Periodic limb movement in sleep (PLMs) are defined as:

Periodic limb movement in sleep (PLMs) are defined as:

• A. At least 2 movements, between 5 and 90 seconds apart, and between 0.5 and 5 seconds in duration for each movement
• B. At least 4 movements, between 5 and 90 seconds apart, and between 1 and 5 seconds in duration for each movement
• C. At least 4 movements, between 5 and 90 seconds apart, and between 0.5 and 5 seconds in duration for each movement
• D. At least 4 movements, between 10 and 90 seconds, and between 0.5 and 5 seconds in duration for each movement

Answer: (C)

Periodic limb movements during sleep are identified by a specific repeating pattern of leg movements rather than isolated events. The definition requires four or more movements, each lasting about 0.5 to 5 seconds, with the movements spaced 5 to 90 seconds apart. This combination establishes a true periodic pattern and helps distinguish PLMS from single twitches or irregular bursts. The option that matches four movements, 5–90 second intervals, and 0.5–5 second durations per movement best fits this definition. The other choices are off because they require too few movements, or they set the interval or duration bounds inaccurately (for example, using 10–90 seconds, or allowing longer durations, or requiring a minimum of only two movements).

Periodic limb movements during sleep are identified by a specific repeating pattern of leg movements rather than isolated events. The definition requires four or more movements, each lasting about 0.5 to 5 seconds, with the movements spaced 5 to 90 seconds apart. This combination establishes a true periodic pattern and helps distinguish PLMS from single twitches or irregular bursts. The option that matches four movements, 5–90 second intervals, and 0.5–5 second durations per movement best fits this definition. The other choices are off because they require too few movements, or they set the interval or duration bounds inaccurately (for example, using 10–90 seconds, or allowing longer durations, or requiring a minimum of only two movements).