Objective: As a standard method, periodic limb movements in sleep (PLMS) are detected by means of polysomnography (PSG). Actigraphic detection of PLMS is a recently developed method for performing of multiple-night recordings in an outpatient setting. The aim of our study was to assess sensitivity-related parameters of actigraphic detection of PLMS in comparison to the PSG, when mounted at ankles and at the base of the big toe.
Methods: We simultaneously performed PSG and actigraphic recordings at both ankles and at the bases of both big toes (Cambridge Actiwatch AW-64) for 40 nights. The PLM index (PLMI), number of periodic movements per hour of sleep, was the primary output of both methods.
Results: We have proven significant correlation of all resulting parameters when comparing actigraphy at either position to the PSG; however, the PLMI values obtained by the actigraphy at toes were significantly higher than by PSG (sign test, p<0.0001). At bases of the big toes, threshold of PLMI=7.6 was used as a cut off for positivity, while PLMI=5 at ankles was used for PSG. Comparing ankle versus toe actigraphic placement, sensitivity was 67% versus 94%, specificity was 95% versus 91% and negative predictive value was 78% versus 95%. The correlation of the results from actigraphy and PSG was not affected by presence of respiratory events.
Discussion: Our results suggest good validity of actigraphic PLM evaluation at the base of big toe using AW-64 devices and therefore, actigraphy seems suitable for screening purposes in both clinical and research usage.