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Open Access Research article

Validation of the post sleep questionnaire for assessing subjects with restless legs syndrome: results from two double-blind, multicenter, placebo-controlled clinical trials

Daniel M Canafax1, Abhijeet Bhanegaonkar2, Murtuza Bharmal34 and Michael Calloway5*

Author Affiliations

1 XenoPort, Inc., Santa Clara, CA, USA

2 West Virginia University School of Pharmacy, Morgantown, WV, USA

3 Current Address: GlaxoSmithKline R&D China, Shanghai, China

4 Previous Address: Quintiles, Rockville, MD, USA

5 GlaxoSmithKline, Research Triangle Park, NC, USA

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BMC Neurology 2011, 11:48  doi:10.1186/1471-2377-11-48

Published: 28 April 2011

Abstract

Background

Because of the subjective nature of Restless Legs Syndrome (RLS) symptoms and the impact of these symptoms on sleep, patient-reported outcomes (PROs) play a prominent role as study endpoints in clinical trials investigating RLS treatments. The objective of this study was to validate a new measure, the Post Sleep Questionnaire (PSQ), to assess sleep dysfunction in subjects with moderate-to-severe RLS symptoms.

Methods

Pooled data were analyzed from two 12-week, randomized, placebo-controlled trials of gabapentin enacarbil (N = 540). At baseline and Week 12, subjects completed the PSQ and other validated health surveys: IRLS Rating Scale, Clinical Global Impression of Improvement (CGI-I), Profile of Mood States (POMS), Medical Outcomes Study Scale-Sleep (MOS-Sleep), and RLS-Quality of Life (RLSQoL). Pooled data were used post hoc to examine the convergent, divergent, known-group validity and the responsiveness of the PSQ.

Results

Convergent validity was demonstrated by significant correlations between baseline PSQ items and total scores of IRLS, POMS, RLSQoL, and the MOS-Sleep Scale (p ≤ 0.007 each). Divergent validity was demonstrated through the lack of significant correlations between PSQ items and demographic characteristics. Correlations (p < 0.0001) between RLS severity groups and PSQ items demonstrated known-group validity. Mean changes in investigator- and subject-rated CGI-I scores for each PSQ item (p < 0.0001) demonstrated the PSQ's responsiveness to patient change as reported by their care provider.

Conclusions

Although these analyses were potentially limited by the use of clinical trial data and not prospective data from a study conducted solely for validation purposes, the PSQ demonstrated robust psychometric properties and is a valid instrument for assessing sleep and sleep improvements in subjects with moderate-to-severe RLS symptoms.

Trial Registration

This study analyzed data from two registered trials, NCT00298623 and NCT00365352.