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← Rheumatology indexChapter sections
OverviewAetiologyPathophysiologyClinical features and red flagsInvestigationsDifferential diagnosisManagementComplicationsMonitoring and follow-upSpecial situationsCommon pitfallsQuestionsSources
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Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.

Psoriatic arthritis

Rheumatology · UK scope · Sources checked 27 Aug 2026 · Clinical review pending

RapidFull
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Time-critical presentation

Urgently assess a single acutely hot joint for infection, a painful photophobic red eye for uveitis, severe spinal neurological symptoms, or rapidly progressive systemic illness. Immunosuppressed patients may have muted signs, and skin infection can seed a joint.

Overview

Recognise the diverse peripheral, entheseal, dactylitic and axial patterns of psoriatic arthritis, coordinate skin and joint priorities, and escalate disease-modifying treatment according to the dominant active domain.

Psoriatic arthritis is a heterogeneous spondyloarthritis. Establish current and previous psoriasis, nail pitting or onycholysis, family history, uveitis, bowel symptoms and infection. Examine every joint, tendon sheath, enthesis, digit and axial region, and document skin extent and patient impact. Arthritis can precede visible psoriasis, and minimal skin disease may coexist with destructive joint inflammation.

Investigations exclude mimics and establish baseline treatment safety. FBC, renal, liver, CRP and ESR may support activity but normal markers are common. RF and anti-CCP help with an RA differential without proving either condition. Aspirate an acutely hot joint for culture and crystals. Radiographs show damage; ultrasound can demonstrate synovitis, tenosynovitis and enthesitis; MRI supports selected axial and deep disease.

Treatment follows the dominant active domain. Exercise, physiotherapy and occupational support accompany medicines. NSAIDs can help short-term symptoms when safe. Conventional DMARDs target peripheral synovitis, with methotrexate often favoured when skin psoriasis also needs systemic therapy. Axial disease generally does not respond to conventional DMARDs. Specialist targeted therapy is selected using NICE approvals and comorbid psoriasis, uveitis, bowel disease, infection risk and pregnancy plans.

Key points

  • Psoriatic arthritis may present as asymmetric oligoarthritis, symmetrical polyarthritis, DIP disease, dactylitis, enthesitis or axial inflammation; actively search all domains.
  • Psoriasis may be subtle or appear after arthritis, so inspect scalp, umbilicus, natal cleft, ears and nails and ask about family history.
  • Dactylitis is whole-digit inflammation and enthesitis affects insertion sites; neither is captured reliably by a standard rheumatoid joint count.
  • RF can be positive incidentally and no blood test confirms PsA; diagnosis rests on phenotype and exclusion of infection and crystals.
  • Treat active peripheral arthritis promptly with a conventional DMARD such as methotrexate, leflunomide or sulfasalazine under rheumatology care; choose according to skin, comorbidity and pregnancy factors.
  • Persistent active disease may require TNF, IL-17, IL-23, PDE4, JAK or other targeted therapy selected for the dominant joint, axial, entheseal and skin domains. Recurrent uveitis or active bowel disease materially constrains class choice.
  • Avoid using systemic corticosteroids casually because metabolic, infection and psoriasis risks can outweigh transient benefit; local injection still requires infection exclusion.
  • Address weight, smoking, cardiovascular risk, mood, work and treatment adherence as core disease management rather than optional additions.

Aetiology

01

Polygenic immune susceptibility

HLA and non-HLA variants influence antigen presentation, skin inflammation and entheseal immune responses, producing variable axial and peripheral phenotypes.

02

Psoriatic skin–joint interaction

Shared TNF, IL-23 and IL-17 pathways link psoriasis with synovial, entheseal, tendon and bone inflammation, although severity in each domain may differ.

03

Mechanical and environmental modifiers

Obesity, smoking, biomechanical stress and trauma can amplify entheseal and systemic inflammation without acting as sole causes.

Pathophysiology

  1. 1
    Enthesis and synovial inflammation

    Immune activation at entheses and synovium produces pain, swelling, tenosynovitis and whole-digit inflammation across characteristic but heterogeneous distributions.

  2. 2
    Erosion with new bone formation

    Osteoclast-mediated erosion occurs alongside abnormal osteoblast activity, explaining destructive joints, periostitis, ankylosis and characteristic pencil-in-cup change.

  3. 3
    Multidomain systemic disease

    Skin, nails, eye, bowel, cardiovascular metabolism and mood interact with musculoskeletal activity, so outcome cannot be measured by joint count alone.

Clinical features and red flags

Dactylitic or entheseal pattern

Whole-digit swelling, Achilles or plantar insertion pain and flexor tenosynovitis strongly support a psoriatic spondyloarthritis phenotype.

DIP and nail linkage

Inflammatory DIP swelling associated with nail pitting, onycholysis or hyperkeratosis supports PsA rather than uncomplicated nodal osteoarthritis.

