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Title: Do expectancy and credibility influence the effectiveness of treatment in chronic low back pain patients?

Authors and affiliation: Rob JEM Smeets1, Saskia Beelen1, Mariëlle E.J.B. Goossens2,3, Johan WS Vlaeyen2, Eric G.W. Schouten2, J André Knottnerus4.

1 Rehabilitation Centre Blixembosch, Eindhoven, The Netherlands
2 Department of Medical, Clinical and Experimental Psychology, University of Maastricht, The       Netherlands
3 Institute for Rehabilitation Research, Hoensbroek, The Netherlands
4 Netherlands School of Primary Care Research, University of Maastricht, The Netherlands

Email address: rsmeets@iae.nl

Introduction: Patients’ expectancies regarding the success as well as the credibility of a treatment aimed at reduction of disability due to chronic low back pain are often mentioned to influence the final treatment outcome but remarkable little research has been done on their relative influence while correcting for other influential factors.

Objective: To what extent do treatment expectancy and credibility predict the short term outcome of rehabilitation treatment in nonspecific low back pain patients?

Methods: In three Dutch rehabilitation centers, 172 patients were randomized to one of the following therapies: 1) Active physical therapy (APT=53), 2) Cognitive-Behavioral Therapy (CBT, n=58), 3) Combination Therapy (CT, n=61) using 1) and 2). After the first session in which the treatment rationale for each particular treatment was explained, each patient was asked to fill out the Dutch version of the Credibility/Expectancy questionnaire of Devilly and Borkovec. Patients were asked whether they believe and expect that the treatment will be effective in reducing their disability due to low back pain. Additionally, several putative prognostic factors at baseline were collected: age, gender, education, working status, fear of injury/movement, pain catastrophizing, internal control of pain, pain intensity and level of disability. Next, for the outcome measures Roland Disability Questionnaire, Patient Specific Complaints, Global Perceived Effect on disability, Treatment Satisfaction and Pain, backward linear regression analyses were performed in which the covariates type of intervention, centre of treatment and duration of disability were corrected for and the influence of all abovementioned prognostic variables including expectancy and credibility was assessed.

Results: For 167 patients the scores of the Credibility/Expectancy questionnaire were available. The two-factor structure of the Dutch questionnaire could be confirmed (credibility and expectancy). Preliminary results show that expectancy appears to significantly influence the final level of disability measured by the RDQ and the treatment satisfaction. Credibility significantly influences the level of patient specific complaints.

Conclusions: Expectancy significantly influences the level of disability and treatment satisfaction in the treatment of chronic low back pain patients and credibility of the treatment specifically influences the level of patient specific complaints. No influence was found regarding the effectiveness on pain and global perceived effect.

Acknowledgements:Supported by Zon/Mw (014-32-007).