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Sleep disorders: Differential diagnosis


The presumptive cause of insomnia can be thought of as the five Ps:

1. Physical causes may relate to the bedroom environment, for example, noise, light, temperature or television.

2. Psychophysiological refers to the development of insomnia after a stressful life event. For example, all the features of a bereavement resolve but the sleep disturbance may persist.

3. Psychological/psychiatric cause of initial insomnia is typically anxiety. Maintenance insomnia (disrupted sleep) occurs in many psychiatric disorders, including eating disorders, dementia and schizophrenia. Terminal insomnia (early morning awakenings) is most characteristic of depression.

4. Pathophysiological insomnia describes medical conditions comorbid with insomnia. These conditions range from pain conditions, including fibromyalgia and arthritis, to hyperthyroidism, to respiratory and cardiac disorders, including emphysema and congestive heart failure. They also include conditions affecting the central nervous system, such as dementia, head injuries, Parkinson's disease and organ failure, and specific sleep disorders, such as obstructive sleep apnea and periodic leg movement in sleep.

5. Pharmacological causes are related to using medications such as antidepressants, stimulants, antihypertensives, including beta blockers, as well as decongestants and corticosteroids. Also consider the rebound effect of withdrawal of sedating agents such as alcohol and short-acting hypnotics.

Excessive daytime sleepiness

Causes of excessive daytime sleepiness that should be considered include:

  • sleep restriction
  • sleep apnea
  • narcolepsy
  • periodic limb movement disorder
  • substance use or use of medications
  • medical disorders
  • psychiatric disorders
  • circadian rhythm disorders
  • miscellaneous conditions

Sleep restriction

Sleep restriction (insufficient sleep) is the most common cause of excessive daytime sleepiness in healthy individuals.

Sleep apnea

People with sleep apnea stop breathing at least five times per hour for greater than 10-second periods due to upper airway occlusion (obstructive sleep apnea) or the cessation of the respiratory effort (central sleep apnea).

Although patients with sleep apnea may seem sleep through the night, their sleep is fragmented by short arousals following apneic episodes and becomes devoid of a sense of having refreshing sleep. People with sleep apnea often complain of morning headaches and daytime fatigue and feel tired when they wake up from naps.


The leading symptom of narcolepsy, a rare condition that is genetic or posttraumatic in origin, is excessive daytime sleepiness with short (10–20 minute) naps, or sudden, irresistible sleep attacks from which patients wake up refreshed. Patients may also experience cataplexy (loss of muscle tone in strong emotional states), sleep paralysis (brief inability to move from awakenings) and sleep-related hallucinations.

Periodic limb movement disorder

Periodic limb movement disorder, which involves repeated twitches of the legs in sleep, is more common in the elderly population, in vertebral degenerative disorders, in women who are pregnant, in patients with Parkinson's disease and in people with chronic kidney disease. It also occurs with low ferritin and with vitamin B12 deficiency. The disorder may be problematic even at the lower end of the normal range for ferritin levels.

Substance use or medication use

The use of drugs such as benzodiazepines and antihistamines, alcohol and withdrawal from stimulants should be considered as the possible cause of excessive daytime sleepiness.

Medical disorders

Acute, systemic infections are a common cause of excessive daytime sleepiness. Neurological disorders (infections, epilepsy, posttrauma) and metabolic disorders affecting the central nervous system are also often associated with excessive daytime sleepiness.

Psychiatric disorders

Although depression is usually comorbid with insomnia, 20 per cent of patients who are depressed describe fatigue and excessive sleepiness. Atypical depression is characterized by hypersomnia. Posttraumatic stress disorder may induce pathological sleep architecture and cause fragmented sleep, depriving patients of restorative sleep.

Circadian rhythm disorders

Circadian rhythm disorders are defined as a discrepancy between the person's sleep schedule and the schedule that is considered the norm for school, work or other obligations. The most common circadian problem in primary care involves patients who are shift workers.

A common problem in adolescents is delayed sleep phase syndrome. In this syndrome, the sleep-wake cycle is shifted to early morning bedtime and mid-day wake-up time. Teenagers with delayed sleep phase syndrome have difficulty getting up in the morning on school days and experience sleepiness until the afternoon.

Miscellaneous conditions

Other conditions that may be causing excessive daytime sleepiness include idiopathic hypersomnia, post-viral hypersomnia, genetic causes and Kleine-Levin syndrome (adolescent hyperphagia, aggression and hypersexuality).

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