Axial psoriatic disease

Inflammatory spinal pain, sacroiliac symptoms and reduced movement may occur with asymmetric structural patterns and require axial imaging and treatment assessment.

Septic or crystal jointRed flag

One abruptly hot restricted joint, fever or immunosuppression requires aspiration and culture even when established PsA explains other symptoms.

Extra-articular priorityRed flag

Painful red photophobic eye, significant bowel activity or severe skin disease may determine urgency and the safest shared treatment choice.

Investigations

  1. 01
    Full musculoskeletal, skin and nail examinationFirst step
    Why
    Define peripheral, entheseal, dactylitic, axial and cutaneous disease domains.
    Interpretation and limitations
    Record active inflammation separately from bony damage and widespread tenderness; skin extent does not predict joint severity.
  2. 02
    FBC, renal, liver, CRP and ESR
    Why
    Assess inflammation, comorbidity and baseline safety for disease-modifying treatment.
    Interpretation and limitations
    Normal markers do not exclude active PsA; obesity and infection can raise CRP independently and require clinical correlation.
  3. 03
    RF and anti-CCP
    Why
    Refine the differential with rheumatoid arthritis when symmetrical polyarthritis dominates.
    Interpretation and limitations
    Positive results can occur in psoriasis; interpret concentration, distribution, erosions, dactylitis and enthesitis together.
  4. 04
    Synovial-fluid analysis
    Why
    Exclude infection and crystals in an acutely inflamed effusion.
    Interpretation and limitations
    Send culture and crystal microscopy together; crystals can coexist with sepsis and psoriasis does not protect against either.
  5. 05
    Radiography, ultrasound or MRI

Differential diagnosis

01

Rheumatoid arthritis

Symmetrical MCP and PIP synovitis with strong rheumatoid serology supports RA, while DIP disease, dactylitis and entheseal inflammation favour PsA.

02

Osteoarthritis

Bony DIP enlargement and load-related pain can coexist with psoriasis; soft swelling, prolonged stiffness and nail-linked digit disease support active inflammation.

03

Gout or septic arthritis

Abrupt severe monoarthritis, systemic illness or marked warmth requires aspiration because psoriasis and metabolic risk do not distinguish crystals from infection.

04

Other spondyloarthritis

Reactive and enteropathic arthritis share axial and peripheral patterns, so infection, bowel, eye and family history determine the broader context.

Management

01New peripheral PsADefine every domain and start disease modificationFirst stepPersistent peripheral synovitis, dactylitis or function-limiting inflammatory disease accompanies psoriasis or a strong psoriatic phenotype.+
  1. 1Document joints, digits, entheses, skin, nails, axial, eye and bowel features and obtain treatment-safety baseline bloods and infection assessment.
  2. 2Refer promptly to rheumatology and coordinate dermatology; begin a conventional DMARD for active peripheral arthritis according to shared domain priorities and contraindications.
  3. 3EscalationSet an objective review interval and escalate if the target is missed rather than continuing ineffective therapy while damage accumulates.
02Axial or refractory domainMatch targeted therapy to the whole patientAxial, entheseal, dactylitic, skin or peripheral disease remains active despite appropriate initial care.+

Complications

01

Erosive and mutilating disease

Persistent inflammation can destroy joints, shorten digits, rupture tendons and cause irreversible deformity, disability and loss of work.

02

Axial and entheseal disability

Spinal, sacroiliac and widespread entheseal disease can substantially impair movement and sleep even when swollen-joint counts are modest.

03

Extra-articular inflammatory morbidity

Associated uveitis or inflammatory bowel disease may threaten sight or intestinal health and can constrain biologic choice, requiring coordinated ophthalmology or gastroenterology care.

04

Cardiometabolic and psychological burden

Obesity, diabetes, dyslipidaemia, cardiovascular disease, depression and stigma cluster with psoriatic disease and influence treatment effectiveness and adherence.

Monitoring and follow-up

  • Record joints, dactylitis, enthesitis, skin, nails, axial symptoms, function and patient priorities at each disease review.
  • Perform DMARD and biologic laboratory monitoring at agent-specific intervals and after dose changes.
  • Ask about infection, eye pain, bowel activity, pregnancy plans and vaccine status before treatment escalation.
  • Review weight, blood pressure, lipids, diabetes, smoking, mood and work as modifiable outcome drivers.
  • Track corticosteroid exposure and reduce repeat systemic use when disease-modifying control is available.

Special situations

Skin and joints diverge

Minimal psoriasis can coexist with severe arthritis, so treatment must follow all active domains rather than skin area alone.

Dactylitis is more than one joint

Synovium, tendon sheath, enthesis and soft tissue contribute to whole-digit swelling and may require targeted systemic control.

Axial disease needs axial therapy

Conventional DMARDs used for peripheral arthritis do not reliably treat spinal inflammation, so persistent axial activity changes sequencing.

Obesity affects outcomes

Mechanical load, inflammation, cardiometabolic risk and reduced biologic response can converge, requiring supportive weight care without stigma.

