are especially prone to such weak external en training stimuli, and even outside the hospi-
tal setting, individuals with major neurocogni tive disorder (i.e., dementia) are exposed to
significantly less bright light. 
Diagnostic Markers
A detailed sleep history and a sleep diary (by a caregiver) or actigraphy help confirm the
irregular sleep-wake pattern.
Functional Consequences of 
Irregular Sleep-Wake Type
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.
Differential Diagnosis
Normative variations in sleep. Irregular sleep-wake type sh ould be distinguished from
a voluntary irregular sleep-wake schedule and po or 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 condit ions and mental disorders or medication,
should be considered.