Idiopathic Hypersomnia: Neurobiology, Diagnosis, and Management

Idiopathic hypersomnia is a chronic neurologic sleep disorder that manifests as excessive daytime sleepiness despite normal or prolonged sleep times for age. Frequently, idiopathic hypersomnia is clinically characterized by marked sleep inertia, long and unrefreshing naps, and a high sleep efficiency. Since the initial description, there has been an ongoing evolution of its nomenclature, approach to diagnosis, characterization of symptoms, and determination of the burden of disease. In addition, an increased attention to and study of its epidemiology, neurobiology, and potential therapeutic strategies has begun to contribute to a better approach to identifying and treating it. At present, idiopathic hypersomnia is considered an orphan disease with unknown frequency and the cause is unknown; however, there is evidence to suggest circadian and sleep structure differences, structural brain changes, and neurochemical changes may contribute to the development and expression of this disease. The approach to treatment can be challenging owing to a limited number of approved treatments (calcium, magnesium, potassium, and sodium oxybates) in idiopathic hypersomnia. However, consideration of therapies shown to improve excessive daytime sleepiness in other disorders is frequently employed. Future directions require a clear consensus on the defining characteristics of idiopathic hypersomnia to enhance the opportunity for improved recognition, diagnosis, and treatment strategies to be established. This article provides a historical review of the evolving diagnostic classification of idiopathic hypersomnia, potential insights to the underlying pathophysiology, and a summary of proposed approaches for diagnosis and therapeutic intervention.