One diagnosis does not explain every flare

Infection, gout, osteoarthritis and fibromyalgia can coexist with PsA and should be actively separated before escalation.

Common pitfalls

  1. 01

    Missing hidden psoriasis or nail disease in arthritis that precedes obvious skin lesions.

  2. 02

    Using RF positivity alone to relabel every symmetrical psoriatic arthritis as RA.

  3. 03

    Treating axial activity with repeated conventional DMARD changes that target only peripheral joints.

  4. 04

    Escalating immunosuppression for one hot joint before aspiration.

  5. 05

    Ignoring obesity, cardiovascular risk and depression while measuring only swollen joints.

Practice

Two practice questions

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Question 1 of 2
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RheumatologyOriginal SBA

Recognising the dominant pattern

A patient with scalp psoriasis has a swollen whole toe, Achilles insertion pain and inflammatory back symptoms. Which diagnosis best unifies these findings?

Choose one answer, then submit
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Sources and review status9 sources · checked 27 Aug 2026 · clinical review pending+
Sources

Sources and review status

National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.

  • NICE NG65 spondyloarthritisRecognition and referral for peripheral and axial disease.
  • NICE TA199 TNF inhibitors for psoriatic arthritisSpecialist biologic treatment criteria.
  • NICE CG153 psoriasisSkin, joint and comorbidity assessment.
  • BSR 2022 psoriatic arthritis guidelineDomain-based conventional, biologic and targeted-treatment selection.
  • Adalimumab UK product informationPsoriatic-arthritis dosing, contraindications, infection and vaccination safety.
  • BSR 2025 conventional DMARD guidelineMethotrexate regimen, monitoring, infection and vaccination safeguards.
  • Methotrexate UK product informationOnce-weekly dosing, contraindications and interactions.
  • BSR pregnancy prescribing guidelineDMARD and anti-TNF reproductive and infant-vaccine planning.
  • NICE CKS septic arthritisUrgent hot-joint sampling and infection treatment principles.

Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem ·

Review must distinguish active inflammation from structural damage, osteoarthritis and fibromyalgia. Coordinate dermatology and gastroenterology decisions because some agents benefit or worsen different domains. Monitor bloods, infection and agent-specific risks; review cardiovascular health, weight and mood; and minimise prolonged corticosteroids.

Why
Document damage, support uncertain active peripheral inflammation or evaluate axial and deep structures.
Interpretation and limitations
Erosion plus new bone formation supports PsA; imaging abnormalities must correspond to the symptomatic domain and do not replace examination.
1
Confirm inflammation and adherence and separate fixed damage, obesity-related load and fibromyalgia from the active domain.
  • 2Assess NICE-approved targeted options with infection screening, vaccination, pregnancy and malignancy review and input from dermatology or gastroenterology where needed.
  • 3Choose and monitor therapy by joint, skin, bowel and eye outcomes, switching when the intended domain does not respond adequately.
    • 03One hot jointPause escalation and exclude infectionEscalationAn established PsA patient develops a disproportionately hot swollen joint or systemic illness.+
    1. 1Obtain urgent synovial culture and crystal microscopy with blood cultures when indicated, and assess current immunosuppression and skin infection.
    2. 2Treat suspected sepsis and arrange drainage according to the acute pathway rather than increasing DMARD or biologic treatment.
    3. 3Agree safe withholding and restart of immunosuppression after microbiology, source control and clinical recovery are clear.
    Key medicines and prescribing safety2 treatments · regimens, roles and cautions+
    Conventional DMARD for active peripheral psoriatic arthritis, particularly when psoriasis also requires systemic treatment.

    Methotrexate with folic acid

    Usually 7.5–15 mg once weekly initially, titrated by rheumatology within the product-specific maximum; record one fixed dosing day and prescribe folic acid at least 5 mg once weekly on a different day.

    Never prescribe or take it daily. Obtain risk-based FBC, liver and renal monitoring and review alcohol, lung and interacting-drug risks, especially trimethoprim or co-trimoxazole. Withhold it through a serious infection until recovered and reviewed. For maternal exposure, low-dose methotrexate must be stopped at least 1 month before planned conception and is not compatible with pregnancy or breastmilk exposure; accidental pregnancy needs immediate cessation, folic acid 5 mg/day and specialist fetal-risk review. BSR regards paternal exposure at no more than 25 mg/week as compatible; arrange specialist pre-conception planning.

    TNF inhibitor for active psoriatic arthritis meeting NICE criteria, with potential benefit across peripheral, axial, entheseal and skin domains.

    Adalimumab

    The usual adult psoriatic-arthritis regimen is 40 mg subcutaneously every other week under specialist prescribing and product information.

    Do not start during active tuberculosis or another serious infection; screen for TB and hepatitis B, and review demyelinating disease. It is contraindicated in NYHA III or IV heart failure and should stop for new or worsening failure. Give no live vaccine during therapy. If continued beyond 28 weeks of pregnancy, BSR advises deferring infant live vaccines until 6 months.

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