Comorbidities Among Several Common Psychiatric Disorders

In this paper we deconstruct the concept of “psychiatric comorbidity.” There’s said to be more of it than ever before, but analyses supporting this proposition are premised on an incorrect assumption. They tend to define comorbidity as an accumulation of separate psychiatric diagnoses, each with its own characteristic symptom profile. If there’s more than one of them, then they’re comorbid. As a result, clinicians end up treating a variety of symptoms without considering their hierarchical structure. In fact, symptoms thought to point to an independent diagnosis often simply are expressions of or sequela to an underlying disorder – effects instead of causes. We explore the possibility space of psychiatric syndrome dynamics and propose a system of ordinary differential equations that identify which is which. We describe how sequelae emerge from primary system dynamics without acquiring separate etiological status. We offer examples throughout, provide testable empirical hypothesis implementing the model we propose and conclude with a discussion of the clinical implications of our approach.