Bipolar disorder (BD) is characterized by significant shifts in mood, energy, and activity levels, cycling between depressive lows and manic or hypomanic highs. Managing the depressive phase, often called bipolar depression, is challenging because traditional antidepressant medications carry a risk of triggering a manic episode. Transcranial Magnetic Stimulation (TMS) is a non-invasive procedure that uses magnetic fields to stimulate nerve cells in the brain. TMS has emerged as a potential treatment for treatment-resistant depression, leading to interest in its safety and effectiveness for managing bipolar depressive episodes.
How Transcranial Magnetic Stimulation Works
TMS utilizes an electromagnetic coil placed against the scalp, generating a rapidly changing magnetic field. This field passes through the skull, inducing a localized electrical current in the underlying brain tissue to modulate neural circuits involved in mood regulation. For depression, the typical target is the dorsolateral prefrontal cortex (DLPFC), a region often underactive during a depressive episode. The magnetic pulses stimulate neurons in this area, which is thought to help restore healthier communication within mood-regulating brain networks. TMS is performed in an outpatient setting, requires no anesthesia, and patients remain awake.
Regulatory Status: TMS for Bipolar Depression
The regulatory standing of TMS differs significantly between unipolar and bipolar depression. The U.S. Food and Drug Administration (FDA) has fully approved TMS to treat Major Depressive Disorder (MDD) in adults who have not responded to antidepressant medication. However, TMS does not currently hold broad, formal FDA approval as a standard treatment for Bipolar Disorder. Despite this, the FDA granted a “breakthrough device designation” in 2020 to a specific TMS system for treatment-resistant bipolar depression. This designation expedites the review process for technologies showing potential for more effective treatment. When used for Bipolar Depression, treatment is often applied off-label and focuses exclusively on the depressive phase. Clinical protocols advise against using TMS during a manic or mixed episode, as stimulation could exacerbate these states.
Safety Concerns and the Risk of Manic Switch
The safety profile of TMS is generally favorable compared to systemic drug treatments. The most commonly reported side effects are localized and mild, including temporary headaches, scalp discomfort or tingling, and lightheadedness. These effects usually diminish after the first few treatment sessions. A significant concern for bipolar patients is the risk of a “manic switch”—a rapid shift from depression into a manic or hypomanic episode. This risk is also present with many antidepressant medications used in BD treatment. Research suggests the risk of a manic switch with TMS may be comparable to that associated with certain antidepressant drugs. To mitigate this complication, clinical guidelines recommend TMS only be administered when a patient is concurrently stabilized on a mood-regulating medication, such as a mood stabilizer or an antipsychotic. Close monitoring by a psychiatrist is maintained throughout treatment to detect early signs of mood elevation.
Patient Suitability and Current Clinical Research
Suitable candidates for TMS are typically those experiencing a moderate to severe depressive episode of Bipolar Disorder that has not responded adequately to standard pharmacological treatments. The decision requires a comprehensive evaluation by a specialized psychiatrist to confirm a stable mood-stabilizing regimen is in place. Suitability also depends on the absence of certain medical devices, such as metal implants near the coil, or a history of seizure disorder. Current clinical research explores ways to optimize TMS for bipolar depression, with promising results emerging from newer stimulation protocols.
Newer Stimulation Protocols
Intermittent theta-burst stimulation (iTBS) is a faster protocol that mimics the brain’s natural activity patterns and may improve treatment efficiency. Deep TMS (dTMS) uses a specialized coil designed to stimulate broader and deeper brain regions, showing positive outcomes in trials for treatment-resistant bipolar depression. Ongoing studies are also using neuroimaging techniques like functional MRI to precisely map and target specific connectivity issues in the brain, aiming to refine treatment protocols and reduce the risk of mood destabilization.