Narcolepsy, diagnosis

Dement WC, Carsadon MA, Guilleminault C, Zarcone V. Narcolepsy. Diagnosis and treatment. Prim Care 1976 3(4) 609-623. 

Although difficult to estimate, the prevalence of narcolepsy is between 0.03% and 0.06%.7 Significant differences have been reported for various ethnic groups. Narcolepsy has a higher prevalence in the Japanese and a lower prevalence in the Israeli populations.8,9 Cataplexy is not required for diagnosis however, between 50% and 80% of patients with narcolepsy have accompanying cataplexy.10... 

Scammell TE. The neurobiology, diagnosis, and treatment of narcolepsy. Ann Neurol 2003 53 154-166. 

Despite the reliability of these diagnostic tests, there are a few alternative conditions that must be considered when entertaining a diagnosis of narcolepsy. 

Insomnia. It may seem odd to include this in the differential diagnosis of a hypersomnia, but insomnia is in fact the most common cause of daytime drowsiness. In addition, it is common for patients with narcolepsy to have some difficulty sleeping at night and for their daytime symptoms to worsen at those times. 

Narcolepsy can usually be distinguished from insomnia by the presence of one of the auxiliary symptoms (cataplexy, sleep paralysis, hypnagogic hallucinations). When the diagnosis remains unclear, then a sleep study is necessary. 

It is relatively infrequent that narcolepsy does not respond to treatment with one of these medications. If the patient experiences no improvement with any of the stimulants, a reconsideration of the diagnosis is certainly warranted. 

Investigation and diagnosis of sleep disorders, especially sleep apnea and narcolepsy... 

Other (less specific) scales have also been used as part of the evaluation of EDS. The basic Nordic Sleep Questionnaire (24) is a quantitative measure of subjective sleep complaints not limited to sleepiness. It focuses on events that happen (during sleep or wakefulness), and grades them on a five-point scale from 1 (never) to 5 (almost every day/night). Thus it is best suited for events but not for sleepiness as such. The Sleep Disorders Questionnaire (SDQ) (25) was extracted from another comprehensive questionnaire, the Sleep Questionnaire and Assessment of Wakefulness (SQAW) of Stanford, but is more geared for the diagnosis of specific sleep disorders (e.g., sleep apnea, narcolepsy) than for the evaluation and quantification of EDS. 

Abnormal sleep-onset REM periods, which occur within 15 min of sleep onset, are of major importance in the diagnosis of narcolepsy. Other causes of sleep-onset REM periods, such as sleep deprivation or other sleep disorders (e.g., obstructive sleep apnea), must be excluded (28). 

Amira SA, Johnson TS, Logowitz NB. Diagnosis of narcolepsy using the Multiple Sleep Latency Test analysis of current laboratory criteria. Sleep 1985 8(4) 325-331. 

Aldrich MS, Chervin RD, Malow BA. Value of the Multiple Sleep Latency Test (MSLT) for the diagnosis of narcolepsy. Sleep 1997 20(8) 620-629. 

Mignot E, Lammers GJ, Ripley B, Okun M, NevsimalovaS, Overeem S, Vankova J, Black J, Harsh J, Bassetti C (2002) The role of cerebrospinal fluid hypocretin measurement in the diagnosis of narcolepsy and other hypersomnias. Arch Neurol 59 1553-1562... 

---