Obstructive sleep apnea (OSA) is a prevalent disorder marked by repeated upper airway obstruction during sleep, leading to fragmented sleep and intermittent hypoxia. Thankfully, treatments like continuous positive airway pressure (CPAP), mandibular advancement devices, and other interventions can significantly reduce apneic events. However, a perplexing clinical challenge remains: why do some patients continue to experience excessive daytime sleepiness (EDS) despite optimal OSA therapy adherence?
In this blog, we’ll explore the prevalence, hidden drivers, and clinical evaluation tools relevant to persistent EDS in treated OSA—an issue that not only frustrates patients but also complicates clinical management.
The Scope of the Problem: How Common Is Persistent Daytime Sleepiness?
You’d expect that treating the root cause—apneic events—should resolve daytime sleepiness. And for many, it does. However, studies indicate that 12% to 18% of patients with well-treated OSA continue to suffer from EDS, even with good therapy adherence and normalized AHI (apnea-hypopnea index) scores.
This residual EDS isn’t a minor inconvenience—it has real consequences:
- Decreased work productivity and increased absenteeism
- Greater risk of motor vehicle accidents
- Lower health-related quality of life
- Mood disturbances and cognitive impairments
The persistence of EDS despite treatment raises important clinical questions: what else is driving this fatigue? Are we missing something deeper?
Hidden in Plain Sight: What Causes Persistent Sleepiness?
1. Suboptimal Sleep Hygiene or Sleep Insufficiency
Often, the simplest explanation is overlooked. Patients may adhere to CPAP therapy but still get less than the recommended 7–9 hours of sleep per night. Lifestyle demands, poor sleep habits, or untreated insomnia can all contribute.
2. Comorbid Sleep Disorders
OSA frequently coexists with other sleep conditions that impair sleep quality:
- Restless legs syndrome (RLS)
- Periodic limb movement disorder (PLMD)
- Circadian rhythm disorders
If these are not identified and treated, patients may experience ongoing sleep fragmentation and unrefreshing sleep.
3. Medication Effects and Substance Use
Some medications (e.g., sedatives, antihistamines, certain antidepressants) and substances (e.g., alcohol, cannabis) have sedating properties that can worsen daytime sleepiness or mask the benefits of therapy.
4. Depression and Mental Health Disorders
Depression, even when subclinical, can manifest as fatigue or low energy. Anxiety can fragment sleep. Cognitive-behavioral symptoms can also interfere with therapeutic engagement, making it critical to screen for mood disorders.
5. Neurobiological and Functional Brain Changes
This is where the science gets particularly interesting—and concerning. Chronic, untreated OSA can lead to neuroplastic changes in brain regions responsible for alertness and wake regulation.
Studies using functional MRI have shown structural changes in areas like the thalamus, brainstem, and frontal cortex, even after OSA treatment. These changes may contribute to a persistent deficit in the brain’s ability to regulate wakefulness—even after the apnea is corrected.
How Do We Evaluate Persistent EDS? Tools, Thresholds, and Limitations
Recognizing persistent sleepiness starts with clinical suspicion, but confirming and quantifying it requires the right tools. Here are the most commonly used assessments:
1. Epworth Sleepiness Scale (ESS)
- What it is: A subjective 8-question tool measuring the propensity to doze in daily life scenarios.
- Threshold: An ESS score >10 is generally considered indicative of excessive sleepiness.
- Limitations: Subjective; prone to underreporting or overreporting. May not reflect subtle functional impairments.
2. Multiple Sleep Latency Test (MSLT)
- What it is: An objective test measuring how quickly a person falls asleep in a quiet environment during the day, across five nap opportunities.
- Threshold: Mean sleep latency <8 minutes is abnormal. <5 minutes suggests significant hypersomnia.
- Limitations: Influenced by prior sleep duration, medication use, and adherence to test conditions. Not always practical in routine clinical settings.
3. Maintenance of Wakefulness Test (MWT)
- What it is: Evaluates the ability to stay awake, rather than fall asleep. Useful in occupational or legal contexts.
- Threshold: Sleep latency <19–20 minutes is often considered abnormal.
- Limitations: Less commonly available, and outcomes can be influenced by motivation.
4. Functional Outcome Measures
- Examples: Functional Outcomes of Sleep Questionnaire (FOSQ), Sleep Apnea Quality of Life Index (SAQLI)
- Purpose: Assess how sleepiness affects day-to-day activities, relationships, and work.
- Limitations: May not correlate directly with ESS or MSLT, but offer holistic insight into patient experience.
Bringing It All Together: A Clinical Approach
Step 1: Reassess OSA Therapy
- Confirm objective therapy adherence (e.g., CPAP use ≥4 hours/night, 70% of nights)
- Evaluate for mask leaks, residual AHI, and patient-reported comfort
Step 2: Screen for Confounders
- Sleep duration and quality (consider actigraphy or sleep diary)
- Comorbid conditions (RLS, PLMD, insomnia, circadian disorders)
- Medication and substance use
- Mood and cognitive symptoms
Step 3: Use Sleepiness Tools Wisely
- Combine subjective tools (ESS, FOSQ) with objective assessments (MSLT/MWT) when indicated
- Reassess periodically, especially when making therapeutic changes
Step 4: Consider Pharmacologic Therapy
In patients with verified residual EDS, despite optimal treatment and no identifiable secondary causes, FDA-approved wake-promoting agents like solriamfetol or pitolisant may be considered.
These should never replace a root-cause analysis but may be a valuable adjunct in select cases.
Conclusion: Persistent EDS in Treated OSA Deserves Attention
Too often, patients with treated OSA who continue to feel tired are dismissed or told to “just give it time.” But persistent daytime sleepiness is not just a nuisance—it’s a sign that something deeper may be going on.
By taking a comprehensive approach—from lifestyle habits to brain health, from subjective scales to neurobehavioral tools—we can offer our patients more than relief from apneas. We can offer them restorative sleep and the alertness they deserve during their waking hours.
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