Psoriatic Arthritis
Summary
Psoriatic arthritis (PsA) is an inflammatory arthritis that occurs in up to 30% of patients with psoriasis. It belongs to the spondyloarthropathy family and is characterised by being seronegative (RF negative). The disease presents with diverse patterns ranging from oligoarticular involvement to destructive polyarthritis. Key clinical features include dactylitis ("sausage digit"), enthesitis, nail changes, and spinal involvement. Early recognition and treatment with DMARDs or biologics can prevent joint damage and disability.
Key Facts
- Definition: Inflammatory arthritis associated with psoriasis; classified as seronegative spondyloarthropathy
- Prevalence: Affects 20-30% of psoriasis patients; 0.1-1% of general population
- Characteristic Features: Dactylitis, enthesitis, nail changes (pitting, onycholysis)
- Arthritis Patterns: 5 subtypes (Moll & Wright classification)
- Key Imaging: "Pencil-in-cup" deformity, periostitis, new bone formation
- Treatment Goal: Early DMARD/biologic to prevent irreversible joint damage
Clinical Pearls
CASPAR Criteria: Diagnosis requires established inflammatory arthritis PLUS ≥3 points from psoriasis (current=2, history=1, family=1), nail dystrophy (1), dactylitis (1), RF negative (1), or juxta-articular new bone formation (1).
Nails Tell the Story: Nail involvement (pitting, onycholysis) is present in up to 80% of PsA patients vs. 40% of psoriasis patients without arthritis — it's a strong predictor of joint disease.
Skin Before Joints: In 85% of cases, psoriasis precedes arthritis by 7-12 years. However, 15% present with arthritis first ("arthritis sine psoriasisis") — check family history and hidden psoriasis areas (scalp, navel, natal cleft).
Why This Matters Clinically
PsA can cause significant joint destruction if untreated. Unlike rheumatoid arthritis, PsA has distinct patterns including enthesitis and spinal involvement. Recognition is crucial as modern biologics (anti-TNF, IL-17, IL-23 inhibitors) are highly effective and can prevent disability.
Incidence & Prevalence
- PsA Prevalence: 0.1-1% of general population; 20-30% of psoriasis patients
- Psoriasis Prevalence: 2-3% of general population
- Incidence: 6 per 100,000 person-years
- Trend: Increasing recognition with better diagnostic criteria
Demographics
| Factor | Details |
|---|---|
| Age | Peak onset 30-50 years; juvenile form exists |
| Sex | Equal male:female overall; axial disease male predominant |
| Ethnicity | More common in Caucasian populations |
| Genetics | HLA-B27 in 20-50% (especially axial); HLA-Cw6 for psoriasis |
Risk Factors
Non-Modifiable:
- Psoriasis (strongest predictor)
- Family history of PsA or spondyloarthropathy
- HLA-B27 positivity
- Severe psoriasis (>3 sites, nail involvement)
- Scalp or intergluteal psoriasis
Modifiable:
| Risk Factor | Relative Risk | Notes |
|---|---|---|
| Obesity | 2-3x | Affects disease severity and treatment response |
| Smoking | Controversial | Less clear association than in RA |
| Trauma (Koebner) | Possible trigger | Joint trauma may trigger arthritis |
Mechanism
Step 1: Genetic & Environmental Triggers
- HLA class I associations (HLA-B27, Cw6, B38, B39)
- Environmental triggers (infection, trauma, stress)
- Dysregulated innate and adaptive immunity
Step 2: IL-23/IL-17 Axis Activation
- Dendritic cells produce IL-23
- IL-23 drives Th17 cell differentiation
- Th17 cells produce IL-17A, IL-17F, IL-22
Step 3: Tissue Inflammation
- Synovium: Synovitis with pannus formation (like RA)
- Entheses: Enthesitis (hallmark of SpA)
- Bone: Erosions AND new bone formation (unique feature)
- Skin: Epidermal hyperproliferation (psoriasis)
Step 4: Structural Damage
- Joint erosion and cartilage destruction
- Characteristic "pencil-in-cup" deformity
- Ankylosis in severe cases (arthritis mutilans)
- Axial involvement: Syndesmophytes (often asymmetric)
Classification (Moll & Wright Patterns)
| Pattern | Frequency | Features | Joints Involved |
|---|---|---|---|
| Oligoarticular | 60-70% | <5 joints, asymmetric | Knees, ankles, wrists |
| Polyarticular (RA-like) | 15-20% | ≥5 joints, symmetric | Small joints, may mimic RA |
