These concepts have existed in the medical and sociological literature for many years, and are best regarded as useful but inexact concepts that refer to different but related aspects of the person affected, namely pathology (disease), personal experience (illness), and social consequences (sickness), respectively. (8) They are useful as a trio because they serve as a reminder that all three levels should be considered in a clinical assessment, even though for different patients they will vary greatly in relative importance. There are no simple answers to questions about how they are best defined and how exactly they are related to each other, but time spent on these issues is not wasted because they reflect quite naturally some of the different interests and priorities of the different health professions (and are therefore often the basis of different viewpoints put forward by various members of a multidisciplinary team).
Another reason for being familiar with these concepts is that in legal and administrative settings, simple and categorical pronouncements about the presence of mental illness or mental disease and their causes and effects may be required whatever the medical viewpoint might be about the complexity of these concepts.
Clinicians of any medical discipline know from everyday experience that the disease-illness-sickness model does not always represent the simple sequence of causation that may appear to be obvious at first sight to a non-medical professional. Although disease usually causes the patient to feel ill and the state of illness then usually interferes with many personal and social activities, this sequence is by no means always present. Potentially serious physical, biochemical, or physiological abnormalities (disease) may be discovered in surveys of apparently healthy persons before any symptoms, distress, or interference with personal activities (illness) have developed, and some patients may have either or both of illness and sickness (interference with social activities) without any detectable disease.
A number of sociologists, anthropologists, and philosophers have joined psychiatrists in trying to define mental illness and mental health, but without achieving much clarification. Aubrey Lewis(9) and Barbara Wootton, (19, although writing from the different contexts of clinical psychiatry and sociology, both arrived at the conclusion that neither mental illness nor mental health could be given precise definitions, although they are useful terms in everyday language (and the same applies equally to physical health and physical illness).
More positive conclusions have resulted from attempts to define disease, in that Scadding (a general physician) has suggested that it should be defined as an abnormality of structure or function that results in 'a biological disadvantage'. (!.1,12) This seems reasonable if one is dealing only with conditions that have a clear physical basis, but if applied in psychiatry it implies that, for instance, behaviours such as homosexuality that reduce the likelihood of reproduction would have to be regarded as diseases alongside infections, carcinoma, and suchlike. This seems to be stretching a traditional concept too far, and different approaches clearly need to be explored.
One way forward is to accept that simple definitions and concepts encompassed by one word cannot cope with complicated ideas such as disease or health, and to take care to differentiate between definitions of these as concepts in their own right, and attempts to develop models of medical practice. The debate noted above refers to concepts of health, disease, and disorder, and it has been continued more recently with respect to psychiatry in two quite extensive reviews, in terms of the types of concepts(l3> and of their possible contents. (14> What follows below is better regarded as about models of medical practice, and two points are suggested as a basis for the discussion. First, more than one dimension or aspect of the person affected always needs to be included in descriptions of health status. Second, models of medical practice and thinking do not necessarily have to start with the assumption that physical abnormalities (diseases) are the basic concept from which all others are derived.
Regarding the first point (of more than one aspect or dimension), soon after the contribution of Susser and Watson (8) noted above, Eisenberg, a psychiatrist with social and anthropological interests,(15) made a plea for all doctors, but particularly psychiatrists, to recognize the importance of appropriate illness behaviours in addition to giving the necessary attention to the diagnoses and treatment of serious and dangerous disorders. (16) He gave special emphasis to the need to minimize problems that may arise from discrepancies between disease as it is conceptualized by the physician and illness as it is experienced by the patient: 'when physicians dismiss illness because ascertainable disease is absent, they fail to meet their socially assigned responsibilities'. A similar model with a more overtly three-dimensional structure usually referred to as 'bio-psycho-social' has also been described by Engel. (17> More recently, Susser(18) has pointed out the close relationships between the disease-illness-sickness trio and the parallel classifications of impairment, disability, and handicap developed by the World Health Organization (WHO)/1..9' Historically, all these can be regarded as variations on and explicit developments of a theme that has been accepted implicitly by generations of psychiatrists influenced by the 'psychobiology' of Adolf Meyer and his many distinguished pupils, manifest in the importance given to the construction of the traditional clinical formulation.
The second point, to do with the disease level not being the best starting point for conceptual models of medical practice, is of more recent and specifically psychiatric origin. Both Kraupl Taylor(29 and, more recently, Fulford(21) give detailed arguments for the conclusion that the illness experience of the patient is the most satisfactory starting point from which to develop a model of medical practice. Taylor presents his case as a matter of logic, and Fulford works through lengthy philosophical and ethical justifications. This new viewpoint has the virtue of starting with the encounter between patient and doctor, which has the strength of being one of the few things that is common to all types of clinical practice. In Taylor's terms, by describing symptoms and distress the patient arouses 'therapeutic concern' in the doctor and so first establishes 'patienthood'. Whether or not a diagnosis is reached or a disease is later found to be present, and whether or not the social activities of the patient are also interfered with, are other issues of great importance, but they do not diminish the primary importance of the first interaction; in this, both patient and doctor play their appropriate roles according to their personal, social, cultural, and scientific backgrounds.
If medical training and practice are guided by this model, there is no interference with the essential obligation of the doctor to identify and treat any serious disease that may be present. However, a parallel obligation to satisfy the patient and family that the illness (comprising complaints and distress) and the sickness (interference with activities) have also been recognized and will be given attention, is equally clear.
How to answer questions by the patient and family about whether the patient has a mental illness or not, and what this implies, needs careful discussion. Within a multidisciplinary team it is usually best for the team to reach early agreement on a particular way of describing the patient's illness so that conflicting statements will not be made inadvertently by different members if asked about it. This is because the patient or family may expect this type of statement, and not because distinctions between, for instance, mental illness and physical illness, or between nervous illness and emotional upset, are regarded as fundamental from a psychiatric viewpoint. This difficult issue will be made easier if something about the patient's ideas about the nature and implications of terms such as 'mental illness' and 'nervous breakdown' is always included as part of the initial assessment information. Similarly, all members of the team need to be familiar with the concept of illness behaviour and the way this is determined by cultural influences(22) (see Cha.p.te.r...,2 6.:.2.).
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