Figure 1.

Proposed algorithm for the diagnosis of narcolepsy without cataplexy and its differential diagnoses. ISS, insufficient sleep syndrome (chronic sleep deprivation); CSF, cerebrospinal fluid; EDS, excessive daytime sleepiness; ESS, Epworth Sleepiness Scale; MSL, mean sleep latency; MSLT, multiple sleep latency test; SOREMP, sleep onset rapid eye movement sleep. ⁽¹⁾ In patients with an atypical history or neurological deficits, other causes of narcolepsy-like findings should be considered, and a brain MRI should be performed. Suggested laboratory parameters include a full iron panel, complete blood count, vitamin B12, and thyroid markers (TSH, T4). Children with Na-2 should receive a more extensive workup for unusual causes of sleepiness (e.g., tumors, metabolic disorders, seizures). ⁽²⁾ Sleep logs or preferably actigraphy over 14 days should be performed before the PSG and MSLT to exclude ISS or shift work. If the habitual sleep schedule is a concern, it may be helpful to schedule the MSLT just after 1-2 weeks' vacation to provide an opportunity for adequate sleep on a regular schedule. ⁽³⁾ During the nocturnal PSG, the patient should be permitted their habitual amount of sleep, which will usually be more than 6 hours of sleep. Long sleepers should be allowed to sleep up to 10 hours. ⁽⁴⁾ MSLT should be performed according to AASM guidelines, and medications that might alter sleep pressure or REM sleep should be discontinued well in advance. For example, antidepressants should be discontinued at least 3 weeks prior to the sleep studies. ⁽⁵⁾ According to ICSD-3 criteria, one SOREMP within 15 minutes of sleep onset on the preceding nocturnal PSG can be included in the total SOREMP count. ⁽⁶⁾ In patients without cataplexy, we recommend measuring CSF hypocretin to distinguish Na-1 from Na-2. ⁽⁷⁾ A clinical history of frequent hypnagogic/hypnopompic hallucinations, frequent sleep paralysis, fragmented nocturnal sleep, or positive HLA DQB1*06:02 typing may increase the likelihood of Na-2. ⁽⁸⁾ Sleep inertia, the need for multiple alarm clocks, and long but unrefreshing daytime naps are more indicative of idiopathic hypersomnia. ⁽⁹⁾ In patients with multiple SOREMPs but normal mean sleep latency or normal hypocretin levels, the MSLT should be repeated, preferably after a period of documented sleep extension.