Investigating the factors associated with meaningful improvement on the SF-36-PFS and exploring the appropriateness of this measure for young people with ME/CFS accessing an NHS specialist service: a prospective cohort study.

Paediatric myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is relatively common and disabling, but little is known about the factors associated with outcome. We aimed to describe the number and characteristics of young people reaching the 10-point minimal clinically important difference (MCID) of SF-36-Physical Function Subscale (SF-36-PFS) and to investigate factors associated with reaching the MCID. Prospective observational cohort study. A specialist UK National Health Service ME/CFS service, Southwest England; recruitment between March 2014 and August 2015. 193 eligible patients with ME/CFS aged 8-17 years reported baseline data. 124 (65%) and 121 (63%) with outcome data at 6 and 12 months, respectively. SF-36-PFS (primary outcome). Chalder Fatigue Questionnaire, school attendance, visual analogue pain scale, Hospital Anxiety and Depression Scale, Spence Young People Anxiety Scale, Clinical Global Impression scale and EQ-5D-Y (secondary). At 6 months 48/120 (40%) had reached the MCID for SF-36-PFS. This had increased to 63/117 (54%) at 12 months. On the Clinical Global Impressions, 77% and 79% reported feeling either a little better, much better or very much better. Those with worse SF-36-PFS at baseline assessment were more likely to achieve the MCID for SF-36-PFS at 6 months (odds ratio 0.97, 95% confidence interval 0.96 to 0.99, p value 0.003), but there was weaker evidence of effect at 12 months (OR 0.98, 95% CI 0.97 to 1.00, p value 0.038). No other factors at baseline were associated with the odds of reaching the MCID at 6 months. However, at 12 months, there was strong evidence of an effect of pain on MCID (OR 0.97, 95% CI 0.95 to 0.99, p value 0.001) and SF-36-PFS on MCID (OR 0.96, 95% CI 0.94 to 0.98, p value 0.001). 40% and 54% of young people reached the MCID at 6 and 12 months, respectively. No factors at assessment (other than SF-36-PFS at 6 months, and pain and SF-36-PFS at 12 months) are associated with MCID of SF-36-PFS at either 6 or 12 months. Further work is needed to explore the most appropriate outcome measure for capturing clinical meaningful improvement for young people with ME/CFS.

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Déclaration de conflit d'intérêts

Competing interests: EC runs the specialist ME/CFS service of the data reported, has received one grant from Medical Research Council, multiple grants from the UK National Institute for Health Research (NIHR) and is an unfunded medical advisor to the Sussex & Kent ME/CFS Society. CM was a co-applicant on two UK NIHR grants in ME/CFS. The other authors declare no competing interests.