|Expert System Programs|
Beginning with the patient and not the Condition or Disease
For over 100 years medical diagnosis has been largely based on invoking lists of disease possibilities. Thus, medical texts and references, such as the Merck Manual® are organized by disease, or conditions. Medical teaching has generally been based on the same formulation, emphasizing the study of disease, not the study of complaints, i.e. Given this disease, do the patient's complaints ( symptoms) or findings (signs) match the diagnosis? This is backwards, of course, and most physicians know this instinctively.
Since patients do not present with diagnoses, the logical question should be: Given this symptom or sign, what are the most likely conditions or diagnoses, in descending order of their probabilities. Because of the way clinical data has been collected anecdotally over the past century, with emphasis on disease occurrence rather than the prevalence of signs and symptoms, this presents significant difficulties. EasyDiagnosis, well aware of the limitations of this approach, has attempted with these programs to present this concept in a coherent, simplified format. The vast majority of patients present with one major symptom or sign, and in a significant majority of these, the top three or four diagnostic probabilities usually add up to over 70%-80%. When there is high suspicion of a specific condition, our method can be used to estimate roughly the probability of its occurrence in a given setting.
Certain caveats and significant limitations must be borne in mind. Our present computer programs embedding expert knowledge and the data now available, exemplified in EasyDiagnosis, are appropriate only for those patients presenting with a single dominant symptom or sign. If there is more than one principal complaint, the programs will be misleading. Furthermore, findings discovered only on physical examination can be critically important in clinical diagnosis, and these are largely excluded since patients cannot be expected to examine themselves. Moreover, since the accuracy of these programs is clearly better for common conditions, these Programs focus on the most common conditions; rarely seen diagnoses are usually lumped together in a miscellaneous category.
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