bell palsy is a neuropathy of the peripheral seventh cranial nerve , usually resulting from traumatic , compressive , infective , inflammatory , or metabolic abnormalities . however , in many cases no etiology is identified , and the eventual diagnosis is idiopathic . its annual incidence was from 0.011% to 0.040% . for many patients , the questions that whether their facial function will return to normal one day and how long this is going to take are mostly concerned about . evaluation of the prognosis of bell palsy is useful for counseling of patients and guiding further management . since 1970s , prognostication has been based mainly on various electrophysiologic tests [ 310 ] , such as electromyography ( emg ) , electroneurography ( enog ) , maximal nerve excitability testing , and facial motor nerve conduction ( mnc ) testing . however , the electrophysiologic tests above are facial nerve orthodromic evoked potentials . abnormal findings from these tests are obtained after the degeneration - process extends to the extratemporal segment of the facial nerve with 1- to 2-week delay . decompression surgery can not play a part in retrieve and prevent degeneration after most of facial nerve function has already degenerated . therefore , if we want to detect nerve degeneration and to predict facial function recovery during its early stages , it is necessary to use a test that can diagnose degeneration within 1 week after the onset of paralysis . the facial nerve antidromic evoked potentials ( fnaep ) was first described by bumm et al . in 1974 . nakatani et al .   had used fnaep to value the prognosis of facial paralysis . however , the correlativity of intra- or extra - temporal facial nerve was not pointed out , and the quantitative analysis was not obtained . the purpose of this study was to evaluate the prognostic use of fnaep quantitatively within three days in a successive series of patients with bell palsy associated with or without taste disorder at a university - based center . from january to december 2010 , there were 46 patients with unilateral bell palsy in a single center ( department of oral and maxillofacial surgery , ninth people 's hospital , shanghai jiao tong university school of medicine ) . out of the patients , the duration from onset to treatment was from 1 to 3 days ( mean , 2.9  d ) . the right side was involved in 24 patients , and the left was in 22 patients . the patients were divided into two groups : 26 patients with taste disorder ( group 1 ) and 20 patients without taste disorder ( group 2 ) . interventions given to the patients were local physical therapy and pharmacotherapy , such as high - dose prednisone within 3 days after onset , besides methylcobalamin and vasodilators in 1 month after onset . forty - three patients ( 93.5% ) were followed up with the average follow - up period of 4.8 months ( ranged from 1 to 9 months ) . the initial and final facial nerve function was reported using the stennert system   ( table 1 ) . clinical recovery rate ( crr ) = ( 200  follow - up score)/200  100% . the recovery outcomes of facial nerve function was graded as follow : excellent ( crr 80% ) , good ( 50%  crr < 80% ) , and poor ( crr < 50% ) .   the fnaep device ( viking quset , nicolet corp , usa ) includes bipolar stimulators , discoid electrodes , needle electrodes , and monitor . the patients were examined by fnaep for the first presentation at the clinic . before the test , the cerumen of external auditory canal was cleared and the degrease cream was embrocated at the external auditory canal and the earlobe . two discoid electrodes with a little conductive paste were located at the posterior wall of the external auditory canal ( recording electrode ) and the earlobe ( reference electrode ) , respectively ( figure 1 ) . fnaep was performed first on the asymptomatic side and then repeated on the symptomatic side . the superficial projection of the homolateral stylomastoid foramen was stimulated by the bipolar stimulator with band - pass filtering of 210000  hz and stimulus intensity of 30  ma . the results of both sides were recorded ( figure 2 ) . the amplitude difference ( ad ) and latency difference ( ld ) between symptomatic side and asymptomatic side were calculated according to the following formula : ( 1)ad=(amplitude  of  symptomatic  sideamplitude  of  asymptomatic  side)amplitude of  asymptomatic  side100%,ld=  ( latency  of  symptomatic  sidelatency  of  asymptomatic  side)latency  of  asymptomatic  side100% . statistical analysis of the data , presented as means  sd , was performed using sas 8.1 software . statistical difference was established when probability was 0.01 < p < 0.05 . no statistical difference was established when probability was p > 0.05 . during the period of followup , the mean crr was 61.63%   18.90% ( ranged from 30% to 90% ) in group 1 . there were 6 cases ( 26.09% ) with excellent result , 12 cases ( 52.13% ) with good result , and 5 cases ( 21.74% ) with poor result . in group 2 , the mean crr was 75.50% ( ranged from 50% to 100% ) . there were 12(60% ) cases with excellent result , 8 cases ( 40% ) with good result , and no cases with poor result ( figure 3 ) . there was a statistical difference between the two groups ( p = 0.0189 < 0.05 ) . for the patients with excellent result , mean  sd of ad and ld were 6.96%   12.66% and 0.54%   7.23% . for the patients with good result , mean  sd of ad and ld were 27.67%   27.70% and 12.11%   7.23% . for the patients with poor result , mean  sd of ad and ld were 66.05%   31.76% and 23.36%   1.61% ( figure 4 ) . there was a significant difference of ad between the  excellent  group and the  poor  group ( p = 