Neurocognitive performance and negative symptoms: Are they equal in explaining disability in schizophrenia outpatients?

Abstract

Objective

The aim of this study is to assess if cognitive variables and symptom dimensions can predict disability in a sample of outpatients with schizophrenia.

Method

A cross-sectional sample of 113 individuals with a diagnosis of schizophrenia (DSM-IV criteria) was selected from a computerized register of five Community Mental Health Centers. Patients were assessed by two trained psychologists, with a neuropsychological battery comprising measures for verbal memory, attention, operative memory and abstraction and flexibility functions. Symptoms were assessed with the Positive and Negative Syndrome Scale (PANSS); a socio-demographic and clinical questionnaire, comprising the Disability Assessment Scale (DAS), was also completed. Test scores were standardized (t scores) to performance of healthy controls. To assess the relationship between clinical and sociodemographic factors and disability and cognitive functioning Pearson's correlation coefficients were computed. In order to establish the predictive capacity of the cognitive, clinical and symptom variables on disability linear regression models were fitted.

Results

Mean age of patients was 41.6 years and 68% were male. Higher ratings in the negative dimension were associated with more cognitive deficits. Association with the positive dimension was present but less strong. All disability areas, except for disability in occupational functioning, were partially explained by the negative dimension. Disability in family functioning was also partially explained by attention and number of admissions since onset.

Conclusion

Negative symptoms are the major source of disability of our sample and are also associated to cognitive functioning. The present findings suggest that further investigation on the mediators between clinical and social outcomes may help to design specific treatments to reduce disability.

Introduction

Schizophrenia is frequently associated with disability in different areas of daily life and impaired social functioning (Murray and Lewis, 1987, Obiols, 2001). Disability is defined as disordered or deficient functioning in roles and domains compared to what it is regarded as normal in a particular society, by the family or social group or by the person affected (World Health Organization, 1988). It is considered one of the most relevant outcome measures of schizophrenia (Strauss and Carpenter, 1974, Strauss and Carpenter, 1972).

Social and role functioning requires the performance of abilities which include the performance of complex cognitive tasks (Ertugrul and Ulug, 2002). Thus impaired cognitive functioning should be related to impaired social functioning. For instance, verbal memory and attention deficits should affect the acquisition of social abilities (Addington and Addington, 1999) and impaired executive functions could also lead to an array of social and occupational difficulties (Liddle, 2000). Even though some studies have reported association between cognitive and social impairment (Dickerson et al., 1996, Ertugrul and Ulug, 2002), the positive effects of remediation programs on cognition do not directly translate to improved social functioning (Greenwood et al., 2005).

On the other hand, several studies have reported associations between symptom measures, specially negative symptoms, and domains of functioning (Norman et al., 2000, Greenwood et al., 2005), but it has not been established how negative symptoms directly influence social outcomes (Green, 1996) and they have been assumed to contribute mostly indirectly through their link with cognition or other mediators with social outcomes (Greenwood et al., 2005, Dickerson et al., 1999). In a previous study with a different sample of patients (Ochoa et al., 2005) the author found that symptom severity was also related to patient needs.

Until now, the association between negative symptoms and cognitive deficits and their relation with disability in social functioning has widely been reported (Penades et al., 2001, Grawe and Levander, 2001, Liddle, 2000, Hammer et al., 1995); but it is unclear how much of this functional impairment can be attributed to the presence of psychiatric symptoms or to impaired cognitive functioning (Dickinson and Coursey, 2002).

Efficient treatment should not only lead to symptom reduction but also decrease the disability of patients (Ertugrul and Ulug, 2002, Voruganti et al., 1997). The search for mediators between clinical variables (symptoms and cognition among others) and functional outcome is important since it will help to understand the relationships between clinical variables and disability and it will also help to reasonably define targets of interventions (Green et al., 2000).

The present study was designed to determine how cognitive variables and symptom dimensions can predict disability in our sample of outpatients with schizophrenia. Specifically, it was hypothesized that: (1) cognitive deficits would be most related to the negative component of the Positive and Negative Syndrome Scale (PANSS) (Kay et al., 1987, Peralta, 1994) and (2) these deficits together with the negative symptoms would have an important role in explaining disability.