Persistent DIP swelling in a patient with psoriasis and nail involvement should trigger prompt PsA evaluation, given the strong predictive association and shared nail–DIP enthesis anatomy.
Marked PASI improvement with refractory nails and emergent PsA suggests pathway mismatch rather than underdosing, aligning with lower ACR50 rates seen with guselkumab versus skin efficacy.
Mechanism switching to deucravacitinib can recapture control across domains, potentially implicating TYK2-linked signaling (including type I interferon biology) not addressed by IL-23 inhibition.
Expectation-setting is essential: clinical nail clearance lags due to slow plate replacement (≈6 months fingernails; up to 18 months toenails), despite early suppression of inflammation.
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In the Chair puts you in the hot spot, challenging you to navigate complex, real-world cases.
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Nail psoriasis is one of the more treatment-resistant manifestations of psoriatic disease. The nail unit’s unique anatomy, slow growth rate, and complex immunopathogenesis mean that drugs that clear the skin reliably don’t always clear the nails — and that gap in response can be clinically significant.1 Nail involvement is also one of the strongest predictors of progression to psoriatic arthritis, which makes it more than a cosmetic concern.2
This case follows a 57-year-old woman whose cutaneous psoriasis responded well to an IL-23 inhibitor while her nail disease remained completely refractory — and who then developed psoriatic arthritis during that same treatment. It describes the first reported use of deucravacitinib, a selective TYK2 inhibitor, for IL-23 inhibitor–refractory nail psoriasis with concomitant PsA.3
Three clinical decision points follow: recognizing PsA developing during established biologic therapy, understanding why IL-23 inhibition failed the nails and joints while clearing the skin, and selecting the right mechanism switch.
THE PATIENT
A 57-year-old woman presents in July 2023 with a 3-year history of nail dystrophy, scaling erythema, and psoriatic plaques on her face, scalp, and axillae. She is diagnosed with psoriasis and started on guselkumab 100 mg (subcutaneous, per standard loading and maintenance schedule). Over the following year, her cutaneous plaques improve markedly. However, her nail changes remain refractory throughout: discoloration, crumbling, pitting, onycholysis, and subungual hyperkeratosis affecting multiple fingers and toes, with a NAPSI of 149 at baseline evaluation in August 2024.
In October 2023 — 3 months into guselkumab treatment — she sustains minor trauma to her left ring finger and develops persistent swelling of the distal interphalangeal (DIP) joint that does not resolve.
CLINICAL DECISION POINT 1—New Joint Swelling During Established Biologic Therapy
Your patient has been on guselkumab for 3 months with good cutaneous response. She now reports persistent DIP joint swelling in her left ring finger following minor trauma 4 weeks ago. The swelling has not resolved. She has no history of joint disease and no prior workup for psoriatic arthritis.
⚠️CLINICAL CONSIDERATION
Nail psoriasis is one of the strongest predictors of psoriatic arthritis development. The nail bed and DIP joint share tendinous insertions, and nail changes may represent a Koebner response to subclinical joint inflammation. Persistent DIP swelling in a patient with psoriasis and nail disease warrants formal PsA evaluation — not just trauma management.
📋WHAT WOULD YOU DO?
Your patient on guselkumab reports persistent DIP joint swelling 4 weeks after minor finger trauma. Her skin is clearing but her nails remain severely involved. What is your next step?
CLINICAL DECISION POINT 2—Understanding the Pattern of Differential Treatment Failure
PsA is confirmed. You now have a patient on guselkumab with three distinct treatment outcomes: cutaneous plaques markedly improved, nail changes completely refractory (NAPSI 149), and new psoriatic arthritis developing during treatment. Guselkumab achieves PASI90 in approximately 84% of patients with plaque psoriasis. Its ACR50 response rate in psoriatic arthritis trials, however, is approximately 31% — substantially lower.
📋WHAT WOULD YOU DO?
Your patient’s skin is clearing on guselkumab but her nails are completely refractory and she has developed PsA during treatment. What does this pattern tell you, and what is the most appropriate next step?
