Emg Readings: Are We Active During Rem Sleep?

REM sleep behaviour disorder (RBD) is a parasomnia characterised by excessive electromyographic (EMG) activity during rapid eye movement (REM) sleep, leading to dream-enactment behaviours. This can result in injury to the patient or their bedmate. Diagnosis of RBD is important as it can be the first sign of a neurodegenerative disease.

EMG activity is recorded from several muscles during polysomnography, including the submental and frontalis muscles. Tonic and phasic EMG activity is then blindly quantified for each muscle. The submental muscle is useful for discriminating patients with RBD from controls, as it is the muscle used routinely in standard PSG to score sleep stages. However, its isolated use has limitations due to its vulnerability to breathing and snoring artefacts, and its low correlation with most behaviours that patients with RBD display during REM sleep.

The frontalis muscle exhibits less between-subject variability than the submental muscle, and its power is greater during wake and across sleep stages. It is also less prone to showing artefacts, and is easier to locate on the body. Therefore, the frontalis muscle may be a more suitable alternative to the submental muscle for the detection of wake and sleep stages, and for future applications towards the assessment of quantitative REM sleep muscle activity in RBD.

The chin EMG variance during polysomnography can be used as an assessment for REM sleep behaviour disorder

The chin electromyography (EMG) is a signal routinely collected during sleep studies, and it can be used to detect early forms of neurodegenerative conditions. The level of chin EMG reflects an inhibitory influence on motor activity and muscle tone. The level of chin EMG drops to its lowest level during REM sleep in normal subjects, but there is an increase in amplitude in rapid eye movement behaviour disorder (RBD) patients.

The chin EMG analysis can be used to evaluate the strength of muscle activation during the REM sleep cycle. The root mean square (RMS) value of the chin EMG in RBD patients is at least 2.5 times the normal value. The increase in tonic EMG activity might reflect disease progression.

The chin EMG analysis can be used as an assessment for RBD. A study on 23 subjects, including 17 with neurodegenerative disorders (9 with probable or possible RBD) and 6 controls, found that a computer algorithm calculated the variance of the chin EMG during all 3-second mini-epochs. The percentage of all REM mini-epochs with variance above a defined threshold created a metric, which was referred to as the supra-threshold REM EMG activity metric (STREAM). The STREAM correlated highly with the visually-derived score for RBD severity.

Another study on 43 records with simultaneous acquisition of differential signals from the submental and frontalis muscles found a strong concordance between submental EMG and frontalis EMG power, with 95% of the records exhibiting at least moderate agreement. The frontalis EMG power exhibited 50% greater power and 50% less across-subject variability than the submental EMG power.

The mentalis muscle is useful to discriminate patients with REM sleep behaviour disorder from controls

The mentalis muscle is useful for discriminating between patients with REM sleep behaviour disorder and controls. The mentalis muscle provided the highest rates of phasic EMG activity in patients with REM sleep behaviour disorder.

The mentalis muscle is one of the muscles in the SINBAR EMG montage, which is a combination of the mentalis, the flexor digitorum superficialis, and the extensor digitorum brevis muscles. This combination of muscles provided the highest rates of phasic EMG activity in REM sleep behaviour disorder.

The mentalis muscle was also evaluated in a study comparing EMG power during sleep from the submental and frontalis muscles. The study found a strong concordance between submental and frontalis muscle power, with 95% of the records exhibiting at least moderate agreement. However, during REM sleep, submental EMG power was significantly less than frontalis EMG power, but exhibited four times greater across-subject variability.

Another study found that the cutoff value required to achieve a specificity of 100% in discriminating between patients with idiopathic REM sleep behaviour disorder and controls was 8.9% for tonic activity and 11.1% for phasic activity in the submentalis muscle.

Upper limb muscles showed the highest discriminative power for REM sleep behaviour disorder diagnosis

The upper limb muscles showed the highest discriminative power for diagnosing REM sleep behaviour disorder (RBD). The flexor digitorum superficialis (FDS) muscle in the upper limb muscles showed a very high AUC (Area Under Curve) of 0.994 (cutoff 16.8%). The AUC in bilateral biceps brachii muscles was even higher, at 1.000 (cutoff 2.9 %).

The study evaluated the electromyographic (EMG) activity in the Sleep Innsbruck Barcelona (SINBAR) montage (mentalis, flexor digitorum superficialis, extensor digitorum brevis) and other muscles to obtain normative values for the correct diagnosis of RBD for clinical practice. The study included 30 RBD patients (15 idiopathic [iRBD], 15 with Parkinson disease [PD]) and 30 matched controls. The participants underwent video-polysomnography, including registration of 11 body muscles. Tonic, phasic, and “any” EMG activity was blindly quantified for each muscle.

The combination of the mentalis muscle (“any” EMG activity) with bilateral FDS phasic EMG activity is a feasible combination for the diagnosis of RBD in routine clinical practice because it provides a very high AUC (0.998); provides the quantification of the metric “any” EMG activity in the mentalis muscle, which eliminates the difficulty of distinguishing phasic from tonic EMG activity; involves the muscle with highest phasic and tonic EMG activity seen in RBD (mentalis muscle); involves limb muscles where clinical motor manifestations of RBD are typical and frequent; involves the FDS, which is the muscle with the highest phasic EMG activity in the limbs; and involves bilateral evaluation of the upper limbs given the fact that in RBD bilateral movements are more frequent than unilateral movements.

Lower limb muscles showed an important overlap in EMG activity among patients with REM sleep behaviour disorder and controls

The study, 'Quantification of Electromyographic Activity During REM Sleep in Multiple Muscles in REM Sleep Behavior Disorder', found that the highest rates of phasic EMG activity were found in the mentalis, flexor digitorum superficialis, and extensor digitorum brevis. The mentalis muscle provided significantly higher rates of excessive phasic EMG activity than all other muscles but only detected 55% of all the mini-epochs with phasic EMG activity. The combination of the mentalis, flexor digitorum superficialis, and extensor digitorum brevis muscles detected 82% of all mini-epochs containing phasic EMG activity. This combination provided higher rates of EMG activity than any other 3-muscle combination.

The study, 'Normative EMG Values during REM Sleep for the Diagnosis of REM Sleep Behavior Disorder', found that the discriminative power was higher in upper limb muscles than in lower limb muscles. Lower limb muscles showed an important overlap in EMG activity among patients with RBD and controls.

The combination of mentalis muscle any EMG activity with bilateral upper extremity muscles such as the FDS is highly recommended for REM sleep behaviour disorder detection

The combination of mentalis muscle EMG activity with bilateral upper extremity muscles such as the FDS is highly recommended for REM sleep behaviour disorder detection. This is because the mentalis muscle is prone to breathing and snoring artifacts, has a low correlation with most behaviours that patients with RBD display during REM sleep, and differentiating between phasic and tonic EMG activity can be challenging. Upper limb muscles such as the FDS are less prone to showing artifacts, are easy to locate in the arms, and are also easier to score without tonic activity interfering.

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