Neuroimaging distinguishes between bipolar and depression in human study.
Mental illness, particularly bipolar disorder and depression, can be difficult to diagnose as many conditions have similar symptoms. These two illness are virtually identical except that in bipolar individuals also experience mania, which means that distinguishing them can be difficult. The wrong diagnosis can be dangerous, leading to poor outcomes for the patient as they undergo treatment for the incorrect disorder, therefore identifying brain markers which could reliably tell them apart would have immense clinical benefit. Now, a study from researchers led by the Westmead Institute for Medical Research shows that neurons deep inside the brain could hold the key to accurately diagnosing and differentiating bipolar disorder and depression. The team state that such a marker could help to better understand both these disorders, identify risk factors for developing these disorders, and potentially enable clear diagnosis from early onset. The study is published in the journal Biological Psychiatry: Cognitive Neuroscience and NeuroImaging.
Previous studies show that approximately 60% of patients with bipolar disorder are initially misdiagnosed as major depressive disorder. Alarming, in some cases it can take up to a decade for these patients to be accurately diagnosed with bipolar disorder. Bipolar disorder often first presents in the depressive phase of the illness and bipolar depression is similar to major depression in terms of clinical symptoms; emotion processing is a core problem underlying both these disorders. The current study shows that independent of level of emotional awareness, amygdala activation and connectivity during facial emotion processing can distinguish bipolar and depressive disorder patients.
The current study utilises fMRI to investigate how the amygdala, a region in the brain which plays a key role in processing emotions, reacts as 73 participants process facial expressions such as anger, fear, sadness, disgust and happiness. Results show that the amygdala responds differently depending on whether the person has bipolar disorder or depression. Data findings show that in people with bipolar disorder, the left side of the amygdala is less active and less connected with other parts of the brain than in people with depression, with 80% accuracy in making this distinction.
Results show that bipolar disorder participants had lower left amygdala activation than patients with depression during a perceived and subconscious threat, sad and neutral processing and for subconcious processing of happy faces. Data findings show that bipolar disorder participants also exhibit lower amygdala connectivity to the insula and hippocampus for threat and to medial orbito-frontal for happy perceived and subconscious processing. Bipolar disorder participants also demonstrated greater amygdala-insula connectivity for perceived and subconscious sad facial processing.
The team surmise their findings provide evidence that the amygdala could be a potential trait-marker to differentiate bipolar disorder and depression largely independent of illness or emotional state. For the future, the researchers state that they are now running phase 2 of this study, which aims to further characterise these identified markers in a larger cohort of patients.