Electroencephalographic features in a case of hypersomnia due to an optic nerve glioma

Background

Orexin is secreted in the lateral hypothalamic area and is essential for wakefulness. Impaired secretion of orexin in patients with hypothalamic lesions results in secondary hypersomnia. However, reports on the EEG features of secondary hypersomnia are limited.

Case presentation

A 16-year-old boy experienced hypersomnia, cognitive impairment, and memory deficits during maintenance treatment for an optic nerve glioma involving the optic chiasm. Brain MRI revealed that the tumor had enlarged beyond the suprasellar region and compressed the hypothalamus, midbrain, suprasellar nucleus, and basal forebrain. EEG recording during hypersomnia showed repetitive high-voltage, frontal dominant delta wave bursts regardless of whether the patient was sleeping or awake, indistinct sleep humps and spindles, and disruption of sleep architecture. Additional chemotherapy alleviated the hypersomnia, and delta wave bursts were no longer observed on EEG. Orexin levels in the cerebrospinal fluid were extremely low on admission but increased after the disappearance of hypersomnia.

Discussion and Conclusion

Hypersomnia in this case may be associated not only with impaired orexin production due to hypothalamic lesions, but also with dysfunction of the other arousal networks, including the basal forebrain and brainstem. The association between repetitive high-voltage delta wave bursts on EEG and secondary hypersomnia has not been previously described. Although the pathophysiological basis remains unclear, the damage to such multiple wake-promoting networks may be involved in the characteristic EEG finding.