Why is it unreliable to treat diseases based on symptoms alone?

What does the word "symptom" mean to doctors? It mainly reflects the patient's subjective discomfort. If there is discomfort, there must be a reason. Finding this reason is one of the important tasks of doctors, which is diagnosis. Diagnosis is made by asking about symptoms. This is part of "medical history collection", also called "interview". Some diseases can be basically diagnosed through interviews.

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You may be thinking, since symptoms are so important, can I judge the severity of my illness by the severity of my symptoms? I can tell you responsibly that this is not possible. Because symptoms reflect subjective feelings, in many cases, the severity of symptoms is not necessarily proportional to the severity of the disease. Sometimes the symptoms are very severe, but the disease is not necessarily fatal; sometimes, although the symptoms are very mild, the disease is very dangerous.

For example, shingles. The main symptom of this disease is pain, and it hurts a lot. How painful is it? Doctors use a term to describe this pain, called "lightning pain." As soon as you hear the name, you can know how severe the pain of shingles is. However, can a disease with such obvious pain symptoms lead to death? The answer is extremely rare.

For example, acute laryngitis and acute epiglottitis, the symptoms of these two diseases are very mild, just sore throat, and the pain is not that severe. However, don't underestimate these two diseases, if they occur, it is easy to cause life-threatening. So when doctors encounter patients with "sore throat", they have to be extremely careful, and there is a reason for this.

You must have understood that symptoms are not necessarily proportional to the severity of the disease. More importantly, it is unreliable to make a diagnosis based solely on symptoms. This is because different diseases may show the same symptoms, while the same disease may have different symptoms when it occurs.

For example, the typical symptom of appendicitis is metastatic right lower abdominal pain, which first hurts around the navel and then gradually moves to the right lower abdomen. This symptom is so typical that when doctors mention the symptom of metastatic right lower abdominal pain, the first thing they think of is appendicitis. However, things are not so absolute. When gastric perforation occurs, the contents of the stomach may flow along the paracolic gutter to the right lower abdomen, which may also cause metastatic right lower abdominal pain, which is very similar to appendicitis in all aspects. You see, the causes of these two diseases are completely different, but the symptoms may be very similar.

As for the same disease showing different symptoms, there are many examples. For example, most patients experience pain in the precordial area, that is, the left side of the chest, when angina pectoris attacks. It is a dull pain, not the sharp pain of a needle or knife. However, not everyone has pain in the precordial area when angina pectoris attacks. Some people will experience toothache, finger pain, and stomachache. Therefore, the same disease may cause different symptoms. In order to distinguish these atypical symptoms, doctors must have a solid foundation and rich clinical experience.

Finally, let me summarize. It is very important to understand the condition through symptoms, but this has limitations because symptoms reflect the patient's subjective discomfort. First, the severity of the symptoms may not be proportional to the severity of the condition. Second, different diseases may have the same symptoms, while the same disease may have different symptoms in different people.

The article is produced by Science Popularization China-Starry Sky Project (Creation and Cultivation). Please indicate the source when reprinting.

Author: Sun Yifei, Director of the Medical Education History Research Office, Hebei Medical University

Reviewer: Chen Gang, deputy chief physician, Peking Union Medical College Hospital