The fifth edition of the Diagnostics and Statistical Manual (DSM-5) was recently released. This is the standard reference of mental disorders and psychiatric illnesses released by the American Psychiatric Association (APA).
As with previous editions there is a great deal of discussion and wringing of hands over the details – which disorders were created or eliminated. For example hoarding is now considered its own disorder, rather than part of obsessive compulsive disorder (it has its own reality TV show, why not its own DSM diagnosis?).
This time around, however, the debate over the DSM goes much deeper than the particulars of specific diagnoses. The real debate is about the very existence of the DSM – its validity and utility. While this discussion is nothing new, it has taken on an unprecedented dimension with the rejection of the DSM by the National Institutes of Mental Health (NIMH). Director Thomas Insel wrote:
The goal of this new manual, as with all previous editions, is to provide a common language for describing psychopathology. While DSM has been described as a “Bible” for the field, it is, at best, a dictionary, creating a set of labels and defining each. The strength of each of the editions of DSM has been “reliability” – each edition has ensured that clinicians use the same terms in the same ways. The weakness is its lack of validity. Unlike our definitions of ischemic heart disease, lymphoma, or AIDS, the DSM diagnoses are based on a consensus about clusters of clinical symptoms, not any objective laboratory measure. In the rest of medicine, this would be equivalent to creating diagnostic systems based on the nature of chest pain or the quality of fever. Indeed, symptom-based diagnosis, once common in other areas of medicine, has been largely replaced in the past half century as we have understood that symptoms alone rarely indicate the best choice of treatment.
Categorization in Science and Medicine
The debate is largely about how we categorize mental disorders (I will use the term mental disorders as a non-specific catchall in this article for mental illness, disease, psychiatric conditions, etc.). This will likely turn out to be bigger than the demotion of Pluto to a dwarf planet.
As with the categorization of planets, this is more than just an issue of definition. In planetary astronomy the issue was with how we understand planetary formation and solar system dynamics. With mental disorders the real debate is about our understanding of underlying cause.
Insel may be overstating the case, but historically he is correct- the DSM is mainly a dictionary of terms, so that psychiatrists can talk to each other and publish using a consistent lexicon. The DSM gives specific diagnoses an operational definition based upon a list of signs and symptoms.
While this approach has been criticized, it is almost universal in medicine as a starting point for our exploration of any new disease. I disagree with Insel in his implication that symptom-based diagnosis is inherently flawed and largely abandoned in the rest of medicine.
When we first identify a new disease or disorder it is almost always first recognized by its symptoms, signs, and course. This is the purely descriptive phase of our understanding. Epidemiology comes next – who gets it, how, and when. Scientists then hunt for an underlying cause – the pathophysiology. It takes years to decades to fully understand a disease, and for many we still lack a full understanding even after decades of active research.
In ALS, for example (motor neuron disease) we know that motor neurons are dying, but we don’t know why. So the diagnosis is defined largely clinically, although based upon exam findings and test results. The diagnosis is not based upon any understanding of cause, however. Further, this means that ALS is likely not one disease but many, that have the same manifestation because the same cell population is dying.
Migraine is another example. Headaches are entirely classified by a list of symptoms (frequency and location of headache and association with other symptoms).
Multiple sclerosis is a mixture, like many diseases. We understand a great deal about pathophysiology, and diagnosis is based upon hard findings. But we don’t know the ultimate cause, and there are subtypes of MS that are entirely clinically based (mostly on the course of the disease – relapsing remitting, chronic progressive, etc.). We don’t know why the different subtypes are different.
In reality, the degree to which medical diagnoses are clinical – based upon signs, symptoms, and course – vs based upon pathophysiology is entirely dependent upon our current understanding of pathophysiology.
Criticizing a diagnostic scheme on this criterion, therefore, seems odd. What is the alternative? If we lack a sufficient understanding of pathophysiology, we need to categorize based upon what we do now (how patients present). These diagnostic labels are placeholders. We expect and hope to replace them one day with a categorization based upon a deeper understanding of the disease.
The reality is that medical diagnoses today are a mishmash of clinical features (signs, symptoms, disease course, age of onset), biological markers, pathology, response to treatment, and pattern of inheritance if any. Psychiatric diagnoses are no different – except that we largely lack biological markers and pathology. This reflects the complexity of mental disorders and the current state of our understanding.
The NIMH, however, is now saying that it also, and predominantly, reflects a flawed approach.
The Biological Model of Mental Illness
The NIMH is taking what critics call the extreme biological approach to mental disorders – that all mental disorders are brain disorders, and properly studied we should be able to figure out those biological causes.
What Insel is saying is that the DSM is not just a convenient list of placeholder diagnoses, but it is a straitjacket. Researchers have been forced to base their studies into biological causes on DSM labels that may not (and probably don’t) reflect underlying reality.
