PSG is the single most important laboratory test for assessment of sleep disorders, particularly in patients presenting with EDS and those suspected of nocturnal seizures, parasomnias, or other abnormal motor activities. However, PSG has considerable limitations. There is no standardized uniform protocol used consistently in all sleep laboratories, making the comparison of the data from one laboratory to another somewhat misleading. The most severe limitations are that an overnight in-laboratory PSG is labor-intensive, time-consuming, and expensive. A single-night PSG may miss the diagnosis of mild OSAS, PLMS, parasomnias, and nocturnal seizures. PSG data and the patient’s clinical findings may not be concordant. Standard PSG study cannot diagnose upper airway resistance syndrome definitively. PSG cannot determine the etiology of apnea–hypopnea syndrome. PSG is not helpful in the diagnosis of insomnia, the most common sleep disorder in the general population. PSG is not helpful in the diagnosis or treatment of circadian rhythm sleep disorders. PSG data may be confounded by first-night effects (e.g., increased wakefulness and stage 1 NREM sleep, and decreased slow-wave and REM sleep). Standard PSG does not measure arterial partial pressure of CO₂ and thus may miss hypoventilation, which is an early abnormality (particularly REM hypoventilation) in neuromuscular disorders. Standard PSG does not adequately measure cardiac function (one channel of electrocardiography [ECG] is inadequate), which may affect the prognosis of OSAS. Furthermore, cardiorespiratory sleep studies, which do not include EEG, may produce false-negative findings in mild-to-moderate OSAS patients. Standard PSG does not include autonomic monitoring, which may be important for assessment of autonomic activation as well as for assessing autonomic changes that are intense during sleep.

A video-PSG study is important for documenting abnormal movements and behavior during sleep at night in patients with parasomnias, including RBD, nocturnal seizures, and other unusual movements occurring during sleep [62]. Parasomnias are generally diagnosed on the basis of a clinical history, but sometimes a video-PSG study is required to document the condition. For suspected nocturnal epilepsy, a video-PSG study using additional electrodes to include multiple-channel EEG and multiple montages covering both parasagittal and temporal regions bilaterally is required for optimal detection of epileptiform activities. Ideally, if sleep epilepsy is suspected, video-PSG recordings should be interpreted using EEG analysis at the standard EEG speed of 30 mm/sec to identify epileptiform discharges. Multiple EMG channels to record from additional muscles (e.g., forearm flexor and extensor muscles, masseter and other muscles) for patients with suspected RBD and bruxism are recommended.

Video-PSG may help characterize the movements, differentiate one jerk from another, identify a specific entity, and most important, differentiate abnormal motor activities from nocturnal seizures. Video-PSG may aid in the diagnosis of other coexisting sleep disorders (e.g., OSAS, RBD, narcolepsy). Video-PSG does help us classify abnormal motor activities during sleep into several identifiable entities (e.g., motor parasomnias, nocturnal seizures, involuntary diurnal movements persisting during sleep, PLMS, excessive fragmentary myoclonus seen in a variety of sleep disorders, dissociative disorders, nocturnal jerks, and body movements seen in patients with OSAS). Many parasomnias may be mistaken for nocturnal seizures (e.g., confusional arousals, sleepwalking, sleep terror, sleep talking, bruxism, rhythmic movement disorder, RBD, nightmares, and dissociative disorders). RBD and nightmares occur during REM sleep. These conditions can be diagnosed and differentiated from one another based on characteristic clinical features combined with EEG and video-PSG findings. Box 26.16 lists indications for video-PSG.

The MSLT is an important test to effectively document EDS (see Chap. 22). Narcolepsy is the single most important indication for performing MSLT. The presence of two or more sleep-onset REM periods (SOREMP) from four or five nap studies (a SOREMP in the preceding overnight PSG study may substitute for one MSLT SOREMP) and sleep-onset latency of less than 8 min strongly suggest a diagnosis of narcolepsy [30] (Fig. 26.4). Abnormalities of REM sleep regulatory mechanisms (e.g., OSAS, insufficient sleep syndrome, use of REM-suppressant medications) or circadian rhythm sleep disturbance may also lead to REM sleep abnormalities during an MSLT.

The maintenance of wakefulness test (MWT) is a variant of the MSLT (see Chap. 23), measuring a subject’s ability to stay awake. It also consists of four to five trials of remaining awake occurring every 2 h. Each trial is terminated if no sleep occurs after 40 min or immediately after the first 3 consecutive epochs of stage 1 NREM sleep or the first epoch of any other stage of sleep [61, 62]. If the mean sleep latency is less than 8 min, it is then considered an abnormal test. The MWT is less sensitive than the MSLT as a diagnostic test for narcolepsy but is more sensitive in assessing the effect of treatment (e.g., CPAP titration in OSAS and stimulant therapy in narcolepsy).

An EEG is necessary to investigate suspected epilepsy (see Chap. 44).

Ambulatory EEG or PSG is sometimes useful for patients with suspected sleep epilepsy, for understanding circadian variation and for studying circadian rhythm sleep disorders. However, technical problems associated with unattended recording are serious limitations.

This is another laboratory test for assessing sleep disorders that use an actigraph (also known as an actometer) worn on the wrist or ankle to record acceleration or deceleration of body movements (Fig. 26.5), which indirectly indicates the state of sleep or wakefulness. The actigraph can be worn for days or weeks, and this test complements a sleep log or diary in diagnosing circadian rhythm sleep disorders (Fig. 26.6) and in assessing patients with insomnia (Fig. 26.7), including paradoxical insomnia or sleep state misperception; inadequate sleep hygiene; and prolonged daytime sleepiness. Actigraphy is useful to document rest–activity patterns over days and weeks when a sleep log is not able to provide such data. Advantages of actigraphy over PSG include the following: easy accessibility; inexpensive recording over extended periods of days, weeks, or months; recording of 24-h activities at all sites (home, work, laboratory); usefulness in uncooperative and demented patients when laboratory PSG study is not possible; ability to conduct longitudinal studies during therapeutic intervention (e.g., cognitive behavioral therapy or pharmacologic treatment) in patients with insomnia; usefulness in paradoxical insomnia; and ability to document delayed or advanced sleep-phase state or circadian rhythm sleep disorder, free-running type. Although not adequately standardized, actigraphy may have a role in patients with RLS and PLMS.