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Elementary concepts of medicine: VI. Genesis of illness: pathogenesis, aetiogenesis

2003; Wiley; Volume: 9; Issue: 3 Linguagem: Inglês

10.1046/j.1365-2753.2003.00419.x

1365-2753

Olli S. Miettinen, Kenneth M. Flegel,

Health Promotion and Cardiovascular Prevention

Illness, a particular case of it, begins when the definition of the somatic anomaly at the core of the concept (as proximate genus) is first satisfied. Antecedent to this time-point, the case has its genesis, coming into being, and from this time-point forward, the case of illness has its course. On first thought it might appear to be obvious that the genesis of a case of illness inherently is entirely antecedent to its inception (and course); but it is not. The course of illness in the population of cells in a tissue can be like that of abnormally high morbidity (epidemic, endemic) in the population of persons in a community – its continuation after its inception sustained by continual conversions from normal to abnormal, that is, by continual genesis. The idea of genesis always being entirely antecedent to an anomaly's inception does apply on the level of individual cells but not on the level of tissue: a person's case of illness may be sustained by continual genesis of it, as in iron-deficiency anaemia, for example. Medical dictionaries define genesis as: 'the coming into being of anything; the process of originating' (Dorland 1994); or 'an origin or beginning process' (Stedman 1995). Though not clear from these definitions, we believe that the medical concept of genesis, in the context of illness, like the biblical and cosmological ones in the context of the world, presupposes that the outcome (here the illness) already has come into being. From the vantage of the illness already being present, its genesis naturally is its origin as a retrospective concept of its having come into being. (From the vantage of the antecedent normalcy, it would not be a matter of originating but a matter of the prospective coming into being of the illness, including, most notably, whether it will.) The coming into being we do not see as a matter of 'process' only; for, beyond this descriptive issue, there is the explanatory – causal – one. Let us consider carcinogenesis as an example. The dictionaries define it as: 'the production of carcinoma' (Dorland 1994); or 'the origin or production, or development of cancer, including carcinomas and other malignant neoplasms' (Stedman 1995). These definitions do not quite cohere with their general, non-specific genesis counterparts above; and the meaning of 'production' in this context is obscure to us. But consistent with our general concept of the genesis of illness (above), carcinogenesis to us is the retrospective, post hoc concept of origin, the 'historical' coming into being of carcinoma (or cancer more generally) that has in fact come into being, a matter of both how and why it came into being. Given this retrospective conceptualization of carcinogenesis, the particular nature (e.g. cell type) and location of the cancer are givens. Thus, as for lung cancer, for example, one distinguishes between the genesis of squamous-cell carcinoma in a central location and that of a peripherally located adenocarcinoma. The genesis of an illness, including carcinogenesis, obviously is a concept related to that of pathogenesis. Our medical dictionaries define pathogenesis as follows: 'the development of morbid conditions or of disease; more specifically the cellular events and reactions and other pathologic mechanisms occurring in the development of disease' (Dorland 1994); or 'the pathologic, physiologic, or biochemical mechanism resulting in the development of a disease or morbid process' (Stedman 1995). Clearly implicit in the concept of pathogenesis is the premise that the illness outcome actually is developing, so that the concept is conditional on this outcome and hence indeed retrospective from this vantage, as we have insisted above. The key word in both of these definitions is that favourite one of modern academic medicine: 'mechanism'. The corresponding concept the dictionaries define as: '1. A machine or machine-like structure. 2. The manner of combination of parts, processes, etc., which subserve a common function. 3. The theory that the phenomena of life are based on the same physical and chemical laws which operate in the inorganic world; opposed to vitalism' (Dorland 1994); or '1. An arrangement or grouping of the parts of anything that has a definite action. 2. The means by which an effect is obtained' (Stedman 1995). These definitions, quite remarkable per se, shed no light on the question of whether pathogenesis is genesis (of illness) in the descriptive sense only; that is, whether it concerns merely how a case of illness developed, or how the illness develops in general – each of these as a matter of successive stages of pathology intermediate between normal soma and the anomaly that is definitional to the illness (as its proximate genus). The other possibility is that pathogenesis is the comprehensive concept of the genesis of illness, inclusive of the causal influences that initiate and/or drive forward the sequence of somatic changes leading to the illness-defining anomaly. Against this background of incomplete clarity we posit that pathogenesis of an illness is that part of its origin (retrospectively, for illness that has come into being) which is constituted by the somatic process of transformation from normal soma to the somatic anomaly that is definitional to the illness. This is a descriptive concept, one of how, rather than why, the anomaly in a given instance did come into being or in general does come into being. The 'why' aspect of the genesis of illness, rather than descriptive, is inferential, causally interpretive, explanatory – a matter of what initiated and/or sustained the pathogenetic process. For this 'neighbour' of pathogenesis a natural term we take to be 'aetiogenesis' (Miettinen 1998; Miettinen 1999). A neologism as this term is, it is not an entry in our medical dictionaries, but its synonym (Miettinen 1998; Miettinen 1999) 'aetiology' is. The concept of aetiology one of these dictionaries (Dorland 1994) defines as follows: 'the study or theory of the factors that cause disease and the method of their introduction to the host; the causes or origin of a disease or disorder'. The other one (Stedman 1995) gives a definition closely similar to this. And the specialists in aetiologic research, epidemiologists, put the essence of aetiology thus: 'Literally, the science of causes, causality; in common usage, cause' (Last 1995). The ordinary medical concept of aetiology we take to be as well-established as it is poorly expressed in the medical and epidemiologic dictionaries. It corresponds to pathogenesis (as a retrospective concept) and is that of causal origin of illness (that has come into being). It is this aetiologic genesis or aetiogenesis, rather than pathologic genesis or pathogenesis, that a clinician is especially prone to contemplate during the process of pursuing diagnosis and especially upon having come to diagnosis of the presence of a particular illness, a commonly iatrogenic (doctor-caused) illness in particular. Insight into the aetiology/aetiogenesis of a diagnosed case of illness is a matter of having come to causal explanation of the occurrence, that is, of its pathogenesis having taken place. This knowing about aetiology/aetiogenesis of a particular, diagnosed case of illness we term 'aetiognosis' (Miettinen 1998; Miettinen 1999). A given antecedent of the illness outcome resulting from the pathogenetic process was aetiologic to the case of illness if, and only if, it had the 'but for' property of: everything else aetiologically relevant having remained the same, the illness would not have developed (at the time it did) but for the presence of that antecedent (in lieu of its defined alternative, as an initiator and/or driver of the pathogenesis). Commonly, a case of illness has multiple causes that jointly constituted a sufficient cause. To take a trivial example, a case of communicable disease arises from the sufficient cause that consists of the joint presence of two necessary causes: effective exposure (environmental) together with susceptibility (constitutional). In general, aetiologic antecedents of illness fall in the three broad categories of constitutional, environmental and behavioural. Even though the consideration of the genesis of an illness ordinarily focuses on the inception of the illness, the concepts of pathogenesis and aetiogenesis apply just as readily to any subsequent stage of illness, including non-recovery outcome.