Classification
Organizing principles of contemporary classifications
Current psychiatric classifications
Current and future issues in psychiatric classification
Introduction
Chapter 1 outlined the symptoms and signs of psychiatric disorder. In Chapter 3 we describe the psychiatric assessment, by which these symptoms and signs are elicited, interpreted, and used as the basis upon which psychiatric diagnoses are made. Before doing so, in this chapter we discuss the principles of psychiatric diagnosis and classification, since this provides the framework within which this clinical process happens. The term nosology is sometimes used to refer to classification and its study.
Classification is needed in psychiatry for several purposes:
• to enable clinicians to communicate with one another about the diagnoses given to their patients
• to understand the implications of these diagnoses in terms of their symptoms, prognosis, and treatment, and sometimes their aetiology
• to relate the findings of clinical research to patients seen in everyday practice
• to facilitate epidemiological studies and the collection of reliable statistics
• to ensure that research can be conducted with comparable groups of subjects.
Of these, the first three are the most relevant to clinical practice. Indeed, it is difficult to imagine how psychiatry could be practised in any reasonable or evidence-based manner without the order which classification provides. In this respect, the position of classification as one of the fundamental ‘building blocks’ of psychiatry is no different from that in the rest of medicine. However, in other respects psychiatric classification does raise particular challenges and controversies, largely as a consequence of the uncertain aetiology of many disorders. These difficulties are of two kinds. The first is conceptual, relating to the nature of mental illness and the question of what, if anything, should be classified. The second difficulty is a practical one, relating to how categories are defined and organized into a classificatory scheme. In this chapter, the conceptual issues and criticisms are covered first, followed by a historical perspective to classification. We then describe and compare the two schemes in widespread use at present, namely Chapter V of the International Classification of Diseases, 10th edition (ICD-10; World Health Organization, 1992b), and the Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV; American Psychiatric Association, 1994, 2000).
Concepts of mental illness
In everyday speech the word ‘illness’ is used loosely. Similarly, in psychiatric practice the term ‘mental illness’ is used with little precision, and often synonymously with ‘mental disorder.’ In this context, the terms ‘mental’ and ‘psychiatric’ are also used interchangeably.
A good definition of mental illness is difficult to achieve, for both practical and philosophical reasons, as outlined here. In routine clinical work the difficulty is important mainly in relation to ethical and legal issues, such as compulsory admission to hospital. In forensic psychiatry the definition of mental illness (by the law) is particularly important in the assessment of issues such as criminal responsibility.
Diverse discussion of the concepts of mental illness can be found in Lazare (1973), Kendell (1975) and Häfner (1987).
Definitions of mental illness
Many attempts have been made to define mental illness, none of which is satisfactory or uniformly accepted. A common approach is to examine the concept of illness in general medicine and to identify any analogies with mental illness. In general medicine there are five types of definition:
• Absence of health. This approach changes the emphasis of the problem but does not solve it, because health is even more difficult to define. The World Health Organization, for example, defined health as ‘a state of complete physical, mental and social well-being, and not merely the absence of disease or infirmity.’ As Lewis (1953) rightly commented, ‘a definition could hardly be more comprehensive than that, or more meaningless.’ Many other definitions of health have been proposed, all equally unsatisfactory.
• Disease is what doctors treat. This definition has the attraction of simplicity, but does not really address the issue. The notion that disease is what doctors can treat has somewhat more merit, since there is evidence that as a medical treatment for a condition becomes available, it becomes more likely that the condition will be regarded as a disease (Campbell et al., 1979).
• Biological disadvantage. The idea of defining disease in terms of biological disadvantage was proposed by Scadding (1967), and is the most extreme biomedical view of disease. Scadding never defined biological disadvantage, but the term has been used in psychiatry to include decreased fertility (reproductive fitness) and increased mortality. Viewing disease in terms of ‘evolutionary disadvantage’ is a similar concept (Wakefield, 1992).
• Pathological process. Some extreme theorists, such as Szasz (1960), take the view that illness can be defined only in terms of physical pathology. Since most mental disorders do not have demonstrable physical pathology, according to this view they are not illnesses. Szasz takes the further step of asserting that most mental disorders are therefore not the province of doctors. This kind of argument can be sustained only by taking an extremely narrow view of pathology. It is also arbitrary, based on current knowledge, and is increasingly incompatible with the evidence of a genetic and neurobiological basis to the major psychiatric disorders, and their associated morbidity and mortality.
