Insomnia vs Sleep Deprivation

Question

Many of my insomnia patients tell me that they sleep for a handful of hours per night, over long periods of time, yet I'm puzzled by the fact that they don't seem to behave like sleep-deprived individuals, ie, they don't seem to fall asleep easily during daytime activities. In fact, many cannot even nap. How can this be?

Response from  Karl Doghramji, MD

Insomnia refers to the inability to sleep adequately, either in length or quality, despite the opportunity to sleep. On the other hand, sleep deprivation refers to curtailed sleep length due to an externally imposed restriction of the opportunity to sleep. In the latter case, the most common scenario is a modest reduction of sleep hours over long periods of time. The effects of sleep deprivation on daytime sleepiness have been well defined by objective means and are not reviewed here.^[1]

Whereas the 2 conditions may cause similar reductions in sleep length in any individual case, it is of interest that they differ widely in the nature and extent of daytime consequences. In the case of insomnia, many demographic surveys have identified impairments in individuals suffering from the condition. These include poor job performance, higher absenteeism from work, increased risk of accidents, and poor physical and mental health, among others.^[2] A number of longitudinal studies have even confirmed that persistent insomnia is associated with a dramatic increase in the risk of the development of psychiatric disturbances in the future in populations that are currently free of psychopathology (see the literature^[3]). What is lacking in all of these surveys, however, is a causal link between insomnia and these impairments. The data are, at best, associational and cannot rule out the possibility that underlying disorders, such as depression, medical illness, substance use, etc, are primary in the genesis of both insomnia and these impairments. That is not to say that insomniacs do not complain of daytime symptoms; indeed, recent surveys have shown that 40% state that daytime sleepiness interferes with daytime functioning.^[4] However, studies have, largely, failed to quantify daytime impairments by objective means; of 9 studies comparing objective tests (multiple sleep latency testing) of daytime sleepiness findings in insomniacs and controls, all showed no difference with the exception of 1.^[5] Only recently have studies been performed in controlled laboratory environments in otherwise "healthy" insomniacs and have shown modest changes in a handful of cognitive areas, including short-term memory and letter-finding ability.^[6]

These findings should not necessarily be taken to mean that insomniacs are not impaired; rather, they may imply that scientific techniques cannot, as of yet, adequately capture the nature of these impairments. Recent work has shown, for example, that insomniacs demonstrate a heightened level of daytime arousal on various neurophysiological measures.^[7] Hyperarousal may, therefore, be central to insomnia and may oppose daytime sleep tendency and prevent adequate expression of sleep need both during the day and at night. Clinically, therefore, the primary goal may be to mute this arousal process with a combination of behavioral and pharmacologic techniques.