Thirteen-year follow-up of patients with tri-ortho-cresyl phosphate poisoning in northern suburbs of Xi’an in China

Based on reports published so far, organophosphorus (OP) compounds do remarkable harm to human health. In 1995 there was an outbreak of organophosphorus-ester induced delayed neuropathy (OPIDN) due to tri-ortho-cresyl phosphate (TOCP) poisoning in northern suburbs of Xi’an in China. The 74 affected patients were treated and followed up after definite diagnosis. 13 years later, all the epidemiological data obtained from 61 survivors were evaluated, and 15 patients underwent clinical, laboratory, neuroimaging and electrophysiological examinations. In addition, a review of the literature about the possible mechanism of OPIDN was made. According to our investigation, of 61 survivors, 35 patients almost regained normal function of limbs and work outside; 23 patients walked with bilateral support and could perform housework; and 3 patients could not self-care. The patients undergoing examinations presented spasticity and minor lower leg muscle atrophy without sensory impairment. Laboratory investigations and brain and spinal cord magnetic resonance imaging examinations were normal. Neurophysiological investigations also showed normal electroencephalogram and visual, brainstem auditory and somatosensory evoked potentials. Motor evoked potential (MEP) obtained from the upper limbs had normal central motor conduction time (CMCT). However, the CMCT of MEP response recorded from the bilateral lower limbs was delayed, or showed even no MEP responses. Motor and sensory nerve conduction velocity and electromyography studies were normal except for two severely affected patients. TOCP showed long-term effects on the nervous system and influenced the quality of life. OP compounds should be strictly regulated to prevent similar occurrences.