CLINICAL DECISION POINT 3—Counseling on Response Timeline and Expectations
Deucravacitinib 6 mg once daily is initiated. At 1 month, facial and auricular lesions have resolved and DIP swelling has markedly improved. At 3 months, nail changes begin to regress. The patient asks you why the joint and skin responses came so much faster than the nail response, and whether full nail clearance is realistic.
⚠️CLINICAL CLUE
Fingernails grow approximately 3 mm per month; toenails approximately 1.5 mm per month. Full nail plate replacement takes 6 months for fingernails and up to 18 months for toenails. Nail structural improvement reflects regrowth from a now-recovering nail matrix — early reduction in inflammation does not immediately translate to visible nail clearance.
📋WHAT WOULD YOU DO?
At 3 months on deucravacitinib, your patient’s skin is clear and DIP swelling has resolved, but nail improvement is minimal. She is discouraged and asking whether the drug is working for her nails and whether she should expect full clearance. How do you respond?
Clinical Takeaways
✓Nail psoriasis is one of the strongest clinical predictors of psoriatic arthritis — persistent DIP swelling in a nail psoriasis patient warrants formal PsA evaluation, not just trauma management
✓Differential treatment response — skin clearing while nails and joints don’t — suggests the pathogenic pathways driving each domain differ and the current mechanism may be insufficient
✓Guselkumab achieves PASI90 in ~84% of plaque psoriasis patients but ACR50 in only ~31% of PsA patients, reflecting distinct pathobiology across disease domains
✓Deucravacitinib (TYK2 inhibitor) blocks IL-12, IL-23, and type I interferons simultaneously — broader cytokine coverage than IL-23 inhibition alone, with an oral route and favorable safety profile
✓Skin and joint responses to deucravacitinib may appear within weeks; nail structural recovery follows nail growth kinetics and requires 6–12+ months to manifest — this is biology, not treatment failure
✓Nail psoriasis NAPSI fell from 149 to 40 over 12 months on deucravacitinib monotherapy with no adverse events reported
THE TAKEAWAY
The differential treatment response in this case — skin clearing, nails refractory, arthritis emerging — is clinically informative in a way that a uniform response would not be. It tells you that IL-23 inhibition is addressing the Th17-driven skin inflammation without adequately suppressing the pathways driving nail matrix damage and synovial inflammation. For NPs and PAs managing patients with psoriasis, that pattern is a signal worth recognizing: when a biologic is working for the skin but not for nails or joints, the mechanism may need to change, not just the dose.
The deucravacitinib selection here is mechanistically specific — the authors hypothesize type I interferon involvement in the arthritis based on the drug’s response pattern, a pathway not targeted by IL-23 inhibition. Whether that hypothesis holds at a population level will require prospective study. But the clinical outcome in this patient — joint resolution within a month, NAPSI reduced by 73% at 12 months, no adverse events — provides a data point in a disease with almost no randomized trial evidence to draw from.
The counseling point on nail growth kinetics is the one APPs will use most often: when a patient sees their skin clear and their joints improve but their nails look the same at month 3, the instinct is to question whether the drug is working. Understanding that nail structural recovery is biologically constrained — and setting that expectation before month 3 arrives — keeps patients on effective therapy long enough for it to work.
References
Hadeler E, Mosca M, Hong J, Brownstone N, Bhutani T, Liao W. Nail psoriasis: a review of effective therapies and recommendations for management. Dermatol Ther (Heidelb). 2021;11(3):799-831. doi:10.1007/s13555-021-00523-x
Langenbruch A, Radtke MA, Krensel M, Jacobi A, Reich K, Augustin M. Nail involvement as a predictor of concomitant psoriatic arthritis in patients with psoriasis. Br J Dermatol. 2014;171(5):1123-1128. doi:10.1111/bjd.13272
Yan T, Wu X, Zhang Z. Successful treatment of IL-23 inhibitor–refractory Nail psoriasis With deucravacitinib: a case report. JEADV Clin Prac. 2026. doi:10.1002/jvc2.70377
