An idiopathic disease is any disease with an unknown cause or mechanism of apparent origin. From Greek ἴδιος idios "one's own" and πάθος pathos "suffering", idiopathy means approximately "a disease of its own kind". For some medical conditions, one or more causes are somewhat understood, but in a certain percentage of people with the condition, the cause may not be readily apparent or characterized. In these cases, the origin of the condition is said to be idiopathic. With some other medical conditions, the root cause for a large percentage of all cases have not been established—for example, focal segmental glomerulosclerosis or ankylosing spondylitis; the majority of these cases are deemed idiopathic.
Advances in medical science improve the study of causes of diseases and the classification of diseases; thus, regarding any particular condition or disease, as more root causes are discovered, and as events that seemed spontaneous have their origins revealed, the percentage of cases designated as idiopathic decreases.
Usage of synonyms
The word essential is sometimes synonymous with idiopathic and the same is true of primary, with the latter term being used in such cases to contrast with secondary in the sense of "secondary to some other condition." Another, less common synonym is agnogenic. The word cryptogenic has a sense that is synonymous with idiopathic and a sense that is contradistinguished from it. Some disease classifications prefer the use of the synonymous term cryptogenic disease as in cryptogenic stroke, and some forms of epilepsy. The use of cryptogenic is also sometimes reserved for cases where it is presumed that the cause is simple and will be found in the future. Some congenital conditions are idiopathic, and sometimes the wordcongenital is used synonymously with idiopathic; but careful usage prefers to reserve the word congenital for conditions to which the literal sense of the word applies.
The term syndrome without a name is used "when a child or young adult is believed to have a genetic condition and testing has failed to identify its genetic cause". It is believed that "about half of children with learning disabilities and approximately 60% of children with congenital disabilities do not have a definitive diagnosis to explain the cause of their difficulties".
