Medical conditions and mental disorders with the symptom of early morning awakening, such as insomnia, can co-occur with the advance sleep phase type.
The diagnosis of irregular sleep-wake type is based primarily on a history of symptoms of insomnia at night (during the usual sleep period) and excessive sleepiness (napping) dur- ing the day. Irregular sleep-wake type is characterized by a lack of discernable sleep-wake circadian rhythm. There is no major sleep period, and sleep is fragmented into at least three periods during the 24—hour day.
Individuals with irregular sleep-wake type typically present with insomnia or excessive sleepiness, depending on the time of day. Sleep and wake periods across 24 hours are frag- mented, although the longest sleep period tends to occur between 2:00 AM. and 6:00 AM.
and is usually less than 4 hours. A history of isolation or reclusion may occur in association with the disorder and contribute to the symptoms via a lack of external stimuli to help en— train a normal pattern. Individuals or their caregivers report frequent naps throughout the day. Irregular sleep-wake type is most commonly associated with neurodegenerative dis- orders, such as major neurocognitive disorder, and many neurodevelopmental disorders in children.
Prevalence of irregular sleep-wake type in the general population is unknown.
The course of irregular sleep-wake type is persistent. Age at onset is variable, but the dis- order is more common in older adults.
Temperamental. Neurodegenerative disorders, such as Alzheimer’s disease, Parkinson’s disease, and Huntington’s disease, and neurodevelopmental disorders in children in- crease the risk for irregular sleep-wake type.
Environmental. Decreased exposure to environmental light and structured daytime ac- tivity can be associated with a low-amplitude circadian rhythm. Hospitalized individuals are especially prone to such weak external entraining stimuli, and even outside the hospi— tal setting, individuals with major neurocognitive disorder (i.e., dementia) are exposed to significantly less bright light.
irregular sleep-wake pattern.
Lack of a clearly discernible major sleep and wake period in irregular sleep-wake type re- sults in insomnia or excessive sleepiness, depending on the time of day. Disruption of the caregiver’s sleep also often occurs and is an important consideration.
Normative variations in sleep. Irregular sleep-wake type should be distinguished from a voluntary irregular sleep-wake schedule and poor sleep hygiene, which can result in in- somnia and excessive sleepiness.
Other medical conditions and mental disorders. Other causes of insomnia and daytime sleepiness, including comorbid medical conditions and mental disorders or medication, should be considered.
Irregular sleep-wake type is often comorbid with neurodegenerative and neurodevelop- mental disorders, such as major neurocognitive disorder, intellectual disability (intellec- tual developmental disorder), and traumatic brain injury. It is also comorbid with other medical conditions and mental disorders in which there is social isolation and/ or lack of light and structured activities.
The diagnosis of non-24-hour sleep-wake type is based primarily on a history of symp- toms of insomnia or excessive sleepiness related to abnormal synchronization between the 24-hour light—dark cycle and the endogenous circadian rhythm. Individuals typically pre- sent with periods of insomnia, excessive sleepiness, or both, which alternate with short asymptomatic periods. Starting with the asymptomatic period, when the individual's sleep phase is aligned to the external environment, sleep latency will gradually increase and the individual will complain of sleep-onset insomnia. As the sleep phase continues to drift so that sleep time is now in the daytime, the individual will have trouble staying awake during the day and will complain of sleepiness. Because the circadian period is not aligned to the external 24—hour environment, symptoms will depend on when an individ- ual tries to sleep in relation to the circadian rhythm of sleep propensity.