Progression of neuropsychological deficits following toluene diisocyanate exposure.

Three wharf workers were acutely exposed to toluene diisocyanate (TDI) during an accidental chemical spill. Toluene is neurotoxic as a solvent, while cyanates can cause nervous tissue injury or death by hypoxia. Chronic symptoms which occurred following the incident included headache, fatigue, concentration problems, irritability, depression, sleep disturbance, memory and sexual dysfunction. Compared with two months post-exposure, at 16 months post-exposure Full Scale IQ dropped an average of 23 points. Results from additional neuropsychological testing at 16 months post-exposure indicated severe deficits in all three subjects in memory, manual dexterity, visuomotor tracking, mental flexibility, ability to detect figure-ground relationships, and word fluency. Nerve conduction velocity testing indicated abnormal peripheral nervous system function in two of the three workers; however, its etiology is not certain. These results may be relevant to the neurotoxicity of methyl isocyanate exposure, such as occurred in Bhopal, India, where an increasing magnitude of depression, anxiety, fatigue, restlessness, and headaches 18 months post-exposure have been reported. In general, continuing decrement in mental function without concomitant environmental exposure should be considered in neuropsychological assessment of chemical toxicity.