Delayed Neurotoxicity from Triaryl Phosphates

For some time, compounds known as triaryl phosphates (eg, triosthocresyl phosphate) have been used as flame retardants, plasticizers, lubricating oils, and hydraulic fluids. They are weak cholinesterase inhibitors, but do inhibit “neurotoxic esterase,” located in the brain and spinal cord. A form of delayed neurotoxicity results from the inhibition of neurotoxic esterase. Triaryl phosphates have caused accidental poisonings in humans and other species (mostly cattle). Some OP insecticides (eg, PEN, leptophos) can also cause delayed neurotoxicity; however, field cases have been rare. The lesions associated with delayed neurotoxicity include demyelination of peripheral and spinal motor tracts due to loss of neurotoxic esterase function. Clinical signs associated with delayed neurotoxicity include muscle weakness and ataxia that progresses to flaccid paralysis of the hindlimbs. Signs are usually not manifest until 8-21 days after exposure to a neurotoxic triaryl phosphate. There are no specific antidotes.