Epidemiological aspects of rheumatic diseases and their relevance to clinicians

1 Epidemiological aspects of rheumatic diseases and their relevance to clinicians P H I L I P H . N. W O O D

The word epidemiology derives from the stems 'epi', meaning upon, and 'dem', meaning the people (as in democracy). The literal meaning of the term is therefore the study of what oppresses the people. More formally, epidemiology is the branch of medical science concerned with studying the health of human communities. Insights derived from this domain impinge on the everyday concerns of rheumatologists in three complementary ways. CLINICAL IMPLICATIONS The most basic clinical skill consists of eliciting evidence relevant to a patient's particular problem. The experienced clinician is selective in how he or she goes about this task, having already formed tentative diagnostic hypotheses on the basis of the presenting complaint. Even at this level recourse is made to epidemiological insights, though these are often unappreciated, in a manner reminiscent of the surprise of Moli~re's 'Bourgeois Gentilhomme' on being made aware that he spoke in prose. It is therefore useful to examine what contributions epidemiology makes. In their work clinicians draw on two major resources of knowledge. The first is what is commonly regarded as the foundation of clinical acumen, and will be indicated here rather sketchily. Essentially qualitative in nature, it consists of a synthesis of personal experience with individual patients complemented by what has been gleaned from other sources, especially the literature. Such knowledge is integrated into a series of modal profiles, characterizing each specific rheumatic disorder. The pattern of a presenting complaint is then almost unconsciously matched against this repertoire of profiles so as to yield preliminary conclusions about the nature of the underlying problem. The archetype of such pattern recognition is a 'spot diagnosis'. Any diagnostic hypothesis needs to be tested and for this purpose the other, more quantitative, resource is also called on. Concerned with group phenomena and collective experience it is basically epidemiological, even though the pertinent data may well have been established by clinicians Bailli~re's ClinicalRheumatology--Vol. 1, No. 3, December 1987

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rather than by epidemiologists. The same resource additionally serves for other aspects of clinical practice, as follows: 1. 2. 3. 4.

Knowledge of the characteristics of occurrence of the various rheumatic disorders (including their frequency) provides a background of likely diagnoses against which tentative conclusions may be set. Comparative information on similar conditions indicates probabilities for differential diagnosis, thus directing attention to features with discriminatory potential which can then be sought. Awareness of natural history, outcomes, and associated attributes (such as age, gender and social status) guides the development of a prognosis. Finally, appreciation of specific impairments and features such as the family history enlightens individual patient management.

It is perhaps helpful if the scientific component in these processes of assessment is made explicit, a topic pursued in greater detail elsewhere (Wood, 1986a). Medicine is often regarded as being born of a marriage between the scientific and an element of indefinable artistry, but unfortunately people tend to get the roles of bride and groom confused. As Medawar (1969) remarked, 'it is the unbiased observation, the apparatus, the ritual of fact-finding and the inductive mumbo-jumbo that the clinician thinks of as "scientific", and the other element, intuitive and logically unscripted, which he thinks of as a creative art'. He went on to say: 'the purpose of scientific enquiry is not to compile an inventory of factual i n f o r m a t i o n . . . We should think of it rather as a logically articulated structure of justifiable beliefs about nature'. In this light one can see that the process of diagnosis is concerned with justifiable beliefs, and that of differential diagnosis with hypothesis testing. For these purposes knowledge of how to assess the function of every joint in the body is essential. However, rheumatologists tend to be more scientific than non-specialists, not because they carry out an exhaustive examination of all these structures, but because they know when it is necessary to look at particular joints with special care in order to expose tentative ideas to falsification. Analogously, hypotheses about the nature of underlying morbid anatomical changes and about prognosis are tested against the course of the illness, and management is adjusted appropriately.

Diagnosis As the range of rheumatic disorders exceeds two hundred in number, it is obviously impossible to offer estimates of frequency for each specific condition within the confines of this short chapter. Readers wanting greater detail will have to look elsewhere (e.g. Wood and Badley, 1986). In the present context all that can be undertaken is to block in the canvas with broad brush strokes. During the course of a year about 40% of the population develop some form of rheumatic complaint; in the UK that means as many as twenty million people are affected. Many of these experiences are perhaps no more than passing twinges, a minor inconvenience, but a similar proportion--

