In Medicine, the existing of more than one condition or disease is common and it is so called “Comorbidity”. This term by definition refers to the co-existence of two conditions without any relationship such as causal. In other word, comorbidity is the co-existing of two conditions in parallel with no relationship, or different pathophysiology and treatment paths. But in fact that is not the case in many situations, as one condition may give rise to another, or in a better sense, one is primary and the other is secondary. For example hypertension or high blood pressure can lead to stroke and its consequences such as hemiplegia, or diabetes as a primary condition could cause many complications as secondary conditions such as diabetic foot and poor vision, etc. The treatment of the primary condition such as diabetes or osteoporosis could prevent the secondary condition such as diabetic wounds and bone fractures.
Although some of these co-conditions that are still commonly labeled as “comorbidity” are very obviously primary and secondary to each other with a causal or consequential relationship, some conditions specially in Psychiatry may not look that much related to each other. For example in ADHD, secondary conditions or complications such as depression, oppositional defiant and anti-social behaviours or disorders, substance use disorders, etc. while not much superficially related, they are in fact so, and treatment of ADHD would prevent majority of the others. For the first time, I coined the term “post-morbidity” in ADHD for these secondary conditions or complications that are still in the literature considered loosely “comorbidity” with no apparent causal relationships. (1-2)
A similar relationship exists between depression and anxiety that are commonly comorbid in psychiatry and it is still considered with no causal or temporal relationship as simply “comorbid” in the literature and among experts. If two conditions are causally related and not appreciated as such, it will affect their treatments and both conditions could be treated with two treatments, e.g. two or more medications. But if there is a causal relationship, the treatment of the primary condition would prevent and treat the secondary or “post-morbid” condition, while their pathophysiologic relationship is more appreciated and understood. In this paper, I will show for the first time that such a primary and secondary or “post-morbidity” relationship exists between depression and anxiety that has never to this date been recognized.
Depression and Anxiety: Are they related?
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