Brain imaging could assist bipolar depression diagnosis

By Eleanor McDermid, Senior medwireNews Reporter

Researchers have identified structural brain differences that could help to distinguish patients with unipolar and bipolar depression.

Differences in grey and white matter volumes in the amygdala, hippocampus and anterior cingulate gyrus (ACG) distinguished the two groups from each other with nearly 70% accuracy, report Udo Dannlowski (University of Münster, Germany) and team.

“These regions are known to be important for emotion processing and regulation”, they observe in JAMA Psychiatry.

The study included 58 patients with bipolar depression, 58 with unipolar depression and 58 age- and gender-matched mentally healthy controls, who underwent structural brain imaging at either a US or German site. When the researchers created and also tested pattern recognition algorithms on participants from the same site, they obtained a classification accuracy for unipolar versus bipolar depression of up to 65.5% for the US site and 75.9% for the German site.

When they created the algorithms at one site and tested them at the other, they obtained an accuracy of up to 63.8% for testing in the US group and 69.0% for testing in the German group.

“Although a performance of less than 70% accuracy may not be regarded as substantial enough to justify a clinical application, it must be emphasized that, to our knowledge, this is the first use of pattern classification algorithms with classifiers trained on a reference sample to data from an independent sample measured on a different scanner platform”, say Dannlowski et al.

Patients with bipolar depression had significantly less grey matter than those with unipolar depression in four areas involving the hippocampus, amygdala, putamen, insula and the temporal pole. By contrast, unipolar patients had less grey matter than bipolar patients only in the ACG.

The researchers say that the reduced ACG volumes in the unipolar patients is consistent with previous research and is thought to result in the “inability to regulate automatic negative self-referential processing and accompanied feelings.”

The results also suggest a “key role” for the amygdala in differentiating unipolar from bipolar depression, “even if the underlying mechanisms remain to be clarified”, they say. However, they caution that hippocampal volumes may not by themselves differentiate between the two groups, because both had reduced volumes relative to the controls. Unipolar patients did not have smaller ACG volumes than controls, and bipolar patients did not have smaller amygdala volumes.

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