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40%--do consult their family doctor; in the UK this represents eight million individuals making contact with primary care services. Such consultations are initiated by 15% of all persons registered with any particular general practitioner though, because patients frequently harbour more than one condition, in aggregate 23% of patients seen by GPs suffer from some sort of rheumatic condition. These observations highlight two areas to which rheumatology has paid insufficient attention--the need to develop material for guidance of the public at large in regard to self-management of more 'trivial' rheumatic experiences, and the need for reorientation in regard to the range of conditions about which non-specialist physicians are taught in formal educational opportunities. The latter point is emphasized by the crude case mix encountered in general practice. Figure 1 shows that there are five major divisions, each of similar magnitude. Rheumatologists tend to devote most of their clinical effort to two of these categories--articular disorders, designated by the colloquial term 'arthritis', and the residual group of conditions, 'other', which includes the connective tissue diseases and a variety of other musculoskeletal disorders, such as Paget's disease of bone. The three other categories--back troubles, non-articular rheumatism and soft-tissue injury--tend to be less well understood and generally attract less interest, although many opportunities for quicker relief at the primary care level get neglected as a result. These three categories also span most of what Hadler (1977) referred to as 'industrial rheumatology'; his focus on extraneous determinants of these experiences was welcome, but the challenge appears to have been largely neglected. Other frequency indicators for these five categories are shown in Table 1, expressed as rates per thousand population at risk. The overall rheumatic "--.

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Trauma Figure 1. Crude case mix in patients with rheumatic problems presenting to a general practitioner. From Wood and Badley (1985b), derived from OPCS (1974).

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sickness incapacity rate is about one-third that quoted for consultations with GPs. This arises because incapacity data for males only are shown in Table 1; the elderly are excluded from this form of social security benefit, and information on insured women is not representative of experience in this sex. In recent years rheumatic disorders have mirrored changes in all causes of sickness, showing a 25-30% fall in new spells of incapacity accompanied, contrarily, by a 3% rise in days lost from work; the latter now total more than sixty five million rheumatic days during a year. These alterations are more likely to reflect changes in other social experiences, notably unemployment levels, than 'real' changes in the frequency of rheumatic disorders. Referral by GPs for a specialist opinion is reflected by new attendances at rheumatology outpatient clinics. The current rate--4.2 patients per thousand--represents a 14% increase over the last 8 years (Khaligh and Wood, 1986); unfortunately diagnostic details are not available in such data, a limitation that also applies to the new orthopaedic attendances of 25.5 patients per thousand. Only a minority are likely to need admission to hospital for a rheumatic disorder, the proportions being one in seven of those unfit for work, or one in 20 of those consulting a GP. Such individuals now account for 7.3% of all non-maternity and non-psychiatric admissions to hospital, representing a 63% rise over the last 12 years. In some 18% of admissions for disorders of the musculoskeletal system, an arthroplasty will be carried out. Two importal~t lessons may be learned from the information presented so far. The first relates to selective perception on the part of physicians engaged at any level of health care activity, due to the fact that the patients seen are not representative of the full spectrum of rheumatic affliction. This means that personal experience can have only limited application when seeking to understand the occurrence of rheumatic disorders, which has implications for how evidence is interpreted (to be considered shortly). The second lesson concerns the planning and organization of health services, which will be examined in the third section of this chapter. At this juncture it should be noted that selectivity in experience is again relevant; the bulk of rheumatological care is in fact carried out by GPs, and even in hospital orthopaedic colleagues bear a larger part of the rheumatological burden, not least because they are more numerous. Criteria

Influences on diagnosis have so far been indicated largely in relation to practical problem-solving for an individual patient. Epidemiological insights impinge in a different way when one wishes to collect experience together and draw conclusions from what has been observed in a group of patients (i.e. an essentially epidemiological exercise). The homogeneity of the sample is a key property, and this rests on the establishment that patients are afflicted similarly. Most rheumatic disorders lack a hallmark--a uniquely defining characteristic, the presence or absence of which can establish whether someone is affected. We are therefore driven to identification on the basis of a cluster

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concept for clinical and related features, and diagnostic criteria have been developed as a means of coping with this difficulty. It may still be necess.ary to stress that such criteria have not been formulated to assist in clinical diagnosis in individual patients, but only to promote homogeneity in clinical studies of groups of patients. Early attempts with criteria were reviewed at international symposia (Bennett and Wood, 1968). Whilst the New York criteria for rheumatoid arthritis (RA) appear to have largely survived the test of time, those for ankylosing spondylitis have proved more problematic (Moll, 1980). Almost paradoxically, the least successful applications have been with population studies. The American Rheumatism Association (ARA) has been particularly active in the field over the last 10-15 years, with work on most of the major rheumatic disorders (Hunder, 1982). However, all the investment on developing criteria has generally neglected two serious problems. The first relates to the fact that criteria tend to depict a modal profile, to which conformity is then sought. Logically, though, the need is to establish when an array of clinical features exceeds a threshold, i.e. which features, and with what severity, are sufficient to allow the boundary for decision to be crossed. That existing criteria in fact resemble a straw man is scarcely demonstrated by paper patients (Kirwan et al, 1983a), though vagaries of judgement compound difficulties in their application. The scaling of supposed probabilities in the original A R A criteria for RA (possible, probable, definite and classical) might appear to cope with the logical criticism, were it not for the fact that in actuality it represents a grading of severity as much as of probability of diagnosis, which is to confound two distinct problems. Moreover, the arithmetic remains rather suspect because of undue weighting such as is inherent in the triad of one joint, a second joint and symmetry, by which means someone with the commonest of musculoskeletal problems--pain and swelling in the knees-would in fact score as probable RA. For this reason it is best to confine attention to definite and classical cases in clinical studies. The second problem is that purposes vary, and criteria need to be modified in different contexts. For example, population surveys are concerned primarily with the separation of disease from non-disease, and exclusions are almost impossible to apply systematically; clinical studies, on the other hand, are more exercised by discrimination between similar disorders, when exclusions come to play a critical role. Criteria probably need to be more stringent for immunogenetic studies than they do for descriptive reviews of clinical experience. The net effect is that differences in both the emphasis and tolerance of criteria are to be anticipated (Wood, 1983). Moreover, although core components may be preserved, any adaptations of standard criteria do require reassessment of the reliability and validity of individual and combined criteria in the new context. Criteria represent a preliminary approach to measurement, by making standards of judgement explicit. The homogeneity they promote is as necessary at the end as at the beginning. So criteria are needed for disease remission (Pinals et al, 1981) and for outcome (Kirwan et al, 1983b), though work in these areas is still in its infancy. Before measures are taken off the

