Changes of attention-related brain activity over 6 months after acute organophosphate pesticide poisoning: a prospective follow-up study

Abstract

Context

Ingestion of organophosphate (OP) pesticides is a common method of self-harm in developing countries. Apart from acute cholinergic effects, limited evidence implicates OP poisoning in long-term neurocognitive deficits. However, prospective neurophysiological evidence of long-term deficits is scarce in humans. We aimed to determine long-term cognitive changes of acute OP pesticide self-poisoning in a prospective follow-up study, using event-related potentials (ERPs), an electroencephalographic index of cognitive functioning.

Methods

We recruited 203 patients (147 men) hospitalised with OP pesticide ingestion (OP group; all had significant erythrocyte cholinesterase inhibition) and 50 patients (23 men) with paracetamol overdose (control group) as a means of self-harm. We recorded their ERPs and behavioural performance in a selective attention task at three post-exposure time points: on discharge from hospital (around 14 days post-ingestion), 6 weeks and 6 months post-ingestion. We compared the reaction time and ERP components of the two groups at each time point, adjusting for sex, age, education and comorbid depression in multiple regression models.

Results

OP group had significantly slower reaction times than the control group on discharge and at 6 weeks, but not at 6 months. On discharge, the OP group also showed significantly prolonged latency of the parietal P3b component, signifying delayed attentional processing. P3b amplitudes were also significantly smaller in the OP group on discharge and at 6 months. Within the OP group, greater clinical severity of poisoning was associated with smaller P3b amplitudes. Early pre-attentive cortical processing (as indexed by N1 ERP component) showed no significant intergroup differences.

Conclusions

Acute OP pesticide poisoning was associated with impaired behavioural and neurophysiological indices of selective attention. These deficits outlast the cholinergic phase of intoxication. The neurobehavioral impairment disappears over months, but neurophysiological deficits seem to last even after 6 months. This impairment could potentially compromise the performance and safety of patients for months following clinical recovery.

Keywords:

• organophosphates
• pesticides
• poisoning
• deliberate self-harm
• cognition
• attention
• event related potentials
• P300
• reaction time

Acknowledgements

We thank doctors Kamal Naser, Ajith Gurusinghe, Upul Vidanapathirana who were the physicians-in-charge of the Toxicology Departments of the Teaching Hospital Peradeniya and the District General Hospital Nuwara Eliya. We also thank doctors Noorul Ikram, Mohommed Azam, Udayaprashanth Gnanaseharan, Shangesh Velayutham and Husain Ameen who assisted in data collection; and Ross Fulham and Tony Kemp who assisted in programming the ERP experiment.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This study was supported by the Australian National Health and Medical Research Council grant [1030069] and University of Peradeniya research grant [RG/2013/21/M]. The Functional Neuroimaging Laboratory of The University of Newcastle, Australia provided equipment and software for EEG/ERP recording and analysis.