Elementary concepts of medicine: VII. Course of illness: manifestations, complications, outcome

Once the illness-defining somatic anomaly has come into being, the course of illness begins. The course is characterized, in its patient-relevant respects, by sickness manifestations (if any) and consequences of the illness (if any), of the illness-defining somatic anomaly. The course of the illness-defining anomaly per se, divorced from its manifestations and consequences, is not relevant to the affected person. A manifestation of an illness is something that, to one extent or another, reflects the presence of the illness-defining anomaly and, on this basis, is indicative of the anomaly's presence. It thus is an available fact simultaneous with the illness at issue – a positive finding of this kind, possibly a report (objective) of a symptom (subjective) or an inherently objective sign gleaned from physical examination or a laboratory test. Any such fact may be at variance with the corresponding truth, which may be difficult to define even. A manifestational fact, however accurate, is not inherently an effect of the somatic anomaly involved in the illness concept; different from effect, it may not be even of the form of a change but merely of a state of being. Even more notably, a patient-relevant manifestation, already present or potentially developing in the future, is integral to the very concept of illness, and it therefore is not really a consequence of illness, causally or otherwise. A consequence of an illness we take to be something wholly extrinsic to the illness. Consequences of illness in this meaning obviously fall into the principal categories of medical (i.e. somatic) and extramedical. Medical consequences we take to be of three generic types: complication, sequela and fatality. Under complication in our medical dictionaries, we find the following definitions: '(1) a disease or diseases concurrent with another disease; (2) the occurrence of two or more diseases in the same patient' (Dorland 1994); and 'morbid process or event occurring during a disease that is not an essential part of the disease, although it may result from it or from independent causes' (Stedman 1995). Although these definitions are surprising to us, they do accord with our idea (above) that a complication of an illness, different from its manifestations, is extrinsic to this illness, and more specifically also another illness, they do not identify complication as inherently a consequence of the illness. As for our proposition that a complication of an illness is a consequence of this illness, a couple of paradigmatic examples may serve to substantiate it. Peptic ulcer and peritonitis are two mutually distinct illnesses. When, and only when, the latter occurs as a consequence of the former, it is referred to as a complication of the former. Similarly, when, and only when, pulmonary embolism results from (occurs as a consequence of) deep-vein thrombosis, it is seen as a complication of the latter. In the meaning of consequence of an illness, thus, complication actually, and more specifically, is another illness caused by the illness at issue. It thus is another illness for which the original illness was aetiogenetic (aetiologic). As for the first example, it should be understood that perforated ulcer is but a stage in the course of ulcer and not another illness, and that it thus is not a complication of ulcer. Similarly, detachment of a segment of deep-vein thrombus is but an event in the course of that thrombosis and not a complication of it. Our medical dictionaries define the essence of sequela as: 'any lesion or affection following or caused by an attack of disease' (Dorland 1994); 'a condition following as a consequence of a disease' (Stedman 1995). Immunity resulting from an infectious disease satisfies the latter definition, but it is not thought of as a sequela of the disease. From the medical vantage, a sequela is not something desirable, nor even an innocent lesion; it is a somatic anomaly other than that which is definitional to the original illness, and it is one that already is, or in the future potentially will be, manifest in sickness. Thus, the medically relevant concept of sequela, like that of complication, has illness as its proximate genus. And further, while a distinction indeed is to be made between sequela and complication, a sequela of an illness is not caused by the illness at issue; it is a non-causal consequence of it. Thus, it is another illness for which the first illness was pathogenetic (rather than aetiogenetic; cf. complication above). This concept of sequela gains clarity when the nature of its non-causal connection to its parent illness is understood to represent a type of outcome of the original illness – just as any illness other than injury is the outcome of its pathogenesis. Stroke is an acute (i.e. non-chronic) disease, and a common outcome of it (of its completed course) is survival with a residual anomaly (chronic defect) in the tissues where the disease process took place. If this residual, post-stroke anomaly is manifest in sickness (say, paralysis), the anomaly represents patent sequela; if sickness is but a potential manifestation in the future, it represents latent sequela; and otherwise the outcome is survival with mere non-illness, non-sequela, innocent anomaly as a residue of it, the outcome now being complete recovery (to effective normalcy, with no material consequences as for outcome). It needs to be understood that just as perforated ulcer is not a causal consequence but merely a stage in the course of peptic ulcer, a sequela of stroke is not a causal consequence but, again, merely the anomaly stage that follows the completion of the course of the somatic process of stroke. Status post mortem is a sequela of life without being caused by life, nor is the transitional event death caused by life. For a sequela, the antecedent, original illness indeed represents pathogenesis (which is a merely descriptive concept) rather than aetiogenesis (which is a causal concept). Beyond sequela and complete recovery, the remaining principal type of outcome of illness, and equally a genuine potential consequence of illness, is of course fatality, death resulting from that illness. (When death results from some other, unrelated cause during the illness at issue, the course of this illness is thereby interrupted and its outcome does not materialize at all.) Different from sequela but akin to complication, the illness is causal to its fatal outcome, although only in the sense that it made death occur earlier than it otherwise would have occurred; but as it is not another illness, it therefore is not a complication. And because the fatal outcome is only the transitional event between living with the illness and being dead from it, and thus not a residual anomaly in vivo, at issue is a type of outcome different in form from that of sequela also. It deserves note that an illness commonly is not the direct, immediate cause of its fatal outcome. Instead, the immediate cause commonly is a complication of the illness to which the death is ascribed – or it is a complication of a complication, possibly many causal steps removed from the illness. Moreover, causation of death from a given illness can be mediated by its sequelae just the same. The illness that is designated as the cause thus commonly is merely a mediate, an underlying cause of the death. As we think of the course of illness in terms of its potential sickness manifestations and the potential medical consequences (complications, sequelae and fatality), we thereby exclude quality-of-life implications of sickness. A meteorologist is concerned with meteorological manifestations and consequences of whatever meteorological situation, but not with its agricultural (or farmers' happiness) implications, for example. A farmer's expert horizon on implications of weather is confined to those in the domain of farming, and the same applies to the implications of farming activities: issues of food production are within the farmer's expertise, effects of food consumption on people's health and happiness are not. Medically, the consequences of illness are medical (i.e. somatic). Health-related quality of life thus is a concern beyond the scope of medicine (Miettinen 2001).

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