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shelf and used it is essential to appraise their logical construction and consider whether this is appropriate to the problem in hand. For example, how much does a bias towards lower limb activities in the Stanford Health Assessment Questionnaire (Fries et al, 1980) distort assessment of outcome when hand involvement is predominant in RA?

Prognosis Unfortunately, and with the notable exception of arthritis in children, there is a dearth of good evidence on the natural history of different rheumatic disorders. This is not unrelated to the fact that such studies for a long time do not generate papers which can be presented at meetings, a point of some relevance in regard to research funding mechanisms. Attributes such as age, gender and social status influence the course of disease as well as its occurrence in the first place. The effects are predominantly social and cultural, and will be discussed in Chapter 2. Inadequate clinical evidence requires further consideration. Variations in the course of rheumatoid arthritis were documented by Short et al (1957). Thirty years later we are still uncertain whether these variations represent different manifestations of a single disease entity or whether we are failing to discriminate between distinct 'variants', and so far available markers have shed little light on the problem (Papiha et al, 1986). The difficulty stems from the unsatisfactory basis for identifying the 'disease', related to lack of a hallmark (referred to previously). Uncertainty extends even to frequency estimates. For instance, are self-limiting forms of polyarthritis [such as Lawrence and Bennett (1960) referred to as benign polyarthritis] distinct or do they form part of the spectrum of RA? The potential implications for aetiological understanding and for rational selection of often dangerous therapies could be considerable were these doubts resolved. A second example is offered by arthrosis. We do not have a sound basis for assessing whether progression of the condition is likely to be uniform or, if not, which characteristics should alert us to accelerated deterioration. Judgements on the appropriateness o f and optimum timing for joint replacement would be influenced by such knowledge. The political case for increased surgical resources would be strengthened were we able to demonstrate that delays not only left people suffering unacceptably but also resulted in irremediable degeneration, but the necessary evaluation has not been carried out. The only pointers we have in these directions concern the still insufficiently appreciated distinction between different types of hip disease (Kellgren and Lawrence, 1961; Marks et al, 1979). This emphasizes another point, that too much of our thought on arthrosis is based on regarding it as a universal phenomenon, with consequent neglect of important differences between the various sites of attack. Even more generally, what is often neglected is that sampling raises problems not just in regard to sample size but also in relation to selection of the joints included for study. For instance, multiple joint involvement in arthrosis tends to be underestimated because other joints are

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not examined with care. Systemic lupus erythematosus (SLE) provides a third example. There is an impression, similar to that developed in regard to multiple sclerosis, that outlook in SLE is far from being as gloomy as was thought formerly. We have examined the evidence in some detail elsewhere (Wood and Badley, 1986). Briefly, an increase in ascertainment has enlarged the pool of identified cases, extending awareness of milder forms. It has been suggested that incidence is increasing, which is not easy to evaluate if the disease spectrum has been expanded, and reductions in case fatality rates are difficult to relate to improvements in therapy if the nature of cases being treated has altered. Certainly it is important to appreciate the broad spectrum of disease involvement, but if the baseline has changed meanwhile then it becomes more difficult to determine whether associated changes are derivative or causal. The disabling effects, particularly of articular disorders, must be self evident. Arthritis and rheumatism form the biggest single class of physically disabling conditions, being responsible for more than one-third of the totals for both impairment and severe disability; in the elderly the proportion is greater--about one-half. Overall more than a million people in the UK are impaired by rheumatic disorders, and more than one-fifth of these are at least severely disabled. Given these effects, two problems emerge. The first concerns how disablement is assessed, one of the more specifically clinical aspects of which relates to the degree of movement possible in the joints (Wright, 1982). The second is the extent to which clinicians acknowledge responsibility for endeavouring to mitigate disablement, which calls for the attitudes and techniques associated with rehabilitation (de B16court et al, 1981). The least favourable outcome is death. Although most rheumatic disorders are not generally regarded as life-threatening, they nevertheless give rise to a measurable mortality, largely attributable to complications. In the UK just over 1% of all deaths during a year are related to rheumatic disorders, a proportion that has fallen by almost 40% over the last 12 years. The major change has resulted from a decline in deaths attributed to rheumatic fever and rheumatic heart disease, which 12 years ago were responsible for 70% of rheumatological mortality and which now contribute only 47% of this mortality. The big problem with most mortality studies is that they are based on people attending hospital. Such patients tend to be the more marked and severe cases, so that an unduly gloomy view of prognosis may be obtained. To generate a representative expression of outcome it is necessary for a comprehensive range of severity to be included (as noted above in regard to SLE), even though this usually returns one to all the uncertainties associated with making a reliable diagnosis in milder 'cases'. A practical aspect of this problem is that assurance companies establish their calculations on life-expectancy on reported studies, despite the fact that these may not reflect the full spectrum of involvement. Computations of risks may therefore tend to exaggerate hazards, a point clinical investigators ought to bear in mind when deciding how to present their results; infelicitous

