Night-to-night variability of periodic leg movements during sleep in restless legs syndrome and periodic limb movement disorder: comparison between the periodicity index and the PLMS index.
BACKGROUND
The number of periodic leg movements during sleep (PLMS index) shows high night-to-night variability, requiring multiple nights for its reliable estimation. It is currently not known if this is also the case for the degree of periodicity of leg movements, quantified by the Periodicity index.


OBJECTIVE
To compare night-to-night variability of PLMS and Periodicity indices in patients with restless legs syndrome (RLS) or periodic limb movement disorder (PLMD).


METHODS
Eighteen idiopathic RLS patients and 9 PLMD patients were recruited. Subjects underwent two consecutive full night polysomnographic studies. Polysomnographic recordings were scored and leg movement activity analyzed during sleep for the computation of the PLMS and Periodicity indices.


RESULTS
In both patient groups, the Periodicity index showed a significantly lower degree of variability than that of PLMS index, being >6.5 times lower in RLS patients and 2 times lower in PLMD patients.


CONCLUSIONS
These data support the use of the Periodicity index in the evaluation of PLMS in RLS and PLMD and indicate that this parameter seems to be more stable than the widely used PLMS index which has higher night-to-night variability.
Sleep Research Centre, Department of Neurology I.C., Oasi Institute for Research on Mental Retardation and Brain Aging (IRCCS), Troina, Italy. rferri@oasi.en.it
Raffaele
R
Ferri
Stephany
S
Fulda
Mauro
M
Manconi
Birgit
B
Högl
Laura
L
Ehrmann
Luigi
L
Ferini-Strambi
Marco
M
Zucconi
D000328:Adult; D000368:Aged; D052160:Benzothiazoles / Q000627:therapeutic use; D018491:Dopamine Agonists / Q000627:therapeutic use; D004569:Electroencephalography / Q000379:methods / Q000592:standards; D006801:Humans; D007866:Leg / Q000503:physiopathology; D008875:Middle Aged; D020189:Nocturnal Myoclonus Syndrome / Q000175:diagnosis* / Q000188:drug therapy / Q000503:physiopathology*; D010507:Periodicity; D010919:Placebos; D017286:Polysomnography / Q000379:methods* / Q000592:standards; D000077487:Pramipexole; D015203:Reproducibility of Results; D012148:Restless Legs Syndrome / Q000175:diagnosis* / Q000188:drug therapy / Q000503:physiopathology*; D012720:Severity of Illness Index; D012894:Sleep Stages / Q000502:physiology
D052160:Benzothiazoles; D018491:Dopamine Agonists; D010919:Placebos; D000077487:Pramipexole