Circadian Rhythm Sleep Disorders
Circadian rhythm refers to a person’s internal sleep and wake-related rhythms that occur throughout a 24-h period. The term circadian rhythm sleep disorder (CRSD) refers to persistent pattern of sleep disruption due to either an altered sleep–wake schedule or an imbalance between an individual’s natural sleep–wake cycle and the sleep-related demands. The sleep disruption leads to insomnia or EDS, resulting in impairment in important areas of functioning and quality of life.3
The CRSDs may be classified into exogenous and endogenous categories. The clinical presentation of most of the CRSDs is influenced by a combination of physiological, behavioral and environmental factors. Therapeutic interventions include sleep hygiene education, timed exposure to bright light and pharmacologic approach with melatonin.11
The primary or intrinsic category includes:
- Advanced sleep phase disorder (ASPD)
- Delayed sleep phase disorder (DSPD)
- Non-24-h sleep–wake syndrome (Free-running type)
- Irregular sleep–wake rhythm
The secondary or extrinsic group includes:
- Shift work disorder (SWD)
- Jet lag
Delayed Sleep Phase Disorder
Delayed sleep phase disorder is characterized by a chronic inability to fall asleep at a desired or acceptable time.
The proposed mechanisms for DSP include the following:
- An unusually long endogenous circadian period.
- Hypersensitivity to evening light, which delays the circadian clock or reduced sensitivity to morning light, which decreases the phase advancing effect of morning light.
- Genetic mutations.
Patients with DSPD typically presents with complaints of difficulty falling asleep, in waking up in the morning and excessive sleepiness that interfere with daytime function. Individuals with DSPD may seek the use of alcohol or sedative hypnotic agents as an alternative to induce sleep, leading to alcohol or drug dependence. The goal of therapy is to advance the timing of the sleep–wake cycle in relation to the desired schedules. Treatment options include chronotherapy, bright light therapy and use of melatonin.
Chronotherapy is a technique in which the bedtime is systematically delayed by 3-h increments every 2 days until an early bedtime schedule is achieved and maintained. The use of bright light early in the morning and avoidance of light in the evening is also an effective approach.
The hypnotic and rhythm-regulating properties of melatonin make it an important addition in the treatment of DSPD. The effect of melatonin on sleep is the consequence of increasing sleep propensity (by inducing a fall in body temperature) and of a synchronizing effect on the circadian clock (chronobiotic effect).12 However, melatonin is not an FDA-approved indication for the treatment of any CRSDs.11
Advanced Sleep Phase Disorder
Advanced sleep phase disorder is a sleep disorder in which there is a stable advance of the major sleep period, characterized by habitual and involuntary sleep onset and wake-up times that are several hours earlier relative to normal times. This results in very early onset of sleep and early awakening in the morning, after a normal amount of undisturbed sleep. Typically, sleep begins between 6 and 9 O’clock in the nighttime and patients usually awaken between 2 and 5 O’clock in the morning. The condition is more common among middle-age and older age population.
The possible etiologies of ASPD include the following:
- Shortened endogenous circadian period.
- Increased retinal sensitivity to light in the morning.
- Genetic mutation.
Bright light therapy is the most widely used treatment approach for ASPD. The therapy helps to improve sleep efficiency, delays wake time and reduces wake time during sleep. Chronotherapy, has also been shown to be effective in the treatment of ASPD.
Non-24-h Sleep–Wake Syndrome
This syndrome consists of a pattern comprising daily delays of 2–4 h in onset of sleep and wake times. When the circadian rhythm is not entrained to the 24-h day, but allowed to run freely, the sleep period will drift later each day. Retinal blindness is one of the common causes of this disorder. Most patients with this type of nonentrained sleep–wake cycles are blind.
The etiology of this disorder in blind people is likely due to lack of light perception. However, the precise etiology in normal-sighted individuals is unknown. The possible contributing factors in sighted group include decreased exposure or responsiveness of the circadian clock to light and/or an unusually long free-running circadian period that is beyond the range of entrainment.
Treatment of this syndrome includes reinforcement of daily time reminder. A combined approach of sleep hygiene education, structured social and physical activities and when indicated, pharmacotherapy with melatonin (in blind individuals) is recommended for the management of this condition.
Irregular Sleep–Wake Rhythm
This pattern consists of disorganized and variable episodes of sleep and wakefulness. The sleep is broken up into multiple short periods of time during each 24-h phase. In addition, there is marked day-to-day variation in the onset of sleep and wakefulness.
The cause of irregular sleep–wake rhythm can be attributed to either disruption of the circadian clock, the entrainment pathways, and/or due to reduced exposure to environmental synchronizing agents. The syndrome may occur in individuals with central nervous system disorders such as head injury and Alzheimer’s dementia. It is also found in a variety of developmental disabilities.
The aim of treatment for this condition is to consolidate sleep during the night and to maintain wakefulness during the day. Treatment modalities include increasing daytime social interactions and physical activity, light exposure during the day and reduction in nighttime light and noise exposure.
Shift Work Disorder
Shift work disorder consists of symptoms of insomnia or EDS that occur in relation to work schedules. The condition usually persists for the duration of the work shift period. The reduction in sleep time generally ranges from 1–4 h and often affects REM sleep. Patients feel unsatisfied with their sleep and awake not feeling refreshed.
In SWD, the prolonged sleep deprivation can impair social and cognitive function while pathologic sleepiness may lead to safety and health hazards. Drug and alcohol dependence may occur from attempts to improve sleep disturbances. Further, women may have problems with menstrual cycle irregularities and difficulty in becoming pregnant.
Sleep hygiene education and CBT is the preferred treatment for all SWD patients with insomnia. Short-acting benzodiazepines and melatonin can help improve sleep quality. The use of bright light as a synchronizer in shift work and judicious use of caffeine may be helpful in individuals with EDS. The only way to avoid SWD is to maintain a regular work schedule and sleep and wake pattern.
Desynchronization of circadian rhythmicity resulting from rapid travel through at least four time zones leads to condition known as jetlag.13 The sleep-related symptoms of jet lag are difficulty in falling sleeping, EDS and daytime drowsiness, leading to irritability and performance impairment. Symptoms are often more severe with increasing time zones crossed and with eastbound flights.
A direct approach for dealing with jet lag includes controlling sleeping and napping to optimize sleep to the appropriate time in the new location. A structured sleep schedule will help in preventing insomnia on arrival. In addition, light therapy and good sleep hygiene should be practiced. Preventive strategies include adequate hydration, avoidance of caffeine and alcohol and practice of static exercises on the plane. When the above options fail, short-acting benzodiazepines and melatonin can be used to enhance sleep.