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wording may lead to unwarrantably unfavourable predictions being applied to the risks being estimated. Patients seeking insurance should be advised not to contact individual companies direct as this may lead to them being placed on what is termed the 'Association Register', which jeopardizes chances of obtaining cover from a competitor (Tomenson et al, 1983). Instead consultation should be undertaken with a broker or a voluntary organization concerned with the interests of persons afflicted similarly.

Management The spectrum of involvement has a different dimension, one which can indicate the likelihood of specific impairments being present in any individual patient. An obvious example is the interference with sexual activity encountered with arthritis of the hip (Currey, 1970). More generally, though, it should be appreciated that disabilities and handicaps represent personal problems much more sensitively than can diagnoses or impairments, even though for operational purposes in relation to medical care the latter are naturally the major focus of concern. It is also instructive to take account of the application of various elements in a clinical database. For example, a family history is often thought of more for its possible contribution to diagnosis, although only rarely is it of much help for this purpose (Wood and Badley, 1986). The greatest clinical value of a positive family history for a rheumatic disease is in arousing one to the need for anticipation. An individual is likely to want to ask, 'Am I going to get like my mother?', and a need for reassurance should be foreseen. Similarly, the wish for counselling may not be made explicit. UNDERSTANDING AETIOLOGY In following a path towards making a diagnosis, and especially in then assessing the significance of a given diagnosis in a particular patient insofar as this will influence management, the clinician draws on current disease concepts and on understanding of how particular forms of ill-health may arise and unfold. This is where one enters the realm of biomedical science, and underpinning such exercises is the discipline of hermeneutics---how evidence is interpreted. Although it may not be immediately apparent, the same cautions apply equally to the more clinical exercise of assessing symptoms and signs elicited from an individual patient; this should be evident from what has been stated already when identifying the scientific component of clinical practice. Observations on pathological processes and possible aetiological determinants have to be reconciled with what is known about the specifics of occurrence of a particular disease. A systematic appraisal of such characteristics, such as is attempted in an epidemiological review, therefore establishes the context in which biomedical insights have to be assimilated. A framework of this type helps to expose ideas to refutation because viable hypotheses must be capable of taking account of all the features of disease

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occurrence. Of particular note are inconvenient facts, of which Charles Darwin (1958) wrote: 'I had, also, during many years, followed a golden rule, namely, that whenever a published fact, a new observationor thought came acrossme, whichwas opposed to my general results, to make a memorandumof it without fail and at once; for I had found by experiencethat such facts and thoughts were far more apt to escape from the memory than favourable ones.'

Validity The background to biomedical activity may be established by drawing on insights from systems theory, such as Black (1984) discussed when referring to levels of biological organization. Biomedical p h e n o m e n a can be arranged in a hierarchy, portrayed in Table 2. The scheme extends from subcellular phenomena, through tissues and organs, to individuals and then to their immediate networks and ultimately to the societies of which they form a part. Validity and meaning have to be approached in relation to the level of organization being considered, recognizing hazards of triviality at one extreme and meaningless generality at the other.

Table 2. The hierarchy of levels of biologicalorganization. Level of biologicalorganization Hazard in research Society (including the ecologicalcomplex) Meaninglessgenerality Family and networks The individual (clinical practice) Tissues and organs Cells SubceUular phenomena Triviality From Black (1984). At lower levels in the hierarchy one can perturb conditions influencing a system selectively, on which is based the concept of controlled observations. At higher levels, concerned with individuals of the human species and with populations of such individuals, one is generally denied the luxury of this simple means of ensuring validity. That doesn't make such enquiries less scientific, even though c o m m o n parlance may often appear to suggest otherwise. It just means that the validity problem has to be confronted in different ways, and of these triangulation (seeking other sources of evidence relevant to the problem) is probably the most important, often offering relatively simple means for falsification. The principle has wider implications because, the aim usually being to generalize, the relevance or applicability of observations and hypotheses developed at one level ought to be considered against higher levels in the scheme of things. Such an approach affords another and quite powerful means for refutation, and it is on such grounds that quasi-unifactorial models of aetiology generally fail (Wood and Badley, 1985a). Lack of precision in the formulation of many of today's fascinating notions can be a problem. For instance, the nature of relationships between microbes and humans is more variable now that these are no longer constrained by Koch's

