Investigators Suggest Better Predictors to Diagnosing Mental Illness

October 11, 2019
Claire Gillan, PhD

Claire Gillan, PhD

In a new study, investigators suggest a need for more individualized approaches to defining mental illnesses because of substantial overlap across different disorders.

A team of investigators, led by Claire M. Gillan, PhD, School of Psychology, Trinity College Institute of Neuroscience and Global Brain Health Institute, recently completed a 285-patient cross-sectional study in the US for individuals diagnosed with obsessive-compulsive disorder (OCD) and/or generalized anxiety disorder (GAD).

The investigators found self-reported compulsivity was more strongly linked with goal-directed deficits than a diagnosis of OCD compared with GAD.

The results could have implications for research assessing the association between brain mechanisms and clinical manifestations, as well as for understanding the structure of mental illness.

The aim of the study was to identify if deficits in goal-directed planning better identified by self-reported compulsivity or a diagnosis of obsessive-compulsive disorder. Each patient completed a telephone-based diagnostic interview by a trained rater, internet-based cognitive testing, and self-reported clinical assessments between 2015-2017.

The investigators collected follow-up data as well to test for replicability.

Performance was measured on a test of goal-directed planning and cognitive flexibility using the Wisconsin Card Sorting Test (WCST), as well as a test for abstract reasoning.

Clinical variables included a DSM-5 diagnosis of OCD and GAD, as well as 3 psychiatric symptom dimensions—general distress, compulsivity, and obsessionality—derived from a factor analysis.

Overall, deficits in goal-directed planning in OCD was strongly tied with a compulsivity dimension than with a OCD diagnosis.

The mean age of the 285 patients was 32, with a range of 18-77 years old. The patient population included 219 females, 111 individuals with OCD, 82 patients with GAD, and 92 patients with both disorders.

“A diagnosis of OCD was not associated with goal-directed performance compared with GAD at baseline (P = .18),” the authors wrote. “In contrast, a compulsivity dimension was negatively associated with goal-directed performance (P = .003).”

This pattern was also found with abstract reasoning tasks as well as WCST.

“The compulsivity dimension was associated with abstract reasoning (P < .001) and several indicators of WCST performance (P < .001), whereas OCD diagnosis was not (abstract reasoning: P = .56; categories completed: P = .38),” the authors wrote.

However, other symptom dimensions related to OCD, obsessionality, and general distress had no reliable association with goal-directed performance, WCST, or abstract reasoning.

Obsessionality also had a positive association with requiring more trials to reach the first category on the WCST at baseline (P = .04), while general distress was linked to impaired goal-directed performance at baseline (P = .01).

Despite this, neither survived correction for multiple comparisons or was replicated at follow-up testing.
 
In the past, dimensional definitions of transdiagnostic mental health problems has been recommended as an alternative to a categorical diagnosis. Using this technique allows clinicians to capture heterogeneity within diagnostic categories and similarity across them to bridge more naturally psychological and neural substrates.

“This study suggests that transdiagnostic compulsivity symptoms may have greater biological validity than a diagnosis of obsessive-compulsive disorder,” the authors wrote.

There are fundamental issues with using popular international categories for neurobiological research such as the DSM-5 and International Classification of Mental and Behavioural Disorders, 10th Revision.

While diagnostic groups are highly heterogeneous, patients often have the same diagnosis with vastly different symptom profiles.

Individuals without a psychiatric diagnosis usually differ from patients with a diagnosis in several ways beyond the diagnosis under investigation, including anxiety, depression, physical illness, and early-life adversity.

As a result, potential biomarkers, intermediate phenotypes, and etiologic substrates often can only show a modest association with a categorical clinical phenotype, but is unlikely to be specific to that phenotype.

The study, “Comparison of the Association Between Goal-Directed Planning and Self-reported Compulsivity vs Obsessive-Compulsive Disorder Diagnosis,” was published online in JAMA Psychiatry.
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