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Christina S. McCrae, PhD
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David N. Neubauer, MD
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Comorbid Insomnia: Current Directions and Future Challenges
Thomas Roth, PhD

Comorbid Insomnia: Current Directions and Future Challenges

Thomas Roth, PhD

Insomnia is a leading cause of absenteeism, presenteeism (lost productivity when employees are at work), accidents, and errors in the workplace. Overall direct and indirect costs exceed $30 billion annually. A significant portion of these costs are attributable to patients with comorbid insomnia, making these conditions a significant clinical public health issue. These comorbid conditions include mood and anxiety disorders; chronic pain; respiratory, urinary, and neurologic conditions; diabetes; and cardiovascular diseases. Traditional treatment for insomnia with comorbid conditions has focused on treating the comorbid condition with the expectation that the insomnia will resolve. Recent studies, however, suggest this approach is not the most appropriate. Instead, treating both conditions simultaneously may improve the outcomes for each.

(Am J Manag Care. 2009;15:S6-S13)

Various studies suggest that the vast majority of insomnia patients seen in psychiatric practices, and about 50% of those seen in primary care practices, have comorbid conditions.1,2 Thus, the issue of insomnia with associated comorbidities, whether the result of, as a contributing factor to, or as a separate entity from the insomnia appears to be a significant patient as well as public health issue,3 although to what extent remains unclear given the lack of consistent diagnosis for insomnia in primary care practices.4 There is also little research on the economic and quality-of-life repercussions of comorbid insomnia versus primary insomnia, defined as insomnia with no identifiable cause.

The phrase “comorbid insomnia” emerged from the 2005 National Institutes of Health’s (NIH) State-of-the-Science Conference on Manifestations and Management of Chronic Insomnia in Adults, to describe the presence of insomnia in the context of a medical psychiatric disorder.3 Previously, the condition was known as “secondary insomnia.” The International Classification of Sleep Disorders-2 defines it in 2 ways: “Other Insomnia Due to a Mental Disorder,” for all psychiatric-related comorbidities; “Other Insomnia Due to a Known Physiological Condition,” for all medical comorbidities. The former requires insomnia as well as a mental disorder classified under the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) criteria, with the insomnia related in time to the mental disorder. Although the severity of each varies together, that of the insomnia exists beyond what might be typically expected as a symptom of the psychiatric condition. The latter requires the presence of insomnia as well as a medical condition known to affect sleep.5 Under DSM-IV, however, the insomnia may be “related” to an Axis I or Axis II disorder, but the temporal continuity is not required between the 2 disorders.6 The problem with both definitions is that each assumes that the insomnia is “secondary” to the primary medical or psychiatric condition. However, as articulated in the 2005 NIH conference, the causal relationships appear to be more complex in most disorders.3 This article explores that assumption and highlights its implications for treatment.

Impact of Insomnia

Insomnia has a significant impact on individuals’ health and quality of life, particularly those with comorbid conditions affecting the central nervous system (CNS).7,8 The impact appears related to theeffect on daytime functioning as well as the status of their comorbid condition. For instance, various studies found that patients with chronic insomnia have significantly higher risks for falls and accidents.1,9 One study reported that 8% of workers with severe insomnia were involved in industrial accidents compared with 1% of good sleepers (P = .0150).10 Other studies have shown sleep-onset insomnia to be a statistically significant risk factor in being involved in a traffic accident11; in fact, those suffering from insomnia are more than twice as likely to have an automobile accident.12

In addition, adults with severe insomnia miss twice as many workdays as those without insomnia, even when matched for work type and schedule.10 In fact, insomnia may be the greatest predictor of absenteeism in the workplace.13 Employees with severe insomnia have been shown to make significantly more errors at work (15% vs 6%; P <.001), and were more than twice as likely to exhibit presenteeism, or poor efficiency, as those without insomnia (18% vs 8%; P = .0004).10

People with chronic insomnia also use significantly more medical services than those without insomnia.4,10,14,15 Leger et al found twice as many individuals with severe insomnia were hospitalized in the year prior to an administered questionnaire (18% vs 9%; P = .0017) than those without insomnia. They also found this cohort used more medications than those without insomnia, particularly cardiovascular, CNS, urogenital, and gastrointestinal drugs.10

There is also data indicating patients with depressive disorders suffering from insomnia have a greater suicide risk than those without insomnia. This translates into higher costs.16,17 Even controlling for age, sex, and chronic disease score, average total health services are approximately 60% higher in those with insomnia than in those without insomnia.18 Ozminkowski et al found that average direct (inpatient, outpatient, pharmacy, and emergency department costs) and indirect costs (absenteeism and the use of short-term disability programs) for adults in the 6 months before a diagnosis for insomnia or beginning prescription treatment for the condition were approximately $1253 greater than for those without insomnia (ages 18-64), whereas average direct costs among adults aged 65 and older were $1143 greater.19

Although the economic and social costs of comorbid insomnia compared with primary insomnia have yet to be investigated, it is likely that they account for the majority of the annual $30 billion to $35 billion in costs for chronic insomnia simply because comorbid insomnia is so much more prevalent.17,20

