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PLM Analysis Noxturnal 6.x

Starting with Noxturnal 6.0, changes were made to the automatic LM / PLMS analysis in order to meet the AASM 2017 requirements. This support article describes the changes made to the algorithm in Noxturnal 6.0, explains the concordance with AASM 2017 and explains PLM automatic analysis in Noxturnal 6 and higher versions while comparing to previous Noxturnal versions.

AASM 2017 Scoring LM / PLMS versus Noxturnal 6.x

LM (Leg movement):

Episodes of high muscular activity or kinetic activity and are identified as limb movement (LM) events. LM events should meet following criteria:


Summary: The limb movement detector detects bursts of muscular activity in the leg EMG channels. In order for a LM event to be scored, the bursts must last at least 0.5 seconds (Minimum Duration) and at most 10 seconds (Maximum Duration). Two adjacent bursts must be separated by at least 0.5 seconds (Maximum Inter-Movement Interval). The muscle activity threshold can either be chosen as relative or absolute and has two levels, for movement onset and offset. These values meet the AASM 2017 requirements and can be seen and modified in the analysis settings.


PLMS (Periodic Leg movement in Sleep)

The PLM algorithm uses LM events that are either scored manually or by the automatic PLM analysis* to identify periodic limb movements. If LM events are scored both automatically and manually (or removed manually), it is needed to run the 'Update PLM' tool for the total amount of LM to be included in the PLM analysis. 




Periodic Leg movement (in Sleep) Series

The periods of PLMS events are called Periodic Leg movement (in Sleep) Series.

Noxturnal: Periodic Leg movement (in Sleep) Series are marked by an PLM event which starts with first and ends with the last PLMS event of the series.


The PLMS index is displayed as a number with a colored background depending on severity in the Recording Result tab in Noxturnal for each study. The severity scale is set after the AASM classification criteria.



Summary: The PLM algorithm uses LM events that are either scored manually or by the automatic PLM analysis* to identify periodic limb movements. If at least 4 LM events occur (Minimum Number of LMs), separated by at least 5 seconds (Minimum Interval Between LM Onset) and at most 90 seconds (Maximum Interval Between LM Onset), the LM events are changed to PLMS events. The LM events from the two leg channels are combined into one scoring for identifying PLMS. In addition, the PLM series are scored as PLM events.


Noxturnal 6 PLMS standard reporting

Nomenclature of Noxturnal events

  • LM: Limb movements (which are also candidates for periodic limb movements in Sleep (PLMS))
  • PLMS: LM events that qualify as PLM are changed to PLMS events
  • PLM: Series of PLMS events.

Noxturnal 6 reporting is focused on PLMS and PLMS series. There is not standard reporting of separate LM events. For any LM reporting a custom report needs to be setup. Previously created custom reports for LM need to be adjusted according the new logic for LM to PLMS event conversion as well as the new automated scoring of PLMS series (PLM).

Noxturnal default PLM / PLMS reporting:



Differences between Noxturnal 5.x and 6. potential x with respect to LM / PLMS representation

The main changes between the PLM algorithm in Noxturnal 5.1.3 and Noxturnal 6.x are the following:

  • The PLM analysis was upgraded to meet AASM 2017
  • ECG artifact filter is automatically applied to the signal prior to event detection, which contributes largely to artefact rejection due to heart signal interference.
  • Improved event presentation: Events that are contributing to the PLMS count have changed from previous Noxturnal 5.x version and got their own event type (PLMS) and event (e.g. color) settings. The PLMS is a new event type which did not exist in Noxturnal 5.x.
  • Recording Result page: Only the PLMS index is displayed (no LM Index).

Updating a scoring from 5.1.3 to 6.x with regards to LM / PLMS

  • As Noxturnal 5.1.3 did not use the PLMS event as the base for the PLMS Index it will display “0” when opening up studies from 5.1.3 in Noxturnal 6.x .
  • Similarly, the report table will not be able to display PLMS events related data.
  • To update PLMS / LM data either a new PLM analysis or the “Update PLM” tool has to be run.

Options to customize / enable reporting LM outside of PLMS series

Below is an example of an optional report variable which can have even more but also less conditions:


Note: if an LM occurs overlapping in both legs, it will be reported as one single event in the report variable.


Noxturnal 5.1.3 and Noxturnal 6 – Automatic Arousal Association

The Arousal Tool in Noxturnal can be used to automatically associate arousals with other events incl. PLMS and LM.


Default PLM Analysis Settings in Noxturnal 6.x



*Please note that not all features or all products are available in all markets. Our products are medical devices and subject to registration/approval in each market area. For more information on product availability please contact

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