What's in a diagnosis?
If you or someone you know has been troubled enough to enter a psychiatrist's office, she or he has probably emerged with a prescription and a diagnosis, possibly even a numerically coded label like 296.33: major depressive disorder, recurrent, severe, without psychotic features; or 309.81: post-traumatic stress disorder.
Diagnoses like these, indeed virtually all psychiatric diagnoses, encompass nothing more than a pattern of symptoms that tend to cluster together in similarly troubled patients. Patients who share these symptom patterns may share other qualities, such as a similar tendency to drink excessively or to respond to pharmaceuticals that block a given neurotransmitter receptor.
But do such diagnoses say anything about the nature of the problem? Throughout medicine, to know a diagnosis is to have some sense of the mechanism by which bodily dysfunction produces symptoms of illness. In pneumonia, the nature of the problem is a bacterial infection in the lungs that arouses an inflammatory response that induces fever and copious amounts of phlegm that must be coughed out or else obstruct airways. In coronary artery disease, the nature of the problem is a buildup of plaque in the blood vessels that feed the heart, that slow the flow of blood, and so starve the heart of oxygen when the heart beats harder and demands more energy.
What about a common psychiatric diagnosis like schizophrenia? We classify it as a "psychotic disorder". But what mental function does a "psychotic disorder" disrupt? Psychosis isn't a function; it's a symptom. Calling schizophrenia a "psychotic disorder" is like calling a heart attack a "chest pain disorder". The term conveys nothing about the nature of the problem, only the quality of the symptoms.
Often, there is no bright line between normal and disordered. For example, in "post-traumatic stress disorder", there is no consensus as to what determines whether a normal response to horrific circumstances crosses over to mental disorder-it could be the nature of the trauma or some biological change in the brain or some pattern of maladaptive behavior that blocks recovery. The faulty assumption that a disorder must exist when some symptoms are present has caused serious trouble when a person who had all the symptoms of post-traumatic stress disorder but no recollection of a traumatic experience was presumed to have been traumatized (and to have repressed the memory), and so an innocent party was falsely blamed or even prosecuted for imaginary "crimes" the patient could not recall without hypnotic suggestion.
You might think: it matters little that we don't know the nature of mental illness, so long as we have treatments that work. But psychiatry's incoherence about the nature of mental illness limits our ability to advance beyond our relative state of ignorance.
When the diagnosis is easily made and the treatment works as expected, there is no problem. But much of the time the diagnosis is murky. Patients may have some symptoms of X, but not enough of them to be sure, or perhaps the patient also symptoms of Y and Z. Does the patient have X, Y, and Z together, or do X, Y, and Z together constitute a different disorder entirely? The answer to such questions is critical, because it means the difference between treating a known problem with medications and other interventions that are known to work for that problem, and simply making guesses about what might work.
I work in an academic medical center where patients with these kinds of complicated or ambiguous diagnoses come for expert opinion and treatment. Most of them would not make the trek to Baltimore if their conventional treatment worked adequately. This leads us to the other major weakness in not having a coherent account of the nature of mental illness: psychiatrists are left with no logical approach to think about what to do when a patient's problems are complex, or ambiguous, or unresponsive to the standard treatments.
I am what you might call a mid-career psychiatrist, experienced enough to have seen a lot of patients and taught a lot of students and to have become frustrated with the lack of conceptual depth in our ability to explain mental illness, but with enough of a career ahead of me to want to try to get things right while it might still matter to my present and future patients and students. Having thought about these questions for my entire career, I have developed some (I'm told) original ideas about the nature of mental illness. I describe them in my book, Trouble in Mind: An Unorthodox Introduction to Psychiatry, and I intend to share them in this blog.