0.0014 < 0.01 ) , and there were statistical differences between the  excellent  group and the  good  group ( p = 0.010 < 0.05 ) and between the  good  group and the  poor  group ( p = 0.0287 < 0.05 ) . there was a statistical difference of ld between the  excellent  group and the  poor  group ( p = 0.0124 < 0.05 ) , and there was a significant difference between the  excellent  group and the  good  group ( p = 0.0041 < 0.01 ) and no significant difference between the  good  group and the  poor  group ( p = 0.2041 > 0.05 ) . the majority of the drug treatments for bell palsy at the early stage are effective . nevertheless , those patients who are not completely improved by medication deserved facial nerve decompression surgery . accordingly , for almost all the patients , the questions that whether their facial function will return to normal and the facial nerve decompression surgery is necessary or not and when to take are mostly concerned about . evaluation of the prognosis of bell palsy is useful for counseling of patients and guiding further management . although electrical tests were already introduced to predict the prognosis of bell palsy in the 1970s , they were still controversial . as the facial nerve is stimulated out of the temporal bone in these tests , the evaluation of nerve function is limited to the extratemporal facial nerve . there is general agreement that abnormal findings from these tests are obtained after the degeneration process extends to the extratemporal segment of the facial nerve with 1-week delay [ 310 ] . we are not able to obtain information about facial nerve damage in the temporal bone at the early stage of facial palsy with extratemporal electrodiagnostic tests , such as mnc , emg , and enog . decompression surgery can not play a part in retrieve and prevent degeneration after most of the nerve function has already degenerated . to raise therapeutic effect , we should precisely evaluate the poor outcome that patients who suffered from bell palsy are possible to gain before completion of facial nerve degeneration . with regards to this , it is necessary to use a test that can diagnose degeneration within 1 week after the onset of paralysis . the fnaep is the only method of monitoring a nerve action potential , among all the electrodiagnostic tests of the facial nerve [ 310 ] . other than traditional electrophysiological testing , fnaep stimulated the extratemporal segment of facial nerve and was recorded at the intratemporal segment . if the lesion occurred , its amplitude would cause abnormal changes , which provided strong evidence of intratemporal location . the waveform of this potential reaction was more constant and had obvious time locked relationship with the stimulus . tashima et al .   reported that the recorder located at the posterior wall of external auditory meatus could represent the vertical portion of facial nerve , and the characteristic waveform of the fnaep was also revealed in animal experiments . taste disorder in facial paralysis implies the lesion of vertical portion of facial nerve intratemporally . in this study , the duration from onset to test was from 1 to 3 days , and the mean of ad of group 1 and group 2 were 33.88% and 5.47% . it was confirmed that fnaep can prompt facial nerve damage in the temporal bone , and recorder at the posterior wall of external auditory meatus was appropriate . with the preliminary assessment , we found that the relativity between fnaep amplitude and the clinical results was closer than that between latency and the clinical results , and the symptom of taste disorder would occur if ad of fnaep was lower than 30% . it was important to evaluate the nerve function of intratemporal segment at the early stage . fnaep was the best choice to evaluate and predict the facial nerve function at the early stage . comparison of fnaep between symptomatic side and asymptomatic side showed that the clinical results were good when only amplitude was temporarily discrete , and the results were poor while amplitude obviously reduced . , it was preliminary considered that when ad between symptomatic side and asymptomatic side was ranged from 0 to 20% , the predicted result was excellent ; when it was ranged from 20% to 50% , the predicted result was good and when it was ranged from 50% to 100% , the predicted result was poor ; facial nerve decompression may be considered .
to analyze the value of facial nerve antidromic evoked potentials ( fnaeps ) in predicting recovery from bell palsy 
 . study design . 
 retrospective study using electrodiagnostic data and medical chart review . methods . a series of 46 patients with 
 unilateral bell palsy treated were included . 
 according to taste test , 26 cases were associated with taste disorder ( group 1 ) and 20 cases were not ( group 2 ) . 
 facial function was established clinically by the stennert system after monthly follow - up . 
 the result was evaluated with clinical recovery rate ( crr ) and fnaep . 
 fnaeps were recorded at the posterior wall of the external auditory meatus of both sides . 
 results . 
 mean crr of group 1 and group 2 was 61.63% and 75.50% . 
 we discovered a statistical difference between two groups and also in the amplitude difference ( ad ) of fnaep . 
 mean  sd of ad was 6.96%  12.66% in patients with excellent result , 27.67%  27.70% with good result , and 66.05%  31.76% with poor result . conclusions . 
 fnaep should be monitored in patients with intratemporal facial palsy at the early stage . 
 fnaep at posterior wall of external auditory meatus was sensitive to detect signs of taste disorder . 
 there was close relativity between fnaeps and facial nerve recovery .