Symptom severity scale of the DSM5 for schizophrenia, and other psychotic disorders: diagnostic validity and clinical feasibility

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Abstract

Innovations in DSM5 include dimensional diagnosis of schizophrenia (SZ) and other psychotic (OP) disorders using the symptom severity scale (SS-DSM5). We evaluated the psychometric properties and diagnostic validity of the SS-DSM5 scale using a cross-sectional design and an unselected convenience unselected sample of 314 inpatients and outpatients with SZ/OP and mood disorders who received standard care in routine clinical practice. The SS-DSM5 scale, the Clinical Global Impression-Severity scale (CGI-S), the Positive and Negative Syndrome Scale (PANSS), and the Bech-Rafaelsen Mania Scale (BRMS) were administered. Factor structure, reliability, internal consistency, convergent and diagnostic ability of the DSM5-SS were evaluated. Factor analysis indicated two latent factors underlying the SS-DSM5 (Psychotic and Deficit sub-scales). Cronbach's alpha was >0.70. Convergent validity of the SS-DSM5 was highly significant. Patients with SZ/PO disorders were correctly diagnosed (77.9%) using the SS-DSM5 scale (72% using PANSS). The agreement of the diagnostic decisions between the SS-DSM5 and PANSS was substantial for SZ/PO disorders (Kappa=0.75). Classifying participants with SZ/PO versus mood disorders using SS-DSM5 provided a sensitivity of 95%, and specificity of 34%. Thus, this study suggests that the SS-DSM5 has acceptable psychometric properties and that its use in clinical practice and research is feasible in clinical settings. The dimensional option for the diagnosis of schizophrenia and related disorders using SS-DSM5 is discussed.

Introduction

Numerous studies in the last century have increasingly emphasized that the boundaries between nosological entities may not be categorical, and putative comorbidity of various disorders may reflect impairments in common clinical dimensions, genetic variation, human behavior and neurobiological functions (e.g., Peralta and Cuesta, 2007, Owen et al., 2007, Ritsner and Gottesman, 2011). The categorical approach defines subgroups within the disorder, whereas the dimensional approach emphasizes the severity of different symptom clusters. As such, it is important to explicitly include dimensional assessments of the core symptoms of psychotic disorders in order to identify pertinent variability. Therefore, the most useful current approach for the classification of schizophrenia (SZ), other psychotic (OP), and mood disorders may be the complementary use of categorical and dimensional representations of functional psychoses (Salokangas, 2003, Brown and Barlow, 2005, Dikeos et al., 2006, Dutta et al., 2007, Helzer et al., 2008, van Os, 2009, Kamphuis and Noordhof, 2009).

Recently, the American Psychiatric Association (APA) posted a draft of the Diagnostic and Statistical Manual of Mental Disorders, 5th ed. (DSM5) on a special web site, www.dsm5.org. One of innovations in the DSM5 is the extensive use of so-called dimensional assessments to account for severity of symptoms of schizophrenia and other psychotic disorders. In particular, the DSM5 Workgroup suggests that each of the diagnostic symptoms for these disorders (‘Criterion A’) may be rated using a new symptom severity scale that we called the Symptom Severity Scale DSM5 (SS-DSM5) in the current study (http://www.dsm5.org/Pages/Default.aspx)1.

The psychometric properties of the SS-DSM5 in terms of reliability, and validity have not been presented. The purpose of our study therefore was to establish the psychometric properties (factor structure, reliability, internal consistency, convergent and diagnostic ability) of the SS-DSM5 scale in an unselected sample of patients with psychotic (SZ/OP) and mood disorders that were receiving standard care in inpatient and out-patient settings of a large university hospital.

Section snippets

Methods

In this study, we used a cross-sectional design enrolling an unselected convenience sample of inpatients and outpatients with SZ/OP and mood disorders who received standard care from February 2010 to March 2011 in the routine clinical practice settings at Shaar Menashe Mental Health Center affiliated to the Rappaport Faculty of Medicine, Technion, Israel. The study included men and women ages 18–80 years. The design adhered to the Declaration of Helsinki and ICH/Good Clinical Practice

Factor structure

Results from an exploratory factor analysis of SS-DSM5 dimensions are summarized in Table 1. We found a model with two latent factors (scales), which were labeled as ‘Psychotic’ and ‘Deficit’ scales. The first factor included negative loadings of delusions, disorganization, abnormal psychomotor behavior and mania scores. The second factor was constructed using restricted emotional expression, avolition and impaired cognition scores with negative loadings. Correspondingly, they accounted for

Discussion

This study aimed to establish the psychometric properties and diagnostic validity of the SS-DSM5 scale for dimensional diagnosis of SZ/OP disorders.

The key psychometric properties of the SS-DSM5 scale are:

  • (i)

    The factorial analysis demonstrates a two-factorial structure of the SS-DSM5 dimensions, which were labeled ‘psychotic’, and ‘deficit’ scales, respectively.

  • (ii)

    The reliability and internal consistency of the SS-DSM5 total score and its scales were shown to be strong. Cronbach's alpha was >0.70 for

Authors' contributions

RMS originated the study design. RMS and AG were responsible for collection of data, statistical analysis, and an interpretation of data and drafted the manuscript. MM and MA participated in acquisition of data and interpretation of data. All authors have given final approval of the version to be published.

Acknowledgments

The authors especially thank R. Kurs, B.A. for editing this manuscript.

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