Sleep-Wake Disorders I

Insomnia Disorder has been linked to disruptions in the circadian rhythm biological clock of the sleep-wake cycle in humans. Insomnia Disorder is a diagnosis assigned to individuals who experience recurrent poor sleep quality or quantity that results in distress or impairment in important areas of functioning. It can lead to associated mental impairment. The diagnostic criteria for duration are acute (less than 1 month), subacute (1 to 3 months), and chronic (longer than 3 months). The disorder may be mild, moderate, or severe.

Contributors to the onset of Insomnia Disorder include:

• Snoring noise of the partner or frequent crying at night by an infant
• Incessant barking of a dog or other noise in the community 
• Overactive mind
• Pregnancy
• Watching TV and movies late at night
• Playing video games late at night
• Stress and anxiety
• Other sleep disorders such as sleep apnea or restless leg syndrome
• Medical conditions: chronic pain, nasal allergies, asthma, arthritis, reflux, and thyroid disorders 
• Substance abuse

Hypersomnolence Disorder, a Sleep-Wake Disorder, is one in which people have difficulty staying awake during the day. It is characterized by excessive daytime sleepiness (EDS), or excessive time spent sleeping, along with a tendency to fall asleep at any time and often unexpectedly. This occurs even with a main sleep period of at least 7 hours, or a prolonged main sleep episode of more than 9 hours per day that is nonrestorative. 

A diagnosis of primary disorder (within the brain) or secondary disorder (the presence of an underlying physical cause) typically is made when symptoms have been present for three months. Hypersomnolence occurs with relatively equal frequency in males and females.

Narcolepsy Disorder is a neurological sleep-wake disorder that involves disturbed sleep-wake cycles. It is characterized by recurrent periods of an irresistible need to sleep, or will fall asleep, or nap excessive sleepiness in the daytime (despite adequate nocturnal sleep), along with suddenly falling asleep during activities. It can occur in childhood, adolescence, or young adulthood. The specific cause of narcolepsy is unknown. 

A diagnosis may be made when individuals experience recurrent periods of falling asleep or napping within the same day, regardless of whether or not the time and place are appropriate. These episodes must occur at least three times per week over the past three months, accompanied by at least one of the following:

• Episodes of cataplexy occur in which there is a sudden and very brief loss of muscle tone without a loss of consciousness following laughter or embarrassment or being startled. Patients may experience a head drop, knees buckling, or the whole body may collapse on the ground with the person suddenly becoming the center of attention. Partial cataplexy may involve sudden tingling, tremor, small muscle jerk or facial twitch, and being clumsy or dropping things. Cataplexy affects approximately 70 percent of people who have narcolepsy and is caused by an autoimmune destruction of hypothalamic neurons that produce the neuropeptide hypocretin, which regulates arousal and has a role in stabilization of the transition between wake and sleep states. Cataplexy without narcolepsy is rare and the cause is unknown.

• Objective measure of a deficiency in the cerebrospinal fluid of the neuropeptide hypocretin.

• Involuntary grimacing or jaw-opening with tongue thrusting, or hypotonia—an abnormally low level of muscle tone—within six months of narcolepsy onset and in the absence of emotional triggers.

• Nocturnal sleep polysomnography study revealing abnormally low Rapid Eye Movement (REM) sleep with specific parameters.

Circadian Rhythm Sleep Disorder, also known as circadian rhythm sleep-wake disorder, is a class of sleep disorders in which a person’s internal sleep wake clock is disrupted, which also affects the timing of sleep. Circadian Rhythm Sleep Disorder is characterized by a discrepancy between the internal setting of one’s circadian clock, and the sleep wake schedule required by one’s occupational/educational or social obligations. The disturbed rest can cause individuals affected by the disorder to be unable to go to sleep and awaken at “normal” times for work, school, and other social obligations. Insufficient sleep and working against one’s rhythm is associated with long-term health problems that can result in a decrease in resting metabolic rate and reduced pancreatic beta cell responsiveness, leading to obesity and risk of adult-onset diabetes.

The word Circadian comes from the Latin “circa” meaning approximately and “diem” meaning day. The human body follows a cycle of circadian rhythms of approximately 24 hours—23.5 to 24.5 hours. Because of this difference, the internal circadian rhythm clock must be continually adjusted, a process known as entrainment. This cycle regulates behavioral and physiological functions including a person’s level of arousal and alertness known as a sleep-wake cycle. The circadian clock is “set” primarily by visual cues of light and darkness that are communicated along a pathway from the eyes to the suprachiasmatic nucleus (SCN). This keeps the clock synchronized or entrained to the approximate 24-hour day. 

Circadian rhythms are intrinsically hardwired into the suprachiasmatic nucleus (SCN) in the brain’s hypothalamus. They are regulated by external cues, the availability of light taken in by the eyes being the primary signal to the SCN. Although Circadian rhythms run synchronized to light, it is early morning light exposure that rewinds the Circadian rhythm. Mid-day light exposure produces little or no rewinding. Bedtime-light exposure produces a delay in the circadian rhythm. A homeostatic process is also involved to produce sound sleep at night and alert wakefulness during the day. A disruption in either the rewinding of the circadian clock or the homeostatic process can result in a Circadian Rhythm Sleep Disorder. The outcome can be trying to sleep when the body wants to be awake or trying to stay awake when the body is insisting on sleep.