Study objectives: In healthy subjects, sleep propensity increases when the distal skin temperature increases relative to the proximal skin temperature. This increase results from increased blood flow in the skin of the extremities and is, among other factors, controlled by the hypothalamic circadian clock, as is sleep. Because narcolepsy is characterized by hypothalamic alterations, we studied skin temperature in narcoleptic patients in relation to their characteristically increased sleep propensity during the day.
Design: Distal and proximal skin temperature and their gradient (DPG) were measured during a Multiple Sleep Latency Test. This allowed temperature to be studied during wakefulness, at sleep onset and during sleep.
Setting: Tertiary narcolepsy referral center in a university hospital.
Patients: Fifteen unmedicated narcolepsy patients with cataplexy and 15 controls.
Interventions: None.
Measurements and results: In subjects in the waking state, DPG was higher in narcoleptics than in controls throughout the day (time by group interaction, p < .0001), due to increased distal skin temperature and decreased proximal skin temperature. The increase in DPG was related to a shorter subsequent sleep-onset latency (p = .02). Once asleep, narcoleptics maintained their elevated distal skin temperature and DPG (p < .0001), whereas proximal skin temperature increased to reach normal levels.
Conclusions: This is the first demonstration of a dramatic alteration of daytime skin temperature control in narcolepsy. Even awake narcoleptic patients showed a DPG higher than that which healthy controls achieve when asleep. This observation suggests that hypocretin deficiency in narcolepsy affects skin-temperature regulation and invites further examination. Skin-temperature control might ultimately even have therapeutic implications for the alleviation of narcoleptic symptoms.