Evaluation of patient-rated stiffness associated with fibromyalgia: a post-hoc
analysis of 4 pooled, randomized clinical trials of duloxetine.
Author(s): Bennett R, Russell IJ, Choy E, Spaeth M, Mease P, Kajdasz D, Walker D, Wang F,
Chappell A.
Affiliation(s): Fibromyalgia Research Unit, Oregon Health & Science University, 3455 SW Veterans
Road, Portland, OR 97239, USA. bennetrob1@comcast.net
Publication date & source: 2012, Clin Ther. , 34(4):824-37
BACKGROUND: Patients with fibromyalgia (FM) rate stiffness as one of the most
troublesome symptoms of the disorder. However, there are few published studies
that have focused on better understanding the nature of stiffness in FM.
OBJECTIVES: The primary objectives of these analyses were to characterize the
distribution of stiffness severity in patients at baseline, evaluate changes in
stiffness after 12 weeks of treatment with duloxetine, and determine which
outcomes were correlated with stiffness.
METHODS: These were post-hoc analyses of 3-month data from 4 randomized,
double-blind, placebo-controlled studies that assessed efficacy of duloxetine in
adults with FM. Severity of stiffness was assessed by using the Fibromyalgia
Impact Questionnaire (FIQ) on a scale from 0 (no stiffness) to 10 (most severe
stiffness). The association between changes in stiffness and other measures was
evaluated by using Pearson's correlation coefficient. The FIQ total score and
items, the Brief Pain Inventory (BPI-modified short form), the Clinical Global
Impression-Severity scale, the Multidimensional Fatigue Inventory, the 17-item
Hamilton Depression Rating Scale, the Sheehan Disability Scale, the 36-item
Short-Form Health Survey, and the EuroQoL Questionnaire-5 Dimensions were
evaluated in the correlation analyses. Stepwise linear regression was used to
identify the variables that were most highly predictive of the changes in FIQ
stiffness.
RESULTS: The analysis included 1332 patients (mean age, 50.2 years; 94.7% female;
and 87.8% white). The mean (SD) baseline FIQ stiffness score was 7.7 (2.0), and
this score correlated with baseline BPI pain score and FIQ function. Duloxetine
significantly improved the FIQ stiffness score compared with placebo (P < 0.001)
and provided a moderate effect size (0.23 for the 60-mg dose and 0.38 for the
120-mg dose). Changes in stiffness were best correlated (range, 0.52-0.75; all, P
< 0.001) with changes in BPI/FIQ pain and interference scores, FIQ nonrefreshing
sleep, FIQ anxiety, 36-item Short-Form Health Survey bodily pain, and Sheehan
Disability Scale total score. Variables related to severity of pain, pain
interfering with daily activities, and physical functioning were predictors of
change in stiffness.
CONCLUSIONS: Stiffness scores were high in this population with FM and best
correlated at baseline with BPI pain score and FIQ function. Not unexpectedly,
improvement in stiffness with duloxetine correlated with many of the other
markers of FM severity, presumably a result of amelioration in FM comorbidities.
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