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postulates (the Epstein-Barr virus offers an obvious example). It is only when the ideas, and particularly their implications, are defined more exactly that the notions can be examined at other levels of biological organization (Wood, 1978). As the concept of triangulation may be unfamiliar, an example of other means of acquiring information that has a bearing on a specific question will be illustrated. In 1961, Lawrence developed a measure of the frequency of R A from population studies. We attempted to estimate prevalence by a different route. Long-term follow-up studies of patients with the disease (Reah et al, 1971) provided an indication both of the frequency of mention of RA on the death certificates of decedent individuals and of the average duration of disease from diagnosis in a sample of affected persons. Juxtaposing these with reported mortality from R A for the whole of Great Britain and applying all this information in the fundamental theorem of epidemiology (prevalence = incidence • duration) generated an independent prevalence estimate that was, encouragingly, of the same order as that developed by Lawrence. The practical implications of these considerations lead one to concentrate much more on the search for inconsistencies in evidence, and particularly to take account of dimensions that may have been neglected. The results of such appraisals often lead to challenge of dearly held notions. An example is provided by the manner in which, 30 years ago, people unwittingly entertained two mutually contradictory notions in regard to gout. This malady was regarded then as an inborn error of metabolism, without fully appreciating that such disorders are biologically disadvantageous and are transmitted as recessive or sex-linked traits. Such a mechanism is incompatible with interpreting familial occurrence of the disorder as manifesting the pattern of a Mendelian dominant character, and yet this was what pedigree studies appeared to indicate. Of more contemporary concern is the manner in which interpretation of m a n y biological epiphenomena is retarded by the poverty of associated clinical study, with the related failure to make important nosological distinctions. Observed frequencies of occurrence of various human leucocyte antigens (HLA) that are intermediate in magnitude illustrate the point, and the difficulty in interpreting such findings is neglected. For example, reports emerged of an approximately 20% frequency of each of rheumatoid factor, antinuclear antibodies (ANA) and the HLA-B27 antigen in groups of children with arthritis. These were not easy to assimilate until a natural history study provided the key. Once different subtypes of juvenile arthritis had been established by clinical follow-up (Ansell and Wood, 1976) the associations fell into place and could be seen to have much greater biological and discriminatory significance. Protection f r o m error

How do you protect against such difficulties? Starting with clinical studies, seven deadly scientific sins have been identified (Morgan, 1986): insufficient information, inadequate sample size, a biased sample, confounding factors, vague end-points, straying from the hypothesis, and poor control of

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numbers (for further amplification readers are directed to the source, a brief editorial). The most important of these considerations are encapsulated in the three questions an epidemiologist customarily asks of such studies: Who is there? How did they get there? Who got away? (Wood, 1983). Although it may seem paradoxical, the underlying problem is that one too often encounters 'the old story of carefully thought out means towards carelessly thought out ends' (NoreU, 1984). One difficulty is that the role of science in clinical research is as misunderstood as it is in clinical practice. As Feinstein (1967) indicated, 'The clinician has been taught to believe that basic clinical science includes all biology except the clinical treatment of patients; that basic clinical science comes from manipulating a dog, fish, pigeon or cell, but not from talking to a person; and that basic clinical science is a birthright granted in the laboratory and lost at the bedside or in the community'. He then went on to conclude: 'The clinician has an ancient and honourable heritage, a tradition of enlightened thought and achievement, and a domain whose humanistic and scientific complexity can challenge the most demanding intellect or spirit, at levels of fundamental enquiry. He need not look for basic science elsewhere. He can make his own'. An example of rigour of the type needed is evident in criteria suggested by Esdaile and Horwitz (1986) for evaluation of validity in two common types of observational'study: cohort and case-comparison designs. They demonstrate their thesis by an appraisal of evidence on whether oral contraceptive usage may reduce the risk of developing rheumatoid arthritis, and conclude that the issue remains unresolved and further research is required. This interpretation is based on identification of unfulfilled criteria in each of the three pertinent studies (Wingrave and Kay, 1978; Vandenbroucke et al, 1982; Linos et al, 1983). The authors appear to have been more concerned with general methodological implications than with the specifics of rheumatology, although they did express misgivings at the inclusion of non-specific disorders under the rubric of'probable RA' (which, as already noted, requires only that two symmetrically swollen joints be present). Understandably, more recent work could not be taken into account by Esdaile and Horwitz. The latest report (Vandenbroucke et al, 1986) was concerned with non-contraceptive hormones, and again a protective effect was identified. However, many of the limitations in the earlier work of these authors were present on this occasion as well, including the eligibility of probable RA for recruitment to the 'case' group. Proceeding to more general attempts to synthesize available knowledge, Williams (1985) has argued that a powerful analytical technique is one which increases our understanding of the nature of a problem, enables us to use systematically all the relevant information we have and clearly indicates what is missing, separates descriptive and evaluative statements, forces assumptions into the open, and is applicable to a wide range of important problems. Bradford Hill (1965) provided an analytical framework that goes some way to satisfying these desiderata (Table 3); although developed to help in evaluation of whether an observed association might be interpreted as

