Zonisamide Adjunctive Therapy in Intractable Childhood Epilepsy with Mitochondrial Respiratory Chain Complex Defects

Abstract

Purpose: Zonisamide (ZNS) is a broad-spectrum antiepileptic drug (AED). Free radical scavenging is also a possible action mechanism of ZNS. As oxidative stress plays an important role in the pathogenesis of mitochondrial cytopathy, we studied the efficacy and safety of ZNS as possible long-term adjunctive therapy in intractable childhood epilepsy with mitochondrial respiratory chain complex (MRC) defects. Methods: MRC defects were confirmed by biochemical assays with muscle biopsies. We evaluated seizure frequencies and adverse effects in 38 childhood epilepsy pati ents with MRC defects who were maintained on ZNS for at least 12 months. Patients with more than 50% seizure reduction after 12 months were defined as responders. Results: As for clinical diagnosis of mitochondrial cytopathy, 13 cases (34.2%) were diagnosed as Leigh syndrome and the remaining 25 (65.8%) had uncategorized mitochondrial cytopathy with nonspecific encephalopathy. The response rates for each seizure type after 12 months of ZNS therapy ranged from 23.1 to 55.6%; partial seizures (55.6%; 10/18), absence seizures (50.0%; 2/4), tonic-clonic seizures (40.0%; 2/5), atonic seizures (36.4%; 4/11), spasms (33.3%; 2/6), tonic seizures (31.8%; 7/22) and myoclonic seizures (23.1%; 3/13). The response rate for epileptic syndromes such as West syndrome and Lennox-Gastaut syndrome after ZNS treatment are 33.3% and 55.6% respectively. Somnolence, irritability, anorexia and weight loss were noticed as adverse effects, but all were transient. Conclusion: ZNS could be an effective and safe candidate for adjunctive therapy in intractable childhood epilepsy with MRC defects. It could be considered preferentially for its free radical scavenging effect.