Treatment-Resistant Depression (TRD)

Treatment-Resistant Depression (TRD) is defined as major depressive disorder that has not responded adequately to at least two courses of antidepressant treatment, given at adequate dose and duration, usually at least 4–6 weeks each, during the current depressive episode. It is one of the main indications for rTMS in depression.

Why it matters

Approximately 30% of patients with MDD do not respond adequately to pharmacotherapy, according to data from the STAR*D trial. These patients carry a disproportionate burden of disability, suicide risk, and healthcare cost. rTMS, particularly accelerated iTBS protocols such as SAINT, offers a rapid antidepressant approach for a population with limited alternatives. Learn more about the clinical procedure in the clinic.

Mechanism

• Neurobiological basis of TRD: reduced prefrontal cortical activity, reduced brain-derived neurotrophic factor (BDNF), glutamatergic dysfunction involving NMDA receptor hypofunction, and impaired neuroplasticity.
• Pharmacological mechanisms: resistance may relate to genetic variation in cytochrome P450 enzymes, such as CYP2D6 and CYP2C19 poor or ultra-rapid metabolism, P-glycoprotein polymorphisms affecting transport across the blood-brain barrier, and pharmacodynamic tolerance.
• rTMS bypasses pharmacological resistance mechanisms by acting directly on neural circuits and targeting the activation of neuroplasticity.

Clinical significance

In patients with TRD, rTMS achieves response rates of approximately 50–55% and remission rates of approximately 30–35% in meta-analyses. The SAINT protocol, an accelerated iTBS protocol using 50 sessions over 5 days, reported remission rates of 79% in an open-label study by Cole et al. in 2020; this result was partially replicated in randomized controlled trial data. Individualized motor threshold measurement is critical for treatment success. Pharmacogenomic (PGx) assessment before rTMS can also help optimize pharmacotherapy at the same time.

Explicit relations (Entity Graph)

• TRD is defined as failure of at least two adequate antidepressant trials.
• TRD is a main indication for rTMS.
• TRD affects approximately 30% of patients with major depressive disorder (MDD).
• TRD is associated with impaired neuroplasticity.
• TRD is associated with pharmacogenomic variation in CYP2D6 and CYP2C19.
• rTMS response rate in TRD is approximately 50–55%.
• Accelerated iTBS / SAINT has shown remission rates up to 79% in open-label studies.
• Alternative treatments for TRD include ECT, ketamine/esketamine, and MAOIs.

References

1. Rush AJ, Trivedi MH, Wisniewski SR, et al. (2006). Acute and longer-term outcomes in depressed outpatients requiring one or several treatment steps: a STAR*D report. American Journal of Psychiatry.
2. O’Reardon JP, Solvason HB, Janicak PG, et al. (2007). Efficacy and safety of transcranial magnetic stimulation in the acute treatment of major depression: a multisite randomized controlled trial. Biological Psychiatry.
3. Cole EJ, Stimpson KH, Bentzley BS, et al. (2020). Stanford accelerated intelligent neuromodulation therapy for treatment-resistant depression. American Journal of Psychiatry.