Primary Sleep Disorders (Dyssomnias)
Psychogenic insomnia is characterized by increased mental tension (inability to relax, anxiety, brooding) and excessive concern about sleep itself (constant complaining about an inability to fall asleep or stay asleep, or about waking up too early). Sleep often improves in a new environment (e. g., on vacation).
Pseudoinsomnia is a subjective feeling of disturbed sleep in the absence of objective evidence (i.e., normal polysomnography).
Restless legs syndrome (RLS) is characterized by ascending abnormal sensations in the legs when they are at rest (e. g., when the patient watches television, or before falling asleep) accompanied by an urge to move the legs. It is sometimes present as a genetic disorder with autosomal dominant inheritance. Periodic leg movements during sleep are repeated, abrupt twitching movements of the legs that may persist for minutes to hours. These two movement disorders may appear together or in isolation; both may be either primary or secondary (due to, e. g., uremia, tricyclic antidepressant use, or iron deficiency).
Narcolepsy is characterized by daytime somnolence and frequent, sudden, uncontrollable episodes of sleep (imperative sleep), which tend to occur in restful situations (e. g., reading, hearing a lecture, watching TV, long automobile rides). It may be associated with cataplexy (sudden, episodic loss of muscle tone without unconsciousness), sleep paralysis (inability to move or speak when awaking from sleep), and hypnagogic hallucinations (visual or acoustic hallucinations while falling asleep). Polysomnography reveals a short sleep latency and an early onset of REM sleep. The presence of HLA antigens (DR2, DQw1, DQB1*0602) is nonspecific, as is the absence of hypocretin-1 (orexin A) in the cerebrospinal fluid.
Obstructive sleep apnea is characterized by daytime somnolence with frequent dozing, nocturnal respiratory pauses, and loud snoring. Impaired concentration, decreased performance, and headaches are also common.
Extrinsic sleep disorders. Sleep may be disturbed by external factors such as noise, light, mental stress, and medication use. Disturbance of the circadian rhythm. Sleep may be disturbed by shift work at night or by intercontinental travel (jet lag).
Parasomnias. These disorders include confusion on awakening (sleep drunkenness), sleepwalking (somnambulism), nightmares, sleep myoclonus, bedwetting (enuresis), and nocturnal grinding of the teeth (bruxism).
Secondary Sleep Disorders
Psychogenic sleep disorders. Depression (of various types) can impair sleep, though paradoxically sleep deprivation can ameliorate depression. Depressed persons typically complain of early morning awakening, nocturnal restlessness, and difficulty in starting the day. Sleep disturbances are also common in patients suffering from psychosis, mania, anxiety disorders, alcoholism, and drug abuse.
Neurogenic sleep disorders. Sleep can be impaired by dementia, Parkinson disease, dystonia, respiratory disturbances secondary to neuromuscular disease (muscular dystrophy, amyotrophic lateral sclerosis), epilepsy (nocturnal attacks), and headache syndromes (cluster headaches, migraine). Fatal familial insomnia is a genetic disorder of autosomal dominant inheritance (p. 252).
Sleep disorders due to systemic disease. Sleep can be impaired by pulmonary diseases (asthma, COPD), angina pectoris, nocturia, fibromyalgia, and chronic fatigue syndrome.