Discussion
chronic pain disorders, pain, CM, headache, migraine, migraine headache, disability
MIGRAINE, MIGRAINE HEADACHE
This post-hoc analyses of the CONQUER study demonstrated the reliability, validity, responsiveness, and meaningful change of the WPAI questionnaire in patients with EM or CM. These results support the validity of the WPAI as a PRO to measure the impact of EM or CM on work productivity (overall and presenteeism) and non-work-related activity impairment. The meaningful change thresholds for the WPAI domain scores may help in evaluating clinically meaningful treatment responses and may be appropriate for inclusion of WPAI in future preventive migraine clinical studies.Test–retest reliability results showed moderate correlations for WPAI presenteeism and WPAI non-work-related activity impairment and a fair correlation for WPAI overall work productivity loss. The modest ICCs for the WPAI may reflect the relatively brief, one-week recall interval. As the number of migraine days and their severity is known to vary within person from time to time, the instability of the phenomenon being measured may contribute to modest ICCs. This may also account for the higher ICCs we observed for CM than for EM. The greater ICCs among patients with CM than patients with EM may be due to the small sample size or the shorter recall period. A longer recall period longer for patients with EM may provide a more stable measurement of reliability.Construct validity was confirmed between WPAI domain scores and continuous anchor variables- monthly migraine headache days, MSQ-RFR, and MSQ-RFP. Using an anchor-based method, a threshold of -20-unit change in scores at Month 3 (from baseline) was found to be meaningful for the three WPAI domain scores. The identified responder thresholds were consistent across patients with EM or CM. The eCDF plots substantiated the findings of the selected meaningful change threshold. A meaningful within-patient responder threshold was defined for three of the WPAI domains (presenteeism, overall work productivity, and non-work-related activity impairment) for patients with migraine (EM or CM).The reliability, validity, responsiveness, and meaningful change of the WPAI among patients with migraine had not been previously established. The findings of this research indicate that this instrument is appropriate for use in this population and provides a within-patient responder threshold that can be used to determine a meaningful change in presenteeism, overall work productivity and non-work-related activity impairment. This threshold can be used in future research to determine the proportion of patients that are experiencing a degree of improvement that is impactful for work and non-work activities.In the present analyses, WPAI absenteeism sub scores alone (i.e. without accounting for presenteeism) were not considered due to a possible lack of sensitivity in patients with migraine. This may be explained by a low mean baseline score of 9.37 and smaller change from baseline of −2.83 for absenteeism versus other domains making the results less sensitive to the present analyses. These low mean absenteeism scores are not unexpected, as qualitative research has revealed that employed patients with migraine frequently ‘power-through’ work, which results in modest levels of absenteeism. When people miss enough work, they may become unemployed. Across a range of chronic pain disorders unemployment rates increase with pain severity and in the highest grades of pain unemployment rates reach 20%. Selecting for persons who are employed may in effect select against individuals with high rates of absenteeism. Presenteeism is strongly influenced by migraine [Strengths of this study include the use of current methods for evaluating psychometric properties, determining meaningful within-patient change thresholds, and the PROs for the analyses were comprehensive including a quality-of-life measure and an electronic daily diary measure of MHDs.There are certain limitations to our study. One of the limitations is that the patient population for the CONQUER clinical trial was specific to patients with migraine who had a history of two to four preventive treatment category failures. In addition, analyses were limited to people with ≥ 4 monthly migraine headache days, which may represent a more impacted sample than the general population. This higher rate of monthly migraine days may have influenced employment status and associated disability, and therefore results may not be generalizable to a sample with fewer monthly migraine days. Moderate reliability or greater was not observed for the WPAI in this patient population, perhaps because the number of headache days varies from week to week and the recall interval for the WPAI is only one week. This study included WPAI data at baseline and Month 3, hence we could not include Month 1 data for analysis. Also, there was no information from the patient perspective regarding what constitutes an important change in WPAI scores. The analysis plan evaluated reliability in a group with no change or a change of only one day over one month when the WPAI evaluated one week of that month; real within person change may have reduced the ICCs for the WPAI. Responsiveness for WPAI absenteeism was not evaluated because of very low score in the patient population. Additionally, the MSQ-RFR and MSQ-RFP as anchors used in the study to validate WPAI should be easy to interpret. Change from baseline is monthly migraine days is a widely used, included in labelling, and recommended in guidelines as a primary endpoint in preventive treatment trials [There is uncertainty if these results can be generalized to the overall migraine population. However, results observed in patients with EM or CM were consistent. Therefore, the identified responder thresholds can be applied to migraine populations without preventive treatment failures until further research is completed to confirm (or contradict) this recommendation. Prior publications show that patients with high frequency EM (10–14 headache days/month) have similar disability to those of CM (≥ 15 headache days/month) [