Association between changes on the Negative Symptom Assessment scale (NSA-16) and measures of functional outcome in schizophrenia

Abstract

We examined whether changes in negative symptoms, as measured by scores on the 16-item Negative Symptom Assessment scale (NSA-16), were associated with changes in functional outcome. A group of 125 stable outpatients with schizophrenia were assessed at baseline and at 6 months using the NSA-16, the Brief Psychiatric Rating Scale, and multiple measures of functional outcome. Baseline adjusted regression coefficients indicated moderate correlations between negative symptoms and functional outcomes when baseline values of both variables were controlled. Results were nearly identical when we controlled for positive symptoms. Cross-lag panel correlations and Structural Equation Modeling were used to examine whether changes in negative symptoms drove changes in functional outcomes over time. Results indicated that negative symptoms drove the changes in the Social and Occupational Functioning Scale (SOFAS) rather than the reverse. Measures of Quality of Life and measures of negative symptoms may be assessing overlapping constructs or changes in both may be driven by a third variable. Negative symptoms were unrelated over time to scores on a performance-based measure of functional capacity. This study indicates that the relationship between negative symptom change and the change in functional outcomes is complex, and points to potential issues in selection of assessments.

Introduction

Schizophrenia and schizoaffective disorder together have been identified as the fifth leading cause of disability world-wide (Jaeger et al., 2003). It has been estimated that the costs for treatment and loss in productivity associated with schizophrenia are as high as 60 billion dollars annually (Wyatt et al., 1995, Souêtre, 1997, Trauer et al., 1998) with approximately 46 billion dollars of this total associated with loss in productivity (Jaeger et al., 2003). Multiple domains of functional outcome are impaired for individuals with schizophrenia including performance of independent living skills, social functioning, and occupational/educational performance and attainment (Sharma and Antonova, 2003) Most patients require some public funding for support, and only 10 to 20% of patients are able to sustain full- or part-time competitive employment (Anthony and Blanch, 1987, Mueser et al., 2001, McGurk and Mueser, 2004). Improving functional outcomes for this group of individuals is a significant mental health priority.

While medication treatments are effective in improving the positive symptoms of schizophrenia, functional outcomes remain poor for those with schizophrenia compared with the general population (Sharma and Antonova, 2003, McGurk and Mueser, 2004). In contrast to the positive symptoms of the illness, negative symptoms are more difficult to treat and often persist long after positive symptoms have resolved or been substantially reduced. Significantly, negative symptoms have been found to be more predictive of concurrent and future functioning in the community than positive symptoms (Mueser et al., 1990, Breier et al., 1991, Velligan et al., 1997, Ho et al., 1998, Milev et al., 2005). In some studies, many cross-sectional in nature, cognition has been found to be a stronger predictor of functional outcome than negative symptoms (Green, 1996, Velligan et al., 1997, Puig et al., 2008). However, in a study of first episode patients followed for 7 years, negative symptoms predicted the majority of the variance in functional outcome over time (Milev et al., 2005). Moreover, negative symptoms and cognition explained shared variance in functional outcome.

In this article, we examine whether change in negative symptoms over time predicts change in functional outcomes over time. If it can be established that a decrease in negative symptoms improves community outcomes, and that improvements in negative symptoms are associated with improved community functioning over and above improvements due to changes in positive symptoms, this would suggest that negative symptoms are important targets for pharmacotherapy and psychosocial treatments, and that they should be the focus of more investigative efforts. We hypothesized that improvements in negative symptoms over time would be significantly correlated with improvements in functional outcomes over time. In the present study, we explored correlations among changes in positive symptoms, negative symptoms, and functional outcomes over a 6-month period. Functional outcomes included global level of social and occupational functioning, an interview-based measure of quality of life, and a performance-based measure of functional capacity.