Approaching Difficult-to-Treat Psoriatic Arthritis

Key Takeaways:

• Difficult-to-treat PsA now has formal consensus definitions: GRAPPA and EULAR each published frameworks within weeks of each other in late 2025, agreeing on a broad category and a narrower treatment-refractory subset, but diverging on terminology and on how many therapies must fail.
• Much apparent drug resistance is not inflammatory. Comorbidities, obesity, and central sensitization inflate composite disease-activity scores and mimic active disease.
• Before escalating immunomodulation, confirm active inflammation objectively, then switch mechanism of action to cover every active domain while managing comorbidities in parallel.

Most patients with psoriatic arthritis (PsA) respond to today's expanding therapies, but a meaningful minority cycle through agents without reaching the target. Across long-extension follow-up trials, roughly 30 to 40 percent of patients treated with a first-line biologic or targeted synthetic DMARD do not reach minimal disease activity.¹

What was once loosely called "refractory" disease now has a more disciplined vocabulary – and the distinctions change what to do next.

Two definitions worth separating

In a recent initiative, the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA) proposed 2 distinct terms. Complex-to-manage PsA is the broad category: persistent, problematic symptoms despite at least 1 adequate biologic or targeted synthetic disease-modifying antirheumatic drug (b/tsDMARD), where the difficulty may stem from comorbidities, non-adherence, side effects, or access barriers. Treatment-refractory PsA is the narrower subset – failure of at least 3 therapies with different mechanisms of action (including 2 or more b/tsDMARDs), symptoms that trouble both clinician and patient, and objective evidence of ongoing inflammation.^2,3

GRAPPA was not alone. Weeks earlier, in October 2025, the European Alliance of Associations for Rheumatology (EULAR) issued its own consensus definitions – and they do not fully align. EULAR labels the broad category difficult-to-manage (D2M) rather than complex-to-manage, a wording GRAPPA changed deliberately after patient research partners objected that "difficult" assigns blame.⁴

The thresholds differ too: EULAR's D2M requires failure of at least 2 b/tsDMARDs spanning at least 2 mechanisms of action – a higher bar than GRAPPA's single-agent trigger – and its treatment-refractory tier is a subset of D2M that adds a second marker of persistent active disease (with objective inflammation mandatory) and requires that comorbid and psychosocial drivers be excluded, rather than counting to GRAPPA's third mechanism of action.⁴

Specialists broadly favor separating the broad category from the refractory one, because only the refractory tier reliably calls for more aggressive immunomodulation. That two societies defined the same clinical construct in the same quarter – while diverging on both label and threshold – is itself a signal of how unsettled the terminology still is.^2,3

When high scores mislead

That first category often has a non-inflammatory driver. Composite indices such as the Disease Activity in Psoriatic Arthritis (DAPSA) score blend tender-joint and patient-reported components, so they rise with pain regardless of its source.^1,5

In one PsA cohort, central sensitization correlated with both DAPSA and the Psoriatic Arthritis Disease Activity Score, and the authors cautioned that composite indices can be inflated by noninflammatory mechanisms and overestimate the true inflammatory burden.⁵

Fibromyalgia, obesity, depression, and osteoarthritis frequently coincide with PsA, and each can push a patient into apparent high disease activity without a matching rise in synovitis.^1,5

Confirm inflammation before escalating

This is why the refractory definition insists on objective inflammation. Before labeling disease drug-resistant, it is worth confirming active synovitis, enthesitis, or axial inflammation through examination, ultrasound, or magnetic resonance imaging, and acute-phase reactants.²

The stakes of getting this wrong are real: When a real-world cohort applied a rheumatoid-arthritis-style difficult-to-treat definition to PsA, only about 3 percent qualified, and the factors independently linked to difficulty were fibromyalgia, nail and pustular psoriasis, and corticosteroid use – a reminder that PsA's multidomain nature resists borrowed criteria.⁶

Switching mechanism, covering domains

When inflammation is confirmed, strategy follows the domains. GRAPPA's 2021 framework organizes therapy around peripheral arthritis, axial disease, enthesitis, dactylitis, skin, and nail, selecting an agent that covers as many active domains as possible. Residual activity in a single domain is a common reason a patient looks refractory.⁷

After a b/tsDMARD fails, the European Alliance of Associations for Rheumatology (EULAR) 2023 update supports switching to another agent, and moving to a different mechanism of action is a reasonable next step.⁸

The menu now spans tumor necrosis factor (TNF), interleukin-17, and interleukin-23 inhibition, plus oral options including Janus kinase (JAK) and tyrosine kinase 2 inhibitors. Among these, JAK inhibitors warrant added caution in patients 65 and older, long-term smokers, and those with cardiovascular, venous thromboembolic, or malignancy risk.^8,9

Treating beyond the joint

Genuine treatment-refractory PsA is uncommon; complex-to-manage PsA is not. For most difficult patients, the highest-yield moves are addressing weight, mood, and central pain alongside – not instead of – optimizing the DMARD, and agreeing on a shared, realistic target. Distinguishing the patient whose disease is truly refractory from the one whose score is driven by something the next biologic will not fix is the central skill in approaching difficult-to-treat PsA.