Einflussfaktoren der Behandlung von medizinisch unerklärten Symptomen: Therapieprädiktoren und ärztliche Kommunikationsstile

Medically unexplained symptoms (MUS) are highly prevalent in the general population as well as in primary care and represent in the context of somatoform disorders one of the most common mental disorders in Europe (Haller et al., 2015; Wittchen et al., 2011). Affected individuals develop excessive symptom-related cognitions, emotions, or behaviors that significantly decrease the quality of life of the patients (Xiong et al., 2017). Due to various treatment aspects of MUS an adequate psychotherapy as well as an appropriate doctor-patient communication are of central importance. However, there is still a potential to optimize both areas (Husain & Chalder, 2021; van Dessel et al., 2014). In this dissertation, specific factors that potentially influence the treatment outcome are examined in two different domains. Study 1 and study 2 analyze different predictors of treatment outcomes of psychotherapy in patients with MUS, while Study 3 examines the influence of doctor-patient communication on the placebo effect in a healthy sample. During the treatment of MUS patients, the cognitive behavioral therapy (CBT) represents an important core element. Unfortunately, current meta-analyses show only a moderate efficacy (van Dessel et al., 2014). One option to improve the treatment outcome is to personalize psychotherapy. In order to tailor current therapies to specific needs of the patients, individual patient-related characteristics that are potentially associated with treatment outcome need to be identified in advance. Therefore, the first part of this dissertation investigates various treatment predictors of CBT by performing several meta-analyses. Study 1 shows significant aggregated correlations of the following cognitive-emotional predictors at the beginning of the CBT and a less favorable therapy outcome: a comorbid affective disorder or anxiety disorder, a higher catastrophizing or somatosensory amplification, as well as a lower symptom acceptance and self-efficacy. The aggregated associations are particularly high in patients with irritable bowel syndrome or chronic fatigue syndrome. In study 2, significant aggregated correlations emerge between the following clinical predictors at the beginning of the treatment and a less favorable treatment outcome: a higher symptom intensity, a lower physical or social-emotional functioning, a longer symptom duration, as well as higher potential symptom-related incentives. The aggregated effect sizes did not differ in specific MUS subgroups or certain levels of methodological quality. Since doctors are often the first contact persons of patients with MUS (Creed et al., 2011), the doctor-patient communication represents a key factor in the treatment of MUS patients (Husain & Chalder, 2021). In clinical practice, a differentiation is made between the patient-centered and the doctor-centered communication style (Mead & Bower, 2000). In addition to the positive impact of the patient-centered communication style on various health variables of MUS (Weiland et al., 2012), there is an increasing research effort on the impact of the placebo effect with respect to the treatment outcome (Enck et al., 2013). In this regard, doctors' communication styles potentially have a decisive influence on the placebo effect (Zion & Crum, 2018). A few studies have already demonstrated positive associations between a specific communication style of the doctors and the placebo effect (Howe et al., 2017; Kaptchuk et al., 2008). However, experimental paradigms comparing the influence of different doctors' communication styles on the placebo effect are currently missing. Thus, in the second part of this dissertation, a standardized doctor-patient interaction with the mentioned communication styles is developed and implemented in an experimental design on a nonclinical sample as a first basic research step (study 3). The influence of doctors' communication styles on the placebo effect and symptom report is examined after one week of taking the placebo pill on a daily basis. The results show no significant influence of the communication styles on the individual’s placebo response. However, the communication styles indicate different effects on the individual’s placebo response when the negative affectivity of the participants is taken into account. In addition, the individuals report significantly more symptoms after they received a patient-centered consultation than after a doctor-centered or no consultation. A reason for the non-significant placebo effects may be the healthy sample without personal medical concerns. Similarly, the intake phase of one week may have been too short for inducing a placebo effect. The studies conducted in the context of this dissertation are able to provide information about treatment predictors of CBT for patients with MUS, which may pave the way for a more personalized adaptation of psychotherapy to individual patient characteristics. Furthermore, this thesis shows that the patient-centered communication style of doctors influences the symptom report of healthy participants, which may be used to encourage patients to talk openly about their physical complaints. Further clinical studies are needed to investigate whether different doctors' communication styles can also be considered as an influencing factor on the placebo effect.