Probable topiramate-induced hemiparesis.

Topiramate is a broad-spectrum antiepileptic medication that is used as monotherapy or in combination with other medications to treat epilepsy in both adults and children. It is also indicated for migraine prophylaxis in adults. An off-label use of topiramate is as a mood stabilizer (with no associated weight gain) in rapid-cycling and mixed bipolar episodes. The mechanisms of action of topiramate suggest a broad spectrum of anticonvulsant activity, including blockade of voltage-gated sodium and calcium channels, increase in inhibitory transmission via enhancement of -aminobutyric acid–stimulated chloride currents, decrease in excitatory transmission via blockade of the adenosine monophosphate-kainate subtype of the glutamate receptor, and weak inhibition of carbonic anhydrase. Despite the benefits of topiramate as listed above, including weight neutrality, patients are still prone to discontinue their medications. This problem is highly prevalent among patients with mental health conditions, most notably schizophrenia and bipolar disorders. In particular, patients may abruptly discontinue their antiepileptic medications secondary to experiencing adverse effects, even if they have been made aware of the potential for such adverse effects through education provided by a pharmacist. Prescribers and other health care providers must be aware of potential adverse effects that may arise with the commencment and maintenance of antiepileptic therapy. Troublesome and relatively common adverse effects associated with topiramate that have been documented in the literature include paresthesia, fatigue, nausea, anorexia, anorgasmia, and changes in memory and concentration. Less common but serious adverse effects include hemiparesis, hypesthesia, abnormal coordination, chest pain, anemia, and bone marrow suppression. Many of these adverse effects are dose-related and result from too-rapid dose titration. As noted above, a common adverse effect of topiramate is paresthesia, which is characterized by abnormal neurologic sensations such as numbness, tingling, burning, prickling, and hypesthesia. In contrast, hemiparesis, defined as weakness of one side of the body, is much more serious. Although parasthesias are thought to be dose-related and occur in 51% of patients taking doses that exceed 100 mg/day, there is no mention of hemiparesis in the product monograph, and only 3 cases of hemiparesis have been reported in the literature. The case reported here illustrates morbidity associated with probable topiramate-induced hemiparesis.