Obstructive Sleep Apnea: Which Epilepsy Patients are at Greatest Risk?

Patients with medically refractory epilepsy may have a higher prevalence of obstructive sleep apnea (OSA) than the general population (Malow et al, 2000) and treating OSA may impact favorably on seizure control (Malow et al, 2003). Therefore, it is important to diagnose OSA in the patient with epilepsy. Which patients are at greatest risk?

Today at the at the 58th annual American Epilepsy Society conference in New Orleans, Beth A. Malow, M.D., Vanderbilt University, and colleagues reported on the clinical characteristics that are predictive of obstructive sleep apnea (OSA) on polysomnography (PSG) in epilepsy patients who have already screened positive for OSA on a screening questionnaire and a clinical interview (conducted by the four authors who are sleep and epilepsy specialists—Malow, Foldvary-Schaefer, Selwa, and Vaughn) (Malow et al, 2004). They were specifically interested in this question because they are conducting a multicenter NINDS pilot clinical trial of the effects of treating obstructive sleep apnea in epilepsy, and want to maximize their yield of subjects who test positive of PSG for OSA. Given the expense of PSG, however, this question is also applicable to epilepsy patients outside of clinical trials to help predict which patients with clinically-suspected OSA really will have OSA on PSG.

The investigators found that 74% of the subjects who screened positive for OSA on a screening questionnaire or by clinical history, with confirmation on a screening interview, actually had OSA on PSG. Age was the only predictor associated with PSG-documented OSA in this sample; although at first glance a history of hypertension appeared important, when adjusted for age it was not significant implying that it was the older age of the hypertensive subjects that was associating hypertension with OSA. Variables useful for predicting OSA in the general population (e.g., male gender, daytime sleepiness, hypertension, body-mass index, habitual loud snoring or witnessed apneas) and in the epilepsy population (seizure frequency, antiepileptic drugs, and nocturnal seizures) were not informative in distinguishing which patients suspected of having OSA had PSG-documented OSA.

Malow and colleagues concluded that identification of OSA in patients with epilepsy is challenging. Relying on the traditional indicators such as excessive daytime sleepiness to predict OSA may be problematic in that seizures and antiepileptic drugs may also contribute to daytime sleepiness. It may be necessary to accept some false positives (patients who are suspected of having OSA but who turn out to have negative PSGs) when diagnosing OSA in this population.

Future directions of this research are to estimate the prevalence of OSA in those with medically refractory epilepsy and determine the impact of treating OSA on seizure frequency, daytime sleepiness, and health-related quality of life.

Malow BA, Chervin RD, Foldvary-Schaefer NR, Selwa LM, Vaughn BV, Weatherwax KJ. Epilepsia 2004,Vol. 54, Supplement 7, p 61-62.

Malow BA, Weatherwax KJ, Chervin RD et al. Identification and treatment of obstructive sleep apnea in adults and children with epilepsy: a prospective pilot study. Sleep Medicine 2003;4:509-515.

Malow BA, Levy K, Maturen K, Bowes R. Obstructive sleep apnea is common in medically refractory epilepsy patients. Neurology 2000; 55: 1002-7.

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