Narcolepsy with cataplexy has high repeatability of positive multiple sleep latency test(MSLT), however, in the study by Trotti, only 33% of patients without cataplexy had a second positive MSLT.
Diagnostic criteria of narcolepsy type 2 in ICSD 3 completely depends on the result of MSLT as symptoms of cataplexy is not included. ICSD 3 over-relies on MSLT, so it results in diagnostic dilemmas. MSLT is validated in diagnosing type 1 narcolepsy, but it appears to have poor repeatability in type 2 narcolepsy. Mignot’s study showed MSLT repeatability was as high in type 1 as 71.7%-81.1%, low in type 2 narcolepsy as 16.7% to 30%. The lowest in control 6.7%-7.6%. It requires re-evaluation of current diagnostic criteria for type 2 narcolepsy and Idiopathic Hypersomnia, as ICSD 3 criteria heavily depends on the MSLT to render these diagnoses. MSLT is the gold standard for type 1 narcolepsy, but it may not be the best test for other pathologies of excessive daytime sleepiness including type 2 narcolepsy. YS Huang reported that type 1 narcolepsy is a well defined clinical entity and has reproducible clinical neurophysiologic findings over time. However, 17.6% of type 2 narcolepsy did not meet the diagnostic criteria of narcolepsy type 2 during the 5 year follow-up. They raised the question about whether we need to use type 2 narcolepsy as follow up MSLT results is variable. SC Hong reported the longitudinal follow up data of narcolepsy type 1. It had a very good repeatability. More than 95% of them retained meeting MSLT criteria. However, type 2 narcolepsy presented test variability, only 48% remained type 2 narcolepsy and 52% were changed as idiopathic hypersomnia or normal.
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