title: Putting the periodicity back into the periodic leg movement index: an alternative data-driven algorithm for the computation of this index during sleep and wakefulness.
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.
  
  
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: 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.
authors.forename: Raffaele
authors.initials: R
authors.lastname: Ferri
authors.affiliation: Sleep Research Centre, Department of Neurology I.C., Oasi Institute for Research on Mental Retardation and Brain Aging (IRCCS), Troina, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Rundo
authors.affiliation: Sleep Disorders Center, Department of Neurology, Scientific Institute and University Ospedale San Raffaele, Vita-Salute University, Milan, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Zucconi
authors.affiliation: Sleep and Epilepsy Center, Neurocenter of Southern Switzerland, Civic Hospital (EOC) of Lugano, Lugano, Switzerland.
authors.forename: Mauro
authors.initials: M
authors.lastname: Manconi
authors.affiliation: Sleep Research Centre, Department of Neurology I.C., Oasi Institute for Research on Mental Retardation and Brain Aging (IRCCS), Troina, Italy.
authors.forename: Debora
authors.initials: D
authors.lastname: Aricò
authors.affiliation: Department of Social and Developmental Psychology, Sapienza University, Rome, Italy.
authors.forename: Oliviero
authors.initials: O
authors.lastname: Bruni
authors.affiliation: Sleep Disorders Center, Department of Neurology, Scientific Institute and University Ospedale San Raffaele, Vita-Salute University, Milan, Italy.
authors.forename: Luigi
authors.initials: L
authors.lastname: Ferini-Strambi
authors.affiliation: Sleep and Epilepsy Center, Neurocenter of Southern Switzerland, Civic Hospital (EOC) of Lugano, Lugano, Switzerland.
authors.forename: Stephany
authors.initials: S
authors.lastname: Fulda
mesh_terms: D000465:Algorithms; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D020189:Nocturnal Myoclonus Syndrome / Q000175:diagnosis* / Q000503:physiopathology; D010507:Periodicity; D012890:Sleep / Q000502:physiology; D014851:Wakefulness / Q000502:physiology
keywords: Index; PLMS; PLMW; Periodic leg movements during sleep; Restless legs syndrome; Sleep scoring