(Beyond Pesticides, July 16, 2008) People exposed to pesticides are more likely to suffer changes in nerve responses and severe weakness in their neck and limb muscles in the days before they succumb to their symptoms. This is according to a new study, which found that the major cause of death was as a result of respiratory failure following acute organophosphate poisoning.
The study entitled, â€śThe Spectrum of Intermediate Syndrome Following Acute Organophosphate Poisoning: A Prospective Cohort Study from Sri Lankaâ€ť published in the open-access journal Public Llibrary of Science (PloS) Medicine was a collaboration between researchers from Sri Lanka, Australia, and the UK. These researchers examined and assessed 78 consenting symptomatic patients with organophosphate poisoning and found that 10 suffered severe weakness in their neck and limb muscles and five of these eventually developed respiratory failure. Respiratory failure is the major cause of death after poisoning by organophosphates.
Lead author Pradeepa Jayawardane, clinical pharmacology lecturer at the University of Sri Jayawardenepura in Sri Lanka, and colleagues realized that there are changes in nerve transmission that are presented before individuals with organophosphate poisoning develop muscle weakness, also known as intermediate syndrome (IMS). IMS results in muscle weakness in the limbs, neck, and throat, and develops in some patients 24â€“96 hours after poisoning. Long-term nerve damage sometimes develops 2â€“3 weeks after poisoning. The functional changes that are associated with IMS (its pathophysiology) are poorly understood however.
Electric shocks were applied to certain muscles of the patients, using a technique called repetitive nerve stimulation (RNS). 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.
“In all 10 patients we demonstrated that the neuromuscular junction progressively fails, leading to muscle weakness,” said Pradeepa Jayawardane. 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 reveal that IMS is a â€śspectrumâ€ť disorder in which the weakness and neuromuscular problems, caused by organophosphate poisoning, gradually progress over time through a series of electrophysiological changes that can sometimes resolve quickly and, only in the most severe cases, result in respiratory failure. Changes in nerve transmission that evolve during the development of IMS can be objectively monitored using RNS. Since the clinical signs of IMS come after changes in nerve transmission, the researchers suggest using these changes as an indicator of future outcome.
RNS tests might also be useful in the clinical management of patients with organophosphate poisoning, particularly since such tests could provide an early warning of impending respiratory failure. However, the researchers note that these findings need to be validated in further studies, particularly since most of the patients in this study had been exposed to a single organophosphate (chlorpyrifos). This would improve diagnostic and prognostic tools for clinical use in organophosphate-poisoned patients
Organophosphates, derived from World War II nerve agents, are a common class of chemicals used in pesticides and are considered to be the most likely pesticides to cause an acute poisoning. Many are already banned in England, Sweden and Denmark. Organophosphates are cholinesterase inhibitors and bind irreversibly to the active site of an enzyme essential for normal nerve impulse transmission- acetylcholine esterase (AchE), inactivating the enzyme. Symptoms include tingling sensations, headaches, tremors, nausea, abdominal cramps, fever, severe forgetfulness, convulsions and movement disorders. Repeated or prolonged exposure to organophosphates may result in the same effects as acute exposure, including delayed symptoms.
Most pesticide poisonings in developing countries result from deliberate ingestion of pesticides. About half the people in developing countries in Asia who kill themselves do it using pesticides, and aid agencies have been lobbying to ban their use.
Source: Medical News Today