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There are a variety of laboratory tests that directly or indirectly may apply to the evaluation of sleep and sleep disorders ( iiTable 2-2.).

Neuroimaging. Neuroimaging is not usually necessary during the evaluation of a primary sleep disorder. If patients present with additional neurological symptoms and signs, or the clinical history is atypical, magnetic resonance imaging may be helpful.

Electrophysiology. Routine EEG may be indicated when a diagnosis of sleep-related seizures is suspected. Likewise, electromyography may provide valuable information if peripheral neuropathy is suspected associated with RLS, or if neuromuscular disorders are thought to be predisposing to sleep apnea. The standard test of sleep is overnight PSG. PSG is an overnight recording of sleep, monitoring EEG, eye movements, chin muscle tone, muscle activity of the limbs, electrocardiogram, respiratory effort, nasal airflow, and oxygen saturation. During polysomnography, a patient is closely monitored by a technician

TABLE 2-2 -- USEFUL STUDIES FOR THE INVESTIGATION OF SLEEP-WAKE CYCLE DISORDERS

Neuroimaging

ElectrophysioOEogy

Fluid and Tissue Analysis

Neuropsychological Tests

Other Tests

Insomnia

Focal abnormality in post-traumatic, atrophy in degenerative diseases

PSG to indicate whether secondary to other sleep disorder EMG evidence of peripheral neuropathy in somepatients with RLS

Metabolic or drug screening

Dementia, depression, anxiety, or other psychiatric disorder

Sleep diary for sleep patterns

Forced immobilization test to assess for restless legs syndrome

EDS

Focal abnormalities, brain stem abnormality in central sleep apnea

PSG assessing for nocturnal sleep disorder (sleep, apnea, PLMD) Multiple sleep latency test with shortened latency with or without REM onset naps

EMG showing neuromuscular disease

Arterial blood gas showing hypoxia, chronic carbon dioxide retention HLA blood typing Serological evidence of viral infection

Dementia, depression, anxiety, or other psychiatric disorder

Reduced attention

Daytime sleepiness scales Sleep diary Oximetry

Pulmonary function tests

Cephalometry Pharyngeal examination

Parasomnia

Focal abnormality in brain stem area, thalamus, or hemisphere causing nocturnal seizure

Brain stem/cerebellar atrophy consistent with multiple system atrophy

PSG with videotaping to show the behaviors and the stage of sleep dunng which they occur Electroencephalography for noeturnal seizures

Evidenee of multiple sclerosis in CSF, prior viral infection

Dementia

Psychological disturbances, post-traumatic stress disorder

None needed

Circadian disorders

Wrist actigraphy, PSG

None needed

Assessment for anxiety, depression

Sleep diary, employment history

CSF, Cerebrospinal fluid; EDS, excessive daytime somnolence; EMG, electromyography; HLA, human leukocyte antigen; PLMD, periodic limb movement disorder; PSG, polysomnography; REM, rapid eye movement.

CSF, Cerebrospinal fluid; EDS, excessive daytime somnolence; EMG, electromyography; HLA, human leukocyte antigen; PLMD, periodic limb movement disorder; PSG, polysomnography; REM, rapid eye movement.

who is present throughout the night. Videotaping abnormal sleep behaviors is possible. PSG testing provides objective data concerning sleep latency, sleep efficiency, sleep staging, severity and type of sleep apnea, periodic limb movements, and parasomnias. PSG is of more limited usefulness in the evaluation of insomnia, unless insomnia arises from a primary sleep disorder, such as sleep apnea. The major drawback to PSG is the need to sleep in a controlled environment. For some patients, the strange surroundings reduce the ability to sleep normally, and obtaining an accurate sleep recording requires 1 night of adaptation before the actual recording night. Moreover, PSG is very labor intensive and expensive. Despite these drawbacks, PSG remains the most reliable test for certain sleep disturbances.

Fluid and Tissue Analysis. In patients with sleep apnea, obtaining a baseline arterial blood gas may be essential in guiding treatment. In patients with suspected narcolepsy, HLA blood typing may be descriptively interesting but does not confirm or eliminate a diagnosis. Obtaining other tests will depend on the individual case. Extensive fluid and tissue analysis is seldom necessary for most primary sleep disorders, but thyroid tests and drug screens should be obtained in most cases.

Neuropsychology Tests. Neuropsychology testing is useful for determining the presence and severity of cognitive impairment and mood disorders.

Other Tests. Sleep diaries allow a continuous subjective report of sleep. Patients are given a 2-week log, with each day divided into 30-minute or 60-minute intervals. Patients are instructed to fill out the log three to four times per day, indicating the time asleep for the previous 6- to 8-hour period. Patients can comment about their sense of alertness on awakening each morning and record unusual daytime or nighttime events. Sleep logs are inexpensive and convenient. Logs can provide valuable information about the circadian pattern of sleep and allow for an indefinite recording period. The drawback to sleep logs is the inaccuracy of self-report of sleep time and the inability to diagnose sleep disturbance. Sleep logs are a useful screening tool and can provide follow-up information for phase shifted sleep and insomnia.

Wrist actigraphy measures movement of the wrist, consisting of a movement detector and memory storage. A wrist actigraph is approximately the size of a large watch and is worn continuously at home. When the recording period is complete, the stored movement data is transferred to a computer for analysis. Interpretation of actigraphic records assumes that movement is reduced during sleep compared with wakefulness. Patients who lie still but are awake for prolonged periods of time will have their sleep time overestimated. Similarly, patients with excessive movements during sleep may be considered to be awake and have an underestimate of sleep time. According to the American Sleep Disorders Association practice parameters, actigraphy serves as a useful adjunct to history, examination, and subjective sleep diary for the diagnosis and treatment of insomnia, circadian-rhythm disorders, and excessive sleepiness. However, actigraphy is not indicated for the routine diagnosis of any sleep disorder. y

The multiple sleep latency test (MSLT) consists of five 20-minute nap opportunities, with each nap separated by 2 hours. The patient is lying down in a darkened room and instructed to try to sleep. The time before any sleep is recorded for each nap, and the mean sleep latency for all five naps is then determined. Patients with a mean sleep latency of less than 5 minutes are considered to have pathological sleepiness; those with a mean sleep latency between 5 and 10 minutes are borderline, and those with a mean latency greater than 10 minutes are normal. During the naps, sleep is staged. If REM sleep occurs during two or more naps, the MSLT is consistent with a diagnosis of narcolepsy, provided other causes of sleep-onset rapid eye movements have been excluded. The MSLT test is accurate if performed the day following overnight PSG. Sleep deprivation from the night before or drugs that suppress REM may yield deceptive results. The MSLT is indicated for assessment of narcolepsy, severity of EDS due to obstructive sleep apnea, other nocturnal sleep disturbances, and idiopathic hypersomnia. y

Ambulatory or portable sleep monitoring allows for recording of sleep in the patients home. It is less expensive than laboratory PSG and more convenient for patients. Portable monitors have been the most widely used tool for the assessment of sleep apnea. The limitations of portable monitoring include the variability in commercially available monitors. Recording channels may be limited, making a complete assessment of sleep problematic. There is no technician present in an unattended study to adjust for malfunctioning equipment or to reapply faulty or loose electrodes. According to the American Sleep Disorder Association's guidelines, portable monitoring is indicated only for patients who cannot be studied in the sleep laboratory or for follow-up studies when the diagnosis has already been established by standard PSG.y

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