Why Stratification Matters<\/p>\n
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], \u2265 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.<\/p>\n
The reframing is the important part. The patient\u2019s poor response is not due to the illness\u2019s stubbornness; it is a mechanistic mismatch between the driver (neuroinflammation acting on reward circuitry) and the drug\u2019s mechanism (monoaminergic modulation).8 Calling such a patient \u201cresistant\u201d 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-\u03b1, IL-1\u03b2); then align the intervention to the biology rather than escalating blindly.<\/p>\n
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.<\/p>\n
What to Do<\/p>\n
None of this requires specialized infrastructure. It requires a change in sequence. Before you accept \u201cresistant,\u201d 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 \u201cresistance\u201d 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\u2019s primary care physician, social supports, and family, and conduct periodic reassessments of the diagnosis itself.<\/p>\n
Case Study Continued<\/p>\n
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.<\/p>\n
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.<\/p>\n
The point is not that an inflammatory marker would have \u201cexplained\u201d Ellen, or that an anti-inflammatory would have fixed her. It is that \u201ctreatment-resistant\u201d closed her case, while \u201cdifficult-to-treat\u201d 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.<\/p>\n
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.<\/p>\n
References<\/p>\n
1. Paganin W. Treatment-resistant depression: time to rethink current definitions and clinical practice.<\/a> Front Psychiatry. 2026;16:1733678.<\/p>\n 2. Fava GA, Rafanelli C. Iatrogenic factors in psychopathology.<\/a> Psychother Psychosom. 2019;88(3):129-140.<\/p>\n 3. McAllister-Williams RH, Arango C, Blier P, et al. The identification, assessment and management of difficult-to-treat depression: an international consensus statement.<\/a> J Affect Disord. 2020;267:264-282.<\/p>\n 4. Rush AJ, Sackeim HA, Conway CR, et al. Clinical research challenges posed by difficult-to-treat depression.<\/a> Psychol Med. 2022;52(3):419-432.<\/p>\n 5. Rush AJ, Aaronson ST, Demyttenaere K. Difficult-to-treat depression: a clinical and research roadmap for when remission is elusive.<\/a> Aust N Z J Psychiatry. 2019;53(2):109-118.<\/p>\n 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.<\/a> Psychol Med. 2019;49(12):1958-1970.<\/p>\n 7. McIntyre RS, Alsuwaidan M, Baune BT, et al. Treatment-resistant depression: definition, prevalence, detection, management, and investigational interventions.<\/a> World Psychiatry. 2023;22(3):394-412.<\/p>\n 8. Paganin W. Stratifying the inflamed endotype in difficult-to-treat depression: a roadmap from biomarkers to precision immunopsychiatry.<\/a> Clin Neuropsychiatry. 2025;22(6):529-539.<\/p>\n 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.<\/a> JAMA Psychiatry. 2013;70(1):31-41.<\/p>\n