October - December 2008: 
Volume 21, Issue 4

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Polysomnography: Recent data on Procedure and Analysis
SUMMARY. Polysomnography is a medical diagnostic test which offers a large amount of information by recording the activity of various organ systems for a period of several hours with the aim of diagnosing pathological conditions associated with sleep. It is used for the diagnosis of apnoea-hypopnoea and upper airway resistance syndromes, and a variety of other sleep conditions related to daytime sleepiness that cannot be classified as breathing disorders, such as restless leg syndrome, disorders during REM sleep and other parasomnias. The first manual- report in Polysomnography published in 1968 by Rechtschaffen and Kales (R & K) contained scoring rules for the assessment of all parameters of sleep, and became a guide for thousands of polysomnographic tests. During the 40 years which have passed since the publication of the first manual, there has been vigorous development in the methodology of recording the parameters of polysomnography and the scoring rules. As a result of these developments, the American Academy of Sleep Medicine (AASM) published a new manual in 2007: The AASM Manual for the Scoring of Sleep and Associated Events – Rules, Terminology and Technical Specifications, which revises some of the rules and adds others concerning disorders and syndromes that have been described since the first edition of the manual. Πνεύμων 2008, 21(4):-.
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The science of sleep emerged as a discipline as a result of the development of tools and techniques able to detect and record brain activity and all the physiological events that occur during the unique state of sleep.

The methods initially employed for detecting the electrical activity of sleep, and used mainly in animals (R. Caton, 1875), included recording of brain surface electrical activity.1 In 1929, Berger described the electrical activity of the human brain during sleep by means of external scalp recordings as intense in the wakeful state and mild in relaxation and during sleep.2 In 1935, Loomis et al conducted the first nightlong polysomnographic sleep study.3 In 1937, polysomnographic recordings were focused on identifiable patterns of brain activity during non rapid eye movement (NREM) sleep, which include alpha and delta activity, as well as isolated waveforms such as K- complexes, spindles and Vertex waves.4,5

The stage of rapid eye movement (REM) sleep, associated with increased dreaming activity, was identified by Aserinsky and Kleitman in 1953.6,7

Sleep staging was accomplished with simultaneous recordings of electroencephalogram (EEG), electrooculogram (EOG) and electromyogram (EMG). Recording of brain activity during sleep in parallel with respiratory recordings was achieved in the mid 20th century.8

Scientific efforts to characterize all the physiological events that occur during sleep4-7,9 provided the rationale for a standardized scoring manual with universally accepted terminology and specifications. After several meetings in the 1960s, the first manual for the recording and scoring of human sleeping activity was published in 1968 by A. Rechtschaffen and A. Κales (R & K).10

Later, in 1971, the identification of qualitative differences in sleep in newborns and children resulted in publication of a separate manual for this age group.11

Since the publication of the first scoring manual of R & K 40 years ago, which proved to be a useful tool for numerous researchers, there has been pronounced evolution in the understanding of sleep. The evolving science of sleep and sleep medicine are now beginning to employ novel metrics to characterize sleep.

Recognition of the nature and importance of sleep- related phenomena such as arousal, cardiac dysrhythmias, respiratory patterns, body movements and behavior dictated the need for a more comprehensive scoring manual that would incorporate these changes, as well as the newer technical methods and capabilities.

In 2003, the American Academy of Sleep Medicine (AASM) preapproved and suggested the development of a new scoring manual. The goal was carefully designed and included a draft for future editions that would broadly reflect the needs of this evolving science. The development, which commenced in 2004 and was completed in 2007, has also incorporated a standardized review for specifications, scoring rules for normal sleep and terminology for the evaluation of findings, pathological or not, during sleep.

The following study provides an outline of the basic principles of The AASM Manual for the Scoring of Sleep and Associated Events - Rules, Terminology and Technical Specifications 2007,12 and demonstrates the basic differences from the previous publications.


2.1. Electroencephalogram (EEG)

According to R & K, electrodes are placed as follows: two mastoid (Μ1, Μ2- formerly known as aural, Α1 & Α2), two central (C3, C4) and two occipital derivations (O1, O2).

