Methods and Theory of Diagnosis

Observation, as the first stage in diagnosis, is the period of analysis, while the next stage is synthesis of the data obtained. It should be understood that both analysis and synthesis occur simultaneously during examination of the patient because the physician not only observes and listens but also thinks. The main methodological problem of diagnosis is to identify disease by its signs and to proceed from a symptom to diagnosis.

In practice, the physician often passes from the symptom directly to diagnosis by a logical jump which is based on a conjecture, memory, and medical experience. This process often occurs subconsciously and the

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method is not reliable. Thus established diagnosis cannot be complete, the diagnostician himself is not sure in his conjecture, and besides, this method, which depends mainly on memory, is partly automatic.

The simplest and elementary method is diagnosis by similarity. It con­sists in comparison of symptoms observed in the patient with the symptoms of known diseases. If the symptoms are similar to signs of a definite nosological unit, the condition of the patient is classified to be identical to it. Unreliability of this method is evident from the fact that the absence of some symptoms makes the diagnosis by similarity difficult, it does not pre­vent mistaking of symptoms, nor does it prove the absence of concurrent diseases. Moreover, this simple method can only suggest the name of the disease without giving a comprehensive picture of the patient himself.

The inductive method is quite rapid and simple. It is based on the primary hypothetic generalization and subsequent verification of the con­clusion by the facts observed. This method of identification occurs simultaneously with observation, and both end simultaneously. A physi­cian observes one or several symptoms and makes a conjecture. Then he suggests that his conjecture is correct provided some other symptoms of the supposed disease are present. Once these other symptoms are found, the diagnosis is considered proved; if the anticipated symptoms are not found, the conjecture is considered to be wrong and another is produced instead, and so on. This method is, however, useful for an abstract diagnosis rather than for a concrete one. Since completeness of diagnosis and orderliness of examinations are not requisite, this method cannot give a comprehensive impression of the patient on the whole, and can only be used to diagnose one disease without revealing many possible pathological changes and various complications of the disease. This diagnostic method based on coincidence and similarity of several symptoms observed in the patient with the symptoms of the conjectured disease can give a diagnosis of a com­plication instead of the disease itself. Finally, this method is based not on the revealing of the relationship between the symptoms, but mainly on mechanical collection and comparison of the symptoms.

The specific feature of the inductive method is a conjecture or a hypothesis. S.P. Botkin emphasized the hypothetic character of diagnosis and wrote that once a diagnosis is established, we produce a more or less probable hypothesis which is either confirmed or disproved by further course of the disease. The physician must undertake actions proceeding from his hypothesis. When the hypothesis is verified and confirmed, it is no longer a hypothesis but a theory or fact; if the hypothesis is disproved, it is declined altogether.

The first and foremost condition for using a hypothesis (in diagnosis in-| eluded) is a critical attitude to it and accurate knowledge of what is a con- ]

jecture and what is fact in a particular case. The main danger consists in mistaking a hypothesis for a fact. It is necessary that a hypothesis (a) would be based on actual facts; (b) would not contradict them; (c) could be check­ed directly or by conclusions that might be derived from it. When the physician has to choose between equally probable conjectures, most fre­quently occurring version should be preferred.

A diagnostic hypothesis can be substantiated by analogy. In this case several symptoms observed coincide with the symptoms of a particular disease, and a conjecture is produced that the patient develops this par­ticular disease and that some other signs of the disease will more or less coincide. Of course, the lesser the number of symptoms, the greater the number of conjectured diagnoses.

Differential diagnosis. The diagnosis established by analogy has only one proof: greater or smaller similarity of the observed signs with the described symptoms of a certain disease. The diagnosis becomes more reliable if the presence of other diseases is excluded. In other words, dif­ferential diagnosis based on the search of differences between a given case and all other possible cases, with exclusion of hypotheses that have not been proved correct, is more positive.

Checking correctness of the diagnosis is the principle of clinical iden­tification not only in dubious and complicated cases but also in diseases whose symptoms suggest a definite conclusion. Nevertheless it is necessary to take into consideration all other possible affections. Consideration of possible cases helps the physician reveal accurately and timely the symp­toms that he might anticipate in the patient with a particular disease.

