Syndrome

In medicine and psychology, a syndrome is the association of several clinically recognizable features, signs (observed by a physician), symptoms (reported by the patient), phenomena or characteristics that often occur together, so that the presence of one or more features alerts the physician to the possible presence of the others. Specific syndromes tend to have a range of possible etiologies or diseases that could create such a set of circumstances. I.e. there is an important distinction between Parkinson's disease and a Parkinsonian syndrome, whereby the latter could be caused by the former, but also by other conditions such as a progressive supranuclear palsy or multiple system atrophy. In other words, in a medical setting, a syndrome might narrow down the possible diseases a patient may possess, just as speaking English might focus a guess as to the country in which that person originates.

In recent decades, the term has been used outside medicine to refer to a combination of phenomena seen in association.

The term syndrome derives from the Greek συνδρομή (sundromē) and means "concurrence of symptoms, concourse", from σύν (sun), "along with, together" + δρόμος (dromos), amongst others "course". It is most often used to refer to the set of detectable characteristics when the reason that they occur together (the pathophysiology of the syndrome) has not yet been discovered. A familiar syndrome name often continues to be used even after an underlying cause has been found, or when there are a number of different primary causes that all give rise to the same combination of symptoms and signs. Many syndromes are named after the physicians credited with first reporting the association; these are "eponymous" syndromes (see also the list of eponymous diseases, many of which are called "syndromes"). Otherwise, disease features or presumed causes, as well as references to geography, history or poetry, can lend their names to syndromes.

Related concepts
Subsyndromal conditions or formes fruste are those medical conditions that do not meet full criteria for a diagnosis, for example because the symptoms are fewer or less severe than a defined syndrome, but that nevertheless can be identified and related to the "full-blown" syndrome.

A culture-bound syndrome is a set of symptoms where there is no evidence of an underlying biological cause, and that is only recognized as a "disease" in a particular culture.

Syndromes and associated conditions
The description of a syndrome usually includes a number of essential characteristics, which when concurrent lead to the diagnosis of the condition. Frequently these are classified as a combination of typical major symptoms and signs—essential to the diagnosis—together with minor findings, some or all of which may be absent. A formal description may specify the minimum number of major and minor findings respectively, that are required for the diagnosis.

In contrast to the major and minor findings typical of the syndrome, there may be an association with other conditions, meaning that in persons with the specified syndrome these associated conditions occur more frequently than would be expected by chance. While the syndrome and the associated conditions may be statistically related, they do not have a clear cause and effect relationship, i.e., there is likely to be a separate underlying problem or risk factor that explains the association. An example would be Down syndrome, which has the associated condition of diabetes mellitus. A knowledge of associated conditions would dictate that they are specifically looked for in the management of the syndrome.

Examples
One recent case study is acquired immune deficiency syndrome (AIDS), so-named because most syndromal immune deficiencies are inborn genetic disorders, rather than something that a previously healthy person can acquire. AIDS was originally termed "gay-related immune deficiency" (GRID), a name revised as the disease turned out to also affect heterosexuals. Several years passed after the recognition of AIDS before HIV (human immunodeficiency virus) was first described, finally explaining the hitherto mysterious "syndrome".

SARS (severe acute respiratory syndrome) is an even more recent example of a syndrome in medicine that was later explained with the identification of a causative coronavirus.

History
Ibn Sina (Avicenna, 980-1037), in The Canon of Medicine, pioneered the idea of a syndrome in the diagnosis of specific diseases.

The concept of a medical syndrome was further developed in the 17th century by Thomas Sydenham.