Neurological syndromes of organophosphorus compounds.

In addition to the acute cholinergic poisoning, organophosphorus (OP) compounds are capable of producing several subacute, delayed and chronic neurological, neurobehavioural and psychiatric syndromes. These include the intermediate syndrome, the organophosphate induced delayed neuropathy (OPIDN) and a number of chronic neurological and psychiatric manifestations lumped in this review under the term chronic organophosphate induced neuropsychiatric disorder (COPIND). A critical review of the concept of the neuropathy target esterase (NTE) inhibition and ageing as a marker of OPIDN and the related hen test is presented. It is concluded that the use of the hen test as an exclusive screening test for neurotoxicity of organophosphorus compounds is flawed. A number of recent studies are presented to demonstrate the unreliability of the test and flaws of scientific concepts underlying the hen test which is used to identify OPs as safe and "non-neurotoxic". The components of this new COPIND syndrome are described and the evidence for its existence is reviewed. Studies are in progress to further determine the profile of this syndrome and to define the overlap between its various components. The review also attempts to determine the clinical features so far described of these components and the investigations or markers used to identify and characterize COPIND and the behaviour of these markers. Evidence for chronic neurological/psychiatric effects of OP compounds have come from case studies, clusters of neurological diseases or from epidemiological investigations. New concepts in neurotoxicology are being produced from recent studies which may necessitate a new radical approach to the assessment of neurotoxicity of pesticides before releasing them for widespread use.