The starting point in differential diagnosis is, as a rule, the leading symptom. The physician then recollects all diseases for which this symptom is common and the course of the disease is now compared with the descrip­tion of those diseases. A particular case may have common features with diseases for which this symptom is common. These differences are used to exclude all other diseases which might first be suspected as having this symptom. Finally in the presence of the greatest similarity and the least number of differences with the disease to which the present case is com­pared (while all other possible diseases are excluded) the physician may conclude that a given patient has this particular disease.

Phases of differential diagnosis. The first phase. The leading symptom, which should be used as the starting point in conjectures, should not be too common (say, fever) because too many diseases will be involved in dif­ferentiation. The more specific the symptom, the smaller is the number of diseases to be differentiated. The procedure becomes the least labour-consuming and more rapid if a combination of symptoms, i.e. symptom complex, rather than a single symptom, is considered as the starting point.

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The second phase. An important condition is consideration of all possi­ble symptoms characteristic for a particular case because if any symptom is disregarded, the reliability of the diagnosis diminishes. Most probable and most frequently occurring disease should be considered first.

The third phase. The studied case is compared with several possible diseases. First, similarity with respect to the number and character of coin­ciding symptoms should be considered. Second, established should be the differences with respect to the absence of symptoms characteristic of the disease with which this particular case is compared, and with respect to the presence of symptoms that are not characteristic of the supposed disease.

The fourth phase. The disease that was first conjectured is excluded if the differences are found which contradict one of the main three principles of differentiation. The first principle is substantial difference. The observ­ed case does not belong to the disease with which it is compared because its permanent symptom is absent. For example, the absence of albuminuria excludes glomerulonephritis, or the absence of intensified basal metabolism rules out exophthalmic goitre. But since there are transient symptoms in most diseases, the physician should be more careful. The absence of a symptom does not exclude a disease. The signs of the early period of some diseases are often so insignificant, transient and non­specific that any of them may be absent during examination. Moreover, in complicated cases these symptoms may either disappear or be masked by complications or other diseases. For example, in rare cases of diffuse affec­tions of the kidneys, albuminuria, which is otherwise a very significant symptom, may be absent, or pneumonia may proceed without elevated temperature, etc.

Another formulation of the first differentiation principle reads: the observed case does not belong to the type with which we compare it because we find a symptom which never occurs in the disease with which we compare it. This formulation is even more conventional because it can­not be applied to complicated cases and therefore does not always rule out the supposed disease.

The second differentiation principle is exclusion through the opposite. It can be put as this: the observed case is not the disease with which we compare it because in the disease with which we compare there is a con­stant, quite opposite symptom. For example, achylia can hardly concur with duodenal ulcer because an opposite symptom, gastric hypersecretion, is observed in this disease. What has been said of the first differentiation principle, holds true for the second as well. It should also be added that some symptoms are transformed into their opposites during the course of the disease. For example, excitation is replaced by inhibition, etc. The im­portance of the antagonism of symptoms is therefore no less relative than their absence.

The third principle is the non-coincidence of signs. As we compare quality, intensity, and special features of an observed symptom with a similar symptom of another disease with which we compare a given case, we can find the non-coincidence and the presence of various properties and different origin, which makes us doubt and rule out the supposed disease. This principle is used for making tables of differential diagnosis.

It should be remembered that comparison of a given case with the pic­ture of a supposed disease is more useful than establishing similarity or dif­ference by one or several symptoms. Differential diagnosis requires further study of the patient in directions that are suggested by the possible presence of this or that disease in order to look for symptoms corresponding to the supposed disease. The advantage of this method is repeated examination of the patient which ensures a more complete observation and discovery of new symptoms.

The fifth phase. The diagnostic conclusion is derived from the established similarity of a given case with the disease to which it is com­pared and from the difference of the case from all other possible diseases.

Thus, differential diagnosis by exclusion not so much establishes the diagnosis directly; it rather gives evidence that the disease, that has greater similarity to it, is more probable than the others; in other words, it proves correctness of the diagnosis by exclusion of all other possible diseases. Diagnosis that is established by direct exclusion of all other diagnoses is called diagnosis per exclusionem.

