Electroencephalography in holoprosencephaly: Findings in children without epilepsy

Objective: To evaluate the electroencephalographic characteristics of patients with holoprosencephaly (HPE) without epilepsy. Methods: We evaluated the electroencephalograms (EEGs) of 18 children with HPE who lacked a history of seizures. Neuroimaging studies were assessed for severity of HPE and thalamic non-separation and the presence of dorsal cysts and cortical malformations. Results: Hypersynchronous theta activity occurred in 50 and 60% of EEGs during wakefulness or drowsiness/sleep, respectively, and correlated with the grade of thalamic non-separation (p<0.05). Hypersynchronous beta activity during sleep occurred in 41% of EEGs. Posterior amplitude attenuation occurred in 33% of EEGs and correlated with the presence of a dorsal cyst (p≤0.0004). Photic driving responses were seen in 50% of the EEGs. If a dorsal cyst was present, the responses were anteriorly displaced. Epileptiform activity was noted in EEGs of 5 patients and did not correlate with the incidence of clinical seizures. Conclusions: Hypersynchronous activity was present frequently in EEGs of HPE patients, possibly attributable to incomplete separation of the thalami and hemispheres. Dorsal cysts were associated with posterior amplitude attenuation and anterior displacement of the photic response. In this selective cohort, the presence of epileptiform activity was not a risk factor for seizures. Significance: To date, this is the largest study of EEGs in children diagnosed with HPE without seizures. This study complements our earlier clinical and neuroradiologic studies by providing neurophysiologic data that serves to enhance our understanding of this complex, rare disorder.