Philosophy of Medicine
PHILOSOPHY OF MEDICINE
The subject matter unique to philosophy of medicine—as opposed to those issues that are best seen under the heading of philosophy of biology—is clinical medicine and its underlying methodology and assumptions. Crucial to philosophy of medicine is the family of terms disease, malady, health, normal, abnormal, condition, and syndrome, all of which have evaluative aspects to their definitions. For all its scientific base, medicine must be a value-laden practice guided by the values of its practitioners and its public. It is in this regard—but not only in this regard—that the claim "Medicine is an art and a science" should be understood.
Disease, Health, and Normality
A stable departure from physiological normality that causes death, disability, pain, loss of pleasure, or inability to achieve pleasure is the sort of entity that is called disease (Clouser, Culver, and Gert 1981). The departure has to be stable enough so that it causes similar problems in similar people and so that it is recognizable by different medical practitioners as the same disease entity. When the departure is less clearly individuatable than a disease, the entity is referred to as a syndrome.
Normality and health are relative terms. They are relative to species, age, gender, (perhaps) social status, race, and ultimately to one's own physiology. A healthy (normal) eighty-five-year-old is different from a healthy (normal) twenty-year-old; and a healthy (normal) professional athlete is different from a healthy (normal) philosophy professor. Normal health is also relative to one's values. Unless a person feels comfortable doing what she wants to do, she can claim to be unhealthy by saying things like: "I just don't feel up to par." In this sense health is a theoretical state of a person.
The concept of biological variability derives its useful sense from the relativity of normal. Biological variability makes generalization problematic in a way that generalizing from one billiard ball to any such object is not. Biological variability—meaning that no two organisms are exactly alike—is trivially true. It is unhelpful, except as a reminder that generalization is problematic.
Diseases are real to the extent that they are stable departures from normality (sometimes called "baseline") as defined above. Obviously, diseases are not like traditional physical objects. They can overlap and be in two places at the same time. (Mental diseases present their sorts of problems, which parallel issues in philosophy of mind and philosophy of psychology.) Diseases are real in that they cause real pain, disability, or both; they are real in the sense that they can be reduced to physiological occurrences. Diseases are theoretical in the sense that they are not traditional physical objects, and they are identified only relative to a value structure that then becomes part of the medical theory. For example, given the current medical theory of European and North American scientific medicine, chronic fatigue syndrome is a disease. But against the backdrop of eighteenth-century medicine, it would have been seen primarily as a characteristic of some women and lazy men. Chiropractic medicine sees disease only in terms of misalignment of vertebrae. The reality of disease, a sense for reduction, and the theory-ladenness of disease exemplify traditional questions in philosophy of science.
What is classifiable as a disease is also a function of what physicians are willing to do, what they are interested in, and what will be reimbursed. Thus, infertility is treated as a disease in large part because it is a terrible burden to some, it is interesting to deal with medically, and people are willing to pay for treatment. Being short is also treated as a condition worth reversing (in children) for the same sorts of reasons. This makes disease relative to culture and economic conditions.
Treating a condition as if it were a disease makes it a disease in a stipulative sense but not in the physiological sense. Baldness and bad breath would be conditions that might be troublesome, most effectively treated medically, and yet still not classified as diseases. However, if they are caused by a disease, they may be considered signs of an underlying medical condition. Psychiatry periodically re-decides whether certain psychological conditions should be considered diseases.
Genetics adds an interesting twist to defining disease and thinking about health. Consider a disease such as sickle-cell anemia, where homozygous recessive is a serious disease but the heterozygous condition can be beneficial in malarial areas (heterozygotes have a better survival rate from malaria than do either homozygotic forms) but still can, in rare instances, cause serious medical problems. Thus, in a nonmalaria infested area, the heterozygous condition might be called a disease. Huntington's disease is caused by a dominant gene whose effects do not manifest themselves until (usually) middle age. Should one consider a teenager with the dominant gene diseased? One could say that the person is healthy now even though the gene is one that will cause a disease later in life. But this is not really correct, because there are subtle changes in body chemistry caused by the dominant gene even when there are no Huntington's symptoms. One normally would say something such as, "a mutation in the normal gene is what causes Huntington's disease." This locution is odd for two reasons: (1) the person (almost assuredly) never had a normal gene to mutate; and (2) using "normal" when speaking of the gene would seem to imply that "abnormal" and "diseased" might be usable for genes as well. But, of course, the gene for Huntington's disease is not a normal gene with a disease.
