Delusional ideation associated with obsessive-compulsive symptoms

This PhD thesis explores the extent and nature of delusional thinking associated with obsessive-compulsive (OC) symptoms across different diagnostic categories, in particular, obsessive-compulsive disorder (OCD) and schizophrenia. In Paper 1 we aim to gain preliminary insights concerning how an intrusive thought in OC cases may become delusional using an on-line survey. Relationships between different measures of proneness to delusional ideation and severity of OC symptoms were assessed, across a variety of self-reported diagnoses. The possible mediating role of metacognitive biases is also considered. Given the reported high prevalence of comorbid OC symptoms in schizophrenia outside Australia, Paper 2 aims to establish the prevalence of any OC symptoms in an Australian sample of people with schizophrenia recruited with the assistance of the Australian Schizophrenia Research Bank (ASRB) Volunteer Register. The ASRB also provided lifetime severity ratings of different delusions, and data for neuropsychological performance, which allowed us to examine relations with self-reported severity of OC symptoms. Paper 3 then focuses on four unusual and more bizarre OCD cases to help identify and quantify the distinction between ‘unusual’ delusion-like and ‘normal’ OCD cases. The case histories of these four single cases are presented and a range of clinical instruments for assessing insight and conviction associated with the primary OC related beliefs are administered. To discover common or possibly distinguishing features of delusion-like thinking in people with OC symptoms with or without a comorbid Schizophrenia diagnosis, Paper 4 reports a preliminary investigation involving in-depth interviews to administer a range of clinical tools for assessing characteristics of belief and insight, as well as self-report inventories to 29 individuals with OC symptoms. In accord with previous research, which proposes that high conviction in an implausible OC belief indicates the presence of delusional thinking, Paper 5 compares a ‘high conviction’ and a ‘low conviction’ OC subgroup on tasks that have revealed impairments in delusional psychotic disorders (i.e., tasks assessing probabilistic reasoning, theory of mind and attributional biases). The whole sample of 29 patients with OC symptoms are also compared to previously reported normative data. A summary chapter then provides an overview of the results showing that: (1) measures of a proneness to general delusional ideation associate with severity of OC symptoms independent of the effects of metacognitive biases; (2) OC symptoms are prevalent in a high proportion of Australian schizophrenia patients (roughly 30%) and associate with some psychotic delusions and poor neuropsychological performance; (3) unusual OCD cases with bizarre beliefs according to their case histories do not show consistently poor insight into their disorder or express consistently high conviction in their primary OC-related belief; (4) while patients with schizophrenia and comorbid OC symptoms are less insightful about their OC symptoms than a ‘primary OC’ sample without schizophrenia, there is substantial overlap in ratings of conviction, strength of belief and insight related to the primary OC-related beliefs, supporting a symptom-focused approach to study the factors that underlie delusional thinking across disorders; and (5) neither high conviction nor poor insight concerning the primary OC-related beliefs nominated by OC cases as causing them most distress associated with poor performances on the same tasks that have revealed impairments in delusional schizophrenia patients. Implications for future research are then discussed.