This situation would then be similar to doing biological research based upon classic Linnaen taxonomy rather than evolution-based cladistic categorization. Linnaeus based his categorization of life upon often superficial features. Now that we understand the origin of the diversity of life, evolution, we can re-categorize all of life in a way that reflects true evolutionary relationships.
Insel is in essence saying that the NIMH has failed to find biological markers for mental illness because they have been forced to labor under a false categorization system, the DSM. A cynic might say that he is blaming the DSM for the failures of the NIMH. A charitable interpretation is that Insel is responding to disappointing progress appropriately by rethinking basic strategy.
Some critics have essentially said, a pox on both houses (the DSM and NIMH).
The DSM is criticized as being “cynically pragmatic” – for putting a practical clinical approach above scientific evidence in drawing DSM diagnoses. At the very least, the DSM needs an evidence-base overhaul, and it probably won’t get it until the old-guard releases its iron grip.
Meanwhile, the NIMH claim that all mental disorders are biological is overly simplistic. Mental disorders are a complex combination of brain function and environmental factors. We will therefore never get completely away from clinical criteria, even if they are better informed by biological information.
As with many disputes, reality is likely in the middle of these two extremes (the pragmatic clinical approach and the biological approach). One area that should have complete agreement, however, is that scientific evidence should be the ultimate determining factor.
The New Approach
Meanwhile, neuroscientists seem to be taking their research into mental disorders away from the DSM and more in the direction indicated by the NIMH. The new emphasis is on genetics and functional brain imaging. This is partly driven by technological development – they are researching in these areas because they have the tools to do so.
Researchers are therefore stepping back from classic clinical diagnoses and trying to think about mental disorders in a more fundamental way. They are trying to identify networks or modules in the brain that correlate to specific fundamental behaviors or experiences. Rather than thinking about full clinical syndromes, neuroscientists are trying to reduce them to specific and well-defined neurological phenomena.
In a recent interview on the SGU with one such researcher, Heather Berlin, she described how in her research on obsessive compulsive disorder she is looking at the brain responses to disgust. OCD patients, it turns out, have an increased disgust response. Perhaps, then, we may eventually understand a subset of what are now called OCD patients as individuals with hyperactive disgust response disorder.
Researchers are also building on the genome project to identify genes that correlate with mental disorders. No one expects to find a single gene that equates to a specific mental disorder, but we are finding gene variants that correlate to increased risk. Autism researchers, for example, have been very successful in identifying genes that correlate with risk of ASD.
Here is where Insel’s complaint about the DSM comes in. He is arguing that genetic research might be doomed to failure if researchers are forced to correlate genetic variants to disease labels that don’t reflect biological reality. Such research is set up to fail from the beginning. It remains to be seen if stepping back from the DSM will yield greater success.
Psychiatry’s critics have been having a field day spinning all of this controversy as the death knell for psychiatry. Rather, I see it all as a very healthy sign of growth. Psychiatry has had a prolonged infancy as a scientific discipline, stuck for decades in the descriptive clinical phase of understanding illness.
This phase is necessary and does have some practical utility. But it can also be a mental straitjacket, if the placeholder labels are mistaken for necessarily real biological entities (they may or may not be). This straitjacket effect is not unique to psychiatry (nothing here is) – I teach students frequently that they need to understand the nature of various diagnoses. Some are specific pathophysiological entities, others are vague clinical syndromes that exist for purely practical purposes. Don’t confuse the two.
All medical specialties are trying to advance their field by deepening their understanding of pathophysiology. All need to practice medicine in the meantime, with imperfect knowledge.
Psychiatry might be suffering from a bit of a complex since it is lagging behind most other medical fields. I don’t think this can be entirely blamed on the DSM, however. Perhaps it is partly due to the fact that the DSM has had a disproportionate effect on categorization in psychiatry. The profession made a bargain with the DSM, trading flexibility for consistency.
Medical practice can have it both ways – we can (and do) use labels as placeholders, but not as iron-clad entities that constrain our thinking or research. The problem, however, is that regulatory agencies take the placeholder labels as iron-clad. The FDA, insurance companies, and research funding agencies use them as constraints.
In this regard perhaps the NIMH had to back away from the DSM.
Part of the lag of psychiatry, however, is that the subject matter is genuinely complex, and there are strong non-biological influences. I don’t think we will ever get to a pure biological categorization of mental disorders. I do think that neuroscience and genetics research will transform the field and our thinking of mental disorders, as all successful scientific research should do.
If I am being hopeful I see this current controversy as a sign that psychiatry is ready to push through to the next level – more evidence-based, and more biologically informed categories and diagnoses.
The DSM is a necessary placeholder, but that means its reign must end one day, and that will not represent failure, but progress.