Periodic limb movement counting in polysomnography: effects of amplitude

This study investigates the relationship between periodic limb movement (PLM) counts obtained with standard scoring criteria and PLM counts scored without amplitude criterion (AC).

Twenty-four sleep laboratory patients with a PLM index (PLMI) >5 per hour of sleep in a previous polysomnography (PSG) underwent a full night of digital PSG. PLM were twice scored manually: first, according to standard criteria, and second, without AC.

The overall PLMI for time in bed was 34.4+/-30.7 with AC and 50.2+/-36.4 without AC. The PLMI in non-rapid eye movement (NREM) sleep was 45.3+/-40.1 versus 63.4+/-47.6 (P<0.001), in REM sleep 11.5+/-15.1 versus 25.7+/-35.4 (P=0.001) and in wakefulness 29.0+/-31.1 versus 46.0+/-36.1 (P<0.001) with and without AC (Wilcoxon tests).

In comparison to PLM counts obtained with standard criteria, PLM counts obtained without consideration of amplitude are remarkably higher. Counting without AC increases the sensitivity to detect small PLM and probably allows for identification of PLM sequences which would not have fulfilled the periodicity criteria otherwise. PLM counts without AC might be more useful to investigate the periodicity of PLM and possible changes with treatment.