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World Sleep 2022 | Muscular activity in the flexor digitorum superficialis – a new tool for REM sleep without atonia

Matteo Cesari, PhD, Medical University of Innsbruck, Innsbruck, Austria, discusses the method of measuring muscular activity in the flexor digitorum superficialis as an alternative screening tool for REM sleep without atonia. REM sleep without atonia consists of an abnormal increase in muscle activity – with the measurement of this being mandatory in the identification and diagnosis of REM sleep behavior disorder (RBD). The problems lie with quantifying REM sleep without atonia; it is time-consuming, and many of the automated methods measure muscular activity from the chin. This can lead to issues regarding extraneous artifacts e.g., respiration having an impact on the results. The SINBAR group introduced a method of measuring muscular activity in the upper extremities in addition to classic polysomnography – through the flexor digitorum superficialis. The results presented at this conference show that this automatic analysis of muscle activity is 100% sensitive and 85% specific – thus, useful in a clinical environment. Dr Cesari states how this method can be used as a potential screening tool; being fast with no hindrance from extraneous artifacts, it demonstrates potential as a superior method of quantifying REM sleep without atonia. Further studies are required in other cohorts, however, there is great promise presented by this method. This interview took place at the World Sleep Congress in 2022 in Rome, Italy.

Transcript (edited for clarity)

One key factor and important requirement for the diagnosis of REM sleep behavior disorder is the quantification of REM sleep without atonia. REM sleep without atonia consists of the increased muscular activity, abnormal increase of muscular activity, during REM sleep. And according to the current diagnosis of the International Classification of Sleep Disorder, as I said, measurement of REM sleep without atonia is mandatory in order to identify and to diagnose RBD; REM sleep behavior disorder...

One key factor and important requirement for the diagnosis of REM sleep behavior disorder is the quantification of REM sleep without atonia. REM sleep without atonia consists of the increased muscular activity, abnormal increase of muscular activity, during REM sleep. And according to the current diagnosis of the International Classification of Sleep Disorder, as I said, measurement of REM sleep without atonia is mandatory in order to identify and to diagnose RBD; REM sleep behavior disorder.

The problem is that the quantification of REM sleep without atonia is time consuming. There are already a lot of different automatic methods which have been proposed, but most of these algorithms measure muscular activity on the chin. And we have seen essentially that chin activity is somehow affected by artifacts, which means respiration, for example. So, if you have abnormal respiration, a lot of apnea during REM sleep, this increases the muscular tone, but this is not real abnormal muscular tone. It’s just muscular tone due to a respiratory event.

The Sleep Innsbruck Barcelona group, since 2012, has introduced a flexor digitorum superficialis, so measurement of muscular activity also in the upper extremities, as additional to the classical polysomnography. Including recording of EMG activity in the legs and in the chin. And we have seen that an automatic analysis of muscular activity in the flexor digitorum alone, can be used as possible screening tool because it’s a fast method and does not have all these artifacts as in the chin. And actually, the results that we present here at this conference show that the automatic analysis of muscular activity in the flexor digitorum superficialis without need of removing artifacts, without need of any additional analysis is 100% sensitive and 85% specific.

And this shows that essentially when a patient comes, we can measure muscular activity with this method, fully automatically. Then essentially, if it’s below a certain cutoff, we can exclude REM sleep without atonia. And if it’s above a certain cutoff and we can then measure and quantify, but this could be used as a possible tool to screen in a quantitative way in the sleep lab. So, this is a possible promising technique, which has to be replicated in of course, other cohorts. But, we think that automatic analysis in the flexor digitorum superficialis can improve quantification of REM sleep without atonia in the clinics.

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