Two Rival Medical Models of Disease

Human society is based on ideas; they inform and shape all of our actions. 

One hundred years ago, at the turn of the twentieth century, the great William Osler was Regius professor of medicine at Oxford University. He was a preeminent teacher who emphasized bedside clinical teaching; disease was a puzzle to be solved by the use of the clinician’s five senses, his knowledge of pathology and his deductive powers. The diagnosis was to reflect the pathological process that accounted for the signs and symptoms. In Osler’s mind the clinical questions were simple: "What disease does the patient have?" And, "How do I treat it?" The patient was somewhat incidental, a representative of the class of people with this disease. Biological individuality was disregarded. Osler was an activist; he saw the patient as a broken machine that needed to be fixed, and his role was to show the world how to fix illness.

Osler was succeeded as Professor of Medicine by Archibald Garrod; there could hardly have been a starker contrast. Osler taught how to treat disease; Garrod taught how to think about diseases and why they exist. For Garrod, individuality was a crucial element in any diagnosis and treatment. He was interested in questions such as "Why did this person get this disease, and why at this time?" And, "What can I do to restore this person’s orientation to his environment?" Garrod studied the chemical individuality of people, including inborn errors of metabolism. He saw this variability as crucially important, for from variability spring the raw materials for natural selection. Garrod was a contemplative man who saw the patient not as a broken machine, but as a consequence of the encounter of a unique individual with an environment for which he was not perfectly suited.

Two models of medicine. The prevailing metaphor of Western medicine continues to be the body viewed as a machine which the doctor is called on to fix when it breaks. (See allopathinc medicine). It is an engineering role: doctors use technology to practical ends. The gold standard for success is cure; improvement is good, but only as a stage on the road to cure.
Science will find cures for diseases not yet understood. Lewis Thomas wrote "Disease comes as a result of biological mistakes" and "I cannot imagine any category of human disease that we are precluded from thinking our way around." The goals of medicine are to apply the theoretical knowledge of the basic medical sciences to relieve pain, to prevent disability and to postpone death. In today’s terms, by knowing the sequence of the base pairs of the genome we shall advance toward our goal of achieving a complete understanding of the biology of disease.

Fast forward to the end of the twentieth century, when cracks had appeared in the engineering approach to medicine. Not only are high-tech diagnostic and curative efforts increasingly costly, but specialization takes us ever further from the ideal of preventing disease in the first place. Because of the impossibility of learning all the facts, medical specialties break down into finer and finer sub-disciplines that focus on ever narrower pieces of the patient. In such a context, how do we maintain an awareness of the identity and human qualities of the patient?
The metaphor of the machine does not explain where the machine came from, or how machines are related to each other, why disease affects one individual and not another, why diseases evolve and change over time, and why healing occurs. Of course, the engineer disregards such questions as irrelevant and metaphysical, but if we do not contemplate them we are destined to limit ourselves to developing ever more complex technical approaches to fixing problems that likely could be anticipated before they arise.
Perhaps we need a new outlook that asks why diseases occur at all, what forms they take, and how we may re-orient our approach to an anticipatory, rather than a reactive, one.

Perhaps it is our focus on cure as a criterion that directs our attention ever more finely onto how things go wrong: from patient to organ, to cell, to molecule. We do not look the other way, to examine how things go right, from the individual to their family, to the environment and to evolution itself.

Evolution proceeds by descent with modifications over time; the fate of individuals depends on their adaptation to the environments they meet. This returns us to variation between individuals, for if the species is to survive through changing environments there must be a stock of diversity from which to choose. In this view, individual variation represents a crucial stock of resources for future evolution of an imperfect organism and not, as the engineering model suggests, errors from the perfect blueprint. There is, indeed, a conflict between a theological view of Man as a perfect creation, and a Darwinian view of man as a work-in-progress. Sometimes, this diversity brings the individual into conflict with their environment, and disease results. Hence, disease can be viewed as the result of mis-match between the person and their environment, not as a broken machine. Disease may be symptomatic of a bad environment, and management may entail adapting the environment as logically as fixing the individual (give people better houses!). The doctor’s role is that of conservation of the individual and restoration of balance; this approach is far more tolerant of prevention than is the engineering conception.

The contrast between the engineering and the natural history or adaptational currents of thought coincide with contrasting approaches to science.
• In the engineering model, the mean values are emphasized; typologies predominate, and discussions of causality address how things occur.
• The adaptational approach pays attention to variability (the standard deviation rather than the mean), and causal questions concern why things occur.
• In the engineering model, diseases are each specific and external to the individual, and are expressed in constant, more or less universal forms. They are seen as randomly afflicting previously healthy persons; the causes are to be found in proximal biological processes. Infectious diseases are good examples and they match the Oslerian approach well.
• The alternative approach may be called the nominal, or physiological approach. It sees disease as a quantitative deviation in normal functions rather than a separate entity. Thus, we hear debates over what should, and should not, be seen as a disease (alcoholism? panic attacks? menopause?). In the adaptational model, the origins of disease derive from qualities of the individual and are rooted in the general nature of mankind. Here, infectious diseases are seen as resulting from a struggle between conflicting interests for survival. Diseases need not be harmful; indeed, we are surrounded by viruses and bacteria which become harmful in conjunction with a person who cannot adapt. Disease becomes illness. The clinical questions become "How and why is this particular person ill, and what treatment is suitable for their constitution?" The same cure need not be appropriate for every patient.

 

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