Moving Away From Treatment-Resistant Depression and Toward Difficult-to-Treat Depression

Case Study

“Ellen,” a woman in her early 60s, is referred to you with “treatment-resistant depression.” Her chart lists 4 antidepressants across 2 classes over 18 months, 2 of them stopped early for adverse effects and one abandoned without explanation. What dominates the picture is not sadness but a flat, effortful anhedonia: she moves slowly, tires within an hour of waking, and complains that her memory “isn’t there anymore.” Buried in her intake and easy to skim past is a history of early-life trauma, a childhood of chronic adversity and fear, that no prior note has connected to the adult in front of you. Her inflammatory status has never been checked, because why would it be? She is, after all, simply treatment resistant. But before you reach for a fifth agent, it is worth asking a different question: Is this resistance, or is it a mismatch?

That question sits at the heart of a shift now underway in the depression literature, one that has not yet reached most of us at the bedside. It is the move away from treatment-resistant depression (TRD) toward the broader, more clinically honest construct of difficult-to-treat depression (DTD) and, within it, toward stratifying patients by the biology and the circumstances that are actually driving their illness.

The Trouble With “Resistance”

A systematic review identified 155 distinct definitions of TRD currently in use.¹ This is not merely a pedantic concern. It means that the same patient may qualify as “treatment-resistant” in one clinic but not in another, depending on how many failed treatment trials are required, how long those trials must last, and whether psychotherapy or neuromodulation is considered at all. The label influences decisions regarding access to advanced treatments and reimbursement, yet it rests on no universally accepted definition.

Worse still, much of what we call resistance may not be resistance at all. A substantial proportion of apparent nonresponders, estimated to be between 30% and 60% in some studies, reflects pseudoresistance: inadequate dosing, insufficient treatment duration, poor adherence, unrecognized comorbidities, or pharmacokinetic variability that renders standard doses subtherapeutic in a meaningful minority of patients.¹ When treatment adequacy is not rigorously assessed and documented, the prevalence of “resistance” is artificially inflated, leading to potentially inappropriate clinical decisions.

The clinical consequences of this label are far from neutral. Fava and Rafanelli have described a process of “cascade iatrogenesis,” whereby clinicians reflexively move from one pharmacological strategy to another, switching, escalating, and augmenting treatment, before adequately addressing adherence and psychosocial determinants or considering whether psychotherapy and neuromodulation should already be part of the treatment plan.² A construct originally intended to identify patients in need of alternative approaches too often results in more of the same.

Reframing the Problem

DTD reframes the problem (Figure). Rather than tallying pharmacological failures, it asks what is actually sustaining the burden.¹ The international consensus defines DTD as depression that continues to cause a significant burden despite usual treatment efforts, and it shifts the therapeutic target from symptom reduction alone to functioning and quality of life.³ That burden is never the patient’s alone: It is carried by families, who absorb the caregiving, the lost income, and the vigilance about relapse, and by clinicians and services, who accumulate repeated visits, escalating polypharmacy, and their own demoralization when nothing works.^3,4 Rush et al make the same move explicit. When remission proves elusive, the goal becomes optimal symptom control and a disease-management approach rather than an endless pursuit of the next agent.⁵

This is more than semantics. DTD integrates the things the TRD frame tends to push aside: treatment adequacy, functional impairment, psychiatric and medical comorbidity, trauma history, symptom profile, patient goals, and even organizational barriers such as access and continuity of care.⁴ It abandons the binary responder/nonresponder logic for a spectrum, and it treats chronic depression the way we treat other chronic illnesses, as something to be managed across domains rather than cured in one. For you as the clinician, the practical consequence is a change in the first question you ask. Not “Which drug next?” but “What is making this depression difficult, and have I addressed it?”

Why Stratification Matters

Among the determinants the DTD frame brings into view, the inflamed subgroup is the clearest illustration of what stratification buys us. Roughly one-fourth of patients with major depressive disorder show low-grade systemic inflammation (high-sensitivity C-reactive protein [hs-CRP], ≥ 3 mg/L).⁶ These patients respond more poorly to standard monoaminergic antidepressants, independent of how severe their depression is.⁷ The phenotype is recognizable: marked anhedonia, psychomotor slowing, fatigue, and cognitive complaints, as with Ellen, the woman in the case study.

The reframing is the important part. The patient’s poor response is not due to the illness’s stubbornness; it is a mechanistic mismatch between the driver (neuroinflammation acting on reward circuitry) and the drug’s mechanism (monoaminergic modulation).⁸ Calling such a patient “resistant” misnames the problem. They are mismatched, and the mismatch is potentially actionable. The logic is simple enough to use: screen with hs-CRP, a test you already order, interpreted during periods of clinical stability and adjusted for body mass index, smoking, and intercurrent infection. In cases where it is elevated, analyze the phenotype further with a parsimonious cytokine panel (IL-6, TNF-α, IL-1β); then align the intervention to the biology rather than escalating blindly.

Here, honesty is essential. At present, inflammatory stratification is a tool for phenotyping, prognosis, and enriching clinical trials, not a validated trigger for routine anti-inflammatory prescribing. The evidence for immunomodulatory agents is genuinely mixed: A large trial of infliximab in TRD found no overall benefit, yet in an exploratory analysis, a subgroup with elevated baseline hs-CRP (> 5 mg/L) improved, which is precisely the argument for enrichment rather than unselected treatment.⁹ So the near-term value of measuring inflammation is not that it tells you to prescribe a biologic. Rather, it tells you why a patient may not be responding; flags those for whom lifestyle, behavioral, and psychosocial interventions are biologically rational early choices; and keeps you from a sixth monoaminergic switch that the mechanism predicts will fail.

