Abstracts

RATIONALE: Zonisamide is a broad spectrum antiepileptic drug (AED) used to treat a variety of seizure types including primary generalized seizures, absence seizures, infantile spasms, and myoclonic seizures. The principal reported adverse effects of zonisamide (ZNS) are drowsiness (17%), dizziness (13%), anorexia (13%), and headache (10%). A visual disturbance, such as diplopia, was reported in 6% of adults. Visual hallucinations have not been reported as an adverse reaction of ZNS.
METHODS: We present observations in three patients with visual hallucinations after the introduction of ZNS.
RESULTS: Patient one is a 7 year old girl with Landau Kleffner Syndrome. Because of progressive language deterioration, ZNS was added to valproci acid (VPA) at a dose of 100 mg/d (2 mg/kg). Five days after introduction, she complained of seeing [dsquote]green worms[dsquote]. Patient two is an 18 year old girl with intractable generalized myoclonic and tonic seizures with moderate developmental delay secondary to perinatal hypoglycemia. She presented with a 10 day history of drowsiness. Medications included carbamazepine, primidone, and ZNS, which had been introduced 3 weeks before and increased to a dose of 500 mg/day (10 mg/kg/d). After admission, she had visual hallucinations in which she reported [dsquote]my grandfather was here, talking to me[dsquote]. Patient three is a 14-year-old girl with cortical dysgenesis and medically intractable complex partial seizures, atonic seizures, and generalized tonic clonic seizures. She presented with lethargy and a decrease in daily activities. ZNS had been added to VPA 4 weeks earlier. The dose was 100 mg/day (2 mg/kg/d). She had an episode of visual hallucinations defined as [dsquote]my doctor was here talking to me[dsquote].
All patients complained of well-formed visual hallucinations described as seeing a person or an animal. Their EEGs showed no changes from baseline. Neuroimaging studies did not show any structural abnormality in the occipital or temporal areas to explain the occurrence of visual hallucinations. Serum levels of other AEDs were in the therapautic range. Since a serum level is not available, ZNS levels were not sent. Visual hallucinations ceased after the changes in ZNS, discontinued in 2 and dose decreased in one, and have not recurred.
CONCLUSIONS: Well formed visual hallucinations and mental status changes occurred 5 days to 4 weeks after the initiation of ZNS. These hallucinations are likely an adverse event of ZNS for the following reasons: 1) absence of clinical/electrographic seizures or change in the baseline EEG, 2) no previous or present history of psychotic problems or behavioral changes, 3) visual hallucinations occurred after the introduction of ZNS, and 4) symptoms disappeared after decreasing the dose. Further experience will be helpful to clarify the nature of this adverse event.