Differential diagnosis may be a more or less important aspect in physi­cian's speculations. The main feature of this method is a thorough revision of all possibilities which is the final stage in the most common pathway of all investigations. Verification of the diagnosis occurs simultaneously with the continuing observation of those effects which are derived from the con­jectured diagnosis. It should be noted that differential diagnosis is used to verify the diagnosis but it does not explain the features of the patient's con­dition.

Diagnosis does not end by identification of the disease because the changing condition of the patient causes the corresponding changes in the process of differentiation. Diagnosis is thus a dynamic process and it must develop and be completed by the analysis of the continuing variations in the patient's condition. The study of these changes is another test for cor­rectness of the primary diagnosis.

The diagnosis (mostly its anatomical part) is confirmed or disproved during a surgical operation, or on postmortem section. It should be noted that the anatomical changes do not always prove correctness of the diagnosis; these changes can explain the patient's condition to the extent to which the results can be used to conclude on the chain of the preceding events, and the structural changes can be used to judge on functional

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disorders. A systematic checking of diagnosis by comparing clinical and pathoanatomical diagnosis has been adopted in the Soviet Union since 1935 (clinico-anatomical conferences).

The described diagnostic methods are used to identify the disease to establish the diagnosis of the disease (diagnosis morbi). Establishing this diagnosis helps the physician systematize the observed phenomena. This diagnosis defines the essence of the disorder, but does not explain all special properties of a given patient, nor does it explain his concrete condi­tion. The nosological diagnosis gives much but not everything that is necessary to a physician to prevent possible complications and to treat the disease. The described methods cannot give a concrete individual diagnosis (diagnosis aergroti). The diagnosis cannot be detailed, the degree of anatomical changes, functional disorders, the character and importance of the aetiological factors cannot be established by these methods. A nosological diagnosis is not thus a synthetic diagnosis.

An additional diagnosis (diagnosis ex juvantibus) should be mentioned. The results of the treatment given are used to make a conclusion on the disease. This method can therefore be regarded as a kind of retrospective diagnosis. Reliability of this method is quite disputable (except in rare cases).

Sometimes the physician has to limit himself to a provisional diagnosis. In the broad sense of the word any diagnosis is provisional because no diagnosis can be complete and it undergoes continuous changes (at least in­significant) with the condition of the patient. In a narrower meaning of this term provisional diagnosis is one which is dubious for the physician himself, mainly due to insufficiency of the data available.

Finally, an early diagnosis should be mentioned as a very important kind of diagnosis and which is a difficult problem of modern clinical medicine. This problem is being solved by two ways. One of them is the search for diagnostic methods suitable for the period of the disease at which a successful therapy can be given (e.g. radical cure of gastric or lung cancer). This diagnosis is only comparatively early as distinct from hopelessly late diagnosis when the physician cannot help the patient. When examining a patient, it is reasonable to suspect in the first instance the most dangerous malignant diseases, because late diagnosis makes cure impossi­ble. A more difficult but necessary way is the search for methods to reveal a disease when the very first signs only appear or even before these signs become detectable. It implies also the problem of the threshold of clinical manifestations of pathological processes, and possible assessment of the quality of the process at its early development. The problem of early diagnosis is also directly connected with the problem of predisposition or susceptibility.

A way to solve the problem of early diagnosis is regular surveillance of practically healthy population. Vivid disorders in the condition of a person may be absent not only during the unitial period of the disease but also in the presence of marked anatomical changes, i.e. when the disease is latent and the sick person does not apply for medical aid. Heart diseases, tuber­culosis infiltration or a cancer node in the lung can be revealed by X rays; chronic nephritis can be detected by urinalysis, etc.

Synthetic diagnosis. Synthetic or pathogenetic method is used to establish a concrete diagnosis of a given disease or condition. The method is based on successive synthesis and establishment of the pathogenetic con­nections between the observed phenomena.

The first problem in the synthetic method is grouping symptoms in compliance with the medical objectives. If a patient is given a systematic and planned examination, the revealed symptoms are naturally grouped ac­cording to the bodily systems. The physician obtains the first preliminary information on the functional condition and the degree of affection of this or that system. Then the physician studies the functional relations between the systems. The obtained material is only " crude" and requires further processing, in the first instance by establishing connections between the revealed symptoms, establishing their origin, and arranging the symptoms in pathogenic groups. The physician proceeds from the symptom to phenomena associated anatomically, functionally, or aetiologically with this symptom.

