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Ictal bradycardia in an infant following surgical treatment for hemimegalencephaly

A female patient, who was the first offspring of healthy Japanese parents without any preor perinatal problems, experienced severe frequent apnea and complex partial seizures with secondary generalization from the 6th day after birth. Her electroencephalogram (EEG) findings showed asymmetrical suppression-burst patterns with a left hemisphere dominance. Brain magnetic resonance imaging (MRI) revealed hemimegalencephaly and cortical dysplasia in the left hemisphere, including the left insular cortex (Fig. 1a). The administration of antiepileptic drugs, such as clonazepam and zonisamide, was not effective and her epileptic seizures persisted. She underwent a functional left hemispherectomy at 7 months of age and thereafter did not show any seizures for the following 4 months. However, she began to experience ictal bradycardia, <60 beats per minute, at 11 months of age. Her ictal EEG, brain scintigraphy and electrocardiography showed focal spike and wave bursts on the left insular cortex lesion and Mobitz type 2 atrio-ventricular blocks (Fig. 1b–e). Carbamazepine effectively resolved her ictal bradycardia and epileptic paroxysms. Ictal bradycardia including epileptic apnea and secondary hypoxic bradycardia has been reported in only 1.4% of patients with epilepsy. Many of these cases are complicated by temporal lobe epilepsy, but the pathophysiology still remains unclear. Although there have been reports describing adult patients with ictal bradycardia, no case of ictal bradycardia during infancy and following surgical treatment for hemimegalencephaly has yet been reported. Based on the results of the cortical stimulation response, functional imaging, ictal EEG and lesional studies, some investigators have suggested the parasympathetic nerve to be lateralized to the left insular cortex and such excessive parasympathetic activity causes a disturbance in atrio-ventricular conduction. In this patient, spike and wave bursts localized on the left post-temporal lesion and a hot spot on the left insular cortex during epileptic seizures were confirmed by scalp EEG recordings and brain scintigraphy, respectively. These left posttemporal spikes, which represent a left insular cortex lesion, might be the responsible epileptic focus in this case. Her ictal bradycardia was revealed after the operation, which might have preserved the left insular cortex and its fiber connections. Her ictal bradycardia might have been caused by a direct stimulation from the left insular cortex to the parasympathetic nervous system, which should be differentiated from epileptic apnea and secondary hypoxic bradycardia.