Audiological assessment in organophosphorous poisoning

INTRODUCTION

Organophosphate (OP) poisoning is a serious problem especially among rural population (either by farmers or traders of insecticides). It is an occupational hazard. Especially among farmers, it is a social problem. Relation between deliberate OP poisoning and psychiatric illness has been demonstrated earlier.¹ Pesticide ingestion is one of the leading methods of suicide with estimated around 3 million cases, resulting in excess of 250,000 deaths.²

Emotional stress has been the most common cause of deliberate self-poisoning in young adults. Agricultural pesticides are the most commonly substances used for self-poisoning.^3,4 OP compounds are involved in 76% of pesticide poisoning especially in the developing countries like India.⁵ Their neuro-toxic nature can cause hearing impairment. A case report has shown permanent, bilateral hearing loss due to acute OP poisoning.⁶

Hearing loss imposes socioeconomic problems like communication difficulties, possible job loss, and stigma. Hearing loss may also increase the risk of occupational injury because of inability to hear warning signals or shouts. Several recent articles have suggested that non-poisoned pesticide applicators exposed to OPs or pyrethroids may also sustain hearing loss.^7-9A case report suggested bilateral sudden deafness due to combined poisoning of malathion and methoxychlor.¹⁰ It has been suggested that OP poisoning may result in oto- and neurotoxicity.¹¹

There have been a few studies on audiological assessment in patients with OP poisoning. In Indian settings, especially in Himachal Pradesh, no such study has been conducted so far. The present study was planned to prospective analyze the auditory functions in the patients diagnosed with OP poisoning at Department of Otorhinolaryngology-Head and Neck Surgery, IGMC Shimla.

METHODS

A total of 26 patients (age <50 years) of OP poisoning over a period of one year from July 2016 to June 2017 were included in the study following ethical approval from Institute Ethics Committee. The study was conducted at Department of Otorhinolaryngology - Head and Neck Surgery, IGMC Shimla. The patients who had a history of hearing loss, middle or inner ear disease and any chronic medical illness resulting in hearing impairment were excluded from the study. Twenty-five healthy subjects served as control.

Each of the subjects was subjected to brainstem evoked response audiometry (BERA) examination. Patient having consumed OP were subjected to BERA analysis. This test was carried out in the supine position, using interacoustics EPIC PLUS systems. Absolute latencies of wave I, III, and wave V and interpeak latencies of wave I-III, I-V, and III-V were measured in milliseconds. The subjects have explained the procedure and test was conducted in the supine position. The skin over the forehead, mastoid, and vertex was prepared by cleaning with spirit. Silver disc electrodes were attached to a specific site. Earphones were adjusted to patient’s ears and recording was made with interacoustics EPIC PLUS system. The stimulus was given at a rate of 11.7 Chrip per seconds. The intensity level of chrip was at 90 dBnHL. 4000 sweeps was taken and frequency band filter was set at 300-3000 Hz.

Data were presented as mean±SD, frequency, or percentages as applicable. Categorical variables were analyzed by Chi-square test. Continuous variables were differentiated by using student t-test. Paired t-test was used to compare second assessment analysis among continuous variables. P<0.05 was considered significant. The analysis was performed using SPSS trial version 21.

RESULTS

We did not observe any significant difference (P=0.802) in mean age of cases (28.46±9.33) when compared with controls (29.05±7.26). 50% of the patients with OP poisoning were aged between 20-29 years. Male outnumbered females in the patients (M:F- 17:9) as well as controls (M:F- 17:8).

On BERA analysis, we found that only absolute wave-V latency (ms) was statistically significantly prolonged in cases when compared with controls in both right (0.035) as well as left ears (0.048). No significant change was observed in absolute wave I and II latency in the patients when compared with controls in both ears (Figure 1).We found no statistical significant difference in interpeak wave I-III, III-V, I-V latency of both ears in cases when compared with controls (Figure 2).

*5 patients did not visit for follow-up.

*5 patients did not visit for follow-up.

