In a recording showing a total sleep time (TST) of 5 hours with 60 periodic limb movements (PLMS), how is the PLM index calculated?

The PLM index is calculated by determining the number of periodic limb movements (PLMs) per hour of sleep. To arrive at the correct index, you take the total number of PLMs and divide it by the total sleep time in hours.

In this specific case, there are 60 PLMs recorded during a total sleep time of 5 hours. To compute the PLM index, you would divide 60 PLMs by 5 hours of sleep, which yields a PLM index of 12.

This metric is important in sleep studies, as it helps clinicians assess the severity of periodic limb movement disorder. A higher PLM index indicates a greater frequency of limb movements that could be associated with sleep disturbances.