Insomnia and Neurologic Disorders: Exploring the Bidirectional Relationship

Disordered sleep is known to increase the risk for neurologic disorders, such as Alzheimer disease (AD) and Parkinson disease (PD). Similarly, patients with neurologic disorders commonly report sleep disorders, including excessive daytime sleepiness and insomnia, suggesting a bidirectional relationship between sleep and brain health.¹

Although researchers have identified a strong association between sleep disorders, specifically insomnia, and neurologic disorders, little is known about their underlying causes, etiology, pathophysiology, and effective treatments.²

Diagnostic Criteria for Insomnia

Recent changes in classification criteria have resulted in the recognition of insomnia as a disorder,³ which is differentiated as transient (persistent symptoms for at least 4 weeks) or chronic (disease duration of at least 3 months). The Diagnostic and Statistical Manual of Mental Disorders (DSM) and the International Classification of Sleep Disorders (ICSD) have been used to define insomnia in clinical practice; however, patients with insomnia may not meet all the criteria.⁴ Overall, insomnia has been described by the cardinal symptom of the inability to initiate and maintain sleep or having “poor” sleep, but the presentation of this disorder is much more complex.⁴

Nonorganic insomnia, which lacks an underlying medical cause, affects 6% of the population in countries including the United States and the United Kingdom. Among individuals with progression to chronic insomnia, 70% still fulfill the diagnostic criteria at 1 year.^3,4

Prevalence of Insomnia in Neurologic Disorders

Compared with the general population, patients with neurologic disorders have a higher prevalence of insomnia.⁵ Based on multinational meta-analyses and reviews, the prevalence of insomnia in neurologic disorders can only be estimated (Table), as the exact prevalence is unknown.^2,5 The worldwide prevalence of insomnia symptoms is 30% to 35%.³

More than 50% of secondary insomnias have been indicated to co-occur with psychiatric illnesses, including addiction, alcohol dependence, anxiety, and depression, followed by diseases of the central and peripheral nervous system, restless leg syndrome (RLS), and sleep-related breathing disorders, including obstructive sleep apnea (OSA).⁴

Research has revealed sex differences in patients with insomnia, with women having a significantly higher prevalence than men do. The increased prevalence of chronic insomnia among women has been attributed to biological factors, including hormonal changes and comorbid medical conditions, and psychosocial factors, including stress and anxiety with regard to burden of family responsibilities.⁶ Notably, the increased prevalence of sleep disorders in women with neurologic disorders has been underappreciated and -treated because of overlapping symptoms.⁷

In older adults, insomnia is typically comorbid to other neurologic and psychiatric illnesses and sleep disorders, including OSA and RLS.Approximately 50% of these patients report sleeping difficulties.⁸

Table: Estimated prevalence of insomnia in neurologic disorders

Neurodegenerative disorders (including PD, AD, and dementia)	11%-74.2%
Migraine	Approximately 70%
Epilepsy	28.9%-74.4%
Multiple sclerosis (MS)	40%-50%
Traumatic brain injury	Approximately 30%
After stroke	26.9%-50%

Screening and Clinical Evaluation of Insomnia

Due to the wide range of sleep-related disorders, health care professionals across various specialties, including psychiatry, pulmonology, neurology, and otorhinolaryngology, may do insomnia screenings for patients with neurologic disorders.⁴

The presence of insomnia in neurologic disorders is known to cause a worsening of symptoms and quality of life, heightened depression symptoms, and increased mortality rates.⁵ Therefore, it is recommended that neurologic evaluations address insomnia while taking patient history, as insomnia may be a distinct entity or the cause of an underlying problem.⁴

Given the higher prevalence of sleep disorders in neurologic disorders, the importance of understanding assessment tools, both subjective and objective, has been emphasized. Nurse practitioners and treating clinicians have been advised to determine the method of assessment for sleep disorders on a case-by-case basis.⁸ In a 2019 update on the assessment and management of insomnia, the researchers discussed choosing the appropriate assessment tool for insomnia, such as the use of a sleep diary, actigraphy, personal monitoring devices, polysomnography, and questionnaires.⁹

Treatment and Management of Insomnia in Neurologic Disorders

Researchers have recommended that insomnia in patients with neurologic disease be treated according to the updated clinical practice guidelines.^10,11 General practitioners, specialists, and certified sleep specialists may collaborate in the treatment of patients with insomnia with neurologic disorders, based on the complexity of the cause.⁴

Based on guideline recommendations, cognitive behavioral therapy for insomnia (CBT-I) is the initial treatment for chronic insomnia disorder because of its significantly favorable benefit:risk ratio.¹⁰

The US Food and Drug Administration (FDA) has approved drugs, including benzodiazepines, nonbenzodiazepine hypnotics, suvorexant, and ramelteon, for insomnia treatment.¹¹ Off-label treatments, such as for major depressive disorder, have also been used to treat insomnia; some of them include trazodone, amitriptyline, mirtazapine, and doxepin. In addition, research has shown that melatonin may be beneficial for patients with comorbid insomnia and neurocognitive disorders. Another second-line treatment option is morning bright light therapy.³

However, for the treatment of secondary insomnia in patients with neurologic disorders, pharmacologic interventions may be more targeted to the symptoms and underlying cause.⁴ Treating physicians have been recommended to continue to counsel patients with neurologic disorders on sleep hygiene.³

Overall, combined therapy of psychologic and pharmacologic treatments may be more beneficial than any single treatment for insomnia.³