Every one of us has gone through the experience of seeing a doctor, or being intervened to some extent by the health care system and its regulatory practices. During a typical first visit a nurse writes down the symptoms, and then a physical examination might take place and then a short interview of the patient by the doctor. Typically a physician orders more exams, then diagnoses and suggests possible treatments. Even though all of us have seen a physician, for a biologist such an experience can be a quite different one. Compared to any other discipline the biologist is perhaps more aware than any other patient of the gaps and limitations of our knowledge of human biology. Awareness of such limitations in knowledge and treatment make the experience of visiting a doctor’s practice unique, and always make us reflect about how medicine is practiced now days. In the next blog entries I will write about what going to the doctor means for a biologist like me. Today my entry will cover briefly how the concepts of normality and pathology are used to diagnose pathology and what the consequences of such uses can be.
Medicine is not science, it’s a technology.
Every culture has medical practices, that is, a set of notions and procedures used to conceptualize disease and health, diagnose illness and treat it. For the most part in the western world medicine is a technology1 rather than a science. This means that even though medicine is supposed to be based on scientific knowledge of human biology, in most cases medicine is practiced as the application of a set of preconceived procedures to regulate, control and intervene the organism and the body. For example, even though drugs require going through clinical trials before being used in humans, or even though the choice between two alternative treatments results from scientific studies that test the effectiveness of a treatment, in most cases medicine is practiced mainly as a set of interventions on the body that are pre-established and that have been accepted by the medical community. In few cases the patient/doctor/health-system interaction results in a revision and renovation of the medical practice. Thus, for the most part, going to see a doctor is subjecting oneself to being examined, diagnosed and treated within a preconceived and for the most part inflexible system. This has clear benefits, but contrasts to how science proceeds. For example, in biology hypothesis about causation, as well as the technologies used to manipulate the organism for experimentation are subject to doubt and constant revision, changing at a much faster pace than their corresponding analogs in medicine.
Illness: a deviation from the population mean or the loss of individual flexibility?
Being a technology that is for the most part a set of preconceived practices, western medicine uses not only physical tools to intervene, regulate and attempt control the organism, but is also uses concepts. Key notions of medical practice are the concepts of normality and pathology. Lets first address what is pathology and what is normal. Here I follow Georges Canguilhem, my favorite philosopher of biology and medicine. In the Le Normal et le pathologique, first published in 1943 and then expanded in 1966, Canguilhem suggested that there are different notions of normality and pathology. First, there is the individual-centered notion of normality. In this case pathology is a deviation from the normal states, and manifests as a loss in flexibility or plasticity in what the individual organism was capable of doing. Disease is a deviation from self-imposed norms that preexisted in the individual’s past, where the organism is incapable of compensating for perturbations and deviations that could be internally or externally triggered. In this case individual flexibility or plasticity refers to the ability of the organism to constantly compensate for deformations (homeostasis), such that during illness such capacity is lost or dramatically reduced. Importantly, this notion of normality and illness primarily relies on the individual history as a point of reference, such that disease only makes sense with respect to the individual. A second notion of pathology that Canguilhem cites is population-centered, where pathology is a deviation from the population mean (“the norm”). In this second case any reference to the individual history is irrelevant, and illness merely depends on whether an individual has a significant deviation from the population mean when a particular physical trait or a physiological variable is considered.
Modern medicine uses both the individual and the population-based concepts of pathology to diagnose and treat disease. Nevertheless, the structure of the medical health care system is such that medicine is practiced as a technology of preconceived and highly regulated practices. Also, funds and time to diagnose are quite limited, and little effort is done to keep track of the individual history (i.e. most individuals do not engage in preventive health care, and only go to the doctor when they feel ill). Even though physicians know the value of individual and family medical history, in practice, unless it is an individual that has been subject to recurrent medical examination and treatment, the individual history is for the most part unknown. In most cases, other than the subject’s account and perception of his/her illness, there is no record of the individual history, and thus it the doctor’s choice is to diagnose using the population-based concept of pathology. As a result, overall the population-based concept is more frequently used to diagnose and treat.
Given that two concepts of pathology exist, and that one is more frequently used than the other, the next important question is to ask whether the individual and population-based concepts are equivalent in terms of their ability to properly diagnose pathology and suggest a correct treatment? My theses are that the population and individual based concepts of normality are not equivalent in terms of their ability to help correctly diagnose an illness and suggest a proper treatment, and that despite the population based concept is of more frequent use, it ignores fundamental aspects of biology, and thus of health.
