Rituximab Treatment for Psychosis And/or Obsessive Compulsive Disorder with Probable Immune System Involvement

The primary objective for this study is to evaluate whether Rituximab as compared to placebo is a clinically effective treatment for a subgroup of patients suffering from psychosis and/or obsessive-compulsive disorder (OCD) or -behavior (OCB) where there is an indication of immune system involvement. The secondary objectives of this study are 1. To assess whether Rituximab treatment (with the doses and timing described below) as compared to placebo is associated with amelioration in psychiatric symptomatology 2. To assess whether Rituximab treatment as compared to placebo is associated with improvement in executive functions 3. To assess whether Rituximab treatment as compared to placebo is associated with amelioration in neurological symptoms 4. To evaluate the longevity of psychiatric, neurological and executive improvements associated with Rituximab treatment for up to 16 months after the first infusion (i.e. 12 months after the last infusion) 5. To evaluate whether Rituximab treatment as described is safe for these patients. The exploratory objectives of this study are 1. To assess changes in blood and cerebrospinal fluid (CSF) markers for immune activity associated with Rituximab treatment compared to placebo 2. To assess statistical associations between biological markers in blood or CSF and clinical response 3. To describe changes in somatic symptoms associated with treatment with Rituximab vs placebo for patients with initial symptoms in the questionnaires 4. To describe changes on MR and EEG associated with treatment with Rituximab vs placebo for patients with initial pathology in these examination 5. To study immune mechanisms coupled with psychiatric symptoms, possibly identifying novel biomarkers with potential for subtyping encephalopathies with immune engagement, using biobank cells, blood and CSF samples collected from the participants.