The new manual recommends the addition of two frontal electrodes (F3, F4) to allow recording of sleep spindles, K-complexes, arousals,12-15 and possible epileptic convulsions that would remain undetected by standard electrodes.16

The recommended derivations are; F41, C41, O21.

Backup electrodes should be placed at F3, C3, O1 and M2 to allow display of F32, C32 και O12 if other electrodes malfunction during the study.

Acceptable alternatives16 include three frontal (Fpz, Fz, F4), three central (C3, Cz, C4), two mastoid (Μ1, Μ2) and two occipital (O1, Oz) derivations. Recommended combinations are: Fz - Cz, Cz - Oz, C4 - Μ1.

Backup electrodes should be placed at Fpz, C3, O1 and Μ2 to allow substitution of F3, Cz, Oz and M1 if other electrodes malfunction during the study.

EEG electrode placement is determined by the International 10-20 System.

International 10-20 System of EEG electrode placement

Guiding marks are nasion, inion, right and left preaurical points (located between zygomatic bone and condyle of mandible). Each electrode is placed at the intersection of two imaginary lines.

Initially we measure the nasion-inion distance and record an original point Cz as the middle (50%), FPz as 10% from nasion and Oz as 10% from inion. Respectively, the distance between right and left preauricular points is marked at 50% as final Cz and at 10% as original C4 and C3 points (Figure 1). Electrodes M1 and M2 are placed postauricularly between the zygomatic bone and the mandibular condyle.

Next, we mark the midline just above the nose at 10% of the distance between inion and nasion and measure cranial diameter in the axis set by this point and 10% above the preauricular points and inion (Fig. 1). Point Oz is determined as the intersection at 50% of that axis and 10% of the inion line. Points 10% from Oz on the perimeter line are also marked, as O1 and O2 (Figures 2, 3).

The same procedure is followed to mark FP1 and FP2. Finally C3 point corresponds to 50% of the distance FP1-O1 through C3. The middle of FP1-C3 equals to F3. Application of the same technique on the right side provides C4 and F4. Fz is marked at 20% from FPz (Fig. 3).

2. 2. Electrooculogram (EOG)

The EOG records eye movements and is used for sleep staging. Two electrodes are placed 1 cm below and 1 cm lateral to the left outer canthus and 1 cm above and 1 cm lateral to the right outer canthus, respectively (Figure 4).18, 20

The recommended derivations are:16 E1- Μ2, E2 - Μ2.

Alternative acceptable derivations are 1 cm below and 1 cm lateral to both right and left outer canthus (Figure 5).

2.3. Electromyogram (EMG)21

According to the new manual, three electrodes should be placed to record chin EMG12: one in the midline 1 cm above the inferior edge of the mandible, one 2 cm below the inferior edge of the mandible and 2 cm to the right of the midline, and one 2 cm below the inferior edge of the mandible and 2 cm to the left of the midline (Figure 6). The third electrode is a backup electrode to allow for continued display of EMG activity if one of the primary electrodes malfunctions or is displaced during the test. The previous edition of the manual suggested using two electrodes.

The EEG and EMG electrodes are held in place by application of collodium or electrolyte cream (EC2 Grass).

Collodium is a type of glue-like volatile solution, which offers great stability and dries instantly with the use of cool air (hair dryer). Its disadvantages are the intense smell, the difficulty in removing it (it can only be removed with alcohol solution) and the possibility of allergic reactions. Its intense smell may not be tolerated well by people with respiratory disorders.

Electrolyte cream is a newer product that tends to replace collodium, as the latter is particularly flammable and requires special storage conditions. Electrolyte cream is odourless and suitable for people with allergic reactions to collodium or respiratory disorders, such as chronic obstructive pulmonary disease (COPD), asthma, etc. It dries with difficulty and offers less stability than collodium, but it can be removed with water. However, the procedure is more time-consuming.

2.4. Electrocardiogram (ECG)22

Numerous studies suggest that breathing disorders during sleep can be associated with significant cardiovascular effects.

During a sleep study, arrhythmias (bradycardia, tachycardia, ectopic atrial or ventricular beats) are the most common findings, especially at the time of apnoea or hypopnoea, and a high quality ECG display is required to detect these disturbances. The right (-) electrode is placed parasternally at the 2nd intercostal space and the left (+) electrode in the anterior axillary line at the 6th intercostal space (Figure 7), which corresponds to lead aVF of standard ECG. These electrode applications have proven superior in minimizing artifacts.

