Validation of the Kohnen Restless Legs Syndrome-Quality of Life instrument.
Due to the symptoms and the sleep disturbances it causes, Restless Legs Syndrome (RLS) has a negative impact on quality of life. Measurement of such impact can be performed by means of questionnaires, such as the Kohnen Restless Legs Syndrome-Quality of Life questionnaire (KRLS-QoL), a specific 12-item instrument that is self-applied by patients. The present study is aimed at performing a first formal validation study of this instrument.



Eight hundred ninety-one patients were included for analysis. RLS severity was assessed by the International Restless Legs Scale (IRLS), Restless Legs Syndrome-6 scales (RLS-6), and Clinical Global Impression of Severity. In addition the Epworth Sleepiness Scale (ESS) was assessed. Acceptability, dimensionality, scaling assumptions, reliability, precision, hypotheses-related validity, and responsiveness were tested.



There were missing data in 3.58% patients. Floor and ceiling effects were low for the subscales, global evaluation, and summary index derived from items 1 to 11 after checking that scaling assumptions were met. Exploratory parallel factor analysis showed that the KRLS-QoL may be deemed unidimensional, ie, that all components of the scale are part of one overall general quality of life factor. Indexes of internal consistency (alpha = 0.88), item-total correlation (rS= 0.32-0.71), item homogeneity coefficient (0.41), and scale stability (ICC = 0.73) demonstrated a satisfactory reliability of the KRLS-QoL. Moderate or high correlations were obtained between KRLS-QoL scores and the IRLS, some components of the RLS-6, inter-KRLS-QoL domains, and global evaluations. Known-groups validity for severity levels grouping and responsiveness analysis results were satisfactory, the latter showing higher magnitudes of response for treated than for placebo arms.



The KRLS-QoL was proven an acceptable, reliable, valid, and responsive measure to assess the impact of the RLS on quality of life.
Posthumously, Research Pharmaceutical Services, Inc, Fort Washington, PA, USA; University of Erlangen, Nuremberg, Germany.
Ralf
R
Kohnen
National Center of Epidemiology and CIBERNED, Carlos III Institute of Health, Madrid, Spain.
Pablo
P
Martinez-Martin
Somi Bene Institute for Medical Research and Sleep Medicine, Schwerin, Germany; Medical Center, University of Rostock, Rostock, Germany.
Heike
H
Benes
Department of Neurosurgery, University Medical Center, Goettingen, Germany; Paracelsus Elena Clinic, Kassel, Germany.
Claudia
C
Trenkwalder
Department of Neurology, Medical University of Innsbruck, Austria.
Birgit
B
Högl
PRA Health Sciences, Nuremberg, Germany.
Elmar
E
Dunkl
Department of Neurology, Vanderbilt University School of Medicine, Nashville, Tennessee, USA. Electronic address: Arthur.Walters@vanderbilt.edu.
Arthur S
AS
Walters
D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011594:Psychometrics / Q000706:statistics & numerical data; D011788:Quality of Life; D015203:Reproducibility of Results; D012148:Restless Legs Syndrome / Q000523:psychology*; D012720:Severity of Illness Index; D012893:Sleep Wake Disorders; D011795:Surveys and Questionnaires
Health-related quality of life; IRLS; Kohnen Restless Legs Syndrome–Quality of Life questionnaire; RLS-6; Restless Legs Syndrome