In hypersomnolence disorder, by contrast, symptoms of excessive sleepiness occur regard- less of nocturnal sleep duration. An inadequate amount of nocturnal sleep, or behaviorally induced insuﬂicient sleep syndrome, can produce symptoms of daytime sleepiness very similar to those of hypersomnolence. An average sleep duration of fewer than 7 hours per night strongly suggests inadequate nocturnal sleep, and an average of more than 9—10 hours of sleep per 24—hour period suggests hypersomnolence. Individuals with inadequate noctur- nal sleep typically ”catch up” with longer sleep durations on days when they are free from social or occupational demands or on vacations. Unlike hypersomnolence, insufficient nocturnal sleep is unlikely to persist unabated for decades. A diagnosis of hypersomno- lence disorder should not be made if there is a question regarding the adequacy of noctur- nal sleep duration. A diagnostic and therapeutic trial of sleep extension for 10—14 days can often clarify the diagnosis.
Poor sleep quality and fatigue. Hypersomnolence disorder should be distinguished from excessive sleepiness related to insufficient sleep quantity or quality and fatigue (i.e., tiredness not necessarily relieved by increased sleep and unrelated to sleep quantity or quality). Excessive sleepiness and fatigue are difficult to differentiate and may overlap considerably.
Breathing-related sleep disorders. Individuals with hypersomnolence and breathing- related sleep disorders may have similar patterns of excessive sleepiness. Breathing- related sleep disorders are suggested by a history of loud snoring, pauses in breathing during sleep, brain injury, or cardiovascular disease and by the presence of obesity, oro- pharyngeal anatomical abnormalities, hypertension, or heart failure on physical examina— tion. Polysomnographic studies can confirm the presence of apneic events in breathing— related sleep disorder (and their absence in hypersomnolence disorder).
Circadian rhythm sleep-wake disorders. Circadian rhythm sleep-wake disorders are often characterized by daytime sleepiness. A history of an abnormal sleep-wake schedule (with shifted or irregular hours) is present in individuals with a circadian rhythm sleep- wake disorder.
Parasomnias. Parasomnias rarely produce the prolonged, undisturbed nocturnal sleep or daytime sleepiness characteristic of hypersomnolence disorder.
Other mental disorders. Hypersomnolence disorder must be distinguished from mental disorders that include hypersomnolence as an essential or associated feature. In particular, complaints of daytime sleepiness may occur in a major depressive episode, with atypical fea- tures, and in the depressed phase of bipolar disorder. Assessment for other mental disorders is essential before a diagnosis of hypersomnolence disorder is considered. A diagnosis of hyper- somnolence disorder can be made in the presence of another current or past mental disorder.
Hypersomnolence can be associated with depressive disorders, bipolar disorders (during a depressive episode), and major depressive disorder, with seasonal pattern. Many individu- als with hypersomnolence disorder have symptoms of depression that may meet criteria for a depressive disorder. This presentation may be related to the psychosocial consequences of persistent increased sleep need. Individuals with hypersomnolence disorder are also at risk for substance-related disorders, particularly related to self—medication with stimulants.
This general lack of specificity may contribute to very heterogeneous profiles among indi- viduals whose symptoms meet the same diagnostic criteria for hypersomnolence disorder.
Neurodegenerative conditions, such as Alzheimer’s disease, Parkinson’s disease, and mul- tiple system atrophy, may also be associated with hypersomnolence.
Relationship to Internatlonai Classification of
The International Classification of Sleep Disorders, 2nd Edition (ICSD-2), differentiates nine subtypes of ”hypersomnias of central origin,” including recurrent hypersomnia (Kleine-