Idiopathic intracranial hypertension is characterized by optic disc edema, elevated intracranial pressure, normal spinal fluid constituents, and absence of evidence of a mass lesion on neuroimaging (1,2). Idiopathic intracranial hypertension occurs predominantly in young, middle-aged, obese women, and case-control studies confirm that obesity and recent weight gain are more common in patients with idiopathic intracranial hypertension than in controls (3–7). Decreased cerebrospinal fluid (CSF) absorption by arachnoid villi or elevated intracranial venous pressures are mechanisms often proposed as final common pathways of multiple inciting factors (8–10).
Sleep apnea is a common sleep-related breathing disorder characterized by daytime hypersomnolence, snoring, and multiple episodes of apnea (cessation of airflow) or hypopnea (reduction in airflow) during sleep (11). A mild form of the disease is called upper airway resistance syndrome (UARS) in which repeated arousals from sleep occur because of an increased effort to breathe to overcome the narrowing of the upper airways (12).
The ocular manifestations of sleep apnea have been described in case reports or small series, and optic disc edema (13–19), glaucomatous (20), and ischemic optic neuropathy (21) have been observed. Seven case reports note the association of optic disc edema with and without increased intracranial pressure in seven sleep apnea patients (13–19). Thus, sleep apnea has been proposed to be an uncommon but recognized cause of idiopathic intracranial hypertension (18). We determined the frequency of sleep-disturbed breathing and sleep disorders in our patient population with idiopathic intracranial hypertension.
METHODS
Our institution's human assurance committee approved the study protocol. We reviewed the records of patients with a diagnosis of idiopathic intracranial hypertension. To be diagnosed with idiopathic intracranial hypertension, patients were required to demonstrate bilateral disc edema, a normal neuroimaging study, and a lumbar puncture showing normal CSF contents and high pressure.
A sleep history was obtained in 53 idiopathic intracranial hypertension patients. Polysomnography was recommended in all patients with a positive sleep history for snoring or daytime somnolence. Polysomnography was performed at night and consisted of 8-hour recordings of electroencephalograms (EEG), oculograms, chin muscle and anterior tibialis muscle electromyograms, electrocardiograms, oronasal airflow, and oxygen saturation. Frequency of apnea (cessation of breathing), hypopnea (reduction in ventilation limit oxygen desaturation), and arousal (increase in EEG frequency of at least 3 seconds) was determined.
Sleep apnea was diagnosed if the frequency of apnea and hypopnea per hour of sleep (i.e., respiratory disturbance index) was five or greater. UARS was diagnosed if the number of arousals per hour of sleep (arousal index) was 20 or greater and the arousals were associated with crescendo snoring.
RESULTS
Thirty-seven of 53 (70%) idiopathic intracranial hypertension patients had a history of sleep disturbance. Fourteen of these 37 patients underwent polysomnography. The demographics of these 14 patients (group A) and the 23 patients who declined polysomnography (group B) are summarized in Table 1. Almost all patients in both groups were morbidly obese (body mass index, > 40). The differences between the two groups were not significant (P > 0.05).
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TABLE 1: Demographics of idiopathic intracranial hypertension patients who did/did not undergo polysomnography
The results of polysomnography in 14 patients are summarized in Table 2. A diagnosis of sleep-related problems was made in 13 of the 14 idiopathic intracranial hypertension patients. Sleep apnea was diagnosed in seven patients and UARS in six patients. One patient had snoring, but the number of arousals was fewer than the minimum required for the diagnosis of UARS.
TABLE 2: Demographics and polysomnography results for idiopathic intracranial hypertension patients
DISCUSSION
Sleep-related breathing problems vary in severity from sleep apnea with respiratory failure to UARS. Patients with UARS usually do not have significant hypoxemia or hypercapnia. It is estimated that 4% of men and 2% of women in the general population have sleep apnea (11). The incidence of UARS may be higher than that of sleep apnea. The risk factors for sleep apnea include snoring, obesity, upper airway abnormalities, and alcohol intake.
The clinical features and pathophysiologic manifestations of patients with idiopathic intracranial hypertension and sleep disorders significantly overlap. Sex and age differences are the main distinguishing features between these two disorders. Sleep apnea is more common in middle-aged men, whereas idiopathic intracranial hypertension is more common in young women. Obesity is a significant risk factor for idiopathic intracranial hypertension and sleep-related breathing disorders. The prevalence of idiopathic intracranial hypertension in obese female patients more than 20% above ideal body weight is 19.3 per 100,000 compared with 1 per 100,000 in the normal, nonobese population (4). In one study, the prevalence of sleep apnea in morbidly obese patients was 77% in men and 7% in women (22). It is likely that obesity may play a central role in sleep apnea and idiopathic intracranial hypertension. Weight reduction is associated with improvement of symptoms in patients in both of these diseases (23,24).
How might sleep disorders contribute to the development of idiopathic intracranial hypertension? Several factors including hypoxia, hypercapnia, polycythemia, and increased venous pressure have been postulated as potential causes for fundus abnormalities described in sleep apnea. Hypercapnia or hypoxia, particularly during sleep, is common in patients with sleep apnea. Nocturnal hypercapnia may be responsible for increased intracranial pressure and secondary papilledema in these cases (25). Episodic elevations in intracranial pressure have been shown during apneic episodes (26). Patients with severe obstructive sleep apnea may demonstrate continuously elevated intracranial pressure (19).
Our data indicate that sleep-related breathing problems are common in patients with idiopathic intracranial hypertension. The high prevalence of sleep-related breathing disorders in our study may be somewhat inflated; patients with sleep apnea may be more likely to agree to have polysomnography than patients without. Those patients who underwent polysomnography, however, did not have substantially different demographic features compared with those patients who did not undergo polysomnography.
Our study suggests that sleep disorders may be a risk factor for idiopathic intracranial hypertension. These findings, however, do not provide evidence for a cause-and-effect relationship. Prospective studies are needed to confirm this strong association of these diseases. It is interesting to note that the only two male patients with idiopathic intracranial hypertension in our population were diagnosed as having sleep apnea. As idiopathic intracranial hypertension is uncommon in men, our findings support speculation that this association may be even more sex significant. We suggest that patients with idiopathic intracranial hypertension should be asked about the presence of symptoms of sleep apnea such as of snoring, disturbed sleep, and daytime somnolence. The presence of these symptoms should be an indication for further evaluation by polysomnography.
Acknowledgment:
The authors thank Richard Rubin, MD, for contributing patients to this study.
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