Comorbid Insomnias: Untangling the Complexities

As noted earlier, the prevalence of comorbidities and insomnia is significant. Kuppermann et al examined the records of 369 employees together with a telephone screen to evaluate various aspects of their physical and mental health and sleep quality, and found those reporting a current sleep problem were 4 times more likely to have a possible mental health problem as those reporting no sleep difficulties. They were also significantly more likely to report gastrointestinal problems, frequent headaches, and muscle, back, or neck pain.21

Simon and VonKorff evaluated functional impairment and healthcare utilization for patients with and without current insomnia. They found that 24% of patients with insomnia had moderate-to-severe occupational disability compared with 14% of those without insomnia (odds ratio [OR], 1.91). Patients with insomnia were also twice as likely as those without insomnia to have days of restricted activity and days spent in bed due to illness.18 Overall, 3.5 days of disability per month were associated with insomnia, an amount similar to that seen with anxiety and somatoform disorders.22

Finally, our work evaluating sleep problems with comorbid mental disorders and role functioning using the National Comorbidity Survey Replication found all sleep problems were significantly and positively related to 1 or more anxiety disorders, mood disorders, impulse-control disorders, or substance abuse disorders.8 We also found significant associations between insomnia and self-reported role impairment that cannot be explained only by comorbid mental disorders, all of which supports the NIH conference report’s assertion that insomnia is a significant patient and public health problem.3

Evaluating Comorbid Insomnia

Differentiating between primary and comorbid insomnia can prove challenging for the clinician. Does the accompanying condition play a causal role in the insomnia, is it the consequence of theinsomnia, is it incidental to the insomnia, or is it comorbid? The complexity increases when the influence of sleep-related disorders on sleep quality and insomnia are considered, including sleep apnea and periodic limb movements. Similarly, circadian rhythm disorders, such as shift work disorder (Drake Sleep) or phase delay, are associated with disturbed sleep. These result in insomnia symptoms and represent special cases of comorbid insomnia. Thus, insomnia may be comorbid with medical, psychiatric, circadian, or sleep disorders.

An accurate history from the patient and possibly even the bedpartner is paramount in correctly diagnosing comorbid insomnia. Clinicians should consider comorbid insomnia when the onset of the sleep disturbances coincides with or shortly follows that of the comorbid condition; when the course of the insomnia remits and recurs in conjunction with fluctuations in the comorbid disorder; or can be directly linked to some feature of the comorbid disorder, such as pain from chronic arthritis disrupting sleep. Complicating the diagnosis, however, is the fact that insomnia often precedes a comorbid disorder, in some instances serving as an early warning sign of an occurrence or recurrence.23,24 Finally, it is important to consider that the treatment of the comorbid condition may lead to the insomnia. Thus, respiratory stimulants, selective serotonin reuptake inhibitors (SSRIs), beta-blockers, and many other drugs are associated with reports of disturbed sleep.

Yet, as noted later in this article and in the article by Neubauer25 in this supplement, the correct diagnosis of comorbid versus primary insomnia is particularly important when determining the appropriate treatment plan.

Medical Comorbid Conditions With Insomnia

Becoming aware of the more common comorbidities, which encompass a wide variety of medical, psychiatric, and sleep disorders, may assist clinicians in managing the condition.

Taylor et al found the following prevalence of conditions in those with chronic insomnia compared with those without insomnia: chronic pain (50.4% vs 18.2%), high blood pressure (43.1% vs 18.7%), gastrointestinal problems (33.6% vs 9.2%), breathing problems (24.8% vs 5.7%), heart disease (21.9% vs 9.5%), urinary problems (19.7% vs 9.5%), and neurologic disease (7.3% vs 1.2%) (Table 1).20

In addition, they found that people with the following medical problems reported significantly more chronic insomnia than those without insomnia: breathing problems (59.6% vs 21.4%), gastrointestinal problems (55.4% vs 20.0%), chronic pain (48.6% vs 17.2%), high blood pressure (44.0% vs 19.3%), and urinary problems (41.5% vs 23.3%) (Table 2).20

Leigh et al found insomnia in 31% to 81% of those with osteoarthritis,26 while other studies found high levels in those with other chronic pain conditions, including rheumatoid arthritis and fibromyalgia.27 Those with myocardial infarction have a 1.9 OR of mild insomnia, those with congestive heart failure a 1.6 OR of mild insomnia and 2.5 OR of severe insomnia.28 Over a 2-year period, Katz and McHorney showed that more patients with hip impairment, osteoarthritis, and peptic ulcer disease reported new or worsened insomnia compared with those without these conditions.28

Patients with chronic obstructive pulmonary disease (COPD) have a particularly high prevalence of insomnia, with more than 50% complaining of difficulties initiating or maintaining sleep, and 25% reporting excessive daytime sleepiness.29 Insomnia may also hold significant implications for pulmonary function in those with COPD and other respiratory conditions. Phillips et al showed small but statistically significant falls in forced expiratory volume in 1 second (1.06 ± 0.11 to 1.00 ± 0.09 L; P <.05) and in forced vital capacity (2.56 ± 0.20 to 2.43 ± 0.17 L; P <.05) following a single night of sleep deprivation. Over time, this could have a significant impact on patients’ overall pulmonary status.30

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