My e-letter on PACE Trial: More data demonstrating why the SF-36 PF threshold of 60+ is problematic

Thanks to a few people here, particularly @Sam Carter, who helped me with this.

 

https://www.ncbi.nlm.nih.gov/pubmed/21334061#cm21334061_77791


Title: More data demonstrating why the SF-36 physical functioning threshold of 60+ is problematic

The PACE trial's principal investigators (PIs) argue that scores of 60 or higher on the SF-36 physical function subscale (SF-36 PF) fall within the "normal range" and use this threshold as one component of their revised definition of recovery from Chronic Fatigue Syndrome (CFS), as well as a post hoc measure in this paper[1,2].

Referring to the normal ranges for physical function and fatigue used in the PACE trial, one of the trial's PIs, Trudie Chalder, stated that “twice as many people on graded exercise therapy and cognitive behaviour therapy got back to normal”[3]. This same terminology, "back to normal", was also used by the PIs in a patient information leaflet[4].

The use of this phrase, which implies full restoration of health, merits closer scrutiny following publication of a new paper containing data from CFS patients assessed at one of the PACE trial's treatment centres, the Chronic Fatigue Research and Treatment Unit in London, UK, between November 2007 and January 2014[5].

The paper, whose corresponding author is Trudie Chalder, reports that 39.6% of the patients diagnosed with CFS (228/576) had SF-36 PF scores of more than 60; i.e., despite having a score within the normal range, they were judged as sufficiently disabled to be diagnosed with CFS. Note that the data given were for more than 60 on the SF-36 PF so the figure for 60 or more would likely be higher again.

Moreover, Dutch researchers recently reported that 39% of patients with CFS had SF-36 PF scores of 65 or higher[6], and in the PACE trial itself patients could start with a SF-36 PF score of 65 at baseline[7]. Also, as we reported in a reanalysis of the PACE Trial data, in a large British community sample 90% of people aged 18–59 without a long-term illness or disability actually score 90 or higher[8].

Taken together, these data suggest that the derived normal range threshold for physical function is too low to serve as a meaningful indicator of recovery and does not, in fact, represent getting "back to normal".

References:

1 White PD1, Goldsmith KA, Johnson AL, Potts L, Walwyn R, DeCesare JC, Baber HL, Burgess M, Clark LV, Cox DL, Bavinton J, Angus BJ, Murphy G, Murphy M, O'Dowd H, Wilks D, McCrone P, Chalder T, Sharpe M; PACE trial management group. Comparison of adaptive pacing therapy, cognitive behaviour therapy, graded exercise therapy, and specialist medical care for chronic fatigue syndrome (PACE): a randomised trial. Lancet. 2011; 377: 611–690

2 White PD, Goldsmith K, Johnson AL, Chalder T, Sharpe M. Recovery from chronic fatigue syndrome after treatments given in the PACE trial. Psychol Med. 2013;43(10):2227–2235.

3 Boseley, S. Study finds therapy and exercise best for ME. The Guardian. Feb 18, 2011 https://www.theguardian.com/society/2011/feb/18/study-exercise-therapy-me-treatment

4 PACE participants newsletter 4. February 2011. http://www.wolfson.qmul.ac.uk/images/pdfs/participantsnewsletter4.pdf

5 Ryan EG, Vitoratou S, Goldsmith KA, Chalder T. Psychometric properties and factor structure of a shortened version of the Cognitive Behavioural Responses Questionnaire (CBRQ). Psychosom Med. 2017 Oct 10. doi: 10.1097/PSY.0000000000000536. [Epub ahead of print]

6 Janse A, Nikolaus S, Wiborg JF, Heins M, van der Meer JWM, Bleijenberg G, Tummers M, Twisk J, Knoop H. Long-term follow-up after cognitive behaviour therapy for chronic fatigue syndrome. J Psychosom Res, 2017. doi: 10.1016/j.jpsychores.2017.03.016.

7 White, PD, Sharpe, MC, Chalder, T et al. Protocol for the PACE trial: a randomised controlled trial of adaptive pacing, cognitive behaviour therapy, and graded exercise, as supplements to standardised specialist medical care versus standardised specialist medical care alone for patients with the chronic fatigue syndrome/myalgic encephalomyelitis or encephalopathy. BMC Neurol. 2007; 7: 6

8 Wilshire CE, Kindlon T, Matthees A, et al. Can patients with chronic fatigue syndrome really recover after graded exercise or cognitive behavioural therapy? A critical commentary and preliminary re-analysis of the PACE trial. Fatigue. 2017;5:1–4.

 

Thanks Tom. More good points. And thanks to Sam too.