Validation of the kohnen restless legs syndrome–quality of life instrument

Publication date: Available online 3 August 2016
Source:Sleep Medicine
Author(s): Ralf Kohnen, Pablo Martinez-Martin, Heike Benes, Claudia Trenkwalder, Birgit Högl, Elmar Dunkl, Arthur S. Walters
BackgroundDue to the symptoms and the sleep disturbances it causes, Restless Legs Syndrome (RLS) impacts on quality of life. Measurement of such impact can be carried out by means of questionnaires such as the Kohnen Restless Legs Syndrome–Quality of Life questionnaire (KRLS-QoL), a specific 12-item instrument self-applied by patients. The present study is aimed at performing a first formal validation study of this instrument.MethodsEight 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.ResultsThere 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, i.e 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.ConclusionsThe KRLS-QoL performed as an acceptable, reliable, valid, and responsive measure to assess the impact of the RLS on quality of life.



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