Can a Bipolar Brain Scan Help in Diagnosis?

Can Brain Scans be Used to Diagnose Bipolar Disorder?

Although brain scans are not currently a reliable tool for diagnosing bipolar, they do have the potential to be a useful tool in the future. Recently, brain scans have begun to be used for mental illness because they can show physical differentiation in brain structure when behaviors can’t paint the complete picture. A study completed in 2020 used a combination of structural and functional MRI imaging techniques to effectively identify patients with bipolar at an accuracy of 87.5%.⁴

A doctor might recommend a brain scan for someone with bipolar symptoms in order to identify and rule out other conditions. Misdiagnoses might occur if there are any coexisting psychiatric or medical conditions, or due to lapses in history-taking.

Although uncommon, other conditions which might mimic symptoms of bipolar include brain trauma, tumor, Multiple Sclerosis, or stroke.¹ More often, people with depression or borderline personality disorder are misdiagnosed as having bipolar disorder.^{2, 3} Diagnostic criteria for both Borderline and Bipolar include mood shifts as well as significant impulsive behavior. The possibility of MRI assisting in bipolar diagnosis could be beneficial in situations such as borderline personality disorder or depression, where the symptoms can mimic bipolar disorder.

Brain Scans of a Bipolar Brain vs. Normal Brain

Several differences exist between the bipolar brain and the normal brain. Knowing when these differences begin to develop or are at risk of developing can help with early detection and prevention. A recent study looked at MRIs of adolescents at high risk for bipolar and compared those to brain scans of adolescents at normal risk. Over a 2-year span, the youth at high risk showed a decrease in connectivity between areas of the brain involved in emotional processing, while the normal risk scans showed an increase in connectivity.^{5, 6}

Physical abnormalities and differences in brain functions within bipolar disorder include:

• Amygdala activation: Using functional MRIs, researchers found lower levels of amygdala activation in Bipolar individuals when not in an acutely depressed mood compared to depressed patients.⁷
• Visual Cortices: Using MRI scans of bipolar vs normal brains, results showed that the bipolar brains responded in the same way to visual stimuli as the normal brains, when they were not in a manic or depressed mood.  When in a manic or depressed mood, the visual cortices of the Bipolar brains showed less activity than the normal brains.⁸
• Subcortical volume, cortical thickness, and white matter integrity: A large scale study using multimodal brain MRIs found consistent patterns of lower subcortical volume, lower cortical thickness, and disrupted white matter integrity in patients with Bipolar. Results were not dependent on being in a depressed or manic mood.^{9, 11}
• Cortical gray matter: MRI scans showed that gray matter was thinner in frontal, temporal, and parietal regions of the brain in Bipolar individuals. These are brain areas that are critical in the control of emotion and inhibition. Results were not dependent on mood state.^{9, 10}
• Subcortical volume: Based upon functional MRI scans, a review article reported widespread patterns of pathology in the subcortical limbic structures, including amygdala and ventral striatum. These findings were not dependent on mood state.¹²

When Are Brain Scans Used in Diagnosing Bipolar Disorder?

Doctors generally do not recommend brain scans to diagnose bipolar disorder. Medical doctors and mental health professionals usually rely on questions about current and past symptoms in order to make the diagnosis. A physician might order blood tests and/or brain scans to check for the presence of other conditions which can cause similar symptoms. For example, a brain scan might be ordered to rule out tumor or stroke as a cause of the symptoms.

The other main reason for ordering a scan of a possible bipolar brain is to be part of research for accurate diagnosis.  Studies of the structural and functional differences between a bipolar vs normal brain are ongoing. It is hoped that this type of research will at some point provide information that allows for the definitive diagnosis of bipolar based upon brain scans.

One of the challenges in diagnosing bipolar is being able to distinguish between one of the four types of bipolar vs. a unipolar depression. There is overlap between the symptoms of bipolar and the symptoms of unipolar depression. However, to be diagnosed with bipolar, the person must have a history of at least one episode of mania or hypomania. At the present time, there is no brain scan that is definitively used to diagnose any of these forms of bipolar.

