Systemic organophosphate poisoning in child following anti-lice lotion application

We report a case of systemic organophosphate (OP) poisoning in a young child following the use of a household shampoo containing diazinon. In previous reported cases, diagnosis is typically made rapidly and indirectly through decreased cholinesterase activity and identification of OPs in commercial containers. In our case, however, the diagnosis was significantly delayed due to nonspecific clinical signs and a language barrier between the family and medical staff, resulting in the development of an intermediate syndrome. Initial symptoms included gastrointestinal disturbances, followed several hours later by neurological and respiratory complications. Plasma, urinary, and hair arsenic levels were first investigated due to the use of a product which may contain organometallic copper acetoarsenite complex. All arsenic concentrations were within physiological concentrations. Clinical presentation and biological cholinesterase activity (313 U/L vs. reference 1900-3800 U/L) later supported the diagnosis of OP poisoning. This hypothesis was reinforced by the analysis of the household shampoo indicating the presence of diazinon. Furthermore, despite the delayed diagnosis, non-targeted high-resolution mass spectrometry (LC-HR-MS/MS) identified diazinon in plasma and multiple phase I metabolites, including the specific marker IMPY, in both plasma and urine. Four previously undescribed metabolites and one phase II metabolite, hydroxy-IMPY-glucuronide, were also detected. Pralidoxime methylsulfate (Contrathion™) was administered on day 4, following toxicological confirmation and lack of clinical improvement. Although late, this treatment led to gradual neurological recovery, suggesting possible slow "aging" of diazinon-inhibited acetylcholinesterase. Nonetheless, the child developed persistent sequelae including hypotonia, peripheral neuropathies, and respiratory dysfunction consistent with intermediate syndrome. This case highlights the importance of considering OP poisoning even in atypical presentations and illustrates the utility of non-targeted HRMS screening in providing direct evidence of exposure when conventional approaches are inconclusive.