Narcolepsy is the second most common cause of excessive daytime sleepiness. It affects 0.03-0.06 percent of population in North America and Western Europe. The typical age of onset of symptoms is second decade of life.
A 52-year-old male with no history of excessive daytime sleepiness suffered insect bite on his back during an outdoor picnic. The bite produced an unusually large local reaction. Three weeks later, he developed episodes of generalized weakness requiring that he lie down, in association with strong emotions such as anger and laughter, persisting for several minutes. In addition, he started having severe excessive daytime sleepiness. He was evaluated by a neurologist and a psychiatrist and underwent testing, which included MRI of brain, EEG and a nocturnal polysomnogram. Polysomnogram revealed very short sleep-latency and no obstructive sleep apnea. Later, a multiple sleep latency test (MSLT) confirmed the diagnosis of narcolepsy with mean sleep latency of 2.5 minutes and no sleep onset REM periods. Rest of his work-up remained non-revealing. He was then treated by a sleep physician with high doses of Methylphenidate and Paroxetine, which significantly improved his daytime sleepiness and cataplexy. Now, some ten years after the onset of his symptoms he continues to have at least some excessive daytime sleepiness and occasional cataplexy despite the above medication.DISCUSSION: The exact pathophysiology of narcolepsy remains unknown. Neurochemical studies of human, canine and murine narcolepsy suggest that narcolepsy is associated with low levels of Hypocretin in cerebrospinal fluid(CSF). Several genetic, neurochemical and autoimmune associations have been described as potential etiologies for the characteristic pattern of neuronal destruction which results in low Hypocretin levels. Possibly, narcolepsy can be a result of an autoimmune process which develops in genetically predisposed humans. Environmental and other host factors, which contribute to the development of this autoimmunity, are not clearly understood.
The precipitous evolution of full blown classical narcolepsy with cataplexy in this older man, following an unusually severe reaction to an insect bite, suggests the possibility of immunologic mechanism as the basis for the development of narcolepsy.This lends support to the hypothesis that immune mediated neuronal destruction results in the development of narcolepsy.
S. Alam, None.