Concepts of Health and Disease

At the core of medicine lie the concepts of health and disease. Medicine aims to cure disease, or at least relieve the suffering related to it, and where possible, to prevent it from arising. Moreover, health promotion is increasingly recognized as an important part of the physician's mission, so that people can lead lives as full and rich as possible. Yet the concepts of health and disease are not so simple and straightforward as we might first suppose. For example, do we distinguish between a person who is merely feeling badly and a person who is really sick? Do physicians and hospitals bear responsibility for treating every form of human suffering? Is health a mere absence of disease and injury, or is it a positive state of well being? If today's medical students and residents are to achieve their full potential as physicians, it is important that they base their practice on a complete and rich vision of what it means to be healthy.

Let us suppose that a patient presents to a physician's office complaining of not feeling well. How do we determine whether patients are sick, and if so, what ails them? One approach would be to obtain sophisticated diagnostic tests on the blood, or to order radiological studies in order to glimpse the anatomy and physiology of the patient's internal organs. In most cases, however, such sophisticated diagnostic studies are not indicated, and the history alone or the history and the physical examination provide more than adequate diagnostic information. Despite the fact that more sophisticated diagnostic studies are usually unneeded, they shape our vision of medical practice to an ever-greater degree. For example, some patients who present with headaches may feel cheated if their physician does not order a computed tomography (CT) scan to ensure that they do not have a brain tumor. Likewise, physicians may feel that we are not doing our best for our patients if we do not avail ourselves of medicine's full diagnostic armamentarium.

We need to understand more deeply what it means to be ill, and to clarify our vision of the state of health in which we seek to enable our patients to live. The World Health Organization's Second International Classification of Functioning, Disability, and Health (ICIDH-2) provides a useful point of departure in this regard. As modified here, it approaches health and disease in terms of four levels or tiers: structure, function, activity, and participation. The underlying presumption is that health and disease cannot be adequately understood on any single level, and a multitiered approach is necessary. Like the molecular, cellular, organic, organismal, and communal approaches to understanding living organisms, we need to look from multiple different angles if we aim to understand fully the impact of illness on a patient's life.

The most basic level of health and disease is structure. This is the traditional forte of the anatomist, the pathologist, the surgeon, and the radiologist. In order to discern what is wrong with a patient, we must discover what portion of their structure is out of shape. To know whether someone is ill, we seek a structural abnormality. If the appendix has a normal appearance, with no trace of inflammation, then we dismiss the diagnosis of appendicitis. If a patient with cough and fever has a normal chest radiograph, we know that they do not have pneumonia, although they could have a raging case of bronchitis. If a febrile patient has a normal white blood cell count and blood smear, we know that bacterial infection is not the culprit. When a patient presents with abdominal pain, we work our way through the organs of the belly until we find one that accounts for the patient's symptoms.

In so doing, we are continually weighing the appearance of the patient's anatomy against that of our mental image of normalcy. The crucial determination we are always trying to make is both stunningly simple and mind-bog-glingly complex: is this normal or abnormal? If the finding is within the range of normal, we dismiss it. If we suspect that it is abnormal, we set about attempting to determine what it might be. We formulate a differential diagnosis, and then take additional steps to sort out which option is most probable. In some cases, we arrive at a definitive diagnosis, as when a bone radiograph clearly reveals a fracture. In other cases, we never know for sure what was the matter with the patient, or even whether the patient was really sick to begin with.

Yet where the structural tier of health and disease is concerned, it is worth remembering that even a completely normal diagnostic test does not definitively rule out the possibility of disease. The bone radiograph may be initially normal, and it is only a week later, after demineralization has taken place and some periosteal reaction has formed adjacent to the fracture that we are able to recognize a nondisplaced hairline fracture. Even our most sophisticated imaging studies may not show us the pathology. For example, a patient with severe psychosis may have a normal magnetic resonance imaging (MRI) exam of the brain. Conversely, there is no guarantee that every patient with an abnormality of diagnostic testing actually has the disease. A solitary pulmonary nodule may represent a granuloma, and not a lung cancer at all.

We need to recall that no diagnostic test is 100% accurate, and the accuracy of every test varies depending on the circumstances in which it is used. We can generate costly false positives by employing a test in circumstances where the initial probability of disease is very low. If medicine is to provide optimal value to patients and our communities, it is important that we educate future physicians to understand not only how to interpret diagnostic tests, but when to use and when not to use them. It is a mistake to suppose that the quality of medical care is directly proportional to the number of tests the physician orders. In many situations, the best test is no test at all. If learners are to understand how to employ diagnostic testing effectively, they need to recognize that ferreting out abnormal structures is not the highest objective of medicine.