What to Do

None of this requires specialized infrastructure. It requires a change in sequence. Before you accept “resistant,” verify the adequacy of the dose, start a trial of at least 6 to 8 weeks, ensure adherence, and complete therapeutic drug monitoring when pharmacokinetics are in doubt.¹ Reconsider the diagnosis, screen for comorbidity, and take a brief trauma history. In the patient who is stalling rather than responding, measure hs-CRP. Assess function and cognition explicitly, not by impression. The Sheehan Disability Scale takes a minute to complete, and a brief cognitive screen, such as the THINC-it tool, captures the deficits patients rate as most disabling.¹⁰ Bring psychotherapy and psychosocial intervention forward rather than reserving them for after the pharmacological options are exhausted.³ In everyday clinical practice, this is concrete rather than aspirational: A brief trauma history, even a handful of adverse-childhood-experience questions, fits inside a standard visit, can be documented in the shared record and flagged to the collaborating primary care clinician, and turns an apparent “resistance” into a life-course vulnerability that makes trauma-focused psychotherapy a rational early move rather than a last resort. It is also essential to work collaboratively with the patient’s primary care physician, social supports, and family, and conduct periodic reassessments of the diagnosis itself.

Case Study Continued

Let us return to Ellen. Read through the DTD lens, her case stops being a dead end and becomes a short list of concrete moves.

• First, confirm adequacy: Were those 4 trials actually delivered at therapeutic dose for 6 to 8 weeks, with adherence verified? Given the 2 early discontinuations for adverse effects, is tolerability the real story rather than resistance?
• Second, rediagnose: Her early-life trauma history, the early discontinuations, and the prominent anhedonia and psychomotor slowing all warrant a fresh look at comorbidity, including posttraumatic presentations, bipolarity, and medical contributors, before another switch.
• Third, read the phenotype rather than the failure count: The anergic, anhedonic, cognitively blunted presentation is exactly the profile in which an hs-CRP, a test already on the order set, earns its place, not as a verdict but as one more piece of information.
• Fourth, measure what matters: An SDS and a brief cognitive screen turn "she isn't better" into a functional baseline you can track.
• Fifth, widen the plan now, not after the next failure: Bring psychotherapy, structured psychosocial support, and family involvement forward alongside any pharmacological adjustment that follows.

The point is not that an inflammatory marker would have “explained” Ellen, or that an anti-inflammatory would have fixed her. It is that “treatment-resistant” closed her case, while “difficult-to-treat” reopens it with a sequence of actions any clinician can run on Monday. The label described our frustration; the framework gives us something to do with it. That is the whole of the shift, and it is available now, in the clinic you already work in, with the tests you already order and the colleagues you already have.

Dr Paganin is a psychiatrist and psychotherapist in the public mental health service and holds a doctoral degree in neuroscience from the University of Rome Tor Vergata in Rome, Italy; he also collaborates with Studio Psicologia Signorini in Guidonia, Italy. His research focuses on difficult-to-treat depression and the neurobiology of psychiatric disorders, with particular attention to the role of childhood trauma, and he works with multifamily and interfamilial therapy approaches.

References

1. Paganin W. Treatment-resistant depression: time to rethink current definitions and clinical practice. Front Psychiatry. 2026;16:1733678.

2. Fava GA, Rafanelli C. Iatrogenic factors in psychopathology. Psychother Psychosom. 2019;88(3):129-140.

3. McAllister-Williams RH, Arango C, Blier P, et al. The identification, assessment and management of difficult-to-treat depression: an international consensus statement. J Affect Disord. 2020;267:264-282.

4. Rush AJ, Sackeim HA, Conway CR, et al. Clinical research challenges posed by difficult-to-treat depression. Psychol Med. 2022;52(3):419-432.

5. Rush AJ, Aaronson ST, Demyttenaere K. Difficult-to-treat depression: a clinical and research roadmap for when remission is elusive. Aust N Z J Psychiatry. 2019;53(2):109-118.

6. Osimo EF, Baxter LJ, Lewis G, Jones PB, Khandaker GM. Prevalence of low-grade inflammation in depression: a systematic review and meta-analysis of CRP levels. Psychol Med. 2019;49(12):1958-1970.

7. McIntyre RS, Alsuwaidan M, Baune BT, et al. Treatment-resistant depression: definition, prevalence, detection, management, and investigational interventions. World Psychiatry. 2023;22(3):394-412.

8. Paganin W. Stratifying the inflamed endotype in difficult-to-treat depression: a roadmap from biomarkers to precision immunopsychiatry. Clin Neuropsychiatry. 2025;22(6):529-539.

9. Raison CL, Rutherford RE, Woolwine BJ, et al. A randomized controlled trial of the tumor necrosis factor antagonist infliximab for treatment-resistant depression: the role of baseline inflammatory biomarkers. JAMA Psychiatry. 2013;70(1):31-41.

10. McIntyre RS, Best MW, Bowie CR, et al. The THINC-Integrated Tool (THINC-it) screening assessment for cognitive dysfunction: validation in patients with major depressive disorder. J Clin Psychiatry. 2017;78(7):873-881.