Case Presentation: A 68 year-old woman with a past medical history of paroxysmal atrial fibrillation, recurrent Clostridium difficile infection and intra-abdominal abscess for which she was treated with ceftriaxone and metronidazole for six weeks, presented to the emergency department with slurred speech and ataxia. CT head showed no acute hemorrhage, infarction or other intracranial disease process. MRI brain showed an acute lacunar infarct in the right frontal lobe as well as hyperintensity in bilateral dentate nuclei concerning for flagyl toxicity. Given her C. difficile infection recurrence, patient was started on a six week oral vancomycin taper and all other antibiotics were discontinued. Patient’s focal neurological deficits resolved and she was discharged to a rehabilitation facility.
Discussion: Metronidazole is a widely used drug in treatment of anaerobic infections as well as C. difficile infections. The side effect profile of this drug is typically overlooked given that it is generally well-tolerated. The most common adverse effects associated with it are gastrointestinal symptoms which include nausea, vomiting, diarrhea, constipation and abdominal cramps. Neurological symptoms are quite rare, however the most common reported symptom is peripheral neuropathy. More recently, cerebellar toxicity linked to metronidazole use has been reported in the literature.
In this case, our patient was found to have cerebellar toxicity secondary to metronidazole use which accounted for her symptom of ataxia. Typical imaging findings of metronidazole-induced cerebellar toxicity reported in the literature include signal changes in the dentate nuclei, splenium of corpus callosum and dorsal brainstem. The pathophysiology related to neurotoxicity remains unclear, however it has been reported that most lesions secondary to metronidazole toxicity are reversible. The offending agent was discontinued in this case and the patient had a repeat MRI that showed improvement in the dentate nucleus lesions.
Conclusions: When evaluating a patient’s symptoms, iatrogenic causes should always be included in the differential diagnosis. Toxicity due to metronidazole use is not dose or duration dependent, thus adverse effects due to this drug should be considered in all patients at all stages of treatment. Given that this is a commonly prescribed agent, clinicians should be aware of its side effect profile.