PLM index
Measurement of periodic limb movements per hour of sleep, excluding movements associated with respiratory events.
Full Definition
The Periodic Limb Movement (PLM) index quantifies the number of periodic limb movements per hour of sleep recorded during polysomnography. Periodic limb movements are repetitive, stereotyped movements typically involving the legs that occur in clusters during non-REM sleep. To be counted in the PLM index, movements must meet specific criteria including duration of 0.5-10 seconds, amplitude increase of at least 8 microvolts above baseline, and occur in sequences of four or more movements separated by 5-90 seconds. The PLM index excludes movements that occur within 0.5 seconds of respiratory events, as these are considered secondary to breathing disturbances. A PLM index greater than 15 per hour is considered elevated in adults and may contribute to sleep fragmentation and daytime symptoms.
Usage
Usage note: May be abbreviated as PLMI in some contexts.
In Context
- "The PLM index of 67 per hour explained the patient's frequent nocturnal awakenings." — Sleep study interpretation
- "Iron supplementation reduced the PLM index from 45 to 12 events per hour." — Treatment response evaluation