Narcolepsy, a disabling disorder that affects approximately 1 of 2000 people worldwide, is characterized by excessive daytime sleepiness (EDS) and frequent overwhelming urges to sleep or inadvertent daytime lapses into sleep. Cataplexy, the sudden, involuntary loss of skeletal muscle tone that lasts from seconds to 1 or 2 minutes, is most often triggered by positive emotions and occurs in up to 70% of cases. Cataplexy can commonly manifest as jaw sagging and/or knees buckling, but it can present more subtly or can result in temporary total-body paralysis, leading to the affected patient falling to the ground. Other characteristic symptoms include sleep paralysis and hallucinations, which classically occur at the transition from wake to sleep, and vice versa (ie, hypnagogic and hypnopompic). In addition, disrupted nighttime sleep is common.
Once they emerge, the symptoms of narcolepsy are usually lifelong, especially when the illness is associated with cataplexy. Although symptoms usually appear in late adolescence or early adulthood, on average there is a delay of 10 years before an accurate diagnosis is established. In part, the delay in diagnosis may stem from a general lack of physician awareness of narcolepsy; the broad array of symptoms that may be difficult to differentiate from symptoms of other disorders; and the wide range of both medical and psychiatric comorbidities associated with narcolepsy, including obesity, other sleep disorders, and psychiatric illnesses. Unfortunately, delay in diagnosing narcolepsy can contribute to the patient’s already significant disease burden, leading to decreased quality of life (QOL).
Diagnosis of narcolepsy
A diagnosis of narcolepsy depends on clinical history and diagnostic testing. Nocturnal polysomnography and the multiple sleep latency test (MSLT) can be used to confirm narcolepsy and evaluate for other causes of EDS. The MSLT quantitates sleep propensity as an objective measure of daytime sleepiness and involves a series of 5 naps separated by 2-hour intervals throughout the day. The diagnostic MSLT findings for narcolepsy include a mean sleep latency (across all 5 naps) of 8 minutes or less with rapid eye movement sleep during at least 2 of the 5 naps.
Accurately diagnosing narcolepsy can be challenging because of a variety of psychiatric comorbidities, including depressive disorders, bipolar disorder, and schizophrenia. The presence of comorbidities may partially mask the symptoms of narcolepsy and result in missed diagnoses. Similarly, narcolepsy without comorbid psychiatric conditions can be mistaken for psychiatric illness, including psychosis. It is important to note that obstructive sleep apnea, often seen in patients with narcolepsy, is also associated with psychiatric disorders.
In addition, there may be symptom overlap between narcolepsy and common psychiatric illnesses; for example, depressed patients may have both EDS and fatigue, and the hypnagogic hallucinations characteristic of narcolepsy may be confused with the hallucinations of psychosis. Furthermore, both patients with narcolepsy and those with psychiatric illnesses may have impaired cognitive performance. Because of the functional impairments characteristic of narcolepsy, including problems at work, at school, and in relationships, and reduced QOL, patients with narcolepsy without comorbid psychiatric disease may be nonetheless referred to a psychiatrist for evaluation.
Given the frequency of missed diagnosis and misdiagnosis of narcolepsy, it is important to have a high index of suspicion and to consider an evaluation for narcolepsy whenever daytime sleepiness is reported or observed. An overnight sleep study and MSLT evaluation should be considered in the diagnostic workup. In the more challenging cases, checking cerebrospinal fluid for hypocretin, which is often decreased or absent in narcolepsy, may help confirm the diagnosis.
An important consideration in the diagnostic evaluation of narcolepsy and other causes of sleepiness is the inclusion of family members or others who know the patient well. Persons close to the patient can often provide essential information that the patient is not fully aware of or is unable to adequatelyarticulate.
Dr Ruoff is Clinical Assistant Professor at The Stanford Center for Sleep Sciences and Medicine and Assistant Program Director at the Stanford Sleep Medicine Fellowship in Redwood City, Calif. Dr Black is Consulting Associate Professor at The Stanford Center for Sleep Sciences and Medicine. Dr Ruoff reports that he attended the Advisory Board Meeting, October 25-26, 2012: Best Practices in Narcolepsy Management for Jazz Pharmaceuticals. Dr Black reports that he is a part-time employee of Jazz Pharmaceuticals.
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