The second tier of health and disease is function. To understand function, we must look beyond the snapshots of the structural tier and think of health and disease as unfolding in time. The coronal, sagittal, and axial dimensions do not tell the whole story. We must see how they are changing from minute to minute, day to day, and year to year. It is not enough to know that there is a hole in the heart. It is necessary to know what that hole means to the function of the car diovascular system. Is it permitting too much deoxygenated blood to enter into the systemic circulation? Is it jamming the lungs with too much blood, and thereby making the heart work too hard to supply an adequate amount of blood to the brain, heart, and kidneys? To know what a structural abnormality really amounts to, we must understand its functional implications.

Although the functional level of understanding cannot simply supplant the structural level, it does enjoy a higher level of explanatory power. We can suffer structural insults of one kind or another, yet through functional redundancy or retraining, return to our formal level of function. For example, some patients recover virtually completely from a stroke, despite the fact that they have suffered the irreversible loss of a portion of their brain tissue. The dominance of function over structure is apparent in the design of prosthetic devices, such as artificial joints. The material of which the joint is constructed changes completely, from cartilage and bone and ligaments to a metal or ceramic. Likewise, the structure is drastically changed, so that the blueprints for the native joint and the artificial joint look quite different from each other. And yet the joints may function quite similarly, enabling a knee that formerly could barely move to regain a virtually full range of motion.

Function refers to the operation of a molecule, a cell, a tissue, an organ, or an organ system, and activity refers to the operation of the whole organism. Consider the example of sickle cell anemia. The structural abnormality is a base-pair substitution in a portion of the gene that codes for the hemoglobin molecule. This translates into a defect in the structure of the protein, which causes it to assume an abnormal sickle shape and to become lodged in capillaries through which it should pass easily. This is a functional defect. The tendency of patients with sickle cell hemoglobin to develop anemia and sequestration crises creates limitations that interfere with daily activities, and abnormality at the level of activity. Patients with sickle cell anemia are unable to win foot races, and may not even be able to get out of bed comfortably on some days.

It is vital that future physicians understand the linkages between structure and function, and between function and activity. If we simply treat the struc-ture,we will miss important functional implications, and if we simply treat function, we will miss important implications for what the patient is able to do. To appreciate the full implications for activity, we need to understand who patients are and what they do. Pain that one patient can easily endure may prove overwhelming to another, depending on what is going on in their lives at the time. To one patient, the ability to swing a golf club may be a crucial feature of a full life, whereas another might value especially highly the ability to sing. Because of this, the same surgical procedures might be tolerable to one and intolerable to the other. We need to ask certain questions. What does the patient care most about in life? How will different diagnostic and therapeutic options differ depending on this particular patient's point of view? We really understand the disease only insofar as we know what it means to the patient.

Participation involves the social dimension of illness. What does a letter or phone call bearing news about an abnormal diagnostic test mean to a patient? For example, suppose a patient receives a message that her screening mammo-gram showed an abnormality that requires further workup. What does that message mean to her? It may produce so much anxiety that she cannot sleep well or carry out her daily activities at her usual level of performance. It may upset not only the patient but her friends and family, as well. It is vital that physicians understand the human implications of such interactions, and tailor not only our bedside manner but our practice patterns in such a way that we spare patients unnecessary suffering and do what we can to promote the psychological and social well being of patients. How can we do a better job of delivering bad news? How can we better prepare patients and families for the trials and tribulations of major surgery or anti-cancer chemotherapy?

When patients are told that they have cancer, they are not thinking primarily in terms of the abnormal structure of some of their cells, or the fact that a nonfunctional mass of cells is proliferating out of control and threatening their normal tissues. They think primarily in terms of what it means for their careers, their families, and their very lives. They begin to think about what it will be like to tell their spouse, their children, and their friends. They think about whether their affairs are in order. They think about all the horrible stories they have heard about the therapy for cancer, and the experiences of people they know who died of cancer. The diagnosis may incite fears of impairment and disfigurement. To young medical students, the loss of a breast or a testicle may not seem so terrible, but perhaps this is because they do not really believe it could happen to them. The more we can help learners understand the threat of illness and what it is like to cope day to day with it, the better we prepare them to care for patients in an effective and compassionate matter.

We also need to understand the social dimension of healthcare, so that we appreciate the complex relationships between different healthcare providers. How do the contributions of the family physician, pathologist, the oncologist, the surgeon, the radiologist, the dietician, the occupational therapist, the nurses, the technologists, and a host of other workers fit together to provide good care to a patient, the kind of care we would want for our spouse or sibling? Each of us needs to know what the other does, what the other needs, and what the other can offer. The more effectively we can help each of our colleagues to do their jobs, the more integrated and beneficial will be the care we provide. We need to understand not only our own specialty but the entire profession of medicine and the field of healthcare in a comprehensive fashion. If our view is fragmentary or overly simplistic, everyone suffers. On the other hand, if we can see health and disease from a truly comprehensive, multitiered perspective, both we and our patients stand to gain much.

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