Obstructive sleep apnea more likely in generalized versus focal epilepsy

By Adriene Marshall


By zeroing in on specific etiologies, researchers found that patients with generalized epilepsy have a higher risk of obstructive sleep apnea (OSA) than those with focal epilepsy. “Possible reasons for higher risk of OSA in people with generalized epilepsy include greater brain stem dysfunction, altered control of the muscles of the upper airway, instability in the respiratory control system, and differences in the anatomy of the upper airway,” said lead author Matthew Scharf, MD, PhD, medical director of the Robert Wood Johnson Sleep Laboratory and assistant professor of medicine and neurology at Robert Wood Johnson Medical School, New Brunswick, N.J.

Dr. Scharf and colleagues reported their findings in Epilepsy & Behavior.

While antiepileptic medication use in his study was similar between the two groups, patients with generalized epilepsy may have started them at a younger age and have used them longer, which could be a factor in the higher OSA risk, he added.

“Possible reasons for higher risk of OSA in people with generalized epilepsy include greater brain stem dysfunction, altered control of the muscles of the upper airway, instability in the respiratory control system, and differences in the anatomy of the upper airway.”

Epilepsy/OSA research

Previous research has established that OSA incidence is high overall among patients with epilepsy. In one study, a retrospective analysis of 197 epilepsy patients, OSA incidence was 15.2% versus 4.41% the general population. For patients with well-controlled epilepsy, older age, male gender, and higher seizure frequency were predictors of an OSA diagnosis. Continuous positive airway pressure treatment for OSA in refractory epilepsy patients improved their seizure control.

Presence of OSA also can affect seizure frequency, as suggested by the results of a study involving 39 epilepsy patients with no prior history of OSA. After they completed sleep questionnaires and underwent polysomnography, 33% of the subjects were diagnosed with OSA. They were more likely than those without OSA to be older and male, and they experienced more seizures during sleep.

The problem is that OSA often goes undiagnosed in epilepsy patients, Dr. Scharf pointed out. “Understanding the risk profile for OSA is important.”

Looking thoroughly at the details

For the current investigation, Dr. Scharf and colleagues conducted a cross-sectional study of patients ages 18 years and older who presented to the Rutgers–Robert Wood Johnson epilepsy center. Patients were classified as having generalized or focal epilepsy based on International League Against Epilepsy criteria. Patients were excluded if epilepsy etiology could not be determined definitively.

Patients completed the Sleep Apnea Scale of the Sleep Disorders Questionnaire (SA-SDQ) to assess OSA risk, where a score of 29 or higher in males or 26 or higher in females was deemed to indicate elevated risk. Prior research suggests that these cutoffs have a sensitivity of 75% and a specificity of 65% for men, and 80% and 67%, respectively, for women.

Patients also were asked to complete the Epworth Sleepiness Scale (ESS) questionnaire. In that measure, a score of 11 or more was considered to indicate abnormal sleepiness. The investigators obtained patients’ medical history from electronic medical records.

A total of 115 patients (27 with generalized epilepsy and 88 with focal epilepsy) were included in the study. Mean SA-SDQ scores were similar for the two epilepsy etiology groups. However, after adjustment for confounding factors, focal epilepsy patients’ SA-SDQ scores were 3.52 points lower than for patients with generalized epilepsy – a significant difference. Older age, higher body mass index, and history of hypertension were associated with higher SA-SDQ scores. Although average ESS scores were not significantly different between the two groups, there was a trend toward higher scores among generalized epilepsy patients (ESS score, 7.8 vs. 6.4 in focal epilepsy patients).

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“Larger studies with the use of objective testing may reveal additional insights.”

The study authors asserted that their study may be the only one to date to find such a distinction between generalized and focal epilepsy in OSA risk. Of the two other known studies that assessed OSA risk in these patient groups, neither adjusted for confounders.

They also pointed out that their cohort “is likely representative of this population” of epilepsy patients. Yet they acknowledged that the limitations of their research include it being conducted in a single center and the use of a screening test rather than the performance of direct clinical assessments. “Larger studies with the use of objective testing may reveal additional insights.”