Positional downbeat nystagmus in metronidazole-induced cerebellar toxicity: a case report

Abstract

We report a case of metronidazole-associated cerebellar toxicity presenting with positional downbeat nystagmus, a relatively uncommon but clinically significant manifestation. A 61-year-old man developed ataxia, dysarthria, and positional nystagmus after nearly 2 months of metronidazole treatment for a brain abscess in the frontal lobe. Brain magnetic resonance imaging (MRI) showed symmetrical T2-weighted/fluid-attenuated inversion recovery hyperintensities in the dentate nuclei and tectal plate. These findings, along with prolonged use of intravenous metronidazole, supported the diagnosis of metronidazole-induced cerebellar toxicity. Discontinuation of the drug led to marked clinical and radiologic improvement. This case highlights the importance of recognizing positional downbeat nystagmus as a potential early indicator of metronidazole-induced neurotoxicity. Early identification of this oculomotor pattern may prompt timely imaging and cessation of the offending agent, potentially preventing irreversible neurologic damage.