As health-care professionals, we are attuned to the stereotypical presentations of both obstructive sleep apnea (OSA) and insomnia. An overweight middle-aged man walks into the office, led by his spouse who is complaining of his snoring and is concerned about his witnessed apneas and daytime fatigue. Our next patient might be a thin, anxious, and hyper-aroused insomnia patient who reports an inability to wind down and shut off the mind at night. However, the situation becomes markedly more complicated when OSA and insomnia coexist in the same patient, resulting in misdiagnosis and incorrect therapy when the two coexisting conditions are not recognized and addressed concurrently.
Consider an overweight, 45-year-old man with hypertension, presenting with difficulty falling asleep and early morning awakening, along with mild snoring reported by his girlfriend. Assuming that both disorders are present in this individual, failure to treat the sleep-disordered breathing may result in an inability to fully control insomnia and ongoing fatigue. Alternatively, failure to recognize the coincident insomnia will likely result in patient frustration with CPAP that further disrupts sleep without "fixing" the complaint, leading to poor CPAP compliance or even rejection of PAP therapy altogether. To effectively treat such patients, providers must understand the frequency of the concurrence of these conditions, as well as diagnostic and treatment strategies that optimize outcomes.
Insomnia and OSA are the two most common sleep disorders; this simple fact makes their co-occurrence likely. However, rates of the coexisting conditions surpass the prevalence that would be suspected based upon the prevalence of each individual disorder. Several studies have examined patients with sleep apnea for comorbid insomnia, revealing that 40% to 55% of individuals with OSA have significant insomnia complaints (Lavie. Sleep Med. 2007;8: S21; Krakow et al. Chest. 2001;120:1923); these complaints are typically divided into sleep-onset insomnia, sleep-maintenance insomnia, and early morning awakening. Most studies used patient-reported symptoms, using the Insomnia Severity Index Questionnaire (Bastien et al. Sleep Med. 2001;2:297), as well as patient estimation of sleep latency, nighttime awakenings, time awake in bed, and frequency of early awakenings.
While one would expect individuals with sleep apnea to have sleep maintenance difficulties due to apneic events, many patients also experience sleep-onset problems, which cannot be explained by the presence of OSA alone. It may be that patients change their sleep habits due to OSA, and this leads to an independent insomnia disorder.
Among insomnia patients recruited for research, 30% to 67% were diagnosed with frank OSA, with an AHI or RDI greater than five events per hour (Lichstein et al. J Consult Clin Psychol. 1999;67:405; Stone et al. Psychol Aging. 1994;9:231). A greater percentage may have more subtle forms of respiratory abnormalities during sleep; one study demonstrated that 91% of insomnia patients had some degree of sleep-disordered breathing with 41% of patients having upper airway resistance syndrome (Krakow et al. Biol Psychiatry. 2001;49:948).
Correctly diagnosing the patient with coexisting OSA and insomnia can be challenging because such patients may present with atypical symptoms, though they can be more severely affected (and have worse outcomes) when compared with individuals who only have one of the two disorders. Such patients have more pronounced sleeping difficulties, including longer sleep latencies, shorter sleep times, and lower sleep efficiency when compared with individuals with only OSA.
Complicating matters, when compared with pure OSA patients, significant anxiety, depression, and pain exists in this population, making it difficult for the clinician to identify whether the insomnia is a manifestation of the psychiatric or pain syndrome instead of an independent sleep disorder needing dedicated attention (Smith et al. Sleep Med. 2004;5:449; Krell et al. Sleep Breath. 2005;9:104). Insomnia is often thought to be secondary to OSA in these patients, preventing the clinician from fully recognizing the role of a separate disorder in the patient’s poor sleep quality.
Additionally, patients with pronounced insomnia may deny sleep-related breathing disturbances or downplay them as extremely mild, often not complaining of daytime sleepiness to the same degree as patients with OSA. A recent paper underscored the difficulty of diagnosing both conditions concomitantly by dubbing the condition "complex insomnia" (Krakow et al. Biol Psychiatry. 2001;49:948).
Though there are effective treatments for both OSA and insomnia, the likelihood of successful therapy for either disease diminishes if the coexisting disease process is not addressed. While middle-of-the-night insomnia may improve with long-term CPAP use, sleep-onset insomnia rarely improves with CPAP therapy (Björnsdóttir et al. Sleep. 2013;36:1901). Imagine the patient with severe insomnia attempting to adjust to the use of PAP lying awake in bed for several hours, growing increasingly frustrated with the PAP machine and mask.