Interference with work in fibromyalgia: effect of treatment with pregabalin and relation to pain response

Abstract

Background: Clinical trials in chronic pain often collect information about interference with work as answers to component questions of commonly used questionnaires but these data are not normally analysed separately.

Methods: We performed a meta-analysis of individual patient data from four large trials of pregabalin for fibromyalgia lasting 8-14 weeks. We analysed data on interference with work, inferred from answers to component questions of Fibromyalgia Impact Questionnaire (FIQ), Short Form 36 Health Survey, Sheehan Disability Scale, and Multidimensional Assessment of Fatigue, including "How many days in the past week did you miss work, including housework, because of fibromyalgia?" from FIQ. Analyses were performed according to randomised treatment group (pregabalin 150-600 mg daily or placebo), pain improvement (0-10 numerical pain rating scale scores at trial beginning vs. end), and end of trial pain state (100 mm visual analogue pain scale [VAS]).

Results: Comparing treatment group average outcomes revealed modest improvement over the duration of the trials, more so with active treatment than with placebo. For the 'work missed' question from FIQ the change for patients on placebo was from 2.2 (standard deviation [SD] 2.3) days of work lost per week at trial beginning to 1.9 (SD 2.1) days lost at trial end (p < 0.01). For patients on 600 mg pregabalin the change was from 2.1 (SD 2.2) days to 1.6 (SD 2.0) days (p < 0.001). However, the change in days of work lost was substantial in patients with a good pain response: from 2.0 (SD 2.2) days to 0.97 (SD 1.6) days (p < 0.0001) for those experiencing >/= 50% pain improvement and from 1.9 (SD 2.2) days to 0.73 (SD 1.4) days (p < 0.0001) for those achieving a low level of pain at trial end (<30 mm on the VAS). Patients achieving both >/= 50% pain improvement and a pain score <30 mm on the VAS had the largest improvement, from 2.0 (SD 2.2) days to 0.60 (SD 1.3) days (p < 0.0001). Analysing answers to the other questions yielded qualitatively similar results.

Conclusions: Effective pain treatment goes along with benefit regarding work. A reduction in time off work >1 day per week can be achieved in patients with good pain responses.

Trial registration: ClinicalTrials.gov NCT00230776 NCT00333866 NCT00645398.

Figure 1

Days of work missed. Days of work missed per week at the beginning and end of trials as assessed by the question "How many days in the past week did you miss work, including housework, because of fibromyalgia?" from the Fibromyalgia Impact Questionnaire (FIQ). Data are presented as a comparison of 'state' and 'improvement' responders; 'non-responders' are neither state nor improvement responders; 'double responders' are both. ** p < 0.01, *** p < 0.001, **** p < 0.0001, NS - no significant difference, SD - standard deviation. FIQ data were not available for trial 105, the only trial with a 150 mg pregabalin group. Therefore no data for participants treated with 150 mg pregabalin are presented here.

Figure 2

Interference with work. Interference with work as assessed by the question "When you worked, how much did pain or other fibromyalgia symptoms interfere with your ability to do your work, including housework?" from the Fibromyalgia Impact Questionnaire; responder categories and abbreviations as in Figure 1.