Sleep-wake disorders and dermatology.

Sleep is an active process that occupies about one-third of the lives of humans; however, there are relatively few studies of skin disorders during sleep. Sleep disruption in dermatologic disorders can significantly affect the quality of life and mental health of the patient and in some situations may even lead to exacerbations of the dermatologic condition. Sleep and skin disorders interface at several levels: (1) the role of the skin in normal sleep physiology, such as thermoregulation, core body temperature control, and sleep onset; (2) the effect of endogenous circadian rhythms and peripheral circadian "oscillators" on cutaneous symptoms, such as the natural trough in cortisol levels during the evening in patients with inflammatory dermatoses, which most likely results in increased pruritus during the evening and night; (3) the effect of symptoms such as pruritus, hyperhidrosis, and problems with thermoregulation, on sleep and sleep-related quality of life of the patients and their families; (4) the possible effect of primary sleep disorders, such as insomnia, sleep apnea, sleep deprivation, and circadian rhythm disorders, on dermatologic disorders; for example, central nervous system arousals from sleep in sleep apnea can result in increased sympathetic neural activity and increased inflammation; and (5) comorbidity of some dermatologic disorders with stress and psychiatric disorders, for example, major depressive disorder and attention deficit hyperactivity disorder (ADHD) that are also associated with sleep-related complaints. Sleep loss in atopic dermatitis (AD) is likely involved in the pathogenesis of ADHD-like symptoms in AD. Scratching during sleep, which may be proportional to the overall level of sympathetic nervous activity during the respective stages of sleep, usually occurs most frequently during non-rapid eye movement (NREM) stages 1 and 2 (vs stages 3 and 4 which are the deeper stages of sleep), and in rapid eye movement (REM) sleep, where the severity of scratching is similar to stage 2 sleep. Patient and parental reports of nocturnal itch and scratching in AD typically do not correlate with objective measures of scratching.