pralidoxime and Neuromuscular-Diseases

A dimethoate-poisoned woman gradually developed a moderately severe cholinergic crisis that was readily treated by atropine. After being symptom-free for nearly two days, she suffered from sudden life-threatening respiratory paresis and weakness of the facial, extraocular, neck flexor and proximal limb muscles. Muscarinic symptoms were absent. Cholinesterase inhibition was severe, and EMG revealed marked decrements at low rates of repetitive nerve stimulation, and increments at a high rate. The clinical course was compatible with the Intermediate Syndrome. This syndrome seems due to persistent cholinesterase inhibition presumably leading to combined pre- and postsynaptic impairment of neuromuscular transmission. Inadequate pralidoxime therapy is proposed but not established as contributory. Prolonged monitoring of respiratory function in patients poisoned by particular organophosphate agents is mandatory.

Topics: Adult; Antidotes; Atropine; Cholinesterase Inhibitors; Cholinesterase Reactivators; Dimethoate; Electromyography; Female; Humans; Neuromuscular Diseases; Pralidoxime Compounds; Respiratory Paralysis; Synaptic Transmission; Syndrome; Ventilators, Mechanical

The neuromuscular transmission failure in acute organophosphate (OP) poisoning occurs because of the irreversible inactivation of the enzyme acetylcholinesterase located in the neuromuscular junction, and is distinguished neuroelectrophysiologically by single electrical stimulus-induced repetitive responses and either a decremental or a decrement-increment response upon high-rate repetitive nerve stimulation (RNS). Understandably, the administration of pharmacological agents with actions at different sites in the neuromuscular junction would alter the neuroelectrophysiological findings in acute OP poisoning.. The effect of several pharmacological agents including pralidoxime (10 patients), magnesium sulphate (4 patients) and pancuronium (7 patients) on the neuroelectrophysiological abnormalities was studied in 21 patients with acute OP poisoning.. Pralidoxime administration produced neurophysiological amelioration in 11 out of 15 occasions. In those cases where it produced a beneficial effect, pralidoxime administration was continued and its neuroelectrophysiological effects were studied daily. The efficacy of pralidoxime administration was demonstrated by neuroelectrophysiological testing for a maximum of 6 days after poisoning. Three types of neuroelectrophysiological responses to pralidoxime were noted: (i) lack of neuroelectrophysiological improvement (two patients); (ii) initial improvement with subsequent lack of improvement (two patients); and (iii) initial improvement with subsequent normalisation of neuromuscular transmission (5 patients). Normalisation of the electrodiagnostic tests and the failure of pralidoxime to ameliorate the neuromuscular transmission abnormalities were neuroelectrophysiological indications for the discontinuation of pralidoxime treatment. The administration of magnesium sulphate (MgSO4.7H2O, 4 g intravenous) resulted in a decrease in the CMAP amplitude, loss of the repetitive response and conversion of the decrement-increment response at high-rate RNS to an incremental response. Repetitive responses and the decremental response at high-rate RNS also disappeared after the administration of pancuronium (0.5 mg intravenous) to 6 patients. However, in one case where pancuronium administration was preceded by pralidoxime, there occurred a dramatic worsening of the neuromuscular transmission defect.. While the administration of all 3 agents-- pralidoxime, magnesium sulphate and pancuronium-- resulted in the reversion of the neuroelectrophysiological defects, only pralidoxime is contended to be therapeutically useful. The therapeutic benefit due to its administration is limited by a short duration of action, and hence it is recommended that it should be administered for a longer period of time under neuroelectrophysiolgical guidance.

Topics: Acute Disease; Antidotes; Electroencephalography; Humans; Insecticides; Magnesium Sulfate; Monitoring, Physiologic; Neuromuscular Diseases; Neuromuscular Junction; Nicotinic Antagonists; Organophosphorus Compounds; Pancuronium; Pralidoxime Compounds; Synaptic Transmission; Treatment Outcome

A prolonged type of organophosphate toxicity, previously characterized as the Intermediate Syndrome, has been recognized in 6 out of 7 prospectively studied patients poisoned by insecticide containing parathion and methyl parathion in equal proportions. The clinical characteristics included respiratory paresis, weakness in the territories of several motor cranial nerves, neck flexors and proximal limb muscles, and depressed tendon reflexes, all lasting for several days or weeks. Electromyography in the early stages disclosed diverse types of impaired neuromuscular transmission. EMG normalization preceded clinical recovery. Severe plasma butyrylcholinesterase and erythrocyte acetylcholinesterase inhibition persisted along with the occurrence of Intermediate Syndrome-related symptoms. We conclude that combined parathion and methyl parathion poisoning is more likely to induce Intermediate Syndrome than parathion poisoning alone. The mechanisms underlying this difference remain obscure. The Intermediate Syndrome shows clinical and electromyographic hallmarks of combined postsynaptic impairment of neuromuscular transmission.

Topics: Adult; Antidotes; Atropine; Butyrylcholinesterase; Cholinesterase Inhibitors; Cholinesterase Reactivators; Cholinesterases; Electromyography; Erythrocytes; Female; Humans; Male; Methyl Parathion; Middle Aged; Neuromuscular Diseases; Parathion; Pralidoxime Compounds; Respiratory Paralysis