Brain Abnormalities Linked to Comorbid ADHD in Bipolar Disorder

Brain structure abnormalities discovered through magnetic resonance imaging (MRI) in bipolar patients may have been wrongly attributed to the disorder.

They may actually be linked to the patient with bipolar disorder also having an attention-deficit hyperactivity disorder (ADHD), according to new research.

Because of the similarities and frequent coexistence of these two conditions, the ability to separate their symptoms and obtain an accurate diagnosis between the two has been a persistent challenge.

ADHD is a frequent diagnosis in individuals with bipolar disorder, with a comorbidity — co-existing together — prevalence of 5-20 percent.  This is often overlooked, though, when looking at brain imaging data.
For the study, researchers from the University of California at Los Angeles set out to unravel how ADHD and bipolar disorder individually contributed to brain abnormalities found during MRI.

They recruited 85 participants, of whom 17 had bipolar disorder only, 19 had ADHD only, 18 had both bipolar disorder and ADHD, and 31 had no mental disorder. All patients with bipolar disorder were in a non-depressed state at the time of imaging and were not taking lithium.

Researchers used MRI to measure participants’ cortical thickness. Analysis of the prefrontal cortex and anterior cingulate cortex showed that overall cortical thickness was lessened in patients with bipolar disorder both with and without comorbid ADHD.

However, the effect of bipolar disorder on cortical thickness was different in patients with and without ADHD in the right orbitofrontal cortex and the left subgenual cingulate.

In the right orbitofrontal cortex, bipolar disorder was associated with significant cortical thinning only when there was no ADHD diagnosis; furthermore, in the left subgenual cingulate, the presence of ADHD eliminated the cortical thinning associated with bipolar disorder compared to controls.

The effects of bipolar disorder and ADHD in these regions were found to be connected, “resulting in a unique phenotypic signature for the comorbid diagnostic group,” write the researchers in the journal Bipolar Disorders.