Insomnia symptoms are typically stratified into difficulty initiating versus difficulty maintaining sleep. These insomnia symptoms, however, are not static over a lifespan. Older adults tend to complain more of issues related to sleep maintenance, while younger adults more often implicate difficulty initiating sleep. These broad categories and specific symptoms of insomnia provide targets for pharmaceutical and non-pharmaceutical intervention.
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The Definition of Insomnia
The International Classification of Sleep Disorders (ICSD-2) defines insomnia as:
A. A complaint of difficulty initiating sleep, difficulty maintaining sleep, waking up too early or sleep that is chronically non-restorative or poor in quality.
B. Sleep difficulty occurs despite adequate opportunity and circumstances for sleep.
C. At least one of the following forms of daytime impairment related to nighttime sleep difficulty is reported by the patient:
a. Fatigue or malaise
b. Attention, concentration or memory impairment
c. Social or vocational dysfunction or poor school performance
d. Mood disturbance or irritability
e. Daytime sleepiness
f. Motivation, energy or initiative reduction
g. Proneness for error or accidents at work or while driving
h. Tension, headaches or gastrointestinal symptoms in response to sleep loss
i. Concerns or worries about sleep
Insomnia is increasingly defined as a “spectrum” of disease rather than one distinct entity. Insomnia is superficially classified as “primary,” meaning that the duration of insomnia is less than one month and other physical or mental conditions have been excluded, versus “secondary,” which implies that insomnia is due to underlying medical, psychiatric or environmental conditions.
Subcategories of Insomnia
A number of other subcategories of insomnia exist. Psychophysiological insomnia is a maladaptive behavior that associates the bed environment with heightened arousal rather than sleep. While there is often a clear precipitating factor, insomnia persists well past resolution of the inciting factor and becomes a chronic condition.
Paradoxical insomnia was previously dubbed “sleep state misperception” and revolves around the disconnect between subjective estimation of total sleep time and objective measurement of sleep time with actigraphy (a small, watch-like device used to quantitate activity and light exposure) or polysomnography (a facility-based sleep test that records the duration and depth of sleep). Patients with paradoxical insomnia will often report dramatically reduced sleep times, such as sleeping only one to two hours per night, although symptoms like daytime sleepiness are absent and impairments in functional status are often minimal. It is the perception of poor sleep rather than insufficient sleep itself that causes the psychological stress.
Insomnia may also be classified as primarily due to an underlying psychiatric, drug or substance-abuse issue. In these patients, identification and treatment of the underlying disorder typically resolves the insomnia. Of note, a variety of common prescription medications prescribed for other health problems, such as beta blockers, corticosteroids, antidepressants, blood pressure agents, cholesterol medications and over-the-counter cold and allergy formulations, can cause insomnia.
Different Form of Insomnia
More recently, research has suggested that a smaller percentage of patients with chronic insomnia have a more biologically active form of the disease — the so-called “short sleep duration insomnia.” Sleep durations less than six hours can be consistently observed and objectively documented in these patients, and they are at substantially higher risk for developing hypertension, heart attack, stroke, diabetes, osteoporosis and neurocognitive impairment than adults with insomnia who average more than six hours of sleep per night. Measurements of stress hormones, such as cortisol and insulin resistance, are also significantly higher in these short sleep duration insomnias and may influence factors like increased caloric intake and body weight in these patients. Overall mortality was fourfold higher in men with objective short sleep duration than in men with paradoxical insomnia.
Enhanced understanding of the individual basis of chronic insomnia in a particular individual will eventually guide treatment decisions. For example, patients with paradoxical insomnia may avoid medication altogether and get referrals for therapies directed at changing their perceptions and behavior, whereas patients with short sleep duration insomnia often require aggressive treatment with sedative-hypnotic medication and multidisciplinary treatment early in the course of their disease to modify health outcomes.