Sleep Studies



Sleep Studies


Andrew J. Westwood

Carl W. Bazil



INTRODUCTION

The National Institutes of Health estimate that 50 to 70 million Americans are affected by sleep problems (see Chapter 114). Sleep deprivation and disorders have been linked to chronic medical diseases such as stroke and diabetes but also to mental health issues and to an increased risk of accidents, particularly motor vehicle accidents. Lack of sleep is not a trivial concern as many patients (and physicians) perceive; it is a very real public health problem.

Evaluation of sleep is complex and is a multidisciplinary analysis. Given the vast spectrum of sleep problems such as sleep-disordered breathing, parasomnias, insomnia, narcolepsy, bruxism, nightmare disorder, circadian rhythm disorders, and nocturnal enuresis, several medical specialties, dentists, and psychologists take an interest in sleep disorders. For physicians, subspecialty certification in sleep medicine can be obtained following primary certification in anaesthesia, internal medicine, pediatrics, neurology, psychiatry, or otolaryngology. Although detailed medical history and examination are critical in the diagnostic evaluation, subjective reports of sleep concerns are marred by recall bias because the primary problem often occurs during sleep such that the patient may be partly or completely unaware of the problem, and observations by bed partners or housemates will also be limited. Validated questionnaires and sleep logs (including those now available as smartphone applications) provide somewhat more detailed, albeit still subjective, information about sleep and can be helpful. For many disorders, however, testing is required for more objective evaluation of physiologic parameters in sleep and to direct correct treatment.


INDICATIONS FOR DIAGNOSTIC SLEEP TESTING

The need for diagnostic testing, and the specific test required, depends on the clinical suspicion and the question at hand. In general, sleep tests evaluate the quality and quantity of sleep along with other physiologic parameters. The major tests used include polysomnography, a measure of overnight sleep and associated phenomena; multiple sleep latency testing, a measure of the ability to fall asleep during the day; and maintenance of wakefulness test, a measure of the ability to stay awake during the day. Additionally, actigraphy uses movement as a surrogate for sleep and can give useful information about sleep patterns over days to weeks. Each of these will be discussed in detail in the following text.

Polysomnography is not usually indicated for suspected insomnia (delayed or interrupted sleep) or circadian rhythm disturbances, as these are generally diagnosed by history. However, if the condition remains refractory to treatment, polysomnography may be indicated to look for other causes. Obstructive sleep apnea is probably the most common reason for overnight polysomnography, as testing is required for diagnosis no matter how high the suspicion. Signs of sleep apnea include excessive daytime somnolence, snoring, morning headache, frequent nocturia, obesity, and a narrow airway; however, all are rarely present in a given individual. Restless legs syndrome is a clinical diagnosis wherein the patient is aware of uncomfortable sensations in the limbs (usually legs but sometimes arms or trunk) that keep him or her awake at night. This may be treated without testing; however, many of these patients will also have periodic limb movements— repetitive movements during sleep that are typically unrecognized by the patient or bed partner and can result in unrefreshing sleep. Periodic limb movements can also occur in the absence of restless legs syndrome. Suspected narcolepsy requires polysomnography to ensure the absence of other causes of sleepiness. This is followed by multiple sleep latency testing; very short sleep latency and presence of rapid eye movement (REM) in more than one nap are highly suggestive of narcolepsy. Parasomnias may sometimes be diagnosed without testing, but due to the possible confusion between them, association with other sleep disorders such as obstructive sleep apnea, and differential diagnosis that sometimes includes nocturnal seizures, polysomnography is often advisable. Parasomnias include night terrors, rhythmic movement disorder, and sleepwalking (especially in adults) and REM behavior disorder. When nocturnal seizures are in the differential, polysomnography should be performed with simultaneous video electroencephalography (EEG).


