This patient presented initially with headaches and sinusitis. CT scanning at presentation (not reproduced here) showed a frontal mass communicating with fluid filled sinuses, for which antibiotics (ceftriaxone and metronidazole) were started. MRI scanning confirmed intracerebral abscesses originating in sinusitis and the bi-frontal abscesses were surgically opened and drained.

Hereafter the patient recovered well until she developed nausea, trouble walking and a sensory neuropathy. A follow-up MRI scan showed a pattern of T2 hyperintense signal consistent with metronidazole-induced toxicity. Metronidazole had been prescribed for more than three months at this point. After ceasing metronidazole the ataxic symptoms subsided in a matter of days.

Central nervous system toxicity is a rare side-effect of metronidazole treatment, causing cerebellar ataxia, altered mental state and neuropathy. A characteristic pattern of T2 and FLAIR hyperintense signal bilaterally in the cerebellar dentate nuclei is most commonly seen, with the corpus callosum, the midbrain, the pons, or/and the medulla also being involved in some cases.