Categorical and dimensional approaches to negative symptoms of schizophrenia: Focus on long-term stability and functional outcome

Abstract

Negative symptoms of schizophrenia represent a heterogeneous psychopathological domain. Both categorical and dimensional approaches have been proposed to reduce negative symptoms heterogeneity.

In the present 5-year follow-up study, long-term stability and impact on outcome of different aspects of negative symptoms were investigated. Following a categorical approach, long-term stability and outcome of deficit schizophrenia (DS), in comparison with nondeficit schizophrenia (NDS), were assessed. Following a dimensional approach, the factor structure and stability of broadly defined negative symptoms and the ability of the identified factors to predict functional outcome were investigated.

DS and NDS subjects included in a previous study were invited to participate. Fifty-one out of 58 patients previously diagnosed as DS and 44 out of 54 NDS patients were included in the present study.

The DS/NDS categorization was confirmed in 82.4% of DS and 79.6% of NDS subjects. At follow-up, DS patients showed more severe negative symptoms and greater social dysfunction than NDS ones.

Schedule for the Deficit Syndrome (SDS) severity scores loaded on two factors: “Poor Emotional Expression” and “Avolition” and the factor structure was stable after 5 years. Avolition was associated to social outcome measures and Poor Emotional Expression to functioning in household activities.

Psychosocial outcome was predicted by SDS factors reflecting the severity of broadly defined negative symptoms, but not by the DS/NDS categorization. This might lend support to the recent shift of research focus from the categorical approach focusing on the presence of primary and enduring negative symptoms to the investigation of key domains of broadly defined negative symptoms.

Introduction

Negative symptoms of schizophrenia represent a heterogeneous psychopathological domain. In fact, they include signs and symptoms favourably responding to currently available treatments (for instance, negative symptoms secondary to positive or depressive symptomatology, that might respond well to available antipsychotics or adjunctive antidepressants), but also signs and symptoms still representing a challenge for the development of new pharmacological and non-pharmacological interventions (for instance, primary and persistent negative symptoms, Kirkpatrick and Galderisi, 2008, Galderisi and Maj, 2009). Research focussing on deconstruction of broadly defined negative symptoms might be crucial to identify key targets for new treatments aimed to improve patients' outcome.

A categorical approach within this research field has been represented by the study of deficit schizophrenia (DS). It is regarded as a distinct subtype within the diagnosis of schizophrenia, characterized by the presence of primary and enduring negative symptoms, and showing different clinical, neuropsychological and neurobiological abnormalities with respect to nondeficit schizophrenia (NDS; Carpenter et al., 1988, Kirkpatrick et al., 1998, Kirkpatrick et al., 2000, Kirkpatrick and Galderisi, 2008, Galderisi and Maj, 2009). Three studies, so far, investigated the stability of the diagnosis across time and the long-term outcome of patients bearing the diagnosis of DS: one was based on a retrospective assessment (Fenton and McGlashan, 1994) and two of them on a prospective design (Amador et al., 1999, Strauss et al., 2010). The frequency of confirmed diagnoses at follow-up ranged from 67% to 83.3%. The lowest figure was reported by Strauss et al. (2010), in a 20-year follow-up study (the longest follow-up interval in the relevant literature), involving 39 patients with schizophrenia categorized as DS (N = 14) or NDS (N = 25) using a proxy method; the highest frequency was reported by Amador et al. (1999) in a study involving 43 patients with schizophrenia or schizoaffective disorder, in which the DS/NDS categorization was performed by means of the Schedule for the Deficit Syndrome (SDS). Few prospective studies investigated long-term functional outcome of subjects with DS or NDS. Two of them reported a poorer outcome in DS than in NDS patients (Tek et al., 2001, Strauss et al., 2010), while Chemerinski et al. (2006), in a group of elderly patients with DS or NDS (the latter ones were subdivided into delusional and disorganized type) reported greatest functional impairment in delusional, lowest in disorganized and intermediate in the DS group, at odds with the other studies showing poorer functioning in patients with DS than in those with NDS.

More recently a dimensional approach to the study of negative symptoms has been revived by investigations based on factor analyses of negative symptoms showing that two separate factors, i.e. Avolition and Poor Emotional Expression, can be identified both when the overall negative domain is assessed (Blanchard and Cohen, 2006, Kirkpatrick et al., 2011, Strauss et al., 2012) and when only primary and enduring negative symptoms are evaluated (Kimhy et al., 2006, Nakaya and Ohmori, 2008). No study, so far, examined the SDS factor structure stability across time and the ability of SDS factors to predict functional outcome.

In the present investigation both a categorical and a dimensional approach were used to assess long term-stability and outcome of negative symptoms. In particular, within the former approach, we investigated the long-term stability of the DS and NDS diagnosis and the long-term outcome of patients with DS or NDS. In the frame of a dimensional approach, we assessed the factor structure and stability of broadly defined negative symptoms and the impact of the identified factors on functional outcome.

Premorbid adjustment, general cognitive abilities and other neuropsychological domains, psychopathological dimensions and neurological signs were investigated in the two groups as these variables can influence functional outcome in patients with schizophrenia (Breier et al., 1991, Dickerson et al., 1996, Dickerson et al., 1999, Green et al., 2000, Galderisi and Maj, 2009, Hunter and Barry, 2012, Peralta et al., 2012).