New diagnostic model for psychiatric disorders proposed

University of Otago researcher Associate Professor Martin Sellbom is part of a group of 50 leading international psychologists and psychiatrists who have put forward a new, evidence-based, system for classifying mental health disorders.

The researchers hope that their recommendations will lead to a paradigm-shift in how mental illnesses are classified and diagnosed. Their study appears in the American Psychological Association's Journal of Abnormal Psychology.

Their new Hierarchical Taxonomy of Psychopathology (HiTOP) addresses limitations to the reliability and validity of traditional models such as the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), the American Psychiatric Association's (APA) authoritative handbook used by clinicians and researchers around the world to diagnose and treat mental disorders.

They hope HiTOP will advance research efforts and improve clinical outcomes related to the causes and treatments of mental disorders.

Associate Professor Sellbom, who is a member of Otago's Department of Psychology, says HiTOP represents a new system for the classification of mental health problems that is rooted completely in cumulative scientific knowledge, unlike the current DSM-5 and the International Statistical Classification of Diseases and Related Health Problems (ICD-10).

"The DSM-5 relies on 'categorical' diagnoses which are assigned if a person has X out of Y symptoms, with no actual scientific basis for a qualitative change when you reach X symptoms. People with fewer symptoms are often just as impaired, but are considered to have no diagnosis," he says.

Instead, HiTOP relies on dimensional (or continuous) representations of mental health problems, which allows for a better consideration of severity, and also recognise the existence of significant problems that don't currently meet full DSM diagnostic thresholds, he says.

"HiTOP organises mental health problems hierarchically, which allows for a better understanding of which causes contribute to what these problems have in common."

A major advantage of the hierarchical 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 instance, several of the anxiety disorders of the DSM-5 have been grouped together based on content themes rather than their scientific associations, he says.

"For instance, Major Depressive Disorder and Generalised Anxiety Disorder have a far more significant overlap than do Generalised Anxiety Disorder and the other so-called anxiety disorders, such as social anxiety disorder or specific phobias. Such scientifically based groupings link classification to shared underlying causes and therefore better targeted treatments than the current arbitrary thematic groups."

The 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.