organophosphate ( op ) and paraquat ( pq ) pesticide ingestion is a serious health problem especially in developing countries , since op compounds were involved in 76% of pesticide poisoning [ 1 , 2 ] and pq self - poisoning has the highest case fatality ( 65% ) for any poisoning in sri lanka .
the two important pathologies behind pq toxicity are the generation of reactive oxygen species ( ros ; superoxide anion , hydrogen peroxide , hydroxyl radical ) and the depletion of nadph which is necessary for normal function .
widespread and robust effects of chlorpyrifos on the genes involved in antioxidant activity have been shown by slotkin et al . .
ros are associated with drugs ( cisplatin , aminoglycosides ) [ 7 , 8 ] and noise - induced [ 9 , 10 ] cochlear pathology .
animal studies showed that pq treatment leads to change in hearing threshold , outer and inner hair cell loss . progressively increasing delay in auditory
event - related potential has been reported in vegetable farmers with long - term exposure to op .
in contrast , kimura et al . reported that there was no statistically significant difference in auditory - evoked responses in farmers who were exposed to various pesticides compared to the controls .
the aim of the study was to identify the effects of deliberate ingestion of op or pq on brain stem auditory - evoked potentials ( baeps ) .
consecutive patients with deliberate self - poisoning with op or pq who were admitted to a secondary and a tertiary care hospital in the southern province of sri lanka were recruited .
the study was approved by the ethical review committee , faculty of medicine , university of ruhuna , sri lanka .
baeps were performed at 1  week ( the first assessment ) and 6  weeks ( the second assessment ) after the exposure .
ingestion of op was confirmed with cholinergic features or patients who were treated at peripheral hospitals with atropine .
pq ingestion was confirmed with positive urine to sodium dithionate test [ 14 , 15 ] .
the control group was recruited from persons accompanying the patients to the tertiary care hospital .
age , gender and occupation - matched healthy volunteers who did not have a history of acute pesticide exposure were recruited .
participants with history of diabetes , neuropathies head injury , and ear infections were excluded from the study .
baep is an electrophysiological method that can be used for neurotoxicity testing of auditory function .
a computer - based neuropack s1 electromyography ( emg)/ep measuring system meb-9400 ( nihon kohden ) was used for the baep .
a piece of cotton moistened with alcohol was used to clean the patient s skin where the electrodes were attached and the skin rubbed with dry gauze to remove any moisture and gel from the skin . recording electrodes ( active and reference ) and grounding electrodes were attached on the patient s head with elefix paste ( fig .  1 ) .
the patient was kept on a chair relaxed with eyes closed . to avoid emg of the neck
, patients were asked not to move their head . to avoid emg of the chin , patient was asked to open his / her mouth slightly .
the hi - cut and the low - cut filters were set to 3  khz and 100  hz , respectively .
the skin  electrode contact impedance was kept below 5  k. the stimulation intensity was 90  db and 1,000 stimulations were averaged .
2 ) [ 16 , 17 ] . anova and post hoc comparison were used for the analysis.fig .
2probable sites of generation of the human baep   electrode placement in baep probable sites of generation of the human baep
there were 70 ( 50 males ) patients recruited following op ingestion and 28 ( 21 males ) patients following pq ingestion .
the mean [ standard deviation ( sd ) ] age of the op and pq patients was 32 ( 12 ) and 29 ( 12 ) years , respectively .
there were 70 controls and their mean ( sd ) age was 33 ( 12 ) years . in op poisoning ,
53/70 came for the second assessment , and in pq poisoning , 18/28 came for the second assessment .
the differences of the mean latency of i  iii , iii  v , and i  v were prolonged in the test group compared to the controls except in right side 1111 difference in the first assessment of the test , right side 1111 and 1v difference in the first and the second assessment in the test group compared to the controls .
