Nosological status and definition of schizophrenia: Some considerations for DSM-V and ICD-11

Abstract

Objective

Although dementia praecox or schizophrenia has been considered a unique disease entity for the past century, its definitions and boundaries have varied over this period. In this article, we examine the changing conceptualization of schizophrenia over the past 100 years and make some recommendations with regards to its definition in DSM-V and ICD-11.

Methods

We summarize clinical features of schizophrenia in terms of symptomatology, course, and outcome. We examine factors that lead to changing definitions of a disorder such as schizophrenia, with specific reference to the evolution of its definition from DSM-1 (American Psychiatric Association, Washington, DC, 1952) to the current DSM-IV-TR.

Results

Efforts to elucidate the etiology and pathophysiology of schizophrenia have been hampered by its imprecise definition and continuing transformations in its conceptualization. The definition of schizophrenia, at any given time, has been influenced by available diagnostic tools and treatments, other clinical considerations, extant knowledge and scientific paradigms. It is now clear that schizophrenia does not represent a single disease with a unitary etiology or pathogenetic process. Despite limitations in the concept, however, alternative approaches thus far have been unsuccessful in better defining the syndrome of schizophrenia or its component entities.

Conclusions

Whereas changing definitions of schizophrenia might impede research into its nature and development of more effective treatments, only a better understanding of schizophrenia can lead to its more precise definition. We consider the implications of our observations for DSM-V and ICD-11 definitions of schizophrenia and summarize some emerging preliminary recommendations.

Introduction

The need to distinguish between different medical conditions that cause human suffering is the reason to classify medical disorders. A useful nosological system (literally, system of classification of disease) (Merriam-Webster, 2008) enables clinicians to provide specific treatments for distinct medical causes of human dis-ease and/or disability whose effects are precise and predictable as also provide guidance to patients and families about the likely course and outcome of such suffering. Additionally, it enables researchers to study circumscribed conditions and elucidate the nature of defined disease entities. Although there have been several efforts to provide a useful nomenclature from the times of the Ayurveda and Hippocrates, our modern system of classification derives from the work of a committee chaired by Dr. Jacques Bertillon that prepared a system of classification of the causes of death which was adopted by the International Statistical Institute in 1893 (Bertillon, 1912). Since that time, this system has been considerably expanded in scope and size and has undergone ten revisions (ICD 1-10); the number of listed conditions has multiplied from 179 in ICD-1 to over 13,000 in the current version of ICD-10 (World Health Organization, 1992).

In the sixth revision of this system (ICD-6) (World Health Organization, 1949) there was a substantial reconceptualization of the section relating to mental disorders (section V). In subsequent revisions (ICD 7–10), changes in this section have been relatively small although a glossary has been added and changes in diagnostic criteria made. Additionally in the most recent revision, three versions of section V of the ICD-10 are provided—the core version (World Health Organization, 1992) and versions for research (World Health Organization, 1993) and the general practitioner (Ustun et al., 1995). Since the first edition of the American Diagnostic and Statistical Manual of Mental Disorders (DSM-1) (American Psychiatric Association, 1952), there have been five revisions (DSM-II, DSM-III, DSM-III-R, DSM-IV, and the current DSM-IV-TR) (American Psychiatric Association, 1968, American Psychiatric Association, 1980, American Psychiatric Association, 1987, American Psychiatric Association, 1994, American Psychiatric Association, 2000). Whereas there was considerable divergence between section V of ICD-6 and DSM-I, there is now considerable similarity between DSM-IV-TR and section V of ICD-10. The process of revising both DSM-IV-TR and ICD-10 are underway and DSM-V is expected to be released in 2012 whereas ICD-11 is expected to be finalized by 2014. Current versions of both ICD-10 and DSM-IV-TR are marked by considerable complexity, variable validity, limitations in clinical and research utility, problems of burgeoning comorbidity, and occasionally blurred boundaries between normality and disease (Maj, 2000, Maj, 2005). As with other medical disorders, any meaningful nosological system of mental disorders must be valid, reliable, and useful (Table 1) (Kendell and Jablensky, 2003) and efforts to revise the DSM and ICD systems of classification of mental disorders towards this objective must address these limitations.

In the remainder of this essay, we briefly summarize the challenges we face with specific reference to the definition and nosological status of schizophrenia.