• Presence of suffering. This approach has some practical value because it defines a group of people who are likely to consult doctors. A disadvantage is that the term cannot be applied to everyone who would usually be regarded as ill in everyday terms. For example, patients with mania may feel unusually well and may not experience suffering, although most people would regard them as mentally ill.
Biomedical versus social concepts
The above concepts may be divided into those that view mental illnesses in purely biomedical terms, and those that consider them to be social constructs or value judgements. This debate is still ongoing, and depends in part on one’s opinion about their aetiology, but it is now generally accepted that value judgements play a part in all diagnoses, even if the disorders themselves are considered from a biomedical perspective (Fulford, 1989). For example, beliefs and emotions are central to most psychiatric disorders, yet it is a value judgement as to whether a given belief or emotion is ‘good’ or ‘bad’, and therefore what, if any, diagnostic significance it has. Would we use ‘good’ or ‘bad’ to decide whether a belief was ‘illness’? Would ‘normal’ or abnormal’ be better?
Impairment, disability, and handicap
It is useful in medicine, and particularly in psychiatry, to describe and classify the consequences of a disorder. This approach is related to the concept of disease as involving dysfunction (Wakefield, 1992), as incorporated into the definitions of mental disorder used in ICD-10 and DSM-IV (see below). Three related terms, derived from medical sociology and social psychology, are used to describe the harmful consequences of a disorder:
• Impairment refers to a pathological defect—for example, hemiparesis after a stroke.
• Disability is the limitation of physical or psychological function that arises from an impairment—for example, difficulties with self-care that are caused by the hemiparesis.
• Handicap refers to the resulting social dysfunction—for example, being unable to work because of the hemiparesis.
Incapacity may be seen as another harmful consequence of illness, although the term usually refers in a legal sense to the effect that illness has on one’s competence to make treatment decisions (see Chapter 4).
Diagnoses, diseases, and disorders
The term ‘diagnosis’ has two somewhat different meanings. It has the general meaning of ‘telling one thing apart from another’, but in medicine it has also acquired a more specific meaning of ‘knowing the underlying cause’ of the symptoms and signs about which the patient is complaining. Underlying causes are expressed in quite different terms from the symptoms. For example, the symptoms of acute appendicitis are quite different from the idea that will form in the mind of the doctor that the appendix is inflamed and producing peritoneal irritation. To be able to make a diagnosis of this type is, of course, satisfying for the doctor and very useful for the patient, since it immediately suggests what investigations and treatment are needed. Its clear utility also makes redundant most theoretical or philosophical concerns about classification. Unfortunately, for most psychiatric patients it is rarely possible to arrive at this type of diagnosis, the only exception to this being, by definition, ‘organic’ psychiatric disorders (see below).
The lack of clear disease categories, in a medical sense, has led to the use of the more general term ‘disorder’ in psychiatry. The definition of a disorder in ICD-10 is:
a clinically recognizable set of symptoms or behavior associated in most cases with distress and with interference with personal functions. Social deviance or conflict alone, without personal dysfunction, should not be included in mental disorder as defined here.
The DSM-IV definition is longer but similar:
… a clinically significant behavioral or psychological syndrome or pattern that occurs in an individual and that is associated with present distress (a painful symptom) or disability (impairment of one or more important areas of functioning) or with a significantly increased risk of suffering death, pain, disability, or an important loss of freedom. In addition, this syndrome or pattern must not be merely an expectable response to a particular event, e.g. the death of a loved one. Whatever its original cause, it must currently be considered a manifestation of a behavioral, psychological, or biological dysfunction in the individual. Neither deviant behavior (e.g. political, religious, or sexual) nor conflicts that are primarily between the individual and society are mental disorders unless the deviance or conflict is a symptom of a dysfunction in the individual, as described above.
Despite the similarity, there is one important and easily overlooked difference between the two definitions. ‘Interference with personal functions’ in ICD-10 refers only to such things as personal care and one’s immediate environment, and does not extend to interference with work and other social roles. In DSM-IV, ‘impairment of one or more important areas of functioning’ refers to all types of functioning.
Both definitions illustrate that most psychiatric disorders are based not upon theoretical concepts or presumptions about aetiology, but upon recognizable clusters of symptoms and behaviours. This reliance also explains much of the debate about the reliability and validity of the categories being classified, as will be discussed later in this chapter.
