Sleep apnea is a disorder where breathing repeatedly stops and starts during sleep, characterized by repeated episodes of airway blockage, known as obstructive sleep apnea (OSA). Seizures are a sudden surge of uncontrolled electrical activity in the brain, resulting in symptoms from subtle staring spells to full-body convulsions. Despite their apparent differences, medical science has identified a clear neurological connection between these two conditions.
The Established Connection Between Sleep Apnea and Seizure Activity
Studies confirm a strong correlation between sleep apnea and an increased risk of seizure activity, particularly in individuals who already have a seizure disorder like epilepsy. The prevalence of obstructive sleep apnea (OSA) is significantly higher in people with epilepsy compared to the general population; up to 40% of epilepsy patients also have OSA. This suggests that sleep-disordered breathing may destabilize the brain’s electrical balance.
Sleep apnea does not cause a seizure disorder to develop on its own, but it lowers the seizure threshold in susceptible individuals. The repetitive disruption of sleep and oxygen supply can increase the frequency and severity of seizures, even in patients whose condition was previously well-controlled. This relationship is bidirectional: sleep apnea worsens seizures, and seizures negatively impact sleep quality, creating a cycle of instability. Addressing the underlying sleep apnea is often a necessary step in achieving better seizure control.
How Oxygen Deprivation Triggers Brain Excitability
The core mechanism linking sleep apnea to brain excitability is repeated, intermittent hypoxia—a lack of sufficient oxygen—that occurs during apnea events. This cyclical pattern of oxygen deprivation and restoration places significant stress on brain cells. Intermittent hypoxia and the associated buildup of carbon dioxide, known as hypercapnia, disrupt blood gases, directly affecting the brain’s environment.
Carbon dioxide readily crosses the blood-brain barrier, and its fluctuating levels alter the pH of the cerebrospinal fluid, which increases neuronal excitability. Furthermore, the brain’s ability to maintain a steady blood supply, known as cerebral autoregulation, is often impaired in people with OSA. This impairment means the brain cannot manage the rapid drops in blood pressure during apnea, leading to periods of cerebral hypoperfusion, or low blood flow.
At a cellular level, oxygen deprivation causes energy failure within brain cells. This energy crisis leads to the abnormal release of the excitatory neurotransmitter glutamate, a process called excitotoxicity. Glutamate overstimulates receptors, causing an excessive influx of calcium into neurons that can trigger the uncontrolled electrical activity characteristic of a seizure. Intermittent hypoxia also promotes oxidative stress and inflammation within the brain tissue, which further damages neurons and lowers the seizure threshold.
Identifying Seizures Linked to Sleep Disruption
When a doctor suspects sleep apnea is contributing to a patient’s seizures, the clinical presentation often involves seizures that occur predominantly at night, known as nocturnal seizures. While any seizure type can be linked to sleep apnea, generalized tonic-clonic seizures are frequently observed in this context. Diagnosis requires confirmation of both conditions simultaneously to establish the link.
The gold standard diagnostic test is an in-laboratory Polysomnography (PSG), or sleep study. The PSG monitors breathing, oxygen saturation, and sleep stages throughout the night to determine the severity of sleep apnea using the Apnea-Hypopnea Index (AHI). Crucially, the in-laboratory setting allows for simultaneous Electroencephalography (EEG) monitoring, which records the brain’s electrical activity. This combined testing allows clinicians to correlate specific breathing events and oxygen drops with the onset of abnormal brain activity or seizures.
Impact of Sleep Apnea Treatment on Seizure Control
For patients with coexisting sleep apnea and a seizure disorder, treating the breathing condition can lead to improvement in seizure control. Continuous Positive Airway Pressure (CPAP) therapy is the most common and effective treatment for obstructive sleep apnea. The CPAP machine delivers pressurized air through a mask, which acts as an air splint to keep the airway open during sleep and stabilize oxygen levels.
By preventing the intermittent hypoxia and sleep fragmentation, CPAP therapy directly addresses the underlying triggers of brain excitability. Clinical studies have shown that patients who are compliant with CPAP therapy experience a measurable reduction in seizure frequency. For example, in one study, compliant patients saw their average monthly seizure frequency decrease from 1.8 to 1 seizure per month.
Patients treated with positive airway pressure have been shown to have more than 30 times the odds of achieving a greater than 50% reduction in seizure frequency compared to those with untreated sleep apnea. Managing sleep apnea with CPAP is recognized as an important component of a comprehensive treatment plan for patients struggling to control their seizures. Effective treatment stabilizes the brain’s environment, reducing the risk of seizure recurrence and improving quality of life.