Nosology

Nosology: a classification scheme within medicine delineating classification of diseases. A chief difficulty in nosology is that diseases often cannot be defined and classified clearly, especially when cause or pathogenesis are unknown. Thus diagnostic terms often only reflect a symptom or set of symptoms. Traditionally diseases were defined as syndromes by their symptoms. When more information is available, they are also defined by the damage they produce. When cause is known, they are better defined by their cause, though still important are their characteristics.