Special Features of Diagnostic Examination

The first and prerequisite condition to identify a disease and assess the condition of the patient is the knowledge of medical subjects and special pathology, i.e. nosological forms of the diseases. But clinical pictures of various diseases are described in textbooks only schematically. Clinical experience shows that actual cases would usually differ from these schematic descriptions since the origin, course and clinical manifestations of the disease strongly depend on the condition of the patient and the environment.

An important diagnostic factor is that the human body responds to various stimuli or aetiological factors by a limited number of general reactions, e.g. the normal response to most infections is fever, to local irritation it responds by inflammation, etc. Moreover, the general reaction of the body to various uncommon stimuli is often the same, especially at the onset of the disease. Clinical signs themselves are not therefore sufficient for the determination of the concrete aetiological factor or for the discovery of specific changes.

Several groups of diseases are distinguished according to various responses of the body to the pathogenic cause or injury. When establishing a diagnosis, the physician first of all decides to what group of the diseases can this particular affection be attributed. In other words, the physician first decides if a particular case is an infectious disease, upset metabolism, inflam­matory process, newgrowth, allergic disease, autoallergy, upset neurohumoral regulation, etc.

Another difficulty is that various combinations of pathological processes are encountered in various patients. And finally, even in seemingly typical cases, there are always special features that do not occur in other patients.

The necessary condition to identify a disease is the professional skill of the physician to apply his knowledge in the varied and changeable conditions of life. The professional skill is acquired with experience in solving diagnostic problems. An independent practitioner is form­ed through mastering the method by which the acquired knowledge can be applied to practical cases. Correctness of the diagnosis largely depends on this skill.

Selection of a particular scientific method depends mainly on the object of study, its pur-Pose, and the working conditions. This explains the difference between diagnostic methods and the methods that are used in other sciences. The diagnostic study is aimed at understan­ding of the patient's condition in order to change it, i.e. at determining the disease as a phenomenon that should be removed. The study should not be limited to finding the gene­ral and typical features (which is common for all theoretical sciences); the physician should direct his studies and thinking to understand any particular case which differs from all simi-'ar cases. This is the necessary condition for carrying out his objectives: prophylaxis and treatment.

An important feature of the object of study, i.e. of man, is its complexity with respect to structure and function and also with respect to connections and interactions with the environ-^ment (morphological, physiological, psychic, social features). This explains the necessity of ^Us'ng many methods. The number of methods that a physician uses to examine the patient is

General Part

Chapter 4. General Methodology of Diagnosis

greater than the number of methods used by representatives of other sciences. The physician uses not only medical methods but those employed in other branches of science, from inquiry by questioning, chemical, physiological, biological and other methods, to very complicated and precise techniques such as electrocardiography, X-ray examination, and others.

This great variety of methods depends not only on the extreme complexity of the object of studies. It is also explained by insufficiency of the methods for complete medical understanding and by the fact that one method cannot be applied to all cases. Moreover, in some cases a certain method cannot be applied without injuring the patient. Medical examina­tion should by no means do any harm to the patient. The physician therefore has to obtain the necessary information by indirect methods and speculations (e.g. incompetence of the heart valves can be determined by percussion, auscultation, type of the pulse, etc.). These dif­ficulties account for diagnostic errors.

Finally, it should be remembered that a physician may have little time to establish a full diagnosis in urgent cases when he has to act immediately to save the patient.

These are the working conditions in which the physician should do his best to apply effi­ciently scientific methods.