Scoring rules:22

Sinus tachycardia during sleep is scored for a sinus heart rate higher than 90 beats/min for more than 30 sec (sustained tachycardia).

Bradycardia during sleep is scored for a heart rate of less than 40 beats/min for more than 30 sec (sustained bradycardia).

Wide complex tachycardia is scored for a rhythm lasting a minimum of 3 consecutive beats at a rate higher than 100 beats/min with QRS duration of greater than or equal to 120 msec.

Narrow complex tachycardia is scored for a rhythm lasting a minimum of 3 consecutive beats at a rate higher than 100 beats/min with QRS duration of less than 120 msec.

Asystole is scored for a cardiac pause of greater than 3 sec.

Atrial fibrillation is scored for an irregular ventricular rhythm (no synchronization between atria and ventriculae), associated with uneven R-R duration and replacement of consistent P waves by rapid oscillations that vary in size, shape and timing (f waves).


According to R & K, sleep is divided into NREM and REM. NREM is further divided in stages 1, 2, 3 and 4. The new scoring manual recommends division of NREM into three stages and merges the previous stage 4 into stage 3.12,55 The scoring of sleep stages is based on EOG, EMG and ECG data.

1)   Sleep stages are scored at 30-sec sequential recordings, named epochs. Before the use of electronic recordings, each epoch lasted 30 sec and was recorded in a 30 cm piece of paper at a rate of 1 cm/sec. This is particularly important as the analyst can recognise distance rather than time. For example, the K complex is defined as a wave lasting more than 0.5 sec, provided that recording rate is 1 cm/sec. Nowadays this procedure is digitalized and efforts are made to record 30 sec in 30 cm of the computer screen. Another factor that needs consideration is the amplitude of the recording channel. For instance, the standard ECG amplitude is 50 μV/ cm, so a wave of 1.5 cm or more is considered as a delta wave.

2)   Every stage is characterized by epochs.

3)   If 2 or more stages coexist during a single epoch, it is characterized by the stage comprising the greatest portion of the epoch.

Classification of EEG activity


Frequency 8-13 Hz, amplitude 20-60 μV. Peak in occipital derivations (O1, O2). Occurs in the waking state when the person is calm with the eyes closed.


Frequency 13-35 Hz, amplitude 5-20 μV. Occurs in the waking state when the person has the eyes open.


Frequency 3-7 Hz, amplitude ≤15 μV. This is the most common activity during sleep and occurs in all stages.


Frequency <2 Hz, amplitude >75 μV. This is particularly visible in frontal and central derivations during stage 3 of sleep.


3.1. Waking state23-27

EEG: Alpha rhythm (8-13 Hz) with eye closure or low amplitude mixed frequency (Beta rhythm) with eye opening.

EOG: Inadvertent slow or voluntary rapid eye movements for less than 0.5 sec.

EMG: Increased chin EMG amplitude compared to other stages.

Alpha rhythm is more distinct in occipital derivations (O1, O2), but not in all subjects.

An epoch is defined as waking when Alpha or Beta rhythm is dominant for more than 50% of the epoch (Figures 8, 9).

3.2. Stage 128-31

This is a transitional phase of sleep (Figure 10).

EEG: In subjects who generate alpha rhythm, in stage 1 it is replaced by low amplitude mixed frequency waves, predominantly 2-7 Hz, for more than 50% of the epoch (Theta rhythm). In subjects who do not produce alpha rhythm, stage 1 is distinguished from the waking state based on the following criteria:

A.   Activity in the range of 4-7 Hz with slowing of background frequencies by ≥1 Hz from those of the waking state.

B.   Vertex sharp waves.

C.   Slow eye movements.

EMG: Chin EMG amplitude is often increased, but at lower levels than in the waking state.

Definition of stage 1 requires absence of sleep spindles and K complexes. In children, stage 1 may be characterized by bursts of high amplitude (hypersynchrony theta).

3.3. Stage 2 (Figures 11, 12)

EEG: Characterized by sleep spindles31,34 or K complexes and predominant theta rhythm.

