Table 1

Characteristic features of sleep disorders defined by the International Classification of Sleep Disorders

Sleep disorderClinical featuresDiagnostic criteriaTreatmentProposed pathophysiology
Chronic insomnia Difficulty falling asleep and/or maintaining sleep, with symptoms impacting daytime activity. Symptoms present on most nights for at least 3 months and occur at least three times per week.Problems initiating sleep, difficulty maintaining sleep, waking up earlier than desired, resistance going to bed on appropriate schedule or difficulty sleeping without parent/caregiver intervention. Sleep/wake complaints cannot be explained by inadequate opportunity or circumstances. In addition, fatigue, impaired performance, prone to errors/accidentsFirst Line: CBT where available.
Other treatments:
antihistamines, melatonin, benzodiazepines
  1. Disinhibition of the VPLO

  2. Impaired disengagement of cortical regions involved in executive control and attention

  3. REM instability

  4. Melatonin deficiency

Sleep-related breathing disorders
Obstructive sleep apnoea Chronic disorder characterised by snoring with episodes of upper airway collapse during sleep, waking with choking or breath holding. Associated fragmented, unrefreshing night sleep, insomnia and excessive daytime sleepiness. Risk factors: hypertension, type 2 diabetes mellitus and congestive cardiac failure.PSG detecting ≥5/hour obstructive respiratory events alongside other criteria (eg, partners reports of habitual snoring or breath interruptions) or ≥15/hour obstructive respiratory events during PSG.CPAP: recommended first-line therapy
  1. Altered arousal threshold

  2. Instability of ventilatory control

  3. Increased glutamate and decreased GABA neurotransmission

  4. Small pharyngeal airway

Central sleep apnoea Abnormal brainstem ventilatory responses leading to reduced or absent respiratory effort, with no evidence of snoring. Results in insufficient/absent ventilation, frequent night-time awakenings and excessive daytime sleepiness.
Common causes: opiate use and cardiac failure
PSG demonstrating ≥5/hour central apnoeas, number of central apnoeas is >50% of the total number of apnoeic and hypopneic episodesCPAP treatment is less effective than in OSA.1. Absence of ventilatory drive
Narcolepsy Orexin/hypocretin-deficiency resulting in daytime sleepiness, sleep paralysis, hypnagogic hallucinations±cataplexy cause by instability in transitions between wake, NREM and REM sleep. Narcolepsy Type 1: Diagnosed by the presence of one or both of (1) cataplexy and a mean sleep latency of ≤8 min and (2) two or more sleep-onset REM periods (SOREMPs) on an MSLT.
Narcolepsy Type 2: Daily periods of irrepressible need to sleep or daytime lapses into sleep confirmed with MSLT. Absence of cataplexy confirmed with CSF hypocretin-1 concentrations (>110 pg/mL or >1/3 of mean values obtained in normal subjects).
Amphetamine-like, modafinil, sodium oxybate
  1. Unstable transitions between wake, REM and NREM sleep caused by loss of hypocretin neurons

  2. Abnormal circadian regulation

  3. Insufficient NREM sleep

  4. Hypothalamic lesions

Idiopathic hypersomnia Excessive daytime sleep and/or sleepiness, prolonged unrefreshing overnight sleep and difficulty waking occurring for at least 3 months.MSLT shows fewer than two sleep-onset REM periods or none if REM latency is ≤15 min. In addition to the presence of either an MSLT of ≤8 min, elevated total sleep time (12–14 hours) on PSG/wrist actigraphy or at least 3 daytime lapses into sleep associated with a sleep log (over seven nights).Changes to routine, behavioural therapy, modafinil.1. Abnormal neurotransmitter signalling of histamine, serotonin, dopamine and GABA
NREM parasomnias Confusional arousal, somnambulism and sleep terrors with incomplete/no recall. Predominantly arise during the first third of the night, during slow wave sleep. Confusional arousal: Recurrent mental confusion on arousal/awakening, absence of fear, walking behaviour or hallucinations in association with episode.
Sleep walking: Ambulation during sleep, difficulty arousing the patient during an episode, amnesia.
Sleep terrors: PSG demonstrates tachycardia in associated with the episode and other sleep disorders for example, nightmares, can be present.
Medical therapy used when episodes are frequent or violent. Melatonin and benzodiazepines, notably clonazepam, most commonly used.
  1. Reduced regional perfusion in the frontal and parietal areas during N3 sleep

  2. Activity in the thalamus and cingulate cortex during N3 sleep

REM sleep behaviour disorder (RBD)RBD occurs with loss of normal REM muscle atonia, resulting in dream enactment, often with injury to the patient/bed partner. Events tend to be memorable and associated with dreams.Repeated episodes of sleep vocalisation and/or motor behaviours documented in video PSG during REM sleep or based on clinical history. PSG demonstrates REM sleep without atonia.Melatonin and clonazepam, although no RCTs to date.
  1. Dysfunction of the subcoeruleus nucleus, the medullary magnocellularis and the sublaterodorsal nucleus

  2. Glutamatergic, GABAergic and cholinergic abnormalities

Sleep-related movement disorders
Restless leg syndrome and periodic limb movements during sleep Unpleasant sensation in the LL, affecting onset and maintenance of sleep.
PLMS are periodic, repetitive LL movements typically co-occurring with RLS
RLS: Sensation begins or worsens during periods of rest (eg, lying down), predominantly at night, which are relieved by movements. Symptoms should cause concern, sleep disturbance or impairment in important areas of functioning (eg, physical, social).
PLMS: PSG demonstrates PLMS with a frequency of >15 hours and causes significant sleep disturbance or impairs other important areas of functioning.
Dopamine agonists (rotigotine, pramipexole, ropinirole), gabapentin and pregabalin
  1. Altered spinal circuits in sensory and motor processing areas

  2. Dopaminergic and glutamatergic dysfunction

  3. Iron deficiency

  • CPAP, continuous positive airways pressure; CSF, cerebral spinal fluid; GABA, gamma aminobutyric acid; LL, lower Limb; MSLT, multiple sleep latency test; N3, non-rapid eye movement stage 3; NREM, non-rapid eye movement sleep; OSA, obstructive sleep apnoea; PLMS, periodic limb movements during sleep; PSG, polysomnography; QoL, quality of life; RBD, REM sleep behaviour disorder; RCTs, randomised controlled trials; REM, rapid eye movement sleep; RLS, restless leg syndrome; VLPO, ventrolateral preoptic nucleus; VPLO, ventrolateral preoptic area.