Neuropsychological evidence for cognitive impairment in obsessive-compulsive disorder: relationship with clinical symptomatology

© 1999 Dr. Kylie WainwrightNeuropsychological studies of obsessive-compulsive (OCD) disorder yield diverging results. Purcell, Maruff, Kyrios & Pantelis (1998a; 1998b) examined cognitive function in a group of patients with OCD, and found specific deficits in spatial working memory, spatial recognition memory, and motor execution. However, no relationships were identified between cognitive impairment and obsessive-compulsive (OC) symptoms. The present study investigated the nature of cognitive impairments in a large sample of patients with OCD and explored the relationship between cognitive impairments, obsessive-compulsive symptoms, and treatment outcome. Study 1 showed that patients with OCD exhibit specific impairments in spatial working memory, spatial span, spatial recognition, attentional set shifting, and motor slowing. This study replicated earlier findings by Purcell et al. (1998a; 1998b) and is consistent with a neurobiological model of OCD which implicates dysfunction in frontal and subcortical brain regions. Study 2 found that levels of OC symptoms in the entire group were not correlated with cognitive impairments. However, when patients were classified according to their predominant symptom subtype, cognitive impairments were greatest in those classified as ‘checkers’. This suggests that cognitive impairment is related to type of obsessive-compulsive symptoms. To determine whether cognitive impairment was secondary to OC symptoms, neuropsychological assessment was repeated in a subgroup of patients with OCD who had significantly reduced symptom levels following cognitive-behavioural group treatment. Despite the symptom reduction, no improvement in cognitive function was found, apart from on one measure of spatial working memory. Results suggest that cognitive impairment in OCD may be more basic to the disorder, rather than arising as a consequence of the obsessive-compulsive symptoms per se. These results expand the body of research exploring neuropsychological function in OCD, and provide the first exploration of the relationship between cognitive impairment, OCD subgroups, OC symptoms, and treatment outcome