Decreased CSF histamine in narcolepsy with and without low CSF hypocretin-1 in comparison to healthy controls

Study Objective: To examine whether cerebrospinal fluid (CSF) histamine contents are altered in human narcolepsy and whether these alterations are specific to hypocretin deficiency, as defined by low CSF hypocretin-1. Methods: Patients meeting the ICSD-2 criteria for narcolepsy with and without cataplexy and who had CSF hypocretin-1 results available were selected from the Stanford Narcolepsy Database on the basis of CSF availability and adequate age and sex matching across 3 groups: narcolepsy with low CSF hypocretin-1 (n = 34, 100% with cataplexy), narcolepsy without low CSF hypocretin-1 (n = 24, 75% with cataplexy), and normal controls (n = 23). Low CSF hypocretin-1 was defined as CSF ≤ 110 pg/mL (1/3 of mean control values). Six of 34 patients with low CSF hypocretin-1, six of 24 subjects with normal CSF hypocretin-1, and all controls were unmedicated at the time of CSF collection. CSF histamine was measured in all samples using a fluorometric HPLC system. Results: Mean CSF histamine levels were: 133.2 ± 20.1 pg/mL in narcoleptic subjects with low CSF hypocretin-1, 233.3 ± 46.5 pg/mL in patients with normal CSF hypocretin-1 (204.9 ± 89.7 pg/mL if only patients without cataplexy are included), and 300.5 ± 49.7 pg/mL in controls, reaching statistically significant differences between the 3 groups. Conclusion: CSF histamine levels are reduced in human narcolepsy. The reduction of CSF histamine levels was more evident in the cases with low CSF hypocretin-1, and levels were intermediate in other narcolepsy cases. As histamine is a wake-promoting amine known to decrease during sleep, decreased histamine could either passively reflect or partially mediate daytime sleepiness in these pathologies.