Blood flow across different regions of the brain may help to distinguish between bipolar depression and ordinary \u201cunipolar\u201d depression, new research suggests. Although it\u2019s a preliminary finding and a relatively small study, the existing difficulty in distinguishing between the two forms of depression and the invasive nature of positron emission tomography (PET scans) gives the approach the potential to become a regular feature in clinical practice. However, finding out the details of the study is essential to understanding which conclusions to draw from it. Different Types of Depression There are numerous types of depression, ranging from minor or major depression to varieties such as psychotic depression, seasonal affective disorder and bipolar disorder. The term \u201cunipolar\u201d depression is merely a method of distinguishing major and minor depression (which cause more traditional depression-like symptoms) from bipolar depression, which is characterized by fits of mania (extreme highs) that intersperse the depression. This creates a \u201ccycling\u201d of moods, which in turn causes the difficulty in diagnosing bipolar depression on the first assessment. In fact, only one in five are correctly diagnosed the first time around. The Study The research, published in the British Journal of Psychiatry, aimed to identify a reliable biological marker that can be used to differentiate between the two with neurological imaging technology. The researchers used a novel scanning technique called arterial spin labeling, which uses water (water is naturally present in the blood) as a marker to measure blood flow through different regions in the brain. This makes it very safe, because nothing has to be introduced to the body in order to obtain the images. They recruited 54 women for the study who were all around the age of 32 and split them into groups of 18. One group had women with bipolar disorder, one group was composed of those with recurrent unipolar depression and the final group of women had no psychological disorders. Every participant in the depression groups was going through a depressive episode at the time of the research. The new imaging technique was used to look at blood flow in areas of the anterior cingulate cortex area of the brain, which is associated with depression. What They Found The researchers were able to identify significant differences in brain patterns between those with unipolar and bipolar depression in one specific region of the target area. Using this method, they were able to determine who had which condition 80.6 percent of the time. This is a very promising result, for obvious reasons, but the results of the tests weren\u2019t so positive when it came to identifying who was suffering from either condition against a \u201ccontrol group\u201d participant (who had neither condition). The method was only able to distinguish between control group participants and those suffering from unipolar depression about 50 percent of the time, the figures just edging into statistical significance. In addition, the result was unfortunately even less promising for bipolar depression - not reaching a statistically significant level. Issues Aside from the difficulty in telling a depressed patient apart from a healthy one (which indicates some problems in the method), there was also an issue in the medication the participants were taking. Of course, it\u2019s extremely difficult to recruit participants who are not taking medication, and unethical to ask them to abstain from their required medicine, but the fact could explain the ease of distinguishing between the two groups. Around 10 times as many of those in the bipolar group were taking mood stabilizers and over twice as many of those with unipolar depression were taking antidepressants (in comparison to each other). Still a Promising Result Despite the potential problems, the result could still have huge implications for the future of diagnosing depression in clinical practice. During the follow-up period for the study, two out of the four unipolar depression sufferers the method identified as having bipolar depression (counted as an incorrect diagnosis in the statistics) were later diagnosed with bipolar depression. This underlines the potential value of this approach in determining who is suffering from bipolar depression much earlier than otherwise possible. Jorge Almeida, MD, PhD, the study\u2019s lead author, commented, \u201cEarlier and more accurate diagnoses can make an enormous difference for patients and their families, and may even save lives.\u201d The preliminary nature of this study means that there will definitely be more research into this possibility in the future. If the method turns out not to depend on another factor (such as medication), it could become a key biomarker in distinguishing between the two types of depression, and the non-invasive nature of the technique means it could become common in clinical practice. In the future, if more useful biomarkers are discovered, it could be possible to solely use neuro-imaging to diagnose depression, ensuring that those in need receive the right treatment.