Researchers outline new diagnostic model for mental illness

Mar 23 2017

A consortium of 50 psychologists and psychiatrists from around the world has outlined a new diagnostic model for mental illness, in what researchers hope will be a paradigm shift in how these illnesses are classified and diagnosed.

Lee Anna Clark, William J. and Dorothy K. O'Neill Professor and Chair of Psychology, and David Watson, Andrew J. McKenna Family Professor of Psychology at the University of Notre Dame, who both are members of the consortium, say that the current model of diagnosis and classification — the DSM-5 — is fundamentally flawed.

"The Diagnostic and Statistical Manual of Mental Disorders (DSM) — which is overseen and published by the American Psychiatric Association — currently is the dominant diagnostic model in North America; it also is highly influential around the world," Watson said. Although he and Clark were involved in the revisions for the DSM's fifth edition, he said, "Quite frankly, we were not satisfied with the revisions that were made. We felt that DSM-5 was far too conservative and failed to recognize and incorporate important scientific evidence regarding the nature of psychopathology."

The model the consortium proposes, called the Hierarchical Taxonomy of Psychopathology (HiTOP), addresses these concerns, which are shared by many psychologists and psychiatrists.

The HiTOP model differs from the DSM in two fundamental ways, Watson said. First, although the DSM's categorical nature means that a specific diagnosis is given only if someone meets a specific number of criteria, the HiTOP model allows for not only a diagnosis but also an assessment of its severity.

"If you meet the DSM's diagnostic criteria for major depression, you are diagnosed as being depressed. If you do not meet these criteria, however, then you simply are classified as not depressed," Watson said. "In contrast, HiTOP conceives of psychopathology as being continuous, that is, dimensional in nature."

The advantages of such classification include more personalized and specific treatment, as well as allowing researchers and clinicians to recognize and acknowledge the existence of significant problems that don't currently meet full DSM diagnostic thresholds.

A second major advantage of the HiTOP model is its use of empirical evidence to classify disorders, a change from the DSM's tendency to group disorders based partly on clinical assumptions about which disorders seem to go together. "For example, generalized anxiety disorder, panic disorder and specific phobia all are classified as 'anxiety disorders' in the DSM because they all involve symptoms related to fear and anxiety," Watson said. "In contrast, most people who are diagnosed with general anxiety disorder also meet the criteria for major depression. Consequently, in HiTOP, generalized anxiety disorder is classified as being more similar to major depression than to specific phobia.

"One major advantage of this approach is that it helps to clarify underlying causes and mechanisms. For instance, many of the same vulnerabilities and risk factors have been linked to both major depression and generalized anxiety disorder. So, this model will help us identify the underlying causes of problems more quickly."

Lesser known conditions, such as sleep and bipolar disorders, still need to be classified within the HiTOP model. "Certain aspects of the system are ready to be developed into clinical applications," said Clark, who is a member of a workgroup within the consortium that developed HiTOP exploring its clinical use. "With sufficient background knowledge, it can be used clinically immediately, but it's clear from our discussions that it will take some time to develop HiTOP to the point that it can be widely used clinically — that is, by clinicians in the community who do not have a research background."

Clark and Watson played a significant role in developing this model. Researchers used several large epidemiological surveys in the United States, Australia, the Netherlands and other countries to gather data about how the most common forms of psychopathology — such as depression, anxiety, substance abuse and personality disorder — are related.