The groups of symptoms should then be evaluated diagnostically, pro-gnostically, and therapeutically. Correct estimation of the symptom from the prognostic and therapeutic aspects requires adequate knowledge of its pathogenesis, which is the subject matter of semeiotics.

Synthesis of the collected data (observed symptoms) begins with group­ing the symptoms by various signs, such as time of appearance, relation to a particular organ, function, origin, and causality.

A group of pathogenetically connected symptoms is called a. syndrome. A syndrome is thus the first result of synthesis and the second step in establishing a diagnosis. Two types of syndromes are distinguished, e.g. anatomical and functional. Combination of physical symptoms or signs which correspond to the structural changes in the organs are called anatomical syndrome. For example, dullness in the region of the lungs, bronchial respiration and intensified fremitus make an anatomical syn­drome of consolidation or infiltration of pulmonary tissue.

Combination of functional symptoms gives a physiological or func­tional syndrome. For example, diminished alkaline reserve of the blood, ^creased ammonia of the urine, and decreased CO₂ tension in the alveolar ^air make the functional syndrome of non-gaseous acidosis. When the

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physician reveals syndromes he proceeds from the statement of symptoms in a given patient to establishing deeper connections and interdependence between them. Separate symptoms and their combinations (syndromes) make it possible to conclude on the anatomical and functional condition of organs. During the transition from symptoms to a syndrome, the physician selects certain diagnostic conjectures by excluding others.

Simple and complicated syndromes are distinguished. In other words, a patient can combine not only anatomical or functional disorders of a par­ticular organ, but have changes in his systems and the entire body. Com­plicated syndromes are called large. They are aggregates of symptoms in­terconnected pathogenetically and involving the entire body in pathology. For example, diffuse affections of the kidneys may be classified as large syndromes: azotaemic, chloruraemic, and hypertensive syndromes. The specific feature of syndromes is their changeability; a syndrome is not a fix­ed condition. Syndromes develop, modify, disappear, combine with one another, or separate from one another. Renal syndromes, for example, are only a moment in the development of nephritis in a given patient; this holds also for many other diseases.

A specific feature of a syndrome is that it can be a result of various pathogenic effects on the body, i.e. a body often responds similarly to various harmful effects by a limited group of similar reactions (e.g. by in­flammation). One and the same syndrome can be observed in various diseases and the same disease (at various stages and clinical forms) can be manifested by various syndromes. Syndromes arise and change depending on the progress and stage of the disease; they may develop due to various causes, and reflect, in the first instance, the special properties of the body's reactions. After establishment of a syndrome, the physician should deter­mine the causes, background, and conditions of the development of the given functional and organic disorders in the patient. He thus determines the sites of therapeutic application.

Correctness of determination of the cause of a particular syndrome depends firstly on the experience and knowledge by the physician of special pathology; secondly on the knowledge of the patient's condition at the pre­sent moment by the clinical picture and by special examination (e.g. microscopy, serological and other tests); and thirdly, on the detailed study of circumstances under which the disease developed, heredity, and also the progress and character of the pathological process, and the patient's condi­tion.

In connection with the study of aetiology of a disease it is necessary to remember the following three circumstances. There are diseases which are essentially polyaetiological but monopathogenic, e.g. certain neuroses, allergic conditions. Accurate determination of pathogenesis is therefore of

decisive importance in such cases. Results of aetiological factors are observed in some diseases, e.g. results of a mechanical, radiation, or psychic injury. Finally, there are diseases whose specific cause is not yet clear.

