![]() The subregion of the hypothalamus containing the hypocretin cells was known to be especially important for the regulation of feeding. The hypothalamus, a region localized deep in the base of the brain, regulates many basic functions such as the release of hormones, blood pressure, sex, food intake regulation and sleep. Only 10,000-20,000 cells in the entire human brain, out of many billions, secrete these specific hypocretin molecules. The first group called them "hypocretin-1" and "hypocretin-2" after discovering that the molecules were found only in the hypothalamus and had some weak resemblance with the gut hormone secretin. Hypocretins (orexins) were discovered by two groups of researchers almost simultaneously, hence the two names "hypocretins" and "orexins". Recent results have shown that the MSLT is only repeatable in NT1, yet it is still used as the main diagnostic tool. Most specific for the diagnosis however is the fact patients with narcolepsy enter into REM sleep frequently in these naps, with at least two REM sleep events observed in 5 naps considered diagnostic for narcolepsy, whether NT1 (with cataplexy or hypocretin deficiency) or narcolepsy type 2 (NT2 without cataplexy or hypocretin deficiency). In narcolepsy or hypersomnia, patients fall asleep much more rapidly than controls, with a mean sleep latency of less than 8 minutes considered revealing of pathological sleepiness. The MSLT, conducted after a PSG, measures the time taken by patients to fall asleep (sleep latency) during naps in a quiet environment and the occurrence of REM sleep in these naps. It is mostly used to exclude obstructive sleep apnea, a common differential diagnosis, but may also reveals abnormalities in REM sleep, such as a very short REM sleep latency in NT1 in 50% of the time. The polysomnogram is an overnight test, which takes continuous measurements of the EEG, EOG, EMG, ECG, breathing and leg movements. ![]() The Multiple sleep Latency test (MSLT) is the gold standard diagnostic test for narcolepsy and hypersomnia.
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