Longitudinal examination of neurocognitive function and community functioning in patients with recent onset and chronic schizophrenia
Introduction: The importance of quantifying the impact of illness on functional abilities is well recognised. Previous research has indicated that the cognitive impairment associated with schizophrenia may have considerable functional significance (Green, 1996. 2000). However, evidence linking these two domains in schizophrenia research has largely come from cross-sectional or prospective short-term investigations. Thus, the predictive impact of these deficits on daily living is still unclear. The current study examined cross-sectional and longitudinal relationships between cognition and different aspects of community function. It also explored the linearity of the relationship between these domains, focusing on cognitive severity as a mediating factor, as well as task complexity. A better understanding of the degree and nature of functional limitations in schizophrenia may help focus on areas for remediation in order to maximise independence of functioning. Methods: Fifty-four patients with a diagnosis of schizophrenia were recruited from community psychiatric clinics serving the Hull and East Yorkshire, and South Humber Health Authorities. The patient group was initially divided into two categories, 'recent onset' and 'chronic', with the majority of these participants being treated as outpatients (57%). A small cognitive comparative group of twenty non-psychiatric, matched controls was also recruited. Symptoms, cognition and social function were comprehensively assessed at baseline, nine-months and eighteen-months. The Independent Living Skills Survey (ll.SS) and Social Behaviour Schedule (SBS) were utilised to quantify levels of community functioning, whilst a battery of manual and computerised neurocognitive tests were administered in order to establish patterns of cognitive deficit Constellations of clinical and affective symptoms were assessed with the Brief Psychiatric Research Survey (BPRS) and the Hamilton Depression Scale (HADRS). Results: Few differences were demonstrated between the two patient groups on predictor and outcome variables, thus the patient groups were pooled for subsequent analyses. Stepwise regression analyses determined that neurocognitive deficits, and in particular deficits of executive function, were important predictors of some aspects of community functioning in patients with schizophrenia, but not community functioning per se. Clinical and affective symptom variables were also found to significantly predict functional outcomes in the study, including overall social behaviour. In most models the variance explained by symptom variables was greater than that explained by cognitive variables. A non-linear relationship between cognitive functioning and social functioning was also suggested. Level of cognitive performance was found to discriminate social performance, whereby severe cognitive disturbance demonstrated poorer outcomes than either moderate or normal performance groups. However, few differences were found between 'normal performance' and 'moderate deficit' groups on social function scores. The study also implied that neurocognitive function did not differentially affect performance on basic and complex instrumental tasks. Conclusions: These findings validate the hypothesis that neurocognitive deficits and clinical symptoms are important 'rate-limiting' factors, but cannot support the notion that neurocognitive impairments are functionally more important than the clinical symptoms of the disorder. A combined psychopharmacological and psychosocial approach that takes account of an individual's neurocognitive deficits would therefore appear to offer a reasonable treatment stratagem. The study also suggests that further investigation in larger studies with increased analytical strategies for capturing the non-linear reciprocal relationships between cognition and social function are needed. Finally, a substantial unexplained variance in social functioning exists, which indicates the need for investigations to evaluate other candidate risk factors in relation to both the clinical and cognitive symptoms of the disorder.