none of the differences were statistically significant ( table  1).table 1the mean latency difference of baep in the test and the control groups in op poisoningcontrol group , n  =  70test groupmean differences95% ci1st assessment , n  =  702nd assessment , n  =  53controls vs 1st assessmentcontrols vs 2nd assessment1st assessment vs 2nd assessmentcontrols vs 1st assessmentcontrols vs 2nd assessment1st assessment vs 2nd assessmentright sidei  iii2.2    0.62.1    0.22.1    0.20.070.110.040.04 to 0.10.1 to 0.050.08 to 0.07iii
 v1.8    0.21.9    0.21.8    0.50.020.080.050.04 to 0.090.08 to 0.060.09 to 0.05i  v4.0    0.34.0    0.23.9    0.20.010.030.040.03 to 0.10.1 to 0.060.1 to 0.07left sidei
 iii2.1    0.22.1    0.22.1    0.20.030.030.0050.2 to 0.070.05 to 0.20.2 to 0.1iii  v1.8    0.21.9   
v3.9    0.23.7    0.23.9    0.20.060.030.030.09 to 0.10.08 to 0.10.15 to 0.07 the mean latency difference of baep in the test and the control groups in op poisoning table  2 shows the difference of mean latency of i  iii , iii 
there was no significant difference detected in the test group compared to the controls.table 2the mean latency difference of baep in the test and the control groups in pq poisoningcontrol group , n  =  70test groupmean differences95% ci1st assessment , n  =  282nd assessment , n  =  18controls vs 1st assessmentcontrols vs 2nd assessment1st assessment vs 2nd assessmentcontrols vs 1st assessmentcontrols vs 2nd assessment1st assessment vs 2nd assessmentright sidei 
iii2.2    0.62.1    0.32.1    0.30.090.090.010.4 to 0.20.4 to 0.40.4 to 0.4iii 
v1.8    0.21.9    0.21.8    0.20.020.010.010.1 to 0.10.1 to 0.10.1 to 0.1i
 v4.0    0.33.9    0.33.9    0.30.010.030.010.2 to 0.20.2 to 0.20.2 to 0.2left sidei 
iii2.1    0.22.1    0.22.3    1.30.030.30.30.3 to 0.30.6 to 0.030.6 to 0.1iii  v1.8    0.21.8    0.21.8    0.10.050.010.050.1 to 0.060.1 to 0.10.9 to 0.1i 
v3.9    0.23.9    0.33.9    0.20.010.0020.010.1 to 0.20.2 to 0.10.1 to 0.2 the mean latency difference of baep in the test and the control groups in pq poisoning
the differences of the mean latency of i  iii , iii  v , and i  v were prolonged in the test group compared to the controls except in right side 1111 difference in the first assessment of the test , right side 1111 and 1v difference in the first and the second assessment in the test group compared to the controls .
none of the differences were statistically significant ( table  1).table 1the mean latency difference of baep in the test and the control groups in op poisoningcontrol group , n  =  70test groupmean differences95% ci1st assessment , n  =  702nd assessment , n  =  53controls vs 1st assessmentcontrols vs 2nd assessment1st assessment vs 2nd assessmentcontrols vs 1st assessmentcontrols vs 2nd assessment1st assessment vs 2nd assessmentright sidei  iii2.2    0.62.1    0.22.1    0.20.070.110.040.04 to 0.10.1 to 0.050.08 to 0.07iii 
v1.8    0.21.9    0.21.8    0.50.020.080.050.04 to 0.090.08 to 0.060.09 to 0.05i  v4.0    0.34.0    0.23.9    0.20.010.030.040.03 to 0.10.1 to 0.060.1 to 0.07left sidei 
iii2.1    0.22.1    0.22.1    0.20.030.030.0050.2 to 0.070.05 to 0.20.2 to 0.1iii 
v1.8    0.21.9    0.21.8    0.20.030.0070.020.09 to 0.10.2 to 0.050.07 to 0.1i
 v3.9    0.23.7    0.23.9    0.20.060.030.030.09 to 0.10.08 to 0.10.15 to 0.07 the mean latency difference of baep in the test and the control groups in op poisoning
table  2 shows the difference of mean latency of i  iii , iii  v , and i  v . there was no significant difference detected in the test group compared to the controls.table 2the mean latency difference of baep in the test and the control groups in pq poisoningcontrol group , n  =  70test groupmean differences95% ci1st assessment , n  =  282nd assessment , n  =  18controls vs 1st assessmentcontrols vs 2nd assessment1st assessment vs 2nd assessmentcontrols vs 1st assessmentcontrols vs 2nd assessment1st assessment vs 2nd assessmentright sidei  iii2.2    0.62.1    0.32.1    0.30.090.090.010.4 to 0.20.4 to 0.40.4 to 0.4iii 
v1.8    0.21.9    0.21.8    0.20.020.010.010.1 to 0.10.1 to 0.10.1 to 0.1i 
v4.0    0.33.9    0.33.9    0.30.010.030.010.2 to 0.20.2 to 0.20.2 to 0.2left sidei 
iii2.1    0.22.1    0.22.3    1.30.030.30.30.3 to 0.30.6 to 0.030.6 to 0.1iii 
v1.8    0.21.8    0.21.8    0.10.050.010.050.1 to 0.060.1 to 0.10.9 to 0.1i
 v3.9    0.23.9    0.33.9    0.20.010.0020.010.1 to 0.20.2 to 0.10.1 to 0.2 the mean latency difference of baep in the test and the control groups in pq poisoning
the current study did not show any significant difference in the interpeak latencies of baep in the patients compared to the controls .
