Differential diagnosis – what is that?
A patient usually comes to the doctor with symptoms that he or she cannot assign to a specific disease. The doctor’s task is to make a differential diagnosis through a patient interview, physical and apparatus examinations. The differential diagnosis includes diseases that occur with similar or the same symptoms as the symptoms described by the patient and therefore also have to be taken into consideration when making the diagnosis.
The differential diagnosis must be distinguished from the suspected diagnosis. This is done with the help of so-called differential diagnosis: This includes all examinations that serve to exclude or confirm a disease that is a differential diagnosis to the suspected diagnosis. A fictitious example: After the patient interview, two possible diseases are considered as explanations for the patient’s symptoms.
One of the diseases is associated with abnormalities in the ultrasound, the other is not. So the doctor will clarify by means of an ultrasound examination which of the two differential diagnoses represents the actual diagnosis. The more characteristic a symptom is for a certain disease, the smaller the number of possible differential diagnoses. For more general symptoms such as fever, on the other hand, the number of differential diagnoses is large because many diseases can be accompanied by fever.
How is the differential diagnosis made?
In order to make a differential diagnosis, the doctor starts with a patient interview. During the so-called anamnesis, the doctor wants to find out which current complaints the patient has, which previous or chronic illnesses exist and which diseases are present in the family. The doctor also needs information about the medication the patient is taking and about his social and professional environment.
All these things are important so that the doctor can classify the current complaints and not forget any symptoms or factors that are related to the patient’s illness. By means of a detailed anamnesis interview, the doctor can exclude possible diseases and make a suspected diagnosis together with alternative differential diagnoses. The various differential diagnoses have both similarities and differences, for example, in the course or in the symptoms described by the patient.
Through a thorough physical examination, the physician finds additional symptoms or findings that speak for or against one of the differential diagnoses. Laboratory tests, ultrasound, X-ray, CT, MRI and other examinations provide further indications for or against a possible differential diagnosis. Of course, not all examinations are always necessary to detect the patient’s disease, because in the course of the various diagnostic examinations, differential diagnoses can gradually be ruled out.
Thorough differential diagnosis is particularly important when making so-called exclusionary diagnoses. These are diagnoses that may only be made if all other possible differential diagnoses have been reliably excluded by anamnesis, physical and apparatus examinations. One example is irritable bowel syndrome, which is a gastrointestinal disorder for which no physical cause can be found.