Sleep spindles:41

Waves with frequency 11-16 Hz (most commonly 12-14 Hz)41-45 and duration ≥0.5 sec,44-46 usually more distinct in central derivations (C3, C4).40 They occur 3-8 times/min in healthy adults, and are more frequent with use of medications, such as benzodiazepines.

K complexes:33-36

Well-delineated sharp negative waves immediately followed by a positive component, with total duration ≥0.5 sec,37-40 usually predominant in central (C3, C4) and frontal (F3, F4) derivations.

EOG: Usually absence of slow eye movements, although they may persist in some individuals.

EMG: Chin EMG tone is of variable amplitude, but usually lower than in the waking state.

The three minute rule10

K complexes and sleep spindles are suggestive of stage 2, but their presence is not necessary in all epochs. However, if a K complex or a sleep spindle does not occur within three minutes of the previous one, this is scored as stage 1.

3.4. Stage 3 (Figure 13) (Former stages 3 and 4)

EEG: Defined by slow waves (delta activity)49,50,52,53 of frequency 0.5- 2 Hz (0.5- 2 sec with a recording rate of 1 cm/sec) and amplitude ≥75 μV (or height ≥1.5 cm at 50 μV/cm), predominant in central (C3, C4) and frontal (F3, F4) derivations for more than 20% of the epoch.

Sleep spindles or K complexes may appear and need to be differentiated from delta waves.47,48

EOG: There may be some activity similar to that on the EEG.

EMG: Chin EMG is usually of very low amplitude.

3.5. REM sleep

EEG57,58 Low amplitude mixed frequency waves similar to those of stage 1. Sharp waves are uncommon. Alpha waves may occur, usually 1-2 Hz lower than in the waking state. Sawtooth waves62,63 with a frequency of 2-6 Hz are suggestive of REM sleep, but not always present. They are predominant in central (C3, C4) derivations and often precede REMs (Figures 14, 15).

EOG56,59-61: Characterized by bursts of rapid eye movements usually lasting less than 0.5 sec.

EMG63: Chin EMG amplitude is lowest than in any other stage. However, transient bursts of muscle activity with duration less than 0.25 sec may occur in chin or limb EMG.


Periodically, especially in the first REM sleep period of the night, K complexes or sleep spindles may be present amongst epochs.10 This period can be defined as REM provided that this activity does not appear in the previous and following epochs.

When 2 spindles (or K complexes) appear in an epoch of 30 seconds, the time space between them is defined as stage 2 NREM, whereas the previous and next as REM. If this time is longer than 15 seconds, then the epoch is characterized as stage 2 NREM, otherwise it is considered REM. For example, if 2 spindles (or K complexes) appear at 10 and 20 sec while the previous and next epochs resemble REM sleep, then REM is extended to all epochs. This is because REM dominates in most of that time (9 seconds at the beginning and 9 at the end of the epoch), whereas stage 2 lasts only 12 seconds in between. However, if spindles (or K complexes) appear at 5 and 25 sec, then that epoch is defined as stage 2, because the total duration of REM is 8 sec and that of stage 2 is 22 sec.

REM is divided in two periods: phasic and tonic.

Tonic REM: defined as a recording adjacent to REM sleep but with absence of rapid eye movements in EOG, relatively low amplitude mixed frequency activity in EEG and distinct REM pattern in EMG, with no movement arousals.

Phasic REM: defined as a recording with rapid eye movements in EOG, relatively low amplitude mixed frequency activity in EEG and low amplitude in EMG.


Movement arousals are movements or muscle artifacts obscuring the EEG for more than half an epoch, to the extent that the sleep stage cannot be determined (Figure 16).

An epoch with a movement arousal is scored as follows:

  • If alpha rhythm is present for part of the epoch (even <15 sec), it is scored as waking state.
  • If the epoch is followed by slow eye movements, it is scored as stage 1.
  • If movement arousals occur during REM sleep, EMG amplitude remains low and the next epoch is REM, then it is scored as REM.

Generally, an epoch with movement arousals is scored as the epoch that follows.


Scoring of arousals during sleep (stages 1, 2, 3 or REM) is suggested in case of sudden shift in EEG frequency including alpha waves, theta waves and/ or frequencies greater than 16 Hz (but not spindles) lasting at least 3 sec, with at least 10 sec of normal sleep preceding the change (Figure 17).

