neurologic disorders
Circadian Rhythm Sleep Disorders
Introduction
Circadian rhythm sleep disorders are caused by desynchronization between internal sleep-wake rhythms and the light-darkness cycle. Patients typically have insomnia, excessive daytime sleepiness, or both, which typically resolve as the body clock realigns itself. Diagnosis is clinical. Treatment depends on the cause. (See also Approach to the Patient With a Sleep or Wakefulness Disorder .) In circadian rhythm disorders, endogenous sleep-wake rhythms (body clock) and the external light-darkness cycle become misaligned (desynchronized). The cause may be internal (eg, delayed or advanced sleep phase syndrome) or external (eg, jet lag, shift work). Circadian rhythm sleep disorders may occur in patients with Alzheimer disease or Parkinson disease and in patients who have had head trauma or encephalitis. If the cause is external, other circadian body rhythms, including temperature and hormone secretion, can become out of sync with the light-darkness cycle (external desynchronization) and with one another (internal desynchronization); in addition to insomnia and excessive sleepiness, these alterations may cause nausea, malaise, irritability, and depression. Risk of cardiovascular and metabolic disorders may also be increased. Repetitive circadian shifts (eg, due to frequent long-distance travel or rotating shift work) are particularly difficult to adapt to, especially when the shifts change in a counterclockwise direction. Counterclockwise shifts are those that shift awakening and sleeping times earlier (eg, when flying eastward, when rotating shifts from nights to evenings or days). Symptoms resolve over several days or, in some patients (eg, older patients), over a few weeks or months, as rhythms readjust. Because light is a strong synchronizer of circadian rhythms, exposure to bright light (sunlight or artificial light of 5,000 to 10,000 lux intensity) after the desired awakening time and the use of sunglasses to decrease light exposure before the desired bedtime speed readjustment. Other drugs used to treat insomnia before bedtime may help. Patients with circadian rhythm disorders often misuse alcohol, hypnotics, and stimulants. Circadian rhythm disorders include the following: Circadian rhythm sleep disorder, jet lag type (jet lag disorder) Circadian rhythm sleep disorder, shift work type (shift work disorder) Circadian rhythm sleep disorder, altered sleep phase types 