The Logic of Diagnosis
Diagnosis and scientific explanation present similar philosophical problems, especially with respect to explanation, causality, and laws. Diagnosis begins with history taking and moves on to the physical examination. The standard history questions assume that disease entities have a typical natural history to them.
Signs are objective characteristics, such as blood pressure and broken bones. Symptoms are the subjective characteristics reported by the patient—for example, pain and lightheadedness. The signs and symptoms of disease vary with the stage of the disease. Thus, an early stage of any disease may be confused for the later stage of another. Physicians look for the best overall explanation for the condition, given the patient's individuating factors such as age, gender, occupation, stress factors, and so forth. The best explanation is assumed to be the most probable explanation, where the disease is considered to be the cause of the condition being investigated.
A standard procedure in diagnosis is the rule-out test. A physician limits the diagnosis to a few conditions and then does a test, which, if negative, will rule out one of the possible causes. This procedure is repeated until only one likely answer is left. This is in keeping with a simplistic version of falsification.
Doctors also use a simple confirmation strategy in diagnosis. Usually, more than one confirmatory test result is required before the diagnosis is accepted. Other predictions will have to be borne out by test results as well as physical findings and consistent history. Laboratory tests are crucial to modern-day diagnoses, although they present problems. Results are subject to false positives (disease reported when absent) and false negatives (disease not reported when present). The best test has a high true positive ratio and a low false positive ratio. Bayes's theorem can be used to calculate the probability that a person with a positive test actually does have the disease in question.
Because test results are continuous, cutoff points must be chosen. The cutoff points are chosen based on how serious an error would be. If a disease is fatal and can be treated safely, then a high false positive rate would be acceptable. For less worrisome conditions, compromise between the two figures is possible. Again, values are part of what looks like a objective aspect of medicine. In this sense, medical diagnosis may be different from the usual picture of the scientific method. There are other differences as well.
Some of the crucial aspects of physical diagnosis—for example, interpreting heart sounds and kinds of rashes—are subjective and cannot be taught so much as they must be learned by practice. The apprenticeship of medical students and physicians (residents) is, in this sense, different from the time graduate students in science spend learning bench laboratory skills. Also, anecdotes play a role in diagnosis in a way that they would not in physics or most other sciences. Related to the reliance on anecdotes is that the best physicians just seem to sense that, no matter where the facts are pointing, something else is going on. Subjectivity, anecdotes, and intuition seem not, in general, to be good scientific methodology, and yet it seems to be precisely what separates the great clinicians from the ordinary ones. The key to understanding these great diagnosticians is probably pattern recognition.
Physicians often wait in order to let a disease show itself more clearly, sometimes confirming their diagnoses by follow-up: Did the condition follow its predicted course? Did the treatment have the expected effect and in the expected manner? If not, the diagnosis may well have been incorrect. Even if the follow-up is consistent with the diagnosis, the actual condition may have been different and may have remitted on its own or have been similar enough to the disease suspected so that it responded to the treatment. In these sorts of cases, physicians do not know that they were wrong; they will count these cases as successes and so use them to support a similar diagnosis the next time. There is no practical defense against this failing.
Holism and Reductionism
Holistic medicine assumes that diseases are primarily a function of lifestyle and life events of the patient. A holistic approach to diagnosis will focus as much on psychosocial history as it will on traditional signs and symptoms. Stress as a factor in disease is important in holistic accounts. Reductionistic medicine focuses more on physiology as the key to diagnosis, treatment, and taxonomy of disease. The reductionistic approach is the legacy of scientific medicine begun in the mid-nineteenth century.
See also Bayes, Bayes' Theorem, Bayesian Approach to Philosophy of Science; Causation: Philosophy of Science; Explanation; Laws, Scientific; Laws of Nature; Philosophy of Biology; Philosophy of Mind; Reduction; Reductionism in the Philosophy of Mind.
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Arthur Zucker (2005)