Abstract

The term, idiopathic, emerged as a key concept in the classification of disease in the 18th century and has become ingrained in our terminology in defining diseases and their aetiologies throughout all fields of medicine. Despite, or perhaps because of this, little has been written about the meaning or meanings of the word itself. Although most medical professionals will be able to offer a definition of idiopathic, different definitions of the word are in use and are often confused or used without an appreciation of the range of meanings. This article aims to clarify these different meanings with reference to historic and current uses. The change from the earlier nosological definition of ‘primary’ to the most widely accepted current definition, ‘of unknown cause’, occurred in the late 19th century, reflecting changing perspectives of disease causation. Far from being an innocent translation of ‘unknown’, idiopathic creates problems for future terminology and adds little to medical understanding. In masking the unknown, the term idiopathic maintains a paternalistic patient–practitioner relationship, and so should be avoided in modern medical terminology.