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Table 3. Criteria for the evaluation of relationships*.

1. Strength of the association (in statistical terms) 2. Consistency (replication) 3. Specificity (criteria of necessity and sufficiency) 4. Temporality (which is the cart and which the horse?) 5. Biological gradient (dose-response relationship) 6. Plausibility (biologicallyt) 7. Coherence (triangulation) 8. Experiment (e.g. animal studies) 9. Analogy From Wood and Badley (1985a), derived from Hill (1965). * Not forgetting the three causal fallacies: post hoc ergo propter hoc, confusion of cause and effect, and the deception of common cause. t Recall the advice of Sherlock Holmes: having eliminated the impossible, whatever remains, however improbable, must be the truth.

indicative of causation, the criteria do provide a fairly rigorous framework against which to examine the nature of interrelationships. I have found this approach to be illuminating when considering the connection between osteophytes and osteoarthritis (Wood, 1986b), and the conclusions challenge assumptions that are widely taken for granted. Of the criteria, it is common for too great a weight to be attached to plausibility and analogy (which in effect also includes most animal experiments), and for too little attention to be paid to coherence and particularly to specificity; the value of testing coherence by triangulation has already been illustrated. As Medawar (1969) noted, a logically articulated structure forms a critical' part of the scientific approach, but a defect of the hypothetico-deductive scheme is that it sets no upper limit to the number of hypotheses that might be propounded to account for observations; this is where Hill's criteria are especially valuable, serving to circumscribe the possibilities. So where might all this discourse get us? It should serve to remind us of three things. First, not only is knowledge always incomplete, with the horizon receding as we advance, but its progress rests more on refinement of the limits of infinite ignorance than it does on spectacular development; the latter tends to be but a reformulation of the limits. Secondly, in Mark Twain's words, 'We should be careful to get out of an experience only the wisdom that is in it and stop there lest we be like the cat that sits down on a hot stove lid. She will never again sit on a hot stove lid--and that is well, but neither will she ever sit on a cold one'. Thirdly, to take heed of C. S. Lewis' caution, 'I still had all the chronological snobbery of my period . . . the assumption that whatever has gone out of date is on that account discredited'. PLANNING FOR CARE

Clinical activities cannot be divorced from what makes them possible--the

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existence of problems that have both individual and social dimensions. Consideration of these dimensions is additionally important because it is by these means that resources are made available for the pursuit of rheumatological excellence. The background for health care planning is provided by an epidemiological appraisal, such as the measures of the community burden of rheumatic suffering indicated in Table 1. Two facets of the organization of care merit comment. First, as patterns of hospital utilization change, rheumatology is becoming responsible for a growing proportion of inpatient admissions. In the last 12 years in England this has been accompanied by a 31% reduction in mean durations of stay in hospital, so that the overall admission rate has increased by 52% despite a 5% reduction in the beds used. Sadly, waiting times for admission have increased by 39% over this period, most notably for arthrosis. Admission rates have shown quite striking differences: that for RA has increased by 14%, arthrosis by 29% and for intervertebral disc disorders by only 10%, whereas for the largest category--'other musculoskeletal disorders'--the rate has more than doubled. Indicators of patterns of practice show quite marked variation. Overall there are still disturbing deficiencies in the availability of specialist care in different parts of the country (Khaligh and Wood, 1986). The second facet of the organization of care is closely linked to the first. There is a need for minimum standards of services to be promulgated, so that dilatory health authorities can be scrutinized more rigorously and their derelictions challenged. The need for audit applies equally to rheumatologists themselves, as much from the point of view of moral obligations to secure the best for patients as from that of political and economic expediency. Any professional has a duty to keep on learning, and self-scrutiny of one's own practice is as important as trying to stay abreast with the literature. Two prerequisites for successful audit are limitation in the scale of the exercise (i.e. focusing on only a narrow area of practice at any one time) and explicit formulation of objectives in regard to those aspects of service submitted to study and of the methods by which these can be assessed. When initial feelings of being threatened have been overcome, pointers to improving services for patients are likely to be perceived fairly readily, often in unexpected directions and not always directly related to the physician's own activities. For example, investigation of why clinic appointments were not kept revealed an administrative fault in the notification of such appointments (A. Bamji, 1987, personal communication). CONCLUSIONS So far the discussion has focused on care activities. Inescapably this involves picking up the bits after something has happened. Ideally, though, one would like to be able to prevent rheumatic disorders from occurring. As soon as systematic initiatives for control of the burden are contemplated it is necessary to draw on more specific epidemiological insights. Knowledge of the circumstances of disease occurrence is exploited for this purpose. For example, appreciation of the interplay of influences associated with develop-

