Comorbid Insomnia and Sleep Apnea (COMISA) is the official term for the co-occurrence of these prevalent sleep disorders. Research suggests that between 30% and 50% of individuals diagnosed with obstructive sleep apnea (OSA) also meet the diagnostic criteria for chronic insomnia. Having both conditions leads to more severe impairment in daytime functioning, mental health, and overall quality of life compared to having either disorder alone. The presence of COMISA creates complex diagnostic and therapeutic challenges that require a specialized, integrated approach for effective management.
Understanding Primary Sleep Apnea and Primary Insomnia
Sleep apnea is a breathing disorder characterized by repeated interruptions in breathing during sleep. The most common form is Obstructive Sleep Apnea (OSA), where the upper airway collapses, leading to a complete cessation (apnea) or partial reduction (hypopnea) of airflow despite continued effort. These breathing events typically last ten seconds or longer, resulting in a drop in blood oxygen levels and a brief arousal from sleep. Central Sleep Apnea (CSA) involves a lack of breathing effort because the brain temporarily fails to send the necessary signal to the respiratory muscles.
Chronic insomnia is a distinct disorder involving persistent difficulty with sleep initiation or sleep maintenance, or waking earlier than desired. These symptoms must occur at least three nights a week for a minimum of three months. Difficulty falling asleep is known as sleep onset insomnia, while problems staying asleep are called sleep maintenance insomnia. The diagnosis requires that these nocturnal symptoms cause significant daytime distress or impairment, such as fatigue, mood disturbances, or poor concentration. Primary insomnia is diagnosed when the sleep difficulty is not directly attributable to another medical condition or substance use.
Comorbid Insomnia and Sleep Apnea: The Interplay
The relationship between sleep apnea and insomnia is bidirectional, meaning each condition can influence and worsen the other. For patients with sleep apnea, repeated episodes of oxygen desaturation and subsequent micro-arousals fragment sleep architecture throughout the night. This continuous cycle of brief awakenings can condition the brain to associate the bed and the act of sleeping with struggle and anxiety, leading to a state known as conditioned hyperarousal. This hyperarousal often manifests as chronic insomnia symptoms, particularly difficulty returning to sleep after an apneic event.
The hyperarousal state defining chronic insomnia also complicates the presentation of sleep apnea. Insomnia is associated with increased sympathetic nervous system activation, which elevates heart rate and overall metabolism. This heightened state of alertness makes the patient more reactive and sensitive to the subtle arousals caused by respiratory events. Consequently, individuals with COMISA report significantly worse subjective sleep quality and more severe daytime impairment compared to those who have sleep apnea alone.
Existing insomnia can also make the treatment of sleep apnea more difficult. The underlying anxiety and hyperarousal may impede a patient’s ability to initiate or maintain use of Positive Airway Pressure (PAP) therapy. The discomfort or novelty of the PAP mask and machine can trigger the hyper-vigilant brain, leading to an increase in sleep onset or sleep maintenance issues. The two conditions thus become intertwined, creating a compounded burden.
Navigating the Diagnostic Process
Diagnosing COMISA presents a clinical challenge because the symptoms of both disorders significantly overlap, making it difficult to determine the root cause of poor sleep. Both conditions can manifest as frequent nighttime awakenings, unrefreshing sleep, and excessive daytime fatigue. The gold standard for diagnosing sleep apnea is an objective overnight sleep study, known as polysomnography (PSG), which measures the frequency of apneas and hypopneas (AHI). However, PSG alone is insufficient for diagnosing the insomnia component of COMISA. While the study accurately measures objective sleep fragmentation, it fails to capture the subjective experience of sleeplessness.
Many patients with COMISA exhibit sleep state misperception, where they feel they have slept much less than the PSG objectively records. Therefore, diagnosis requires a two-pronged approach that pairs objective data from the sleep study with subjective clinical assessment. Clinicians rely on detailed patient history, sleep diaries, and validated questionnaires, such as the Insomnia Severity Index (ISI), to accurately identify the presence and severity of chronic insomnia symptoms.
Integrated Treatment Strategies
Effective management of COMISA requires an integrated strategy that targets both the respiratory and behavioral components simultaneously. Treating only the sleep apnea with devices like Continuous Positive Airway Pressure (CPAP) often fails to resolve chronic insomnia if the underlying conditioned hyperarousal is not addressed. PAP therapy mechanically keeps the airway open to prevent apneas and subsequent arousals. The gold standard for treating the insomnia component is Cognitive Behavioral Therapy for Insomnia (CBT-I). CBT-I is a structured, multi-component therapy that addresses the maladaptive thoughts and behaviors perpetuating the chronic hyperarousal state. Studies show that CBT-I is effective even when sleep apnea is present and can significantly improve a patient’s willingness to use their PAP device. The typical sequence of care involves initiating PAP therapy first to stabilize breathing, and then introducing CBT-I if insomnia symptoms persist.