There is no sharp line between health and disease. (See a previous post in this blog “The concept of health and disease” please). Deviations from what we consider as “normal” that are detrimental to the individual are labeled as illnesses or diseases. The ways in which a person’s condition deviates from normality take innumerable forms and shapes. Every patient’s disease is in fact unique. There are similarities and differences between diseases of different individuals. Because we think that similar diseases may progress in similar ways and respond to our intervention in similar ways we try to group them into one disease entity and give it a name. There are grades of similarity between the individuals in the same disease entity. We might see patients whose diseases fit very well with the classical description of that entity and patients whose diseases differ from the classical description to various degrees. There are no sharp lines of separation between disease entities. Some diseases may not fit well into any of the artificial entities that we create or fall in the boundary between two entities or more. We then either force them into one of the entities that we consider the nearest possible or include them into more than one entity or create a new entity with a different name to accommodate them.
These facts explain at least partly the differences between doctors about the diagnosis of a patient’s disease and why in many instances a patient’s disease does not behave in the way we expect it to.
Much of the controversy in medical discussions is about language rather than fact. It is semantics. Nevertheless it is important because language dictates our acquisition of knowledge. It is the language, the names, that makes it possible for us to learn about diseases and to get the help of the book or the literature to guide our prediction of prognosis and our management. It is not an ideal situation but that is the case with almost everything in life.