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ment of a particular disease may indicate factors that could be manipulated as a means of prevention. Alternatively, the attributes of persons affected may be used as the basis for identifying populations at risk, such as by screening or in campaigns for early detection, so that protective measures and prompt treatment may be initiated. There is one other important point not brought out so far, concerning how rheumatologists conceive their role. As indicated in the Brindle Lodge Report (Wood and Badley, 1976), the specialist's job 'is not so much to run a service at a particular hospital or hospitals, but to respond to the needs of the community those hospitals serve'. As the report went on to say, specialists should assume more of an educational role at the expense of some management responsibility for individual patients, 'in other words, substituting teaching for a proportion of more paternalistic doing'. The rheumatologist constitutes a vital educational resource for GPs and other health professionals, one that is all the more essential because of limitations in how professionals have been trained in the past. Without such input it is very difficult for the primary health care team to play its full part, so that resources get dissipated in less effective initiatives. Of even greater concern, the patient is likely to get a suboptimal service. Finally, attempting to draw all the threads together, it is worth emphasizing that the various issues raised in this chapter have all emerged from an epidemiological appraisal of rheumatic disorders. Although diverse in nature, I hope their relevance to most aspects of the concerns of rheumatologists is by now apparent. Some of the insights are complex, and a few may even be unwelcome, but they all have a potential to enrich everyday clinical practice and improve the care which patients receive. REFERENCES AnseU BM & Wood PHN (1976) Prognosis in juvenile chronic polyarthritis. Clinics in Rheumatic Diseases 2: 397-412. Bennett PH & Wood PHN (eds) (1968) Population studies of the rheumatic diseases. International Congress Series No. 148 Amsterdam: Excerpta Medica Foundation. Black D[AK] (1984) An Anthology of False Antitheses (the Rock Carting Fellowship), p 3. London: Nuffield Provincial Hospitals Trust. de Bl~court J J, Wood PHN & Badley EM (1981) Aims of rehabilitation for rheumatic patients, Clinics in Rheumatic Diseases 7: 291-303. Central Statistical Office (CSO) (1984) Regional Trends. London: HMSO. Currey HLF (1970) Osteoarthrosis of the hip and sexual activity. Annals of the Rheumatic Diseases 29: 488-493. Darwin C (1958) The autobiography of Charles Darwin, Barlow N (ed.), p 123. London: Collins. Department of Health and Social Security (DHSS) (1984) Sickness and~or Injury Benefit-Statistics on Spells of Certified Incapacity, Year Ending 2 April 1983. London. Esdaile JM & Horwitz RI (1986) Observational studies of cause-effect relationships: an analysis of methodologic problems as illustrated by the conflicting data for the role of oral contraceptives in the etiology of rheumatoid arthritis. Journal of Chronic Diseases 39: 841-852. Feinstein A R (1967) ClinicalJudgement. Baltimore: Williams & Wilkins. Fries JF, Spitz PW, Kraines RG et al (1980) Measurement of patient outcome in arthritis. Arthritis and Rheumatism 23" 137-145.

