Raffaele Ferri1, Francesco Rundo2, Marco Zucconi3, Mauro Manconi4, Debora Aricò2, Oliviero Bruni5, Luigi Ferini-Strambi3, Stephany Fulda4. 1. Sleep Research Centre, Department of Neurology I.C., Oasi Institute for Research on Mental Retardation and Brain Aging (IRCCS), Troina, Italy. Electronic address: rferri@oasi.en.it. 2. Sleep Research Centre, Department of Neurology I.C., Oasi Institute for Research on Mental Retardation and Brain Aging (IRCCS), Troina, Italy. 3. Sleep Disorders Center, Department of Neurology, Scientific Institute and University Ospedale San Raffaele, Vita-Salute University, Milan, Italy. 4. Sleep and Epilepsy Center, Neurocenter of Southern Switzerland, Civic Hospital (EOC) of Lugano, Lugano, Switzerland. 5. Department of Social and Developmental Psychology, Sapienza University, Rome, Italy.
Abstract
OBJECTIVE: To evaluate an alternative index for periodic leg movements during sleep (PLMS) and wakefulness (PLMW) expected to be similar to the standard index when leg movement activity is genuinely periodic, but significantly lower when periodicity is low. SUBJECTS AND METHODS: One-hundred-and-seven subjects with restless legs syndrome (RLS) were retrospectively identified and included (47 males, 60 females, mean age 56.9 years), along with 63 controls (33 males, 30 females, 42.2 years). Night-to-night variability was analysed in a subgroup of 17 subjects with RLS. PLMW were evaluated in a subgroup of 66 RLS subjects. Two 'alternative' PLMS/PLMW indices were calculated: one increased the lower limit of the inter-movement intervals from 5 to 10 s ('Alt1') and another additionally considered only series not interrupted by LMs with a short inter-movement interval ('Alt2'). RESULTS: Despite a high correlation between methods, only the Alt2 algorithm provided significantly different results, with PLMS/PLMW indices being consistently lower than those provided by the other two methods. The difference was more evident in the controls and during wakefulness, when periodicity was lower. The difference between the Alt2 and the standard PLMS index showed a significantly negative correlation with the Periodicity Index. Night-to-night variability was similar for all PLMS indices and significantly higher than the variability seen in the Periodicity Index. CONCLUSION: This methodological study introduces an alternative to the standard PLMS/PLMW indices, initiating the validation process for a new way of computing the PLMS/PLMW index, more adherent to the parameters that allows a reliable evaluation of their periodicity.
OBJECTIVE: To evaluate an alternative index for periodic leg movements during sleep (PLMS) and wakefulness (PLMW) expected to be similar to the standard index when leg movement activity is genuinely periodic, but significantly lower when periodicity is low. SUBJECTS AND METHODS: One-hundred-and-seven subjects with restless legs syndrome (RLS) were retrospectively identified and included (47 males, 60 females, mean age 56.9 years), along with 63 controls (33 males, 30 females, 42.2 years). Night-to-night variability was analysed in a subgroup of 17 subjects with RLS. PLMW were evaluated in a subgroup of 66 RLS subjects. Two 'alternative' PLMS/PLMW indices were calculated: one increased the lower limit of the inter-movement intervals from 5 to 10 s ('Alt1') and another additionally considered only series not interrupted by LMs with a short inter-movement interval ('Alt2'). RESULTS: Despite a high correlation between methods, only the Alt2 algorithm provided significantly different results, with PLMS/PLMW indices being consistently lower than those provided by the other two methods. The difference was more evident in the controls and during wakefulness, when periodicity was lower. The difference between the Alt2 and the standard PLMS index showed a significantly negative correlation with the Periodicity Index. Night-to-night variability was similar for all PLMS indices and significantly higher than the variability seen in the Periodicity Index. CONCLUSION: This methodological study introduces an alternative to the standard PLMS/PLMW indices, initiating the validation process for a new way of computing the PLMS/PLMW index, more adherent to the parameters that allows a reliable evaluation of their periodicity.