What is Narcolepsy? The main symptoms of narcolepsy are daytime sleepiness and abnormal features of dream sleep (i.e, rapid-eye-movement, or, REM, sleep). A subgroup of patients (~ 1/3rd) have disrupted nocturnal sleep, although sleep time across 24 hours is typically normal. The usual age of onset is in the mid-to-late teens although it can begin in the pre-teens or at a later age, and it is a life-long illness. Narcolepsy occurs in two forms with different underlying causes: narcolepsy with cataplexy and narcolepsy without cataplexy. Narcolepsy without cataplexy shares some features in common with narcolepsy with cataplexy and other features with idiopathic hypersomnia. The remainder of this section refers to narcolepsy with cataplexy. Daytime sleepiness in narcoleptics typically occurs as irresistible urges to fall asleep – sometimes referred to as “sleep attacks” — at random intervals throughout the waking day. These short bouts of sleep are usually refreshing or ‘restorative’ in quality, as is night-time sleep. Abnormal features of dream sleep include: hallucinations, sleep paralysis, and cataplexy. Patients can experience dream-like auditory or visual hallucinations upon falling asleep or dozing that are termed hypnagogic hallucinations. Sleep paralysis can be a frightening sensation of feeling paralyzed and unable to move upon falling asleep or awakening from sleep that lasts for several minutes. Cataplexy is a symptom unique to narcolepsy in which the patient experiences a sudden loss of muscle tone for tens of seconds to minutes, and these are provoked by emotional situations such as laughter, hearing or telling a joke, fear, or anger. Cataplexy varies greatly in intensity and duration from a patient’s knees buckling or jaw becoming lax briefly, to the eyelids and head drooping (thus, mimicking sleep to an observer), to the patient falling down and being unable to move for several minutes. It is a critical distinction that conscious awareness of the environment is preserved in patients during an attack of cataplexy although it might appear to an observer that the patient has “passed out” or “fainted”. A substantial proportion of patients with narcolepsy have disrupted dream sleep that can manifest as acting out dreams (e.g., rapid-eye-movement (REM) – sleep behavior disorder) and periodic leg movements in sleep.
What causes narcolepsy with cataplexy? Narcolepsy is a disorder of the nervous system in which there is immune system mediated destruction of brain cells that contain hypocretins (aka orexins). These brain cells are located in a brain region called the hypothalamus and are critical to maintenance of wakefulness, continuity of sleep, and coordination of the timing and features of dream sleep (i.e., rapid-eye-movement, or REM, sleep).
Diagnosing Narcolepsy: Cataplexy is a symptom that occurs almost exclusively in patients with narcolepsy, so its presence strongly suggests this diagnosis. However, cataplexy can sometimes be subtle or mild, making additional testing necessary. As in idiopathic hypersomnia, diagnosis depends on ruling out causes of secondary hypersomnia and a polysomnogram with multiple sleep latency test (MSLT). On the MSLT, it takes less than 8 minutes on average for patients to fall asleep, and dream sleep is observed on at least two naps. Patients with narcolepsy without cataplexy show the same results on MSLT as those with cataplexy. In cases with persistent diagnostic uncertainty (e.g., because cataplexy is subtle or not clearly present), testing for hypocretin within cerebrospinal fluid (by lumbar puncture) can be valuable. Patients with narcolepsy with cataplexy will demonstrate low or undetectable hypocretin levels.