We hear the words “disease” and “disorder” thrown around all the time, often as near synonyms. But there are marked differences between the two, most of which go unrecognised.
Diseases are distinct - measurable, and well defined. Diseases have specific causes; they fit predetermined processes of the body. A disorder, on the other hand, is the interruption of typical bodily function. It is not as restricted, and the cause of a disorder is not always known. For disease, particular symptoms are a necessity. For disorder, they are a possibility.
Another important distinction between diseases and disorders has to do with structural versus functional change. Function can be said to be a result of structure. Function is external, what we can do; where structure refers to the internal workings allowing this function to occur. Disease encompasses precise structural change -- disorder, on the other hand, is tied to more functional change. The closest disorder gets to structural change is its impact on chemical imbalances. For instance, depression -- also known as Major Depressive Disorder -- is linked (not directly caused by) chemical imbalance in the brain. This is indicative of its status as a disorder.
Both diseases and disorders can be hereditary, and both are accompanied by a set of symptoms (a syndrome). Certain disorders can point to the possibility of certain diseases. For instance, Graves’ disease -- a disease caused by the acting up of the thyroid (a throat gland) -- is also described as an autoimmune disorder. Its classification as a disease is simply a step up in diagnosis after being recognised as a disorder.
This is not true for every disorder, however. Many mental illnesses are seen as disorders and simply disorders because their exact causes cannot be easily pinpointed. However, they undoubtedly cause certain symptoms and functional change, hence their place as disorders. Nor is this true for every disease -- Coronavirus disease, for example, is not an extension of a disorder. It is a disease due to its known cause (a virus) and the manner in which it implements structural change on one’s body, by infiltrating bodily systems and activating the immune system.
Sometimes, these terms are put into a hierarchy -- symptoms below syndromes (a group of symptoms) below disorders below diseases, based on how well understood each group is. However, even doctors sometimes use the terms disorder and disease interchangeably -- so despite their differences, don’t beat yourself up for getting them confused. The world of biology is a confusing one; this is a simply a peek.
By Maya Ford
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