STUDY OBJECTIVES: To examine repeatability of Multiple Sleep Latency Test (MSLT) results in narcolepsy type 1 (NT1) and narcolepsy type 2 (NT2) according to the criteria of the International Classification of Sleep Disorders, Third Edition (ICSD-3). METHODS: Repeatability of the MSLT was retrospectively evaluated in NT1 (n = 60) and NT2 (n = 54) cases, and controls (n = 15). All subjects had documented HLA-DQB1*06:02 status and/or hypocretin-1 levels from cerebrospinal fluid. All subjects had undergone 2 MSLTs (≥ 1 meeting ICSD-3 criteria for narcolepsy). Repeatability was explored in children versus adults and in those on versus not on medication(s). Subsample and multivariate analysis were performed. RESULTS: Both MSLTs in unmedicated patients were positive for narcolepsy in 78%, 18%, and 7% of NT1, NT2, and controls, respectively. NT2 cases changed to idiopathic hypersomnia or to a negative MSLT 26% and 57% of the time, respectively. Although NT1 cases were 10 to 14 times more likely to demonstrate a second positive MSLT compared to NT2 cases (P < 10-5) and controls (P < 10-4), respectively, NT2 cases were not significantly different from controls (P = .64). Medication use (P = .009) but not adult versus children status (P = .85) significantly decreased the likelihood of a repeat positive MSLT. CONCLUSIONS: In a clinical setting, a positive MSLT for narcolepsy is a more reproducible and stable feature in NT1 than NT2. The retrospective design of this study hinders interpretation of these data, as there are many different, and possibly opposing, reasons to repeat a MSLT in NT1 versus NT2 (ie, ascertainment bias). Additional systematic MSLT repeatability studies independent of confounds are ideally needed to confirm these findings.

Center for Sleep Sciences and Medicine Department of Psychiatry and Behavioral Sciences Stanford University School of Medicine Palo Alto California

Department of Neurology 1st Medical Faculty Charles University Prague Czeck Republic

Department of Neurology Emory Sleep Center Emory University School of Medicine Atlanta Georgia

Department of Preventive Medicine University of Madison Wisconsin Madison Wisconsin

Department of Pulmonary Medicine Peking University People's Hospital Beijing China

IRCCS Istituto delle Scienze Neurologiche ASL di Bologna Bologna Italy Department of Biomedical and Neuromotor Sciences University of Bologna Bologna Italy

Sleep Center Cincinnati Children's Hospital Medical Center Cincinnati Ohio Division of Pulmonology and Sleep Medicine Cincinnati Children's Hospital Medical Center Cincinnati Ohio

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