Organophosphates are a common class of chemicals used in pesticides, herbicides, and nerve gases. Each year, thousands of people are poisoned by these chemicals and die as they develop intermediate syndrome – when muscles weaken and the respiratory system fails. A study published in the open-access journal PLoS Medicine reveals how researchers from Sri Lanka, Australia, and the UK have uncovered new findings related to organophosphate poisoning. Specifically, lead author Pradeepa Jayawardane and colleagues realized that there are changes in nerve transmission that are presented before individuals with organophosphate poisoning develop intermediate syndrome (IMS).

The relationship between the consumption of organophosphates and the development of IMS previously has not been understood very well. There were no clear predictors that physicians could use to accept the occurrence of IMS. “There has been tremendous controversy in the toxicology world concerning the true definition and existence of IMS as an isolated entity,” writes Cynthia Aaron (Children’s Hospital of Michigan, Detroit) in an accompanying commentary.

The findings by Jayawardane and colleagues come from an analysis of 78 patients who were admitted to Nuwara Eliya General Hospital and Teaching Hospital, Peradeniya in Sri Lanka with organophosphate poisoning. Though the patients received standard care and were managed according to routine procedures, physicians evaluated them with repetitive nerve stimulation. This technique allows researchers to trace changes in nerve transmissions during the course of poisoning. About 12.8% of patients (10 of 78) were diagnosed with IMS and the researchers saw specific changes in their neuromuscular transmission patterns – often before a physician could make in IMS diagnosis from clinical signs. About 38% of patients (30 of 78) presented muscle weakness that was not severe enough for an IMS diagnosis. In these patients, the researchers also found defined changes in their neuromuscular transmission patterns.

The findings led the researchers to conclude that, “IMS is a spectrum disorder. At one end of the spectrum the patients demonstrate only the electrophysiological abnormalities without clinically detectable muscle weakness, and at the other end, patients progress to severe muscular weakness with deterioration of electrophysiological measurements and the risk of respiratory failure.” Since the clinical signs of IMS come after changes in nerve transmission, the researchers suggest using the changes as an indicator of future poor outcome.

Aaron adds in her commentary: “If these distinctive electrophysiological changes are subsequently validated in further studies, they should lead to improved diagnostic and prognostic tools for clinical use in organophosphate-poisoned patients”.

The spectrum of intermediate syndrome following acute organophosphate poisoning: A prospective cohort study from Sri Lanka
Jayawardane P, Dawson AH, Weerasinghe V, Karalliedde L, Buckley NA, et al.
PLoS Medicine (2008). 5(7): e147.
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Organophosphate poisoning induced intermediate syndrome: Can electrophysiological changes help predict outcome?
Aaron CK.
PLoS Medicine (2008). 5(7): e154.
Click Here to View Perspective Article

About PLoS Medicine

PLoS Medicine is an open access, freely available international medical journal. It publishes original research that enhances our understanding of human health and disease, together with commentary and analysis of important global health issues. For more information, visit

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Written by: Peter M Crosta