Stefan Elbers

29 Evaluating IMPT programmes over time INTRODUCTION Interdisciplinary multimodal pain treatment (IMPT) programmes are recognized as treatment of choice for patients with chronic pain (Gatchel et al., 2014; Turk, 2003). Since the 1970s these programmes have evolved towards interventions that combine (cognitive) behavioural approaches with exercise, medical treatment and education based on a biopsychosocial model. The aim of these programmes is not to target pain itself, but to help patients to optimize daily life functioning and to increase social, physical and psychological wellbeing (Gatzounis et al., 2012; Kaiser et al., 2017; Penney & Haro, 2019). This approach is typically provided by rehabilitation centers or hospitals and requires the expertise of an interdisciplinary team of healthcare providers. Generally, these disciplines cover the biopsychosocial spectrum and continuously coordinate their treatment activities and align them to patient-specific goals. Despite common historical roots and a biopsychosocial perspective on chronic pain, substantial variation in content, duration and outcome evaluations of IMPT programmes has been reported. For example, systematic reviews found that the total treatment duration varied between 6.4 and 196.8 hours, programmes were delivered in both inpatient and outpatient settings, and pain-related disability was measured with 12 different measurement instruments (Kamper et al., 2014; Scascighini et al., 2008; Waterschoot et al., 2014). This variability not only hinders a meaningful interpretation of pooled effect sizes, it also reflects uncertainty regarding optimal dose, content and the selection of measurement instruments (Waterschoot et al., 2014). A second problem regarding the current evidence-base of IMPT programmes is that it is unclear to what extent treatment gains are maintained over time. Although RCTs often indicate a statistically significant effect compared to control interventions, post treatment assessments still suggest a considerable impact on daily life functioning (Kamper et al., 2014). From a clinical perspective, this indicates that most patients continue to experience the burdening effect of pain after treatment. This may be problematic, as the newly learned pain management strategies are considered to be fragile and vulnerable to disruptions (e.g. unexpected exacerbations of symptoms, an unforeseen event in the personal context or nocebo's). Continuing occurrences of pain interference could prompt pre-treatment coping strategies, resulting in a declined effect over time (Carver & Scheier, 2017; Vlaeyen et al., 2016). Although this so-called 'triangular relapse pattern' – with an improvement from pre-intervention to post-intervention, followed by an unfavorable trend at follow-up – has been observed in other healthcare domains, this topic has been neglected in the field of pain rehabilitation (Brouwer et al., 2019; Morley, 2008; Opozda et al., 2016; Turk & Rudy,