When periodic limb movements of sleep are scored as an event, which statement is false?

When periodic limb movements of sleep are scored as an event, which statement is false?

• A. Timing of the event begins at the point of an 8uv increase on EMG
• B. An event ranges in duration from 0.5-10 seconds, with an EMG amplitude of 8uv or more
• C. Timing of the event ends with a period, lasting 0.5 seconds longer, during which EMG doesn't rise more than 2uv
• D. An event requires four or more consecutive leg movements with the interval between movements ranging from 5-90 seconds

Answer: (D)

The key idea is how a single leg movement is scored as an event versus how a repeating pattern (PLMS) is identified. For a single movement to be counted as an event, the onset is when the EMG rises to at least 8 microvolts above baseline, and that movement lasts between 0.5 and 10 seconds with an amplitude of 8 μV or more. The end of the event is marked by a period, lasting at least 0.5 seconds, after which the EMG does not rise more than 2 μV. A periodic limb movements pattern is then defined by four or more such events occurring with inter-movement intervals between 5 and 90 seconds. That cluster criterion describes a sequence over time, not a single event itself. Therefore, stating that an event requires four or more consecutive leg movements is incorrect; four or more movements pertain to identifying a PLMS pattern, not to scoring an individual PLM event. The other statements correctly reflect the onset threshold, the duration and amplitude of a single event, and the end criteria.

The key idea is how a single leg movement is scored as an event versus how a repeating pattern (PLMS) is identified. For a single movement to be counted as an event, the onset is when the EMG rises to at least 8 microvolts above baseline, and that movement lasts between 0.5 and 10 seconds with an amplitude of 8 μV or more. The end of the event is marked by a period, lasting at least 0.5 seconds, after which the EMG does not rise more than 2 μV.

A periodic limb movements pattern is then defined by four or more such events occurring with inter-movement intervals between 5 and 90 seconds. That cluster criterion describes a sequence over time, not a single event itself. Therefore, stating that an event requires four or more consecutive leg movements is incorrect; four or more movements pertain to identifying a PLMS pattern, not to scoring an individual PLM event. The other statements correctly reflect the onset threshold, the duration and amplitude of a single event, and the end criteria.