Background: The urine immunochromatographic assay is a useful screening tool for patients suspected of acute drug intoxication in emergency conditions. Diphenhydramine intoxication shows symptoms similar to those of tricyclic antidepressant (TCA) intoxication.
Case presentation: We examined a case of diphenhydramine intoxication showing cerebellar ataxia and prolonged false positive results for TCA in the urine. The urine TCA test showed persistently positive results even 60 h after the patient's initial drug screening. We observed negative conversion 90 h after the initial drug screening.
Discussion: Considering the similarities of clinical symptoms between diphenhydramine and TCA intoxication, emergency physicians should consider the possibility of cross-reactivity in the diagnosis of a patient with unknown acute drug intoxication showing positive results of TCA immunochromatographic assay in the urine.
Conclusion: The present case suggests that diphenhydramine overdose may cause cerebellar ataxia and show prolonged cross-reactivity as TCA in the urine.
Keywords: ataxia; cross reactivity; diphenhydramine; tricyclic antidepressants; urine immunochromatographic assay.
© 2023 Dongsun Kim et al., published by Sciendo.