Arousal scoring during REM sleep requires concurrent increase in chin EMG lasting at least 1 sec.

EEG arousals are more distinct in occipital (O1, O2) and central (C3, C4) derivations.

Calculation of the number of EEG arousals has been correlated to increased respiratory effort in the absence of standard apneas or hypopneas and without haemoglobin desaturation. This condition is called "Upper Airways Resistance Syndrome" (UARS) 85 and the respective arousals have been named Respiratory Effort Related Arousals (RERA's).


Detection of an underlying breathing disorder during sleep requires the placement of a sensor that records incoming airflow, two elastic belts-sensors placed round the thorax and abdomen that record respiratory movements, and a pulse oximetry placed on a finger or ear lobe to detect the fluctuations of haemoglobin saturation.

Recordings of airflow require:

Special thermistors that detect variations of temperature in inspiration (cold air from the environment) and expiration (warm air from the human body), which reflect nasal and oral airflow. They are used for the detection of apnoeas but are considered unreliable in diagnosing hypopnoeas and UARS.70,71,77

A nasal pressure cannula that measures nasal air pressure and airflow variations. It can record apnoeas and hypopnoeas and diagnose UARS.74-77 It is inadequate in the presence of oral breathing, which is relatively uncommon. Therefore, the readings of nasal airflow are routinely used for evaluation.

      Airflow recordings with oral thermistor and nasal pressure cannula are considered the best combination for the examination of respiratory disorders.

Oesophageal manometry.72,73 Measurement of oesophageal pressure by oesophageal balloon catheter and detection of respiratory effort is considered the best method to characterize apneas and hypopneas as central or obstructive, but it is rarely used because of patient intolerance.

Pulse oximetry for the detection of blood oxygen saturation.78,79

In rare instances, respiratory effort can be alternatively recorded with diaphragmatic- intercostal EMG.


Breathing disorders during sleep include the apnoea-hypopnoea syndrome and UARS.

Discrimination between sleep apnea and the apnoea-hypopnoea syndrome: Sleep apnoea is defined by an abnormal apnea-hypopnea index (AHI) in polysomnography, whereas the apnoea-hypopnoea syndrome is defined by a pathological number of apnoeas-hypopnoeas, combined with clinical symptoms such as daytime sleepiness.

Pathological values of AHI82 are >1/h for children, >5/h for adults and >10/h for the elderly.

7.1. Types of apnoea and hypopnoea81

Apnoa is defined as disruption of breathing (oronasal inflow pause) lasting 10 seconds. Apnoeas are classified as obstructive, mixed and central.

Obstructive apnoea is associated with increased inspiratory effort. Opposing thoracic and abdominal movements due to the obstruction can be seen. This phenomenon is called paradoxical breathing movement (Figure 18).

Central apnoea is defined by the absence of inspiratory effort or thoracic and abdominal movements (Figure 19).

Mixed apnoea is an initially central apnea that progresses to meet the criteria of obstructive apnoea (Figure 20).

Mixed apnoeas are considered variations of obstructive apnoeas and usually follow a period of intense hyperventilation causing a drop in PaCO2 and a counteractive pause in inspiratory effort, which resolves as soon as PaCO2 is restored.

Hypopnoea12 (Figure 21) is defined by the AASM scoring rules as a reduction in airflow by 30% or more of baseline for a period of at least 10 seconds and followed by at least 4% desaturation.

Alternatively, hypopnoea is a reduction in airflow by 50% or more of baseline, for a period of at least 10 seconds and followed by at least 3% desaturation or the appearance of EEG arousal.

Classification of hypopnoeas as central and obstructive is only reliable by oesophageal balloon catheter. Consequently, obstructive or central breathing disorders are determined by the type of apnoea.

Note: An apnoea or hypopnoea is measured from the commencement of the first breath that is clearly impaired compared with the baseline.