For a biologist it is not difficult to imagine scenarios where either the population based or the individual based concept of pathology could succeed in helping diagnose and treat disease. For example, if an individual is born with certain malformations in the heart ventricular structure, such that the heart does not pump the blood at the normal frequency (thus deviating from the population norm), it is likely that bringing the pumping rate closer to the population norm through surgical intervention could make the organism become better at creating its own norms. This example shows that in some cases intervening an individual using the population-based concept of pathology could make the individual dynamics perform better, even in cases where the organism never had the chance to experience such different set of states and impose its own norms within an experienced set of states. In such cases there was no loss of flexibility that led to abnormality, but abnormality occurred from the start, as it was acquired through development. From the individual point of view that population “abnormality” was instituted as the norm. Nevertheless, this example also shows that “becoming healthy” for such an individual still relied on the individual concept (make the organism become better at creating its own norms) and not ultimately on the population mean (see below).
On the opposite side, it is easy to imagine cases where using the population based concept could not help but cause harm to a subject. For example, a person feels recurrent neck pain and decides to go to the doctor to do something that could change the pain. The doctor examines the patient and requests x-rays. When examining the images the doctor diagnoses that the pain comes from compression of the nerves from the discs in between the vertebrae, since for that age compared to a population measurement the space between the discs is “less than the normal distance”. But, is that difference really the cause of the pathology? Can one infer causation, diagnose and treat merely pointing to a deviation from the population mean? From the point of view of developmental biology it is sounder to base the judgment on the individual rather than the group, that is, use as the primary point of reference the individual history instead of the population mean to decide what the norm should be, using it to infer causation. Following again the case cited previously, it would be required to have some knowledge about the previous state of the patient (i.e. previous x rays to compare with, taken at a time when the patient did not feel pain). Our bodies are so complex that it could have been that despite having no neck pain, the person simply has a deviation from the population mean (has a smaller space between the discs), and that the pain is caused by a completely different cause that is not related to the space between the discs. Thus, diagnosing and pointing to a cause merely basing a judgment on a deviation from the population mean is really prescribing a preconceived disease, (i.e. a deviation from a group norm), and ignoring the real underlying causation of the illness, since it is plausible that that difference in the inter-vertebrae space was simply variation (biodiversity), and that the cause of the neck pain was completely different.
For any attribute or character conceived, over generations populations constantly and inherently generate variation (biodiversity), that is, significant deviations from the population mean. But the crucial point is not that variation exists, it is that variants can be coupled: when variation in two or more traits co-occur in the same individual it is possible for the organism to establish regimes where the individual is healthy, but it deviates from the population mean significantly for those two or more traits. Let’s think about another example that might become more relevant to personalized genomics (personalized medicine). Imagine cases where people with infrequent combinations of polymorphisms at the DNA level, and thus unusual combinations of enzyme structures and activities, could have abnormal levels of certain metabolites or proteins in their bodies, such that when measured such molecules would look “abnormal” if compared to the population mean. Despite such variation in structure or activity of some molecules, the person should not necessarily be considered ill, in a pathological state, or even at risk. Simply, through creating variation the population gave rise to an individual organism that might have a configuration and dynamics that simply remains in a different part of the set of physiological states when compared to the population average, but does so without significantly compromising its health in any other way. Such an individual establishes its norms of response and flexibility within a somewhat different fraction of that the set of physiological states, and might even do so robustly, such that deviation from a mean can not be interpreted in the sense that the organism has lost its ability to properly compensate for changes, lost its flexibility and become ill, or even entered in a “pathological developmental path”.
The examples cited in the previous paragraphs show that practicing medicine using a population-mean that tends to ignore the real meaning of biodiversity, or merely genotyping or metabolic profiling individuals without knowledge of the individual history, such that populations serve as the first aid to diagnose illness and treat “disease” could not only be pointless, but also harmful for patients. Given the complex structure of our bodies, it is possible that variants that deviate from the norm might function more robustly within the norms that their bodies establish. In such cases medical intervention to bring them closer to the population mean might even cause harm. Thus, ultimately, normality and pathology should have an individual reference point. Even in cases where the population mean is applied as the ruling principle, diagnosis and treatment should only be considered successful if such procedures result not merely in bringing the individual closer to the population mean, but if making that particular variable or trait be closer to the population mean results in establishing a more robust organism, capable of better creating its own norms successfully given internal or external perturbations.
Unfortunately, when it comes to diagnosis and treatment, ignoring biological diversity and its consequences on the individual histories is exacerbated by how the health care system is set up (i.e. limited resources that translate into little or no preventive medicine for most individuals, as few exams for diagnosis as possible, very short consulting time with the doctors, etc.). So when you have your next visit to your health care provider, ask yourself if you are being diagnosed as an individual that has lost its capacity to robustly create its own historically established norms, or if you are being merely seen as a deviant from the population mean given the lack of knowledge about you. It is likely that you will find out that the second case is taking place. Then it would be worth considering practicing preventive medicine and build a better medical history, so that when the next diagnoses occur, more history about your own norms is available.
— Nicolás Peláez
Canguilhem, G. (1966). Le normal et le pathologique, augmenté de Nouvelles réflexions concernant le normal et le pathologique . (English translation: The Normal and the Pathological, trans. Carolyn R. Fawcett & Robert S. Cohen, New York: Zone Books, 1991).