Can we predict intermediate syndrome? A review

Ingestion of organophosphorus insecticides (OPI) is a common method of deliberate self harm in the developing world. Deaths mainly follow as a result of the respiratory failure associated with both cholinergic crisis and the intermediate syndrome. Even though death can be prevented by early mechanical ventilation of these patients, limited studies are available regarding the prediction of intermediate syndrome and subsequent respiratory failure.

To systematically review articles that are published with regard to possible prediction of intermediate syndrome using clinical, biochemical and electrophysiological parameters.

A systematic review on literature published in English language was done in the PubMed database without a date limitation. Two sets of search terms were used. The first set consisted of MeSH Terms "organophosphates", "organophosphate poisoning", "op poisoning" "organophosphate insecticide poisoning" and "organophosphorus". The second set included the MeSH Terms "Intermediate syndrome", "proximal muscle weakness", "cranial nerve palsies", "respiratory depression" and "neck muscle weakness". Articles containing at least one word from each set were reviewed.

At least one MeSH term from each set was incorporated in 179 articles. Of these, 69 were rejected as they were not related to organophosphate poisoning or intermediate syndrome.

Clinical prediction is mostly based on ICU scoring systems. Biochemical markers such as reduced levels of serum and erythrocyte acetylcholine esterase have been studied many times. Both clinical and biochemical markers show a modest relationship in predicting IMS. Single fibre electromyography show promising results as it directly assesses neuromuscular junction.

The intermediate syndrome which follows organophosphate poisoning still remains a significant problem with its high morbidity. Clinical and biochemical markers show modest results in predicting IMS. Neurophysiological markers such as single fibre EMG should be studied further as they measure activity of affected nicotinic receptors directly.