P084 Is there a clinical role for repeating the Multiple Sleep Latency Test across childhood?

INTRODUCTION: The gold standard investigation for central disorders of hypersomnolence in children is the Multiple Sleep Latency Test (MSLT). MSLT diagnostic cut-offs are extrapolated from adult data. Currently there are no guidelines available regards the utility and timing of repeating paediatric MSLTs. METHODS: Retrospective review of children with ≥2MSLTs at our tertiary centre between 2005–2022. Narcolepsy defined as mean sleep latency (MSL) <8min with ≥2 sleep onset REM (SOREM); idiopathic hypersomnolence (IH) defined as MSL <8min with <2 SOREM. MSLTs not meeting these criteria were labelled non-diagnostic. PROGRESS: 19 children (9F) with initial non-diagnostic MSLT underwent repeat MSLT with 5 proceeding to a 3rd MSLT following 2 non-diagnostic MSLTs. Repeat MSLT resulted in diagnosis in 6/19 (32%) (3 narcolepsy, 3 IH); whereas only 1/5 3rd repeat MSLT was diagnostic (IH). Median age at initial MSLT was 7.5y (range 3.4-17.8y), with repeat after 2.9y (range 0.9-8.2y), and 3rd after 2.1 years (range 1.2-4.2y). Mean change in MSL on repeat testing was -2min (range -15.5min to +4.9min, p=0.18). MSL reduced to <10 minutes in one child, allowing access to PBS subsidised treatment. Of the 7 diagnostic repeat MSLTs, 2 had ≥2 SOREM and reduced MSL, 1 had reduced MSL (with 3 SOREM on initial and subsequent test), 4 had reduced MSL without SOREM. OUTCOME: A third of repeat MSLTs became diagnostic, suggesting repeat MSLT in childhood should be considered if clinical suspicion persists. Further work needs to address the repeat interval between MSLTs and current diagnostic cut-points in the paediatric population.