7.2. Upper airway resistance syndrome (UARS)74,84

UARS was first described in 1993 by Guilleminault85 in people who snored and experienced daytime sleepiness without the typical pattern of obstructive apnoea-hypopnoea and desaturation. Sleep study revealed frequent EEG arousals, which according to esophageal manometry were caused by intense inspiration effort due to increased negative intrathoracic pressure. Thereafter, these respiratory effort related arousals (RERAs) are scored just as apnoea or hypopnoea.

RERAs are recorded by assessing nasal pressure with nasal cannulas, instead of using oesophageal manometry, which is not tolerated by many patients.

They are detected as a sequence of breaths lasting at least 10 seconds, characterized by increasing respiratory effort or flattening of the nasal pressure waveform leading to an arousal from sleep that does not meet the criteria for an apnoea or hypopnoea.

The reduction of airflow is caused by increased upper airway resistance. In UARS, blood saturation variations are less than 3% (Figures 22, 23).

7.3. Hypoventilation80

Hypoventilation during sleep is present if there is ≥ 10 mm Hg increase in PaCO2 in comparison to the alert supine value.

Persistent oxygen desaturation is not sufficient to document hypoventilation. An increased PaCO2 value obtained immediately upon awakening from sleep is suggestive of sleep hypoventilation.

7. 4. Cheyne Stokes Respiration87-89

Cheyne Stokes respiration is defined as alternate crescendo and decrescendo changes in breathing depth, followed by periods of apnoea.

It is scored as at least 3 consecutive cycles of crescendo and decrescendo changes in breathing depth, with at least one of the following criteria:

I.    Five or more central apnoeas or hypopnoeas per hour of sleep.

II.   Duration of the cyclic crescendo and decrescendo change in breathing depth and following apnoea of at least 10 seconds (Figure 24).

The following should be noted:

i)    Arousals appear after reestablishment of normal breathing and not at the end of the apnea, as in obstructive apnoea.

ii)   The haemoglobin desaturation curve shows regular sinusoidal fluctuations, whereas in obstructive apnoea there is progressive decrease followed by sudden increase of saturation.

iii)  In obstructive apnoea there is paradoxical movement of the thorax and abdomen, whereas in central apnoea there is not.

iv)  The breathing curve has a typical pattern of progressive increase and decrease alternated with pauses.

Causes of Cheyne Stokes respiration

Congestive heart failure

Pathological conditions of the central nervous system (especially cerebrovascular disease, meningitis, encephalitis, brain tumours)

Metabolic alkalosis

Normal during a transient stay at high altitude



8.1. Periodic limb movement in sleep (PLMs)90-93

This syndrome is characterized by an unpleasant feeling in the limbs, but mostly the lower limbs, when the patient is in the resting position. This feeling may be described as pain, burning or numbness and is associated with an overwhelming desire to move the legs.

PLMs are usually accompanied by eye movements during sleep (periodic eye movements) causing frequent awakenings and chronic sleep deprivation. They are considered responsible for insomnia and daytime sleepiness.

EMG recording of PLMs requires 2 electrodes placed longitudinally over the anterior tibialis muscle of both lower limbs in a distance of 2-3 cm (Figures 25, 26).

One leg movement (LM) event is scored according to the following rules:

- Duration of at least 0.5- 10 sec

- The timing of the onset of a LM is defined as the point at which there is 8 μV increase in EMG voltage above resting EMG.

- The timing of the ending of a LM is defined as the start of a period lasting at least 0.5 seconds during which the EMG does not exceed 2 μV above resting EMG.

Criteria for scoring PLM series:

- The minimum number of consecutive LM events needed to define a PLM series is 4 LMs.

- The period length between PLMs is 5-90 sec

- In a two-limb recording, LMs on different legs are counted as one LM when they are separated by less than 5 sec; otherwise, they are counted as two LMs.

Criteria for scoring a PLM disorder:

A.   Polysomnographic findings:

- Limb movement duration of 0.5-5 sec.

- Limb movement equals to or is greater than 25% of the finger dorsal flexion, measured during calibration.

- At least 4 consecutive LMs.

- Period length between PLMs 5-90 seconds.

B.   PLMs index ≥15/hour for adults and ≥5/hour for children.

C.   Daytime sleepiness or morning tiredness.

D.  Rule out other sleeping disorders (e.g. apoea or hypopoea), nervous system disorders (e.g. lumbar pain), mental disorders or the use of medication that may cause limb movements.

