Symptom dimensions within bipolar disorder may have distinct causes

Key takeaways:

• Researchers found a strong association between MDD and the depression dimension.
• They also found a strong association between schizophrenia and the psychosis dimension.

Symptom dimensions within bipolar disorder may have distinct causes, supporting the hypothesis that genetic heterogeneity underpins clinical heterogeneity, according to a study published in The Lancet Psychiatry.

“Our results challenge current diagnostic systems that [emphasize] a distinction between unipolar and bipolar depression, [conceptualize] mania and depression as the opposite ends of a single [etiological] dimension, and poorly explain mixed states, which are a common presentation in bipolar disorder,” Judith Allardyce, MBChB, MPH, MSc, PhD, of the University of Edinburgh, and colleagues wrote. “The development of dimensional stratification could increase the precision and specificity of current classification systems and facilitate [etiological] research.”

In a study of 4,148 individuals using data from the UK Bipolar Disorder Research Network, Allardyce and colleagues analyzed psychopathological variables via interviews with trained research psychologists or psychiatrists and psychiatric case notes to identify statistically distinct symptom dimensions.

The researchers identified three reliable dimensions: mania, depression and psychosis.

Allardyce and colleagues found a strong association between schizophrenia and the psychosis dimension, as well as a strong association between major depressive disorder and the depression dimension. They also found a weak association between bipolar disorder and the mania dimension.

“Our findings support the hypothesis that genetic heterogeneity underpins clinical heterogeneity, suggesting that within bipolar disorder, different symptom dimensions have partly distinct causes,” they wrote. “Furthermore, our results suggest that a symptom dimension might have a similar cause irrespective of the primary psychiatric diagnosis, supporting the use of symptom dimensions in precision psychiatry.”