| DIP-Predominant | 5-10% | Classic but less common | Distal interphalangeal joints |
| Spondylitis | 5% | Axial involvement | Spine, sacroiliac joints |
| Arthritis Mutilans | <5% | Severely destructive | Digits (opera-glass deformity) |
Anatomical Considerations
- Entheses: Inflammation at tendon/ligament insertions; Achilles, plantar fascia, epicondyles common
- Dactylitis: "Sausage digit" — diffuse swelling of entire digit from tenosynovitis + synovitis
- Eyes: Anterior uveitis occurs in 7-25%
- Spine: Usually less severe than ankylosing spondylitis; often asymmetric syndesmophytes
Symptoms
Typical Presentation:
Atypical Presentations:
Signs
Red Flags
[!CAUTION] Red Flags — Seek urgent specialist review if:
- Arthritis mutilans (severe telescoping deformity)
- Rapidly progressive joint destruction
- Acute uveitis (red eye, photophobia, pain)
- High fever with arthritis (exclude sepsis)
- Cervical spine involvement with neurological symptoms
Structured Approach
General:
- Full skin examination (scalp, nails, umbilicus, natal cleft, ears)
- Observe gait and posture
- Assess overall disease activity
Joint Examination:
- Systematic joint count (tender and swollen)
- Compare sides for asymmetry
- Examine DIPJs specifically
- Check for dactylitis
- Spinal mobility (Schober's test, chest expansion)
Enthesis Examination:
- Achilles insertion
- Plantar fascia insertion
- Lateral epicondyles
- Greater trochanters
Special Tests
| Test | Technique | Positive Finding | Significance |
|---|---|---|---|
| Dactylitis Assessment | Observe entire digit | Uniform swelling of whole digit | Pathognomonic for SpA |
| Nail Exam | Inspect all nails | Pitting, onycholysis, dystrophy | Supports PsA diagnosis |
| Schober's Test | Measure lumbar flexion | <5cm expansion | Axial involvement |
| FABER Test | Flexion, abduction, external rotation | SI joint pain | Sacroiliitis |
| Squeeze Test (MTP) | Compress MTP joints mediolaterally | Pain | Inflammatory arthritis |
First-Line (Bedside)
- Complete skin and nail examination
- Full joint assessment (66/68 joint count)
- Enthesitis count
Laboratory Tests
| Test | Expected Finding | Purpose |
|---|---|---|
| ESR/CRP | Elevated in active disease (not always) | Monitor disease activity |
| RF | Negative (usually) | Part of CASPAR criteria if negative |
| Anti-CCP | Negative | Differentiate from RA |
| HLA-B27 | Positive in 20-50% (especially axial) | Supports diagnosis in axial disease |
| FBC | Anaemia of chronic disease possible | Baseline |
| LFTs, Creatinine | Before DMARD therapy | Pre-treatment baseline |
Imaging
| Modality | Findings | Indication |
|---|---|---|
| X-ray (Hands/Feet) | Erosions, "pencil-in-cup", periostitis, new bone | Baseline assessment |
| X-ray (SI joints) | Sacroiliitis (often asymmetric) | Suspected axial disease |
| Ultrasound | Synovitis, enthesitis, dactylitis | Early detection, monitoring |
| MRI | Bone marrow oedema, early sacroiliitis | Active inflammation assessment |
| CT | Detailed bone erosion/formation | Complex cases |
Diagnostic Criteria (CASPAR)
Inflammatory articular disease (peripheral, spinal, or entheseal) PLUS ≥3 points from:
| Feature | Points |
|---|---|
| Current psoriasis | 2 |
| History of psoriasis | 1 |
| Family history of psoriasis | 1 |
| Psoriatic nail dystrophy | 1 |
| Negative RF | 1 |
| Dactylitis (current or history) | 1 |
| Juxta-articular new bone formation on X-ray | 1 |
CASPAR criteria: Sensitivity 91%, Specificity 99%
Management Algorithm
PSORIATIC ARTHRITIS MANAGEMENT
↓
┌─────────────────────────────────────────────────┐
│ TREATMENT TARGETS │
│ • Minimal disease activity (MDA) │
│ • Remission or low disease activity │
│ • Prevent structural damage │
└─────────────────────────────────────────────────┘
↓
PERIPHERAL ARTHRITIS
↓
┌─────────────────────────────────────────────────┐
│ Mild: │
│ • NSAIDs ± local corticosteroid injection │
│ │
│ Moderate-Severe: │
│ • csDMARD (Methotrexate 15-25mg/week first-line)│
│ • Alternative: Leflunomide, Sulfasalazine │
│ • Assess response at 3-6 months │
│ │
│ Inadequate response or poor prognostic factors: │
│ • Switch to biologic +/- csDMARD │
└─────────────────────────────────────────────────┘
