Precise characterization of clinical subtypes allows us to better understand common pathogenic mechanisms, more accurately predict an individual's clinical course, and, one hopes, obtain better treatment results. Carefully developed clinical definitions also add precision and reproducibility to clinical research. However, the process of pattern recognition that underpins our efforts to categorize disease is imperfect and sometimes arbitrary, so our classifications are always subject to revision when new information comes to light or when prior interpretations are questioned. It is easy to become so immersed in a familiar way of thinking that we fail to see that most disease classifications are merely working definitions that are bound to change over time. In fact, evolution of our concepts and terms generally mirrors an improved understanding of a disease, so we should not resist such change.
Roach ES. Is Neuromyelitis Optica a Distinct Entity?. Arch Neurol. 2007;64(6):906. doi:10.1001/archneur.64.6.906