POLYSOMNOGRAPHY

The in-laboratory polysomnogram is the gold standard diagnostic test of most sleep disorders (Table 29.1). Clinical polysomnography consists of the simultaneous recording of multiple physiologic variables, allowing objective documentation of sleep state and for evaluation of common sleep disorders. Practitioners will routinely use a minimum of four EEG channels, covering the occipital and central regions required for scoring of sleep, but most will use more. Electro-oculography (EOG); mentalis electromyography (EMG); surface EMG of the anterior tibial muscles for detection of leg movements in sleep; electrocardiography (ECG); and measurement of nasal and oral airflow, respiratory effort, and oxygen saturation as well as audio and video recording are also standard. Additional variables analyzed may include CO2 monitoring and esophageal manometry.

The recordings are analyzed at 30-second intervals or epochs. Each epoch is evaluated based on muscle tone, EOG, and EEG to determine sleep stage or wakefulness. Each epoch is also evaluated for abnormalities in respiratory flow/pressure, oxygen saturation, heart rate, and any movements (Fig. 29.1). The American Academy of Sleep Medicine provides guidance on recommended scoring for sleep stage, respiratory disturbances (apneas, hypopneas, respiratory-related arousals), as well as limb movements. Once each epoch has been analyzed, a convenient way to display this significant amount of data is the hypnogram. This can show the macroarchitecture over the course of the entire night and can
be modified to provide additional information such as timings of respiratory disturbances and body position.








TABLE 29.1 Indications for Polysomnography





































  • Diagnosis of sleep-related breathing disorders




  • PAP titrations for sleep-related breathing disorders




  • Preoperative evaluation prior to upper airway surgery for snoring or obstructive sleep apnea




  • Follow-up after good clinical response to oral appliance treatment




  • Follow-up after surgical treatment




  • Recurrence of symptoms despite initial response to surgical or dental treatments




  • Follow-up in patients with substantial weight loss after PAP initiation




  • Follow-up in patients with substantial weight gain after PAP initiation




  • Insufficient response to PAP therapy despite a good initial response




  • Patients with systolic or diastolic heart failure with sleep complaints despite optimal cardiac treatments




  • Patients with neuromuscular disorders and sleep complaints despite optimal sleep hygiene




  • Narcolepsy (followed by MSLT)




  • Periodic limb movement disorder




  • Uncertainty of restless legs syndrome


PAP, positive airway pressure; MSLT, multiple sleep latency test.


Based on Kushida CA, Littner MR, Morgenthaler T, et al. Practice parameters for the indications for polysomnography and related procedures: an update for 2005. Sleep. 2005;28(4):499-521.


Polysomnography must always be interpreted in the context of potentially relatable history. Therefore, patients should ideally fill out sleep logs for at least 1 week prior to the test. Medications and napping on the day of the study should be noted, and it is often helpful to have the patient’s impression of his or her sleep during the study. A patient with 6 hours of documented sleep on polysomnography who believes only 1 to 2 hours of sleep occurred likely has a diagnosis of paradoxical insomnia.


EVOKING PARASOMNIAS

Parasomnias such as sleepwalking and sleep terrors typically arise from slow-wave sleep (stage N3). They may not occur on a nightly basis. In order to increase the yield of recording such events, a patient may sometimes be asked to restrict his or her sleep the night prior in order to provoke a rebound of slow-wave sleep. There is some data that deliberate external stimuli, such as sound, during slow-wave sleep may also cause provocation of the events.


EVALUATING RAPID EYE MOVEMENT BEHAVIOR DISORDER

Recording of dream enactment behavior during REM sleep (Fig. 29.2) is helpful, however not required to support a diagnosis of REM behavior disorder. One of the cardinal features of this disorder is the lack of atonia during REM sleep. Atonia is usually identified in the chin lead; however, it may be present in one or more limb leads. Some practitioners may apply additional leads to all four extremities in cases where REM behavior disorder is a concern. It is important to note that melatonin can suppress the atonia and should be stopped prior to the study.

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Jul 27, 2016 | Posted by in NEUROLOGY | Comments Off on Sleep Studies
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