title: Benefit of repeat multiple sleep latency testing in confirming a possible narcolepsy diagnosis.
abstract: OBJECTIVE
  The clinical diagnosis of narcolepsy is usually uncomplicated in the presence of cataplexy. Objective testing is more important in ambiguous disease. The gold-standard objective test in these cases is the multiple sleep latency test (MSLT). Repeat testing can be burdensome but is reasonable when faced with a diagnostic dilemma. However, there is limited evidence to support this approach. In this study, we assessed the diagnostic utility of a repeat MSLT in patients suspected of narcolepsy whose first MSLT result was nonconfirmatory.
  
  
  METHODS
  Of 125 patients who underwent an MSLT between 2004 and 2009, we identified 10 (9.6%) who had undergone repeat studies. We analyzed changes in MSLT parameters while taking account of other relevant differences between testing.
  
  
  RESULTS
  Two patients (20%) met narcolepsy criteria during the second MSLT. Nine patients (90%) met sleepiness criteria (mean sleep latency <8 minutes) during the second MSLT while only 5 did during the first (P = 0.05).
  
  
  CONCLUSIONS
  We demonstrate that a repeat MSLT confirmed the diagnosis of narcolepsy in 20% of patients whose results had been nonconfirmatory on a first MSLT. This study provides support for a repeat MSLT in cases where clinical suspicion for narcolepsy is high despite an ambiguous first test.
authors.affiliation: Division of Neurology, Department of Medicine, Sunnybrook Health Sciences Centre, University of Toronto, Ontario, Canada.
authors.forename: Fernando M S
authors.initials: FM
authors.lastname: Coelho
authors.forename: Hlynur
authors.initials: H
authors.lastname: Georgsson
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Murray
mesh_terms: D006801:Humans; D009290:Narcolepsy / Q000175:diagnosis* / Q000503:physiopathology*; D017286:Polysomnography / Q000379:methods*; D012890:Sleep / Q000502:physiology; D012894:Sleep Stages / Q000502:physiology*; D013997:Time Factors