the number of the participants in the pq arm was small and this may not be adequate to come to firm conclusions .
the number of participants in the op arm may have not provided adequate power to detect statistical differences .
baep is a sensory - evoked potential used to assess the integrity of the auditory pathway from the eighth nerve to the auditory cortex .
the interpeak latencies ( i  iii , iii  v , and i  v ) of baep provide a straightforward method to roughly localize lesions in the auditory pathway .
animal studies by bielefeld et al . and harris et al . showed shifting of evoked potential threshold and loss of inner and outer hair cells following the application of 10 , 5 , and 3  mm of pq to cochlea through a surgical incision [ 9 , 11 ] .
clerici and yang demonstrated the disruption of generation and transmission of afferent cochlear signals by generation of reactive oxygen species within the perilymphatic space with artificial perilymph and hydrogen peroxide .
even though both op and pq produce reactive oxygen species after ingestion , the concentration of substances reaching the perilymphatic space may not be sufficient to damage the cochlea .
kimura et al . studied the effects of the event - related evoked potentials in tobacco farmers who were exposed to different pesticides including op .
there were no significant lesions in the auditory pathway in op or pq poisoned patients compared to the matched controls .
the generation of reactive oxygen species within the perilymphatic space following the ingestion of op or pq may not be sufficient to cause lesions in the auditory pathway .
further studies with the assessment of auditory threshold in acute op or pq poisoning are needed .
 organophosphate ( op ) and paraquat ( pq ) ingestion is a serious health problem . 
 a common pathology behind op or pq poisoning is the generation of reactive oxygen species ( ros ) which is known to cause ototoxicity . 
 the aim of the study was to identify the effects of deliberate ingestion of op or pq on brain stem auditory - evoked potentials ( baeps ) . 
 consecutive patients with deliberate self - poisoning with op or pq who were admitted to a secondary and a tertiary care hospital in the southern province of sri lanka and matched controls were recruited . 
 baeps were performed at 1  week ( first assessment ) and 6  weeks ( second assessment ) after the exposure . 
 interpeak latencies of i  iii , iii  v , and i  v were measured . 
 there were 70 and 28 patients in the op and pq arms with the mean age of 32    12 and 29    12  years , respectively . 
 there were 70 controls and their mean age was 33    12  years . in op and pq 
 poisoning , 53/70 and 18/28 came for the second assessment , respectively . 
 the interpeak latency was not statistically different in the controls vs the first assessment , controls vs the second assessment , and the first vs the second assessment . 
 there were no significant lesions in the auditory pathway in op or pq poisoned patients . 
 the generation of ros within the perilymphatic space following the ingestion of op or pq may not be sufficient to cause lesions in the auditory pathway . 
 further studies with the assessment of auditory threshold are needed . 
Introduction
Materials and Methods
Results
BAEP in OP Poisoning
BAEP in PQ Poisoning
Discussion
Conclusion