Notes: Sometimes PLMs are misinterpreted as leg movements of other causation. For instance, limb movements often follow a period of apnoea or hypopnoea. Therefore, a LM should not be scored if it occurs during a period of 0.5 sec preceding or following an apnoea or hypopnoea.

An arousal and a PLM should be considered associated with each other when there is an interval of < 0.5 seconds between the end of one event and the onset of the other.

Previous editions of the ICSD classify the PLM index as ≥ 5/hour. The newest edition of ICSD recommends the pathological value of PLM index to be ≥15/hour for adults and ≥ 5/hour for children and emphasizes that even a high PLM index with arousals is not associated with symptomatic sleeping disorders (such as insomnia or hypersomnia) and actual PLMD is rare in adults.

8.2. Hypnagogic foot tremor (HTF)94, 95

HTFs are wide jerks of the body, resulting in wakening of the patient. They usually occur with the onset of sleep and they may involve one or both lower limbs, the spine and, less frequently, the upper limbs. They are associated with dreams or sensory stimuli and should not be considered epileptic convulsions.

HTF is caused by stimulation of various nervous centres at the onset or during the early stages of sleep, which causes paroxysmal unintentional movement activity. It most often occurs when a person is feeling very stressed.

Scoring rules:

At least 4 consecutive jerks recorded as EMG activity.

Frequency in EMG between 0.3- 4.0 Hz.

Duration of the jerks of between 0.25 and 1 sec.

8.3. Bruxism92,96

Bruxism occurs mostly at night, but can also occur during the daytime. It can occur at any age and may cause serious dental conditions.

It is caused by intense contraction of the masseter and temporalis muscles, most commonly in periods of great stress. Other causes of bruxism are malocclusion, malposition, orthodontic procedures and cavity fillings. When a cause cannot be established, bruxism is characterized as idiopathic.

Scoring rules for bruxism:

1.   Clinical:

      a) Report of mouth contraction or trismus during sleep by the patient or sleeping partner.

      b) One or more of the following:

- Teeth grinding.

- Jaw pain.

- Masseter hypertrophy, which can be detected by voluntary teeth grinding.

      c) Rule out other causes of masticatory muscle activity, such as other sleeping disorders, neurological disorders or use of medication.

2.   Signs in the EMG recording (Fig. 27):97

      a) Brief temporary (phasic) or sustained (tonic) elevations of chin EMG activity of at least twice the amplitude of background EMG.

      b) Phasic EMG activity with duration of at least 0.25- 3 seconds, with intermediate periods of baseline EMG lasting at least 3 seconds.

Tonic EMG activity with duration of at least 2 seconds.

Mixed signs of bruxism (phasic and tonic).

The combination of teeth grinding and polysomnography provides reliable results provided that at least 2 episodes of teeth grinding are recorded (Figures 27-28).

8.4. REM sleep behaviour disorder (RBD)98-100

RBD is a common sleeping disorder of adults and it is observed most often in the elderly. It is characterized by epochs of intense and often dangerous motor activity that accompanies vivid dreams. This activity is caused by absence of muscle laxity that is typical in REM sleep. The prevalence of RBD varies.

It is characterized by:

-  Raging and incomprehensive speech, often followed by screams or violent bursts causing self- injury or injury to the sleeping partner.

-  Difficulty in wakening.

-  Detailed recollection of the dream.

This condition is encountered exclusively during REM sleep and the patients show no evidence of violent behaviour on arousal.

The polysomnographic characteristics of RBD are:101

Sustained tonic muscle activity in REM sleep. In an epoch of 30 seconds, there is chin EMG amplitude greater than the minimum amplitude in NREM for at least 50% of the epoch.

Transient phasic muscle activity in REM sleep. In a 30-second epoch divided into 10 sequential 3-second mini-epochs, there are bursts of muscle activity in at least 5 of them (50%). In RBD, excessive transient muscle activity bursts are 0.1-5 seconds and at least 4 times as high in amplitude than baseline chin EMG activity.

Muscle activity can be recorded in both chin and limb EMG.

Time synchronized video polysomnography and an extended history of sleeping behaviour is necessary to make the diagnosis of RBD, according to European guidelines.


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