A no less important stage of diagnosis is the study of circumstances under which a disease develops. Social, home and working conditions, and constitutional properties are important for a correct diagnosis, because the character and clinical manifestations of the disease mainly depend on the patient's condition before the onset of the disease, which in turn depends on constitutional factors and the mode of previous life. Knowledge of all these factors provides conditions for passing from a diagnosis to the study of the patient. This helps explain the patient's individual properties and the course of the disease which is observed exactly in this concrete case and which distinguish him from other cases. This is especially important for prescription of the appropriate therapy and for prognosis of the disease. The synthetic method begins with grouping the collected data (symp­toms) and continues by identifying the syndromes occurring in the patient. It leads to substantiation of the observed phenomena by aetiological basis (in the broad sense of the word) with due consideration of the patient's traits and the environmental factors. The physician thus definitely and ac­curately identifies the disease and studies the patient. He keeps in mind that individualization of each particular case based on the factual scientific data is the object of clinical medicine and is at the same time the most solid ground for therapy (S.P. Botkin). This method consists in revealing symp­toms of the disease, explaining their causes, and proceeding from one form of connection to another, deeper and more general. The synthetic method includes successive and repeated phases of analysis and synthesis to give finally a concrete understanding of the patient. The study passes from a symptom to a syndrome (which gives a new understanding of the patient's condition) in which each particular symptom becomes part and moment in the development of the whole syndrome. A similar transition from a syn­drome to a symptom complex (large syndrome) is a new step in which the syndrome is only a component element. The transition from a syndrome to a disease as a nosological unit through knowledge of causes and interaction between the body and the environment gives a new, more perfect notion of the disease. The most essential factor in this method is the successive character in the synthesis of a diagnosis, in the transition from a lower stage to a higher one (i.e. orderliness), and also in the search for and ^establishment of connections between phenomena in a given patient by their causal dependence and interaction. Compared with the other Methods, the synthetic method is more rational and reliable.

Comparison, conjectures, and tests are characteristic of each step in

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establishing a diagnosis. The object of a concrete diagnosis is to reveal all individual properties, causes and conditions of the development of pathology in a given patient. This diagnosis brings the physician closer to a better understanding of the pathogenesis of the disease.

Attributing a case to a certain nosological unit, i.e. abstract diagnosis, reveals to some extent the essence and also possible aetiology of a pathological process. A concrete diagnosis of the patient's condition discloses the specific reaction of the body and the degree of disorder in the patient, as well as the constitutional and social background of the disease. The most complete diagnosis is a combination of the symptomatic, anatomical, functional, aetiological and social investigation. In other words, this is a synthesis: establishing the unity of various aspects of the patient's condition and specific properties. Understanding the cause and essence of a phenomenon is the necessary condition for a successful action, i.e. modification or eradication of this phenomenon.

It follows that two stages of understanding a disease can be distinguish­ed. The first one is the simplest. In each particular case the physician tries to find out or remember what he already knows about the observed phenomenon. Here is simple recognition rather than a cognition process. By recognition, the physician, first, determines the elements of the disease and its symptoms as revealed by observation and experiment; second, the recognition process extends to the determination of the nosological unit corresponding to this particular symptom. This type of cognition in in­vestigating the case is the simplest; it does not reveal any newness but only establishes the known in a new object. The second process is diagnosis. The physician faces the problem of cognition of the new and unknown. This happens when the physician proceeds from an abstract to a concrete diagnosis, to determination of all specific properties of the patient and the role of his working and living conditions. Novelty here is the disclosure of connections, casual relationship between the symptoms, and finally, the determination in each case of combination of all specific properties of the patient's reactions and the conditions (endo- and exogenic) for the origin of the given disease. The diagnostic cognition follows the general rule: " From living perception to abstract thought, and from this to prac­tice —such is the dialectical path of the cognition of truth, of the cognition of objective reality".*

Unfortunately, incomplete investigation and incorrect diagnosis of a disease occur rather often. Comparison of clinical and pathoanatomical diagnoses shows that, according to different statistical data, almost 10 per

cent of intravital diagnoses are incorrect. Pathoanatomical diagnosis is im­possible in almost 3 per cent of cases.

Causes of incorrect diagnosis. The causes of erroneous diagnoses can be divided conventionally into three groups. First, a disease may remain without being diagnosed if this particular disease has not yet been studied by the present time. New diseases are being discovered and described every year and the number of unstudied diseases is considerable. Second, the disease might have been described but its clinical picture and diagnosis are not studied sufficiently well, which is an obstacle to correct diagnosis. Finally, the disease is known and studied well, but the physician may be unaware of it, or be acquainted with it only theoretically (without practical acquaintance).