The main types of bipolar disorder include:

• Bipolar I disorder: The person must have had at least one manic episode, and also has had depressive episodes. If a person with bipolar I reports only their symptoms of depression and doesn’t disclose symptoms of mania (irritability, elevated energy level, impulsiveness), they might be misdiagnosed as having depression.
• Bipolar II disorder: The person alternates between episodes of severe depression and hypomania but has never had a full manic episode. A person with bipolar II might not recognize the symptoms of hypomania due to their shorter duration or intensity compared to mania. They might also be diagnosed as depressed.
• Cyclothymic disorder: The person has had both mild depression and hypomanic episodes for at least 2 years. Since neither the depressed nor the hypomanic states are as severe as full manic or depressed episodes, the person with cyclothymic disorder might not acknowledge their shifts in mood between highs and lows.
• “Other specified” and “unspecified”: The person has had hypomanic episodes that don’t meet the full criteria for other bipolar types, with explanation that is either specific or vague. An unspecified bipolar disorder diagnosis can easily be missed due to the lack of clear symptoms of mania or hypomania.

With continued research, bipolar brain scans may become useful for differentiating between the different types of bipolar disorder. This would have implications for treatment since medication regimens differ among the four types of bipolar. For example, in one study, scans of bipolar I brains showed abnormalities in function and structure of brain areas involved in emotion regulation. These abnormalities were not seen in the scans of bipolar II brains. The results suggested basic differences in these two types of bipolar disorder.¹³

Reasons for misdiagnosis include the presence of coexisting conditions, lapses in history-taking, and similarity to other mental health conditions such as depression and borderline personality disorder.^{2, 3} Misdiagnosis can lead to many individuals not receiving a diagnosis for bipolar disorder into their adulthood and inadequate or insufficient treatment. Research into the structural and functional differences between bipolar brains and normal brains is extremely important for early detection and treatment.

Clinical Trials

If someone is interested in getting a brain scan but their medical provider doesn’t think it’s necessary for diagnosis, they might still participate in a clinical trial for research purposes. Ongoing national clinical trials for bipolar research can be found at www.clinicaltrials.gov.¹⁴ Also, the National Institute of Mental Health provides information about clinical trials.¹⁵ If interested, you might talk to your doctor or mental health provider about participating in a clinical trial.

What is the Future of Brain Scans and Bipolar Disorder?

While brain scans are not yet used for diagnosis of bipolar, they do hold a lot of promise for future use in both diagnosis and treatment. By continuing to improve mapping of affected brain areas in bipolar individuals, researchers will learn more about where in the brain to look for treatment effects. For example, studies have shown that treatment with lithium was associated with less thinning of gray matter, as compared to treatment with antipsychotics or anti-epileptics.¹⁰

Another direction of research is the use of novel imaging techniques which allow for looking at different regions of the brain in unique ways. Neurologists and neurosurgeons are teaming up to study the option of specific surgery to affect activity in the white matter of the brain.¹⁶ This could provide another option for bipolar patients whose symptoms are treatment-resistant.

Improved diagnosis also allows for more specified therapy for bipolar disorder. As an example, cognitive behavioral therapy (CBT) is effective for bipolar, while dialectical behavior therapy (DBT) is the preferred therapy for borderline personality disorder. Medication regimens for bipolar differ in important ways from medication for depression, making accurate diagnosis critical for treatment planning.

Final Thoughts

In the future, brain scans may allow for the confident diagnosis of bipolar disorder and for ruling out another type of bipolar or another mental health disorder which can cause similar symptoms. Someone struggling with treatment-resistant bipolar might talk with their doctor about participating in a clinical trial for research into making diagnosis more accurate as well as optimizing treatment for bipolar. Bipolar is a complex disorder which requires accurate diagnosis for determining the optimal treatment approach.