↓
AXIAL DISEASE
↓
┌─────────────────────────────────────────────────┐
│ • NSAIDs first-line (continuous if active) │
│ • csDMARDs NOT effective for axial disease │
│ • If inadequate → Biologic (TNFi or IL-17i) │
└─────────────────────────────────────────────────┘
↓
ENTHESITIS/DACTYLITIS
↓
┌─────────────────────────────────────────────────┐
│ • NSAIDs, local steroid injection │
│ • If refractory → Biologic (particularly IL-17) │
└─────────────────────────────────────────────────┘
Conservative Management
- Patient education about disease
- Physiotherapy and exercise
- Occupational therapy for joint protection
- Weight management (obesity worsens disease and treatment response)
- Smoking cessation
Medical Management
| Drug Class | Drug | Dose | Notes |
|---|---|---|---|
| NSAIDs | Naproxen, Etoricoxib | Standard doses | Symptom control; first-line for axial/enthesitis |
| csDMARDs | Methotrexate | 15-25 mg/week | First-line for peripheral arthritis |
| csDMARDs | Leflunomide | 20 mg/day | Alternative to MTX |
| csDMARDs | Sulfasalazine | 2-3 g/day | Third-line; less effective |
| Anti-TNF | Adalimumab, Etanercept | Various | Excellent for all domains |
| IL-17i | Secukinumab | 150-300 mg SC | Excellent for skin, enthesitis, axial |
| IL-17i | Ixekizumab | 80 mg SC | Similar to secukinumab |
| IL-12/23i | Ustekinumab | 45-90 mg SC | Good for skin and arthritis |
| IL-23i | Guselkumab | 100 mg SC | Emerging evidence |
| JAKi | Tofacitinib, Upadacitinib | Oral | Oral option; monitor safety |
| PDE4i | Apremilast | 30 mg BD | Mild-moderate; oral option |
Biologic Selection Considerations
| Domain | Preferred Agents |
|---|---|
| Peripheral arthritis | Anti-TNF, IL-17i, JAKi |
| Axial disease | Anti-TNF, IL-17i |
| Enthesitis | IL-17i often preferred |
| Skin disease (severe) | IL-17i, IL-23i superior |
| IBD co-morbidity | Anti-TNF; AVOID IL-17i |
| Uveitis | Anti-TNF (monoclonal preferred) |
Disposition
- Rheumatology referral: All suspected PsA for confirmation and DMARD initiation
- Dermatology liaison: Severe psoriasis; coordinate biologic choice
- Follow-up: 3-monthly until stable; 6-monthly long-term
Immediate (Minutes-Hours)
| Complication | Incidence | Presentation | Management |
|---|---|---|---|
| Joint injection complications | Rare | Infection, flare | Antibiotics if infection |
| Biologic infusion reaction | Uncommon | Rash, dyspnoea | Stop infusion, antihistamines, steroids |
Early (Weeks-Months)
- DMARD side effects: Hepatotoxicity (MTX), GI upset, cytopenias
- Biologic infections: Increased risk; screen for TB before anti-TNF
- Flare during dose reduction: Restart effective dose
Late (Years)
- Progressive joint destruction: Despite treatment in some
- Arthritis mutilans: Severe telescoping/opera-glass deformity
- Cardiovascular disease: Increased risk in inflammatory disease
- Metabolic syndrome: More common in PsA
- Anterior uveitis: Occurs in 7-25%; ophthalmology referral
- IBD: Associated with SpA; IL-17i contraindicated
Natural History
Without treatment, PsA can cause significant joint damage within years of onset. Unlike previously thought, PsA is NOT a "mild" form of arthritis — up to 47% develop erosive disease within 2 years. Early intervention with DMARDs/biologics can prevent irreversible damage.
Outcomes with Treatment
| Variable | Outcome |
|---|---|
| Minimal Disease Activity achievable | 50-60% with modern biologics |
| Erosive disease | 20-50% develop radiographic damage |
| Work disability | Reduced with early effective treatment |
| Mortality | Slightly increased (cardiovascular) |
Prognostic Factors
Good Prognosis:
- Oligoarticular pattern
- Early treatment with DMARDs
- Good response to initial therapy
- Absence of erosions at baseline
- Normal inflammatory markers
Poor Prognosis:
- Polyarticular disease
- Dactylitis at onset
- Elevated inflammatory markers
- Erosions at presentation
- HLA-B27 positive (axial progression)
- Delayed treatment initiation
Key Guidelines
-
EULAR (2019) — Overarching principles and recommendations for management of PsA. Recommends treat-to-target approach, MTX first-line csDMARD, biologics for inadequate response.
