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Abstract
There is a need for an easily administered instrument which can be applied to all
patients with restless legs syndrome (RLS) to measure disease severity for clinical
assessment, research, or therapeutic trials. The pathophysiology of RLS is not clear
and no objective measure so far devised can apply to all patients or accurately reflect
severity. Moreover, RLS is primarily a subjective disorder. Therefore, a subjective
scale is at present the optimal instrument to meet this need.
Twenty centers from six countries participated in an initial reliability and validation
study of a rating scale for the severity of RLS designed by the International RLS
study group (IRLSSG). A ten-question scale was developed on the basis of repeated
expert evaluation of potential items. This scale, the IRLSSG rating scale (IRLS),
was administered to 196 RLS patients, most on some medication, and 209 control subjects.
The IRLS was found to have high levels of internal consistency, inter-examiner reliability,
test-retest reliability over a 2-4 week period, and convergent validity. It also demonstrated
criterion validity when tested against the current criterion of a clinical global
impression and readily discriminated patient from control groups. The scale was dominated
by a single severity factor that explained at least 59% of the pooled item variance.
This scale meets performance criteria for a brief, patient completed instrument that
can be used to assess RLS severity for purposes of clinical assessment, research,
or therapeutic trials. It supports a finding that RLS is a relatively uniform disorder
in which the severity of the basic symptoms is strongly related to their impact on
the patient's life. In future studies, the IRLS should be tested against objective
measures of RLS severity and its sensitivity should be studied as RLS severity is
systematically manipulated by therapeutic interventions.