The Neurocognitive and Behavioural Impact of Comorbid Obsessive–Compulsive Syndrome in Schizophrenia

In this chapter, we review the results of neurocognitive and behavioural studies in patients with OCD and schizophrenia and use these data to attempt to identify the key neuropsychological mechanisms. We explore the extent to which associated neuro-behavioural changes may characterise schizo–OCD either as a distinct and clinically relevant schizophrenia subgroup, a more severe form of schizophrenia or a true comorbidity that integrates the psychopathology of both its parent disorders. We conclude that, compared to schizophrenia, schizo–OCD may be associated with additional executive deficits (neurocognitive double jeopardy) featuring impaired performance on specific executive tasks, notably tasks measuring attentional set-shifting and cognitive flexibility and likely to involve fronto-striatal neurocircuitry known to be linked to OCD. However, whilst patients with schizo–OCD and OCD share most OC ritualistic attributes, they also demonstrate behavioural differences, which imply a separate phenotype for the compulsions of schizo–OCD. These differences represent an easily evaluable clinical sign that could contribute toward an improved nosological classification of a range of OC spectrum disorders.