Chapter 61 Obstructive Sleep Apnea
Clinical Features, Diagnosis, and Treatment*
The clinical presentations of obstructive sleep apnea (OSA) are legion. Common clinical features can be divided into major and minor categories, as summarized in Box 61-1. Patients may present with daytime and/or nocturnal complaints, but commonly, spouses and living companions are the first to push for medical attention.
Common Clinical Features in Obstructive Sleep Apnea
Snoring is the most frequent nocturnal symptom of OSA, occurring in up to 95% of patients with the condition. Snoring has poor predictive value owing to a high prevalence in the general population. In population surveys, the prevalence of snoring increases progressively with age, yet snoring is a hallmark of OSA, and in its absence, the diagnosis of OSA is unlikely. Snoring occurs after sleep onset, although in some patients with OSA it is present even during drowsiness. Its intensity increases with nighttime alcohol consumption and use of sedative drugs. In general, snoring is loudest in the supine position (dorsal recumbency) and decreases in volume in the side-lying position. Periods of silence interrupting loud snoring may reflect occurrence of pathologic apneas.
Patients with OSA usually fall asleep quickly, although many of them report insomnia and frequent nocturnal awakenings. Insomnia is most likely to reflect the perception of recurrent arousals from sleep and its nonrestorative pattern. Repetitive episodes of airway obstruction can be associated with snorting, gasping, diaphoresis, and restlessness that lead to sleep fragmentation. In severe OSA, choking is reported by more than 30% of patients. Nocturnal awakenings raise a differential diagnosis that should include nocturnal asthma, cardiac failure, and gastroesophageal reflux. Pathologic nocturia (2 episodes or more per night) has a prevalence of 50% among patients with OSA. It is thought to be secondary to hypoxia and atrial stretch, leading to increased atrial natriuretic peptide secretion and subsequent increment in intravascular volume. Effective therapy with continuous positive airway pressure (CPAP) reduces occurrence of these symptoms, thus suggesting a causal relationship between them and OSA.
Bed partners often volunteer witnessing breathing pauses followed by snorting or gasping during sleep, and this is a common reason for referral of the patient to a sleep clinic. Witnessed apneas are considered a good diagnostic predictor of OSA; nevertheless, this finding does not correlate with objective measurements and hence does not predict the severity of the disorder.
Sleepiness is difficult to define and is a subjective feeling of impairment of concentration and increased craving for sleep. Excessive daytime sleepiness (EDS) is a nonphysiologic complaint that is not satisfied by a restorative sleep. Sleepiness is reported by 30% to 50% of the general population, so EDS alone is a poor predictor of OSA and requires a differential diagnosis to exclude many other medical conditions associated with this daytime symptom, such as depression, fibromyalgia, chronic insomnia, or hypothyroidism. Patients with OSA sometimes refer to EDS as abnormal daytime tiredness or lack of energy and convey the impression that they must make stringent efforts to remain alert and awake. It is believed that the loss of the restorative function of sleep due to repetitive arousals is the main mechanism to explain the presence of EDS in OSA. The Epworth Sleepiness Scale (Box 61-2) is the most popular tool for subjective evaluation (self-assessment) of EDS. A score above 10 of 24 is considered to be clinically relevant. The relationship between the Epworth score and the apnea-hypopnea index (AHI) (as a surrogate index of OSA severity) is relatively poor. In fact, 35% patients with severe OSA identified within sleep clinics do not complain of EDS. This discrepancy is partly due to underestimation or intentional underreporting the severity of sleepiness for personal gain, such as to avoid job loss. On the other hand, patients scoring high in the Epworth scale could have just mild to moderate OSA. EDS is the most disabling symptom among patients with OSA. One example is drowsiness while driving, which is associated with a three-fold increase in risk of accidents in patients with OSA. Poor school or job performance also is frequently reported.
Box 61-2 Epworth Sleepiness Scale
How often are you likely to doze off or fall asleep in the following situations, in contrast with feeling just tired? This refers to your usual way of life in recent times. Even if you have not done some of these things recently, try to work out how they would have affected you. Use the following scale to choose the most appropriate number for each situation:
From Johns MW: A new method for measuring daytime sleepiness: the Epworth Sleepiness Scale, Sleep 14:540–545, 1991.
On wakening in the morning, half of sufferers report headaches. Morning headache usually is generalized and lessens as the patient begins the usual activities of the day. This symptom may be due to hypercapnia and associated cerebral vasodilatation with resultant increase in intracranial pressure. Often, morning headaches disappear after effective treatment of OSA. Symptoms related to cognitive impairment such as memory loss, irritability, personality changes, and depression are frequent but nonspecific. Both sleep fragmentation and nocturnal hypoxemia have been advocated to explain decreased vigilance and psychomotor impairment, respectively. One concern is the observation that OSA treated with CPAP causes only partial resolution of those deficits, suggesting a potentially irreversible anoxic brain damage. In men with OSA, sexual dysfunction including impotence and decreased libido have been reported in 30% to 50% of the cases and appears to be fully reversible with effective treatment of the OSA. Past medical history should be obtained, particularly for those conditions that may occur as a result of OSA, such as hypertension, cardiac failure, myocardial infarction, and motor vehicle crashes.
After a complete history has been obtained, a systematic examination should be performed. In nonobese patients (body mass index [BMI] less than 30 kg/m2), common physical findings can be observed in the craniofacial, nasal, pharyngeal, and dental areas (Box 61-3). Radiographic cephalometry is indicated if craniofacial abnormalities are suspected or if upper airway surgery is planned to treat the patient. The oropharynx must be examined, and the degree of oropharyngeal crowding can be scored using the Friedman Tongue Position, formerly called the modified Mallampati score. For this assessment, the patient is asked to open the mouth widely without protruding the tongue. The observer can assign scores as indicated in Figure 61-1. Higher scores suggest the presence of OSA.
Physical Findings in Patients with Obstructive Sleep Apnea
Figure 61-1 Friedman tongue position index for visualization of oral structures. A, Score I: all of the structures of the oropharynx are seen (soft palate, uvula, lateral pharyngeal pillars, and tonsils). B, Score II: allows visualization of the uvula but not the tonsils. C, Score III: allows visualization of the soft palate but not the uvula. D, Score IV: only the hard palate is seen.
(From Friedman M, Tanyeri H, La Rosa M, et al: Clinical predictors of obstructive sleep apnea, Laryngoscope 109:1901–1907, 1999.)
Obesity frequently is associated with OSA, in both men and women, but up to 30% of newly diagnosed patients are not obese or overweight. Neck circumference greater than 40 cm is considered a reliable clinical predictor of OSA, and the size of the neck correlates with the severity of disease. Peripheral edema should be sought as a sign of possible coexisting heart failure. Careful assessment for the presence of hypertension, thyroid abnormality, and acromegaly is indicated. Blood samples should be obtained routinely for testing thyroid function and to check for any other hormonal abnormality. In children, the clinical assessment should include evaluation for evidence of Down syndrome, craniofacial disorders, and enlarged tonsils.