Major Categories of Sleep Disorders

Sleep disorders are classified based on the International Classification of Sleep Disorders (ICSD-3). Neurologists focus on those with primary or secondary neurological involvement. Key categories include:

 

Insomnia:

Definition: Difficulty initiating or maintaining sleep, or non-restorative sleep, despite adequate opportunity.

Neurological Perspective: Chronic insomnia may involve hyperactivity in the brain’s arousal systems, particularly the hypothalamic-pituitary-adrenal axis or cortical hyperarousal. Functional imaging shows increased activity in the prefrontal cortex and limbic areas.

Subtypes:

Primary Insomnia: Not attributable to another condition.

Secondary Insomnia: Linked to neurological disorders (e.g., stroke, Parkinson’s disease), psychiatric conditions, or medications.

Clinical Features: Daytime fatigue, irritability, impaired concentration, and sometimes memory deficits.

Diagnosis: Clinical history, sleep diaries, actigraphy, or polysomnography (PSG) to rule out other disorders. Neurologists assess for comorbidities like anxiety or neurodegeneration.

Management: Cognitive-behavioral therapy for insomnia (CBT-I) is first-line. Pharmacotherapy (e.g., non-benzodiazepine hypnotics like zolpidem) is used cautiously due to dependency risks. Addressing underlying neurological conditions is critical.

Hypersomnias of Central Origin:

Definition: Excessive daytime sleepiness (EDS) not due to inadequate sleep or other sleep disorders.

Neurological Perspective: Often tied to dysfunction in the hypothalamus or monoaminergic pathways (e.g., dopamine, histamine). Narcolepsy, a prototypical hypersomnia, involves loss of orexin-producing neurons in the lateral hypothalamus, possibly autoimmune-mediated.

Subtypes:

Narcolepsy Type 1: With cataplexy (sudden muscle weakness triggered by emotions), low CSF orexin levels.

Narcolepsy Type 2: Without cataplexy, normal or untested orexin levels.

Idiopathic Hypersomnia: EDS without clear cause, prolonged sleep duration.

Kleine-Levin Syndrome: Rare, episodic hypersomnia with cognitive and behavioral changes.

Clinical Features: Uncontrollable sleep attacks, hypnagogic hallucinations, sleep paralysis, and cataplexy in narcolepsy. Cognitive and mood disturbances are common.

Diagnosis: Multiple Sleep Latency Test (MSLT) showing short sleep latency and multiple sleep-onset REM periods (SOREMPs) in narcolepsy. CSF orexin levels confirm Type 1. Brain MRI rules out hypothalamic lesions.

Management: Stimulants (modafinil, methylphenidate) for EDS, sodium oxybate for narcolepsy symptoms, or antidepressants (e.g., venlafaxine) for cataplexy. Scheduled naps and lifestyle adjustments are key.

Circadian Rhythm Sleep-Wake Disorders:

Definition: Misalignment between the internal circadian clock and external environment, disrupting sleep timing.

Neurological Perspective: The suprachiasmatic nucleus (SCN) in the hypothalamus regulates circadian rhythms via melatonin and other signals. Dysfunction in SCN or its inputs (e.g., retinal ganglion cells) underlies these disorders.

Subtypes:

Delayed Sleep-Wake Phase Disorder: Late sleep onset and wake times.

Advanced Sleep-Wake Phase Disorder: Early sleep onset and wake times.

Non-24-Hour Sleep-Wake Disorder: Common in blind individuals due to lack of light entrainment.

Shift Work Disorder: Misalignment from irregular work schedules.

Clinical Features: Insomnia or EDS depending on timing, impaired social/occupational functioning.

Diagnosis: Sleep logs, actigraphy, and sometimes dim-light melatonin onset (DLMO) testing. Neurologists assess for SCN lesions or neurodegenerative causes.

Management: Timed melatonin, light therapy, or chronotherapy to realign circadian rhythms. Behavioral interventions address sleep hygiene.

Neurological Comorbidities and Sleep

Many neurological conditions exacerbate or are exacerbated by sleep disorders:

 

Epilepsy: Nocturnal seizures mimic parasomnias; sleep deprivation lowers seizure threshold.

Parkinson’s Disease: RBD, insomnia, and RLS are common. Dopamine dysregulation plays a role.

Alzheimer’s Disease: Sundowning, circadian disruption, and sleep fragmentation worsen cognition.

Stroke: OSA increases stroke risk; post-stroke insomnia or hypersomnia may occur.

Multiple Sclerosis: Fatigue and sleep disruption from lesions affecting sleep-wake pathways.

Traumatic Brain Injury: Hypersomnia, insomnia, or circadian disorders due to hypothalamic or cortical damage.

Diagnostic Approach

Neurologists employ a stepwise approach:

 

History: Detailed sleep complaints, onset, triggers, medications, and family history. Standardized scales (e.g., Epworth Sleepiness Scale) quantify severity.

Physical/Neurological Exam: Assess for signs of neurodegeneration, cranial nerve deficits, or motor abnormalities.

Sleep Studies:

Polysomnography: Monitors EEG, EOG, EMG, ECG, respiratory effort, and oxygen saturation. Essential for OSA, RBD, PLMD, and narcolepsy.

MSLT: Measures daytime sleep propensity for hypersomnias.

Actigraphy: Tracks sleep-wake patterns over weeks for circadian disorders or insomnia.

Imaging/Labs: MRI for structural lesions, DAT-SPECT for synucleinopathies in RBD, CSF orexin for narcolepsy, or ferritin for RLS.

Comorbidity Screening: Evaluate for epilepsy, depression, or cognitive impairment.

Management Principles

Multidisciplinary Care: Collaboration with pulmonologists, psychiatrists, and sleep specialists.

Non-Pharmacological: Sleep hygiene, CBT-I, light therapy, or safety measures for parasomnias.

Pharmacological: Tailored to disorder (e.g., stimulants for narcolepsy, clonazepam for RBD). Minimize sedatives in neurodegenerative diseases to avoid worsening cognition.

Treat Underlying Conditions: Optimize control of epilepsy, Parkinson’s, or stroke to improve sleep.

Long-Term Monitoring: Especially for progressive disorders like RBD, which may herald Parkinson’s or dementia.

Emerging Insights

Recent research highlights:

 

Biomarkers: Tau and alpha-synuclein in CSF may predict progression in RBD.

Neuroinflammation: Chronic sleep disruption promotes microglial activation, accelerating neurodegeneration.

Genetics: HLA-DQB1*0602 in narcolepsy, BTBD9 in RLS, suggest genetic predispositions.

Technology: Wearables and AI improve diagnosis by analyzing sleep patterns in real-world settings.