Categories of transdiagnostic processes: Qualitative data from psychotherapy practitioners

The processes involved in the development, persistence and maintenance of psychopathology have been subject to frequent debate. A particular focus of discussion is the one comparing categorical and dimensional approaches to diverse psychopathological patterns (e.g. Hopwood et al., 2018; Kraemer, Noda, & O’Hara, 2004; Widiger, 1992). Categorical systems rely on signals (observed by the clinician) and symptoms (reported by the patient), which are viewed as important indicators of the presence of a disorder (such as in the DSM-V or the ICD-10). There are specific diagnostic criteria for each disorder, and a patient is diagnosed with one or more disorders when meeting those criteria. Dimensional systems, on the other hand, rate patients on different dimensions that aim to consider important individual variability and avoid a dichotomous decision between a present and an absent diagnosis. An individual is thus assessed in a set of domains, which arguably allows to draw a deeper profile of impairment or severity across them (Helzer, Kraemer, & Krueger, 2006; Rodriguez-Seijas, Eaton, & Krueger, 2015). Traditional categorical systems have been subject to extensive criticism in recent years (Hengartner & Lehmann, 2017; Hopwood et al., 2018), in favour of dimensional approaches (e.g. the RDoC initiative in Yee, Javitt, & Miller, 2015). These dimensional approaches, however, can be seen as complementary, instead of substitutive. Psychopathology is widely acknowledged as a dynamic construct, which has been leading to the discussion of perspectives that can complement the categorical view, thus allowing for a better understanding of its underlying mechanisms (Nelson, McGorry, Wichers, Wigman, & Hartmann, 2017). While some authors consider that categorical or dimensional approaches are more appropriate depending on the clinical circumstances and research questions being addressed (Kraemer, Noda, & O’Hara, 2004), others argue that a dimensional component should be added to the traditional categorical systems, thus preserving their existence (Helzer, Kraemer, & Krueger, 2006). One such dimensional perspective, for which discussion has been reignited in the literature, is the transdiagnostic perspective. This perspective can be seen as an alternative to the widespread division of psychological disorders in categorical and discrete entities, as well as to diagnosis-based interventions. As such, it can offer new insights when approaching the underlying processes implicated in mental health (Dalgleish, Black, Johnston, & Bevan, 2020). A particular transdiagnostic approach consists of studying and conceptualising common processes underlying the development or maintenance of different disorders (for an example, see the shared mechanisms approaches as discussed in Sauer-Zavala et al., 2017). It is suggested that such a transdiagnostic scope could help to reduce the complexity caused by the high levels of comorbidity observed between various categorical diagnoses (Rodriguez-Seijas et al., 2015; Taylor & Clark, 2009). Although this transdiagnostic perspective has recently been gaining more attention, some authors point to its historical roots (Mansell, Harvey, Watkins, & Shafran, 2009; Nolen-Hoeksema & Watkins, 2011). For instance, both the psychoanalytic view and the first behavioural approaches discussed general principles (e.g. defence mechanisms in the former, operant and classical conditioning in the latter) that could be applied to several clinical patterns, such as phobia, depression or schizophrenia (reviewed in Nolen-Hoeksema & Watkins, 2011). This idea has been examined again in more recent articles. Serving as an example, Gellatly and Beck (2016) conducted a comprehensive literature review on the role of catastrophic beliefs (originally discussed by Ellis, 1962) as a predictor of several disorders, such as panic, phobia, health anxiety, obsessive–compulsive