Original ArticleMeasurement properties of the Medical Outcomes Study Sleep Scale in patients with fibromyalgia
Introduction
The American College of Rheumatology (ACR) defines fibromyalgia syndrome (FM) using two criteria: (1) chronic widespread pain and (2) pain upon digital palpation in at least 11 of 18 defined tender point sites [1], [2]. In addition to musculoskeletal pain, FM is associated with symptoms such as fatigue, sleep disturbance, and morning stiffness [3]. Further, patients report they experience depression and cognitive difficulties, and that FM interferes with their usual activities [4]. Assessing the effectiveness of new therapies therefore requires accurate assessment of a multi-dimensional array of symptoms and problems.
This paper focuses on the measurement of sleep problems in patients with FM. Disturbed sleep is consistently ranked by patients as a highly bothersome symptom of the disease. For example, Bennett et al. [5] conducted a web-based survey of over 2000 patients with FM and found that the self-reported intensity of non-restorative sleep was ranked third, behind symptoms of morning stiffness and fatigue. Mease et al. [4] conducted a patient symptom ranking and found that sleep ranked high among the most important symptoms (following pain, aching joints or pain, and lack of energy or fatigue).
To evaluate FM-related sleep problems and the impact of treatment on these symptoms, the clinical program for pregabalin (Lyrica®) included a well-established standardized (generic) patient survey—the Medical Outcomes Study (MOS) Sleep Scale [6]—as a secondary efficacy endpoint. The MOS Sleep Scale includes 12 questions about initiation and maintenance of sleep, respiratory problems during sleep, amount of sleep, perceived adequacy of sleep, and daytime somnolence [6]. It was developed and initially tested in a large sample of individuals with chronic illnesses. It has been further validated in a nationally representative sample of adults in the United States (US) [7] and in other pain populations including postherpetic neuropathic pain [7], neuropathic pain of broad etiology [8], and rheumatoid arthritis [9]. The objective of this study was to evaluate the measurement properties of the MOS Sleep Scale in a specific population of patients with FM.
Section snippets
Studies and subjects
This paper reports the psychometric properties of the MOS Sleep Scale using data from two clinical trials of pregabalin conducted in the US: 1077 [10] and 1056 [11]. The study designs for these trials have been described elsewhere [10], [11]. The studies were randomized, double-blind, and placebo-controlled clinical trials of three doses of pregabalin (300, 450, and 600 mg/day). Patients were 18 years of age or older with FM as defined by the ACR criteria [1], [2].
During the baseline phase,
Descriptive analysis
The 1056 and 1077 studies included 748 and 745 patients, respectively. Most patients were female (94.4% in the 1056 study and 94.5% in the 1077 study) and white (90.2% in the 1056 study and 91.0% in the 1077 study) (Table 1). In the 1056 study, the mean age of patients was 48.8 years and the average duration of FM was 9 years. In the 1077 study, the mean age of patients was 50.1 years and the average duration of FM was 10 years. In both studies, baseline mean pain scores were approximately 7 on
Discussion
The analyses reported here from 1056 and 1077, two high-quality trials, suggest that the MOS Sleep Scale is an appropriate measure of this outcome and is likely to be useful in future FM research. The MOS Sleep Scale captured the magnitude of sleep decrements experienced by individuals with FM and accorded with expectations. Baseline MOS Sleep Scale scores in the 1056 and 1077 studies were significantly and substantially poorer than general population normative scores in the US. It is important
Acknowledgments
The research reported in this paper was funded by Pfizer Inc. Drs. Cappelleri and Petrie and Mr. Bushmakin are full-time employees of Pfizer Global Research and Development, New London, CT; Drs. Dukes and Sadosky are full-time employees of Worldwide Pharmaceutical Operations, Global Outcomes Research, New York, NY. Ms. Martin was a full-time employee of Pfizer Global Research and Development, Outcomes Research, Ann Arbor, MI, when this work was performed and RTI Health Solutions during the
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