Brief communicationValidation of the Johns Hopkins restless legs severity scale
Introduction
For clinical evaluation of patients with a disorder it is useful to have a simple, easy-to-use scale for assessing the severity of the disorder. We have standardized one such scale for evaluating severity of the restless legs syndrome and have used this scale in prior studies. We present in this paper our evaluation of the validity and reliability of this scale.
To simplify clinical evaluation of restless leg syndrome (RLS) severity we chose to focus on only one of the clinical symptoms, usual time-of-day for onset of symptoms. We did not feel that this was in anyway a better predictor of RLS severity, but it seemed to avoid some of the following measurement problems that we thought might occur for the other RLS symptoms. The time spent at rest before symptoms start, the subjective intensity of either sensations or amount of movement and a general subjective global rating, each lack an objective reference causing potential problems with inter-subject variability. Sensations, in particular, are notoriously hard for patients to rate on a severity scale, particularly for chronic conditions, such as RLS, where the patient is likely to adjust his sense of intensity based on his usual experience. Subjective assessments of the amount of leg movement and sleep efficiency have similar problems but fortunately can be assessed by objective assessments with a suggested immobilization test [1], polysomnogram [2], or activity meters [3]. These, however, require special recording equipment. Another severity indicator-the number of days with symptoms, has a major problem with insensitivity to any but the mildest severity of RLS. Almost all patients who seek treatment have nearly daily symptoms. Even after what they consider very successful treatment their persisting mild symptoms may occur briefly nearly every day [4]. The usual time of onset of symptoms, being during each day has an advantage for the patient in that the time symptoms start is an objective reference which is usually fairly well known by him/her. This dimension of RLS severity also relates to the length of each day the patient will be struggling with RLS and focuses on the circadian rhythm of the disorder, which is both required for diagnosis of RLS and distinguishes RLS from other neurological disorders. Moreover, when augmentation of RLS occurs as an adverse effect of treatment, the increasing severity of RLS is described by this clinical dimension; i.e. earlier onset during the day [5].
The time of symptom onset as a subjective clinical measure of RLS severity can be objectively validated by comparison with polysomnographic measures of the degree of sleep disturbance. The polysomnogram provides two well-established objective measures of the severity of RLS sleep disturbance that have been used in prior studies; i.e. number of periodic leg movements per h of sleep (PLMS/h) and sleep efficiency, measured to include initial sleep latency [6].
Section snippets
Materials and methods
The Johns Hopkins restless legs severity scale (JHRLSS) was scored based on the patients report of the usual (>50% of days) time of the day that symptoms started. A four point scale was established with: 0 for no symptoms; 1, for bedtime only symptoms (after or within an hour of going to bed); 2, for evening and bedtime symptoms (starting at or after 18:00 h); and 3, for day and night symptoms (starting before 18:00 h).
A clinician trained in using the JHRLSS reviewed each patients chart to
Subject selection
Until about 1997, a standard polysomnogram (PSG) with measurement of the periodic leg movements in sleep (PLMS) was frequently, but not always used to confirm a diagnosis of RLS. A consecutive case series was developed by selecting the charts of all patients for a 2 year period, ending in April 1997, with a diagnosis of primary RLS who also had a polysomnogram. The diagnosis was made by a diplomate of the American Board of Sleep Medicine based on diagnostic criteria established by the RLS
Data analyses
The inter-scorer reliability was determined as the percentage of agreement and the correlation between the two scorers.
The validity of the subjective JHRLSS was determined by the degree of correlation between the JHRLSS and either sleep efficiency or PLMS/h.
Results
Thirty-one subjects (20 females, 11 males) ages 29–81 (average±SD, 62.7±13.1) were entered into the study. They had a wide range of values for both the JHRLSS (range 1–3) and the objective sleep measures (ranges: sleep efficiency 2–91%, PLMS/h 1.6–193.0).
The two clinicians agreed on 90% of the scores for the JHRLSS and the disagreements were only at most by one category. The Spearman correlation (Rho) between their scores was 0.91 (P<0.05). Cramers V for inter-rater agreement was 0.87 (P<0.05).
Discussion
Overall the JHRLSS appears to provide a reasonable, easy to use subjective clinical scale for rating severity of RLS symptoms. As expected, it has excellent inter-scorer reliability and a very good correlation with objective measures. As far as we know this is the first objective validation of a clinical severity measure of RLS. The use of an essentially three-point scale, however, may limit its usefulness for making finer grade distinctions between patients or for some treatment effects.
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