entrance of the external ear canal and simultaneously at the anulus tympanicus. Subtraction between the responses evoked at both sites was performed to eliminate the CMAP. RESULTS: The ADFNR was recorded after subtraction of the response recorded at the entrance of the external ear canal from that at the anulus tympanicus. The normal ADFNR had a triphasic waveform. With the placement of the reference electrode at the entrance of the external ear canal, the responses were similar to the subtracted responses. CONCLUSIONS: We recommend the subtraction method and placement of the reference electrode at the entrance of the external auditory canal to record an analyzable ADFNR and to simplify the recording techniques.
OBJECTIVE: The purpose of this study was to obtain an analyzable wave of the antidromic facial nerve response (ADFNR) without interference of the compound muscle action potential (CMAP) at the outpatient clinic setting. BACKGROUND: To evaluate intratemporal facial nerve function with the ADFNR, it is necessary to analyze the waveform of propagating nerve impulses in the temporal bone. However, this small nerve response is easily disturbed by the CMAP, which is simultaneously evoked by electrical stimulation. METHODS: The ADFNR was recorded at the entrance of the external ear canal and simultaneously at the anulus tympanicus. Subtraction between the responses evoked at both sites was performed to eliminate the CMAP. RESULTS: The ADFNR was recorded after subtraction of the response recorded at the entrance of the external ear canal from that at the anulus tympanicus. The normal ADFNR had a triphasic waveform. With the placement of the reference electrode at the entrance of the external ear canal, the responses were similar to the subtracted responses. CONCLUSIONS: We recommend the subtraction method and placement of the reference electrode at the entrance of the external auditory canal to record an analyzable ADFNR and to simplify the recording techniques.