The second group of diagnostic errors is determined by the incomplete or incorrect examination of the patient. This may be due to insufficient skill of the physician in techniques of clinical examination, the lack of knowledge of laboratory and instrumental methods that should be used in a particular case to identify the disease, or due to the absence of the ap­propriate laboratories (remote rural areas, etc.). The patient himself may be responsible for incomplete examination. For example, it is very difficult to obtain an anamnesis of a deaf and dumb patient or a foreigner. A pa­tient in coma cannot be given a complete examination either (even by the main methods such as auscultation, percussion, or palpation): in emergen­cy cases the physician has no time for a detailed examination.

The third cause of erroneous diagnosis is incorrect conclusion due to in­adequate knowledge of symptomatology and methodology of diagnosis or due to conceptions forced on the physician by an authoritative conclusion of a more experienced physician. Unfortunately some cowardly physicians choose to abstein from speaking out their conjectured diagnosis in the face of high-rank or more experienced physicians even in very important cases. Incorrect diagnosis may also be due to overestimation by the physician of his own experience and due to his vanity, or when he is guided by his own intuition and experience and disregards the opinion of his colleagues or declines the necessity of carrying out some examination procedures.

An incorrect diagnosis due to an honest delusion of a physician should be differentiated from a deliberately incorrect diagnosis, which is crime.

It should be remembered that today diagnosis is not the responsibility of only one physician but of many medical specialists such as specialists in internal diseases, surgeons, highly skilled consultant physicians and diagnosticians, roentgenologists, endoscopists, laboratory technicians, etc.

The following two groups of difficulties can be distinguished in diagnostics: (1) quantitative difficulties, due to avalanching scientific in­formation; (2) the necessity of as early and accurate diagnosis as possible

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(which facilitates effective treatment of the disease) and even of revealing predisposition to the disease in practically healthy persons.

The first-group difficulties are due to an ever increasing amount of scientific information which should be collected in each particular case. For example, for diagnosis of liver affections it is necessary to carry out up to 30 biochemical tests (more that 100 tests are used for the purpose). This vast information is an additional obstacle to correct thinking (perception, storage and analysis of information, selection of the necessary conclusions from an increasing amount of facts such as diseases, syndromes, symp­toms, tests, etc.).

But there is room for optimism however, because medicine borrows methods of investigation from more precise related sciences. Human think­ing is now aided by computers which have flawless memory, a strictly definite order of comparison and selection of information (algorithm) and which solve various problems at a surprisingly short time. In 1960

A. A. Vishnevsky introduced cybernetics into clinical practice.

B. V. Petrovsky wrote that " computers and mathematical methods will
acquire higher importance in the development of medical science and prac­
tical health care". The progress in medicine is now backed by many new
accurate methods of examination and by computers which accelerate the
thinking process. Using special charts, which are filled in by patients, and
also diagnostic machines will be indispensable in mass-scale prophylactic
examination of the population.

But it should be understood that no computer or a diagnostic machine will rival the physician at the patient's bedside. Computers will only help the physician and never take his place. The physician has to collect an anamnesis, detect haemorrhage, hear the systolic sounds, discover (in a microscope) tuberculosis mycobacterium, in other words, the physician " feeds" the computer which " digests" the information using its electron " memory" and yields conclusion. Furthermore, at the present time the computer cannot reveal or describe new diseases or syndromes.

Computers help solve the problem of early and accurate diagnosis. There are other ways by which diagnostic difficulties may be overcome. These are broad-scale research, special training of physicians, improving their medical education, improvement of diagnostic apparatus, etc. The USSR public health system and the prophylactic trend in the Soviet medicine open further prospects for improving diagnostics. Larger part of the population undergoes regular prophylactic observations. Medical aid in the USSR is not only free of charge but is readily available. The purpose of diagnostics is broadened in the direction of revealing premorbid conditions and latent forms of diseases. New methods and plans for examination of various groups of the population are being created, the number of

laboratories increases, new diagnostic and therapeutic centres open, and many new diagnostic tools and instruments are supplied to the medico-prophylactic institutions.