Comorbidity sounds precise, yet psychiatry may be using the word wrongly
When a patient has two or more conditions at once, doctors call it comorbidity. The term dates only from 1970, and critics argue it can mislead: in psychiatry, apparently separate diagnoses may really be one illness seen from different angles, a puzzle some reviewers treat as a crisis for modern diagnostic manuals.
The word joins the Latin morbus, sickness, with co-, meaning together. A researcher named Feinstein introduced it into medicine in 1970 to describe a distinct extra clinical problem appearing before or during treatment of an index disease, the primary diagnosis. It has since acquired three overlapping meanings: two conditions that coexist independently, two that are causally linked, and any conditions that coexist regardless of cause.
That middle meaning blurs into the idea of a complication. In long-standing diabetes, for example, it is hard to say how far coronary artery disease is an independent problem and how far a consequence, because both illnesses involve many factors at once. Syndromes are often recognised long before anyone confirms whether they share a mechanism, so the true relationship can stay unknown.
Later studies found that the criteria for choosing an index disease were subjective and flawed, and that singling out one condition as the driver could hinder understanding of interdependent illnesses. Multimorbidity emerged as the answer: two or more chronic conditions with none given priority. The distinction matters in practice. Multimorbidity suits holistic, person-centred care that looks at every symptom, while comorbidity often remains the more useful framing in areas such as drug research.
Psychiatry is where the concept strains most. Major depressive disorder commonly appears alongside other diagnoses, and personality disorders show comorbidity rates approaching 60 percent in some cases, which critics read as evidence that the categories are too loosely drawn. Multiple labels may simply reflect an inability to find one diagnosis that explains everything. Some writers call psychiatric comorbidity a Kuhnian anomaly pushing the DSM towards scientific crisis, and the Hierarchical Taxonomy of Psychopathology has been put forward as an alternative classification designed to address the problem.
Source: Comorbidity
