P109 Role of Multiple Sleep Latency Test (MSLT) in the workup of children with hypersomnolence

Abstract Introduction Hypersomnolence and excessive daytime sleepiness (EDS) can be idiopathic or associated with narcolepsy. The Multiple Sleep Latency Test (MSLT) is gold standard for diagnosing narcolepsy, though significant gaps currently exist in understanding the interpretation of MSLT in diagnosing and managing paediatric hypersomnolence. This retrospective study aims to describe a) a cohort of children investigated for hypersomnia and b) their MSLT outcomes. Methods Clinical, demographic, and MSLT data were retrospectively collected from children who underwent hypersomnolence investigation at a tertiary paediatric hospital (January 2015-December 2023). Data included age, gender, BMI, comorbidities, medications, polysomnography, MSLT results, diagnoses, treatment, and outcomes. The association between MSLT parameters and diagnostic outcomes was explored using American Sleep Association criteria. Results 125 children (56F) were identified through our hospital database, with data on 72 (30F; median age 12.42 years, IQR=4.11) collected. 19 (26%) were HLA-positive for narcolepsy. MSLT parameters suggested narcolepsy in 13 (18.1%) children; 1 additional child had low orexin levels. Median sleep latency was significantly shorter in the narcolepsy group compared to non-narcolepsy (01:39 minutes vs. 12.58 minutes, p<0.001). No age or gender differences were observed between groups. Diagnostic PSG on the preceding night led to alternate diagnoses in 5 children. Discussion While the data is only partially complete, interim analysis suggests narcolepsy is present in a minority of this cohort. PSG from the preceding night changed in the diagnosis in 5 children. However, the fifth nap did not change any outcomes, so the utility of this practice needs to be re-explored.