-
GRAPPA (2015/2021) — Treatment recommendations considering specific disease domains (peripheral, axial, enthesitis, dactylitis, skin, nails). Domain-specific approach.
-
ACR/NPF (2019) — Conditional recommendations for DMARDs, anti-TNF, and IL-17i based on disease phenotype.
Landmark Trials
PALACE 1-4 (2014-2016) — Apremilast trials
- Phase 3 RCTs of apremilast in active PsA
- Key finding: Significant improvement in ACR20, enthesitis, dactylitis
- Clinical Impact: Established oral PDE4 inhibitor as treatment option
FUTURE Trials (2015-ongoing) — Secukinumab
- Phase 3 trials in PsA
- Key finding: IL-17A inhibition highly effective for all domains; superior skin clearance
- Clinical Impact: Established IL-17 inhibition as major treatment option
Mease et al. (2000) — Etanercept in PsA
- First RCT of anti-TNF in PsA
- Key finding: Anti-TNF highly effective for joint and skin disease
- Clinical Impact: Revolutionary; established biologic era for PsA
Evidence Strength
| Intervention | Level | Key Evidence |
|---|---|---|
| Methotrexate | 2a | Systematic reviews; GRAPPA recommendations |
| Anti-TNF biologics | 1a | Multiple RCTs, meta-analyses |
| IL-17 inhibitors | 1a | FUTURE trials, systematic reviews |
| IL-23 inhibitors | 1b | Phase 3 RCTs |
| Treat-to-target | 2a | TICOPA trial, EULAR recommendations |
What is Psoriatic Arthritis?
Psoriatic arthritis is a type of joint inflammation that occurs in some people who have the skin condition psoriasis. It causes pain, swelling, and stiffness in the joints. The arthritis can affect different joints in different ways — sometimes just one or two joints, sometimes many joints like rheumatoid arthritis. It can also cause whole fingers or toes to swell up ("sausage digits").
Why does it matter?
If left untreated, psoriatic arthritis can permanently damage your joints. We now have very effective treatments, especially newer medications called biologics, which can stop the damage from happening. That's why early diagnosis and treatment are so important.
How is it treated?
-
Anti-inflammatory medications (NSAIDs): For mild symptoms — help with pain and stiffness.
-
Disease-modifying drugs (DMARDs): Usually methotrexate first. These slow down the disease and prevent joint damage. They take a few weeks to work.
-
Biologics: Newer, more targeted medications (given as injections). These are very effective and used when DMARDs don't work well enough or for certain types of the disease.
-
Physiotherapy: Helps maintain joint movement and muscle strength.
-
Skin treatment: Managing psoriasis alongside arthritis, often with the same medications.
What to expect
- Treatment usually controls symptoms well
- Most people can live normal, active lives with proper treatment
- Regular blood tests are needed to monitor medications
- You'll see your rheumatologist regularly (every 3-6 months)
When to seek help
Contact your doctor urgently if:
- You have sudden severe joint pain
- A single joint becomes very hot and swollen
- You develop a red, painful eye
- You have high fevers
- You notice your fingers becoming very deformed
Primary Guidelines
-
Gossec L, Baraliakos X, Kerschbaumer A, et al. EULAR recommendations for the management of psoriatic arthritis with pharmacological therapies: 2019 update. Ann Rheum Dis. 2020;79(6):700-712. PMID: 32434812
-
Coates LC, Kavanaugh A, Mease PJ, et al. Group for Research and Assessment of Psoriasis and Psoriatic Arthritis 2015 Treatment Recommendations. Arthritis Rheumatol. 2016;68(5):1060-1071. PMID: 26749174
Key Trials
-
Mease PJ, Goffe BS, Metz J, et al. Etanercept in the treatment of psoriatic arthritis and psoriasis: a randomised trial. Lancet. 2000;356(9227):385-390. PMID: 10972371
-
McInnes IB, Mease PJ, Kirkham B, et al. Secukinumab, a human anti-interleukin-17A monoclonal antibody, in patients with psoriatic arthritis (FUTURE 2). Lancet. 2015;386(9999):1137-1146. PMID: 26135703
-
Taylor W, Gladman D, Helliwell P, et al. Classification criteria for psoriatic arthritis: development of new criteria (CASPAR). Arthritis Rheum. 2006;54(8):2665-2673. PMID: 16871531
Further Resources
- American College of Rheumatology: rheumatology.org
- National Psoriasis Foundation: psoriasis.org
- GRAPPA (Group for Research and Assessment of Psoriasis and Psoriatic Arthritis): gfrappa.org
Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate guidelines and specialists for patient care.