Sunday, July 19, 2015

Is depression and allergy or infection?

Depression has been a difficult disease to figure out scientifically. The frustration with a lack of progress leads to a natural tendency to want to hit a home run. Perhaps this is something like a football team that falls behind in the score, and starts throwing "long bombs" as a wishful strategy to pull out a victory. This mindset is currently colouring the interpretation of recent findings of a correlation between depression and various inflammatory indicators. Very frequently, we see non-critical representations of these findings as a possible revolution in our understanding of depression, here is a recent example. The idea that some of the behavioural and psychological manifestations of depression may be mediated by inflammatory messengers is decades old and was once discussed as a relationship between these medications and the syndrome of sickness behaviour seen in inflammatory states. There are, of course, many important implications of this finding, including the explanation that they provide for the negative impact of depression on the course of some inflammatory diseases (such as coronary artery disease) and the sometimes puzzling tendency for the strength of association of depression with medical illnesses not to associate closely with the degree of threat associated with those illnesses, e.g. see here. However, the overselling of this idea often seems to act against the aim of developing a comprehensive understanding of this condition - an overselling that, to me, seems driven by an excessive need to crow-bar knowledge of this condition into a more familiar disease model, an idea that I discuss in more detail here.