Clinical caveat: prior sleep deprivation can affect the MSLT for days.

It is common practice to forcibly awaken patients from an all-night polysomnographic study prior to performance of a multiple sleep latency test (MSLT); either for reasons of protocol or for the convenience of the laboratory personnel. We report a case of a young woman who, by formal sleep study criteria, received the erroneous diagnosis of narcolepsy due to the effects of severe sleep deprivation, and document that the effects of prior sleep deprivation require more than one night of ad libitum sleep. Forced awakening prior to MSLT may permit sleep deprivation or delayed sleep phase syndrome to masquerade as narcolepsy or idiopathic central nervous system (CNS) hypersomnia.