The diagnostic process

Establishing a diagnosis is central to medical activity. In general, a diagnosis must be made before starting therapy. To equip students with diagnostic thinking skills is one of the most difficult tasks of all for a clinical teacher. In the framework of a scientific research project at the Horten Centre for Applied Research and Science in Zurich, Switzerland, we have now developed a model that can be used in clinical teaching. For the purpose of this model, the diagnostic process is divided into six steps (see figure). The first step is information gathering by primarily having the patient describe his or her symptoms. Further information is then obtained by questioning and examining the patient. In a second step, any symptoms mentioned are described in more detail by using attributes, thereby raising them to a more abstract level. A patient who has been experiencing difficulty in breathing for two hours suffers "acute respiratory distress", while a patient with knee pain has an ache in only one joint and, more specifically, in a large and not a small joint. In a third step, these precisely described symptoms serve as a basis for elaborating a "mental representation" of the clinical problem. Empirical studies show that this third step is an essential factor in determining whether or not a student or a not too experienced physician reaches a diagnosis. The fourth step consists in comparing this mental representation of the clinical problem with the student’s stored knowledge of different diseases. This process can be described as pattern recognition. By comparing the attributes of a clinical problem with the memorised attributes of different diseases, it becomes possible to recognize those diseases which are consistent with the patient's symptoms. This is the fifth step – the actual differential diagnosis. The sixth step consists in identifying the correct diagnosis, usually among several possibilities. This requires further examinations such as blood tests or X-rays.