Saturday, November 19, 2016

Chronic Conditions and Major Depression

When I was training (many years ago) in Psychiatry, all of the textbooks used to have long lists of medical conditions that could "cause" depression. The idea was that such lists would serve as a reminder that physical causes should be considered when assessing patients. For example, if there was a reason to suspect hypothyroidism, then that patient's thyroid should be checked. However, in current times this way of thinking - that depression would be distinguished as being "caused" by a physical OR a psychological cause seems very simplistic. Certainly, there are physical mechanisms that could link some chronic conditions to depression, but every chronic condition can have psychological and social implications too. Depression likely arises as a result of the multiple contributing causes in every case, not a different single cause in different cases. We recently conducted an analysis of national survey data to look at patterns of association between major depressive episodes and various chronic medical conditions. The meta-analysis (published here) uncovered three previously undescribed patterns of association. First, we found that most conditions are more strongly associated with depression in younger people. This effect was most prominent for high blood pressure and cancer. I believe that this probably indicates that developing such a condition is more stressful and threatening for a younger than older person. This is of course mere speculation. This was not a universal pattern. Migraine was an exception: the strength of association increased with age, especially in men. Second, especially for conditions predominantly affecting older age groups (arthritis, diabetes, back pain, cataracts, effects of stroke and heart disease) an epidemiological occurrence called confounding (by age) was evident. Because depression prevalence diminishes with age, and because these conditions affect older people, statistical adjustments were needed to see the true association. Finally, a surprising result was that thryoid disease, long considered the "classical" physical cause of depression, was only weakly associated with depression, and only in women. Epilepsy, had a unique pattern than didn't depend on age or sex. 

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