What is the approach to diagnosing and treating psoriatic arthritis?

Diagnosing Psoriatic Arthritis

Diagnose psoriatic arthritis using the CASPAR criteria, which requires established inflammatory articular disease plus at least 3 points from a 7-feature scoring system, with current psoriasis weighted most heavily at 2 points. 1, 2, 3

Diagnostic Approach

Step 1: Confirm Inflammatory Musculoskeletal Disease

Look for these specific inflammatory features 1, 3:

• Joint pain with erythema, warmth, and swelling 1
• Prominent morning stiffness (typically >30 minutes) 1
• Rest-induced stiffness that improves with activity 3
• Involvement of joints, spine, and/or entheses 1

Step 2: Apply CASPAR Scoring System

Calculate points from these 7 features (need ≥3 points) 3:

Skin and Nail Features:

• Current psoriasis on examination = 2 points 3
• Personal history of psoriasis (if no current psoriasis) = 1 point 3
• Family history of psoriasis (if no current or personal history) = 1 point 3
• Psoriatic nail dystrophy (onycholysis, pitting, hyperkeratosis) = 1 point 3

Musculoskeletal Features:

• Current dactylitis or documented history = 1 point 3
• Juxta-articular new bone formation on hand/foot X-rays = 1 point 3

Laboratory:

• Rheumatoid factor negative (by ELISA, not latex) = 1 point 3

Step 3: Specialist Confirmation

Ideally obtain dual confirmation 1, 2:

• Dermatologist confirms psoriasis 1