On second assessment after six week in the patients, we observed a statistical significant decrease in absolute wave III and V latency, and interpeak I-III interval in right ear when compared with wave latency at first assessment (Table 1). In left ear on second assessment, when compared with wave latency at first assessment a significant decrease in absolute wave I, III, and V latency was observed in the patients (Table 2).

We also observed that there was no significant difference in absolute wave I, III, and V latency, and interpeak interval of I-III, III-V, and I-V between ICU and non ICU patients in right (Table 3) and left ears (Table 4).

DISCUSSION

In the present study, we observed that the most of the patients with OP poisoning were aged 20-29 years and 68% of the patients were males. In Himachal Pradesh, economy is agriculture-based and the most of the patients were farmers. 20-29 year age-group is a beginner age to practice farming in the fields where OP poisoning may occur due to easy availability. Our results have been supported by previous investigators who observed that male are more prone to suffer from OP poisoning than females.^12,13

Our study found that there was a significant delay in absolute latency in wave V for right and left ear in cases when compared with controls. However, no significant difference was observed in wave I and III. On second assessment, inter-peak wave latency and absolute latency compared with a first assessment, there was a significant improvement in a delay in absolute latency in right ear in wave III and V, left ear in wave I, III and V. Also significant improvement in interpeak wave latency between I-III in right ear was observed.

This finding also supported by Jaisinghe et al who observed there was a non-significant prolongation of interpeak wave latency in between I –III, III- V and I-V in the test group compared to control group.¹³ Murthy et al studied the effect of OP on the auditory pathway in 100 patients with OP poisoning.¹¹ They found that 56% of the patients had prolonged interpeak latency in the right ear and 68% had prolonged interpeak latency in the left ear. Considering individual waves, in wave-I, 34% of the ears had prolonged absolute latency. In wave-III, 28% of the ears had prolonged absolute latency. In wave-V, 34% of the ears had prolonged absolute latency.

In our study, there was no significant difference in wave latency in patients with respiratory failure (ICU) and non-respiratory failure i.e. non ICU cases. However, Murthy et al found prolonged absolute latency of wave I, III and V and prolonged interpeak wave latency in both ears in respiratory and non-respiratory failure cases.¹¹ We also compared the effect of organophosphate toxicity on BERA with the study of Soni et al on BERA changes in bilirubin toxicity.¹⁴ They found that 10%, 13.3%, and 13.3% cases had prolonged absolute wave I, III, and V latency respectively. However, in our study, there was an increase in absolute latency of the only wave V was observed.

We also compared the results with drug-induced toxicity. Gurkov et al compared ototoxicity, tolerability, and efficacy of artemisinin-based combination therapy with that of quinine and atovaquone/proguanil in the treatment of uncomplicated falciparum malaria in a randomized controlled trial.¹⁵ There was no permanent drug-related latency prolongation in the patients with Artemether-Lumefantrine. In our study, we also observed an improvement in wave latency on follow up.

Our study results are also consistent with the drug-abuse ototoxicity studies. Weich et al suggested that with time there was an increase in absolute and interpeak wave latencies; however, the prolongation was not significant; which was consistent with our study.¹⁶ They also concluded that hearing loss is related to drug abuse; however, duration of the drug does not significantly affect the hearing loss as shown by no significant difference in absolute and interpeak latencies. Garg et al found the statistical difference of absolute latencies of waves of brainstem auditory evoked potentials (I, II, III, IV, V) of the right ear between drug abusers and controls. They also found that the difference in interpeak latency I-III was statistically highly significant, and the difference in interpeak latency I-V and III-V was statistically significant.¹⁷ In our study, prolongation of absolute latencies of wave V was observed in both the ears.

CONCLUSION

Our study showed that organophosphate may affect entire neural auditory pathway. We observed that OP poisoning may play an important role in altered auditory response in the population which improved with time. Our study also showed BERA as an important tool to determine auditory function in the patients with OP poisoning. These patients reflect the inconsistent change in BERA response which could be more clarified with studies considering a large population of the patients.

Funding: No funding sources

Conflict of interest: None declared

Ethical approval: The study was approved by the Institutional Ethics Committee

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