Medical Comorbidity of Sleep Disorders

Insomnia

Insomnia is one of the most frequent conditions around the world.^[4–6] It is considered to be the subjective complaint of compromised sleep quantity and/or quality and it can be assessed accordingly.^[7] It can be either primary or comorbid with mental or somatic disorders;^[3] in the case of somatic comorbidities, the medical condition may be the result of, a contributing factor to, or a separate entity from insomnia.^[8] The prevalence and consequences of insomnia have significant implications for both the patient and public health. Various studies have shown that people with chronic insomnia use significantly more medical services than those without insomnia^[9] and have significantly higher risks for falls and automobile and industrial accidents, make significantly more errors at work, exhibit less productivity and miss twice as many workdays as those without insomnia.^[8,10,11]

A multitude of medical conditions are associated with insomnia: chronic pain associated or not with skeletomuscular disorders and/or cancer; diabetes and cardiovascular disorders; as well as various respiratory, gastrointestinal, urinary, neurological and menopausal disorders. It also seems that presence of any chronic disease and number of hospitalizations in the previous year are significantly associated with insomnia.^{[6,8,12–14]}

Insomnia in Chronic Pain and Associated Conditions

Among insomniac individuals, chronic pain is much more frequent than among noninsomniac individuals (50 vs. 18%);^[12] 25–40% of patients with various chronic pain conditions complained of insomnia vs. 13% of the general population,^[6] whereas insomnia was found to be 4.3 times more frequent among chronic pain patients in the Ibadan study of ageing on 2152 participants;^[15] chronic pain was mainly due to arthritis (predominantly rheumatoid), spinal pain and fibromyalgia.^[6,15,16] In a large cross-sectional study on 47 700 participants in Norway assessing comorbidity of insomnia, mental conditions and chronic pain were the only correlates of insomnia that remained strongly significant after adjustment for other confounders.^[6] The prevalence of insomnia among cancer patients is about double that of the general population, this association considered to be due to cancer itself, various symptoms of pain and discomfort or various treatment complications; it has been suggested that research on the circadian timing of treatments may provide results that could help reduce sleep disorders in cancer patients undergoing therapy.^[6,17,18]

Insomnia in Diabetes and Cardiovascular Disorders

Diabetes mellitus is another condition that is associated with insomnia, although this association is relatively weak.^[19] In a recent study, however, it was found that short sleep duration is a clinically significant risk factor for type-2 diabetes.^[20] Impaired glucose tolerance is also associated with short sleep in individuals with or without diabetes.^[21] In one cross-sectional retrospective study based on a mailed questionnaire, presence of heart disease was reported by 22% of individuals with insomnia vs. 10% of those without insomnia, whereas 44% of hypertensive patients reported insomnia vs. 19% of individuals without hypertension.^[12] In the large cross-sectional Norwegian study, however, the prevalence of insomnia among hypertensive patients was greater than that of the general population, but the difference was by far less pronounced (15 vs. 13%, respectively).^[6] Myocardial infarction and congestive heart failure patients were more likely than individuals with mild hypertension to suffer from mild insomnia [respective odds ratios (ORs) were 1.9 and 1.6]; for congestive heart failure, the OR for severe insomnia was 2.5.^[22] Particularly for acute myocardial infarction, sleep disturbance is a frequent complaint in the initial period, but it seems to subside over a 6-month period.^[23]

Insomnia in Conditions Associated with other Systems

A great proportion (60%) of patients with breathing problems complain of chronic insomnia (vs. 21% in a control sample), whereas 25% of individuals with insomnia report breathing problems (vs. 6% in individuals without insomnia).^[12] More than half of all patients with chronic obstructive pulmonary disease (COPD) complain of difficulties in initiating or maintaining sleep and 25% present with excessive daytime sleepiness,^[24] and asthmatic patients were found to have an OR for insomnia of 1.4 compared with the general population.^[6] Similarly, individuals with insomnia report a higher proportion of gastrointestinal problems vs. controls (34 vs. 9%) and 55% of patients with disorders of the gastrointestinal tract (especially gastroesophageal reflux^[25]) complain of insomnia (vs. 20% of the control sample).^[12] Sleep problems are also particularly common among end-stage renal disease (ESRD) patients undergoing dialysis, among whom the prevalence of insomnia is between about 60 and 85%;^{[26–28,29•]} female sex, afternoon haemodialysis, other sleep disorders (RLS, obstructive sleep apnoea) and depression seem to be independent predictors of insomnia among ESRD patients.^[27,28] Self-reported insomnia and reduced sleep quality are, in addition, very frequent among patients with nocturia of any cause.^[30] Various neurologic diseases are associated with insomnia;^[12] 50% of Parkinson's disease patients have insomnia, which seems to wax and wane over time,^[31••] and 30–70% of traumatic brain injury (TBI) patients report insomnia symptoms.^[32] Finally, in women, insomnia is associated with menopause and with the severity of the vasomotor symptoms that accompany it.^[33,34]

Curr Opin Psychiatry. 2011;24(4):346-354. © 2011 Lippincott Williams & Wilkins