Etiopathogenesis and neurobiology of narcolepsy: a review

Abstract

Narcolepsy is a chronic lifelong sleep disorder and it often leaves a debilitating effect on the quality of life of the sufferer. This disorder is characterized by a tetrad of excessive daytime sleepiness, cataplexy (brief loss of muscle tone following strong emotion), hypnogogic hallucinations and sleep paralysis. There are two distinct subgroups of Narcolepsy: Narcolepsy with cataplexy and Narcolepsy without cataplexy. For over 100 years, clinicians have recognised narcolepsy, but only in the last few decades have scientists been able to shed light on the true cause and pathogenesis of narcolepsy. Recent studies have shown that a loss of the hypothalamic neuropeptide Hypocretin/Orexincauses Narcolepsy with cataplexy and that an autoimmune mechanism may be responsible for this loss. Our understanding of the neurophysiologic aspect of narcolepsy has also significantly improved. The basic neural mechanisms behind sleepiness and cataplexy, the two defining symptoms of narcolepsy have started to become clearer. In this review, we have provided a detailed account of the key aspects of etiopathogenesis and neurobiology of narcolepsy, along with a critical appraisal of the more recent and interesting causal associations.We have also looked at the contributions of neuroimaging to the etiopathogenesis of Narcolepsy.

Keywords: Cataplexy; Human Leukocyte Antigen (HLA); Hypocretin/ Orexin; Narcolepsy; Rapid eye movement (REM) sleep.

[Table/Fig-1]:

A diagrammatic model summarizing the Etiopathogenesis and Neurobiology of Narcolepsy., Key: SLD nucleus – Sublaterodorsal nucleus; vlPAG – Ventrolateral Periaqueductal Gray; vLT- LateralTegmentum of Pons; (+) → Excitatory signal; (-) → Inhibitory signal; (+) → Loss of Excitatory signal; (-) → Loss of Inhibitory signal