An idiopathic disease is any disease with an unknown cause or mechanism of apparent spontaneous 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.
The word essential is sometimes synonymous with idiopathic (as in essential hypertension, essential thrombocythemia, and essential tremor) and the same is true of primary (as in primary biliary cholangitis, or primary amenorrhea), with the latter term being used in such cases to contrast with secondary in the sense of "secondary to [i.e., caused by] some other condition." Another, less common synonym is agnogenic (agno-, "unknown" + -gen, "cause" + -ic).
The word cryptogenic (crypto-, "hidden" + -gen, "cause" + -ic) 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 word congenital 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 (that is, those whose pathophysiology has existed since the neonatal period).
Syndrome without a name
The term syndrome(s) without a name (SWAN) 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 (50%) of children with learning disabilities and approximately 60% of children with congenital disabilities (disabilities which are apparent from birth) do not have a definitive diagnosis to explain the cause of their difficulties". The registered charity Genetic Alliance UK runs SWAN UK, a support group for families of children with undiagnosed genetic conditions. SWAN USA became a 501c3 organisation in 2006.
- Diagnosis of exclusion
- Embolic stroke of undetermined source
- Functional disorder
- Idiosyncratic drug reaction
- The dictionary definition of idiopathic disease at Wiktionary