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Hadler NM (1977) Industrial rheumatology--vlinical investigations into the influence of the pattern of usage on the pattern of regional musculoskeletal disease. Arthritis and Rheumatism 20: 1019-1025. Harris AI (1971) Handicapped and Impaired in Great Britain, Part I (Social Survey Division, Office of Population Censuses and Surveys). London: HMSO. Hill AB (1965) The environment and disease: association or causation. Proceedings of the Royal Society of Medicine 58: 295-300. Hunder GG (1982) Recent developments in the classification of rheumatic diseases. EULAR Bulletin 11: 52-55. Kellgren JH & Lawrence JS (1961) Osteoarthrosis of the hip in random population samples. Comunicazioni Del X Congresso Della Lega lnternazionale Contro I1 Reumatismo 2: 1-3. Torino: Ediz Minerva Medica. Khaligh N & Wood PHN (1986) Arthritis and Rheumatism in the Eighties. Report on an investigation into the burden of suffering from arthritis and rheumatism and the availability of facilities for treatment and relief. London: Arthritis and Rheumatism Council. Kirwan JR, Chaput de Saintonge DM, Joyce CRB & Currey HLF (1983a) Clinical judgement analysis--practical application in rheumatoid arthritis. BritishJournal of Rheumatology 22 (supplement): 18-23. Kirwan JR, Chaput de Saintonge DM, Joyce CRB & Currey HLF (1983b) Advances in assessing rheumatoid arthritis. British Journal of Rheumatology 22 (supplement). Lawrence JS (1961) Prevalence of rheumatoid arthritis. Annals of the Rheumatic Diseases 20: 11-17. Lawrence JS & Bennett PH (1960) Benign polyarthritis. Annals of the Rheumatic Diseases 19: 20-30. Linos A, Worthington JW, O'Fallon WM & Kurland LT (1983) Case-control study of rheumatoid arthritis and prior use of oral contraceptives. Lancet i: 1299-1300. Marks JS, Stewart IM & Hardinge K (1979) Primary osteoarthrosis of the hip and Heberden's nodes. Annals of the Rheumatic Diseases 38:107-111. Medawar PB (1969) Induction and intuition in scientific thought. Memoirs of the American Philosophical Society 75: 42. Now reissued and incorporated in Medawar PB (1982) Pluto's Republic. Oxford: Oxford University Press. Moll JMH (1980) Diagnostic criteria and their evaluation. In Moll JMH (ed.) Ankylosing Spondylitis, Chap. 12, p 137. Edinburgh: Churchill Livingstone. Morgan PP (1986) From the editors: the seven deadly sins of clinical studies, Canadian Medical Association Journal 134: 1225. NoreU J (1984) What every doctor knows, the William Pickles lecture 1984. Journal of the Royal College of General Practitioners 34: 417-424. Office of Population Censuses and Surveys (OPCS) (1974) Morbidity Statisticsfrom General Practice, 2nd National Study 1970-71 (The Royal College of General Practitioners, Office of Population Censuses and Surveys, and Department of Health and Social Security; Studies on Medical and Population Subjects 26). London: HMSO. OPCS (1985) Hospital In-Patient Enquiry 1983, main tables, series MB4, 23. London: HMSO. Papiha SS, Lanchburg JS & Pal B (1986) Genetic structure of the population with rheumatoid arthritis in north east England--a genetic approach to define different subtypes. Annals of the Rheumatic Diseases 45: 881-891. Pinals RS, Masi AT & Larsen RA (1981) Preliminary criteria for clinical remission in rheumatoid arthritis. Arthritis and Rheumatism 24: 1308-1315. Reah TG, Benn RT & Wood PHN (1971) Mortality in rheumatoid arthritis. Abstracts of Vll European Rheumatology Congress 40 (7). London: Arthritis and Rheumatism Council. Short CL, Bauer W & Reynolds WE (1957) Rheumatoid arthritis: a definition of the disease and a clinical description based on a numerical study of 293 patients and controls. Cambridge (Massachusetts): Harvard University Press. Tomenson J, Crombie IK & Wood PHN (1983) Insurance and the disabled. International Rehabilitation Medicine 6: 1-7. Vandenbroucke JP, Valkenburg HA, Boersma JW et al (1982) Oral contraceptives and rheumatoid arthritis: further evidence for a preventive effect. Lancet ii: 839-842. Vandenbroucke JP, Witteman JCM, Valkenburg HA et al (1986) Noncontraceptive hormones and rheumatoid arthritis in perimenopausal and postmenopausal women. Journal of the American Medical Association 255: 1299-1303.

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Williams A (1985) Economics of coronary artery bypass grafting. British Medical Journal 291: 1507-1508 (letter). Wingrave SJ & Kay CR (1978) Reduction in incidence of rheumatoid arthritis associated with oral contraceptives. Lancet i: 569-571. Wood PHN (1978) The mathematical theory of infectious diseases and its applications (book review). Immunology 34: 955-956. Wood PHN (1983) Epidemiological contributions to immunogenetic studies. International Congress Series 602: 55-67. Wood PHN (1986a) The basis of rheumatological practice. In Scott JT (ed.) Copeman's Textbook of the Rheumatic Diseases, 6th edn, pp 19-58. Edinburgh: Churchill Livingstone. Wood PHN (1986b) Osteophytes--Their Role in Osteoarthritis. Pendragon Papers no. 2; Thould AK, Dieppe PA & Dixon AStJ (eds). Nottingham: Boots Company. Wood PHN & Badley EM (1976) Options in the Delivery of Medical Care. Report of a working conference sponsored by the Department of Health and Social Security. London: Arthritis and Rheumatism Council. Wood PHN & Badley EM (1985a) The origins of ill-health---an appraisal of strategy for health for all and its implications. Recent Advances in Community Medicine 3: 11-37. Wood PHN & Badley EM (1985b) Musculoskeletal system. In Holland WW, Detels R & Knox EG (eds) Oxford Textbook of Public Health, iv, pp 279-297. Oxford: Oxford University Press. Wood PHN & Badley EM (1986) Epidemiology of individual rheumatic disorders. In Scott JT (ed.) Copeman's Textbook of the Rheumatic Diseases, 6th edn, pp 59-142. Edinburgh: Churchill Livingstone. Wright V (1982) Measurement of joint movement. Clinics in Rheumatic Diseases 8: 521-725.