Criticisms of classification
Despite its advantages, the use of psychiatric classification is on occasion criticized as being inappropriate or even harmful. In part, such criticisms arise from the various controversies outlined above: if the concept of mental disorder is itself disputed, then so will any classifications thereof. These criticisms were most prevalent and trenchant at the height of the ‘anti-psychiatry’ movement in the 1950s and 1960s. Three main criticisms were made.
• Allocating patients to a diagnostic category distracts from the understanding of their unique personal difficulties. However, the good clinician always considers and takes into account a patient’s unique experiences, qualities, and circumstances when making diagnoses, not least because this contextual information often affects treatment and prognosis.
• Allocating a person to a diagnostic category is simply to label deviant behaviour as illness. Some sociologists have argued that such labelling serves only to increase the person’s difficulties. There can be no doubt that terms such as epilepsy or schizophrenia attract stigma (see below), but this does not lessen the reality of disorders that cause suffering and require treatment. However, it does emphasize that mental illness should not be defined solely in terms of socially deviant behaviour. The presence of the former must be separately established based on the psychiatric history and mental state examination. Moreover, if mental illness is inferred from socially deviant behaviour alone, political abuse may result (see below). A further reason for excluding purely social criteria from the definition of mental illness, and from diagnostic criteria, is that many behaviours are appraised differently in different countries and at different times. For example, homosexuality was considered to be a mental disorder until the 1970s.
• Individuals do not fit neatly into the available categories. Although it is not feasible to classify a minority of disorders (or patients), this is not a reason for abandoning classification for the majority.
It is certainly true that at times classification has been inappropriately used as part of a broader abuse of psychiatry, whether for political, financial, or other reasons. A serious example occurred in the former Soviet Union, where some psychiatrists colluded with the government in being willing to classify political dissent as evidence of mental illness.
Although such abuses are fortunately rare, they are an extreme illustration of the fact that making diagnoses and classifying patients are not neutral acts, but carry significant ethical and other implications (see Chapter 4). One of these implications concerns stigma, which remains a serious problem for patients with mental health problems, even if one does not accept the rest of the sociological thesis outlined above (Thornicroft, 2006). The issue of stigma in psychiatry is discussed in Box 2.1. It is incumbent on all those who use psychiatric diagnostic terms that they do so appropriately, paying due attention to their correct usage and purpose, and the context in which they are being applied. Doing so can help to reduce the problem of stigmatization, but cannot solve it, because stigma results from many other factors too, as noted in Box 2.1.
Although these criticisms are important, they are arguments only against the improper use of classification. Disorders and their harmful consequences cannot be made to disappear by ceasing to give names to them. The ICD-10 and DSM-IV approaches, which will be discussed later, emphasize that classification is a means of communication and a guide to decision making, but acknowledge that they are provisional and imperfect schemes. Clinicians and researchers must use their experience and common sense, as well as being guided by the descriptions of the disorders that make up the classifications.
Other criticisms of classification in psychiatry are mostly concerned with the specifics rather than the principles—for example, whether a specific diagnostic category is reliable and valid. These issues are introduced later in this chapter, and at various points throughout the book.
The history of classification
Efforts to classify abnormal mental states have occurred since antiquity. One reason for including a chronological perspective here is that contemporary psychiatric classifications are, in part, a ‘hybrid’ of various historical themes and opinions.
The early Greek medical writings contained descriptions of different manifestations of mental disorder—for example, excitement, depression, confusion, and memory loss. This simple classification was adopted by Roman medicine and developed by the Greek physician Galen, whose system of classification remained in use until the eighteenth century.
Interest in the classification of natural phenomena developed in the eighteenth century, partly stimulated by the publication of a classification of plants by Linnaeus, a medically qualified professor of botany who also devised a less well-known classification of diseases in which one major class was mental disorders. Many classifications were proposed, notably one published in 1772 by William Cullen, a Scottish physician. He grouped mental disorders together, apart from delirium, which he classified with febrile conditions. According to his scheme, mental disorders were part of a broad class of ‘neuroses’, a term that he used to denote diseases which affect the nervous system (Hunter and MacAlpine, 1963). Cullen’s classification contained an aetiological principle—that mental illnesses were disorders of the nervous system—as well as a descriptive principle for distinguishing individual clinical syndromes within the neuroses. In Cullen’s usage, the term neurosis covered the whole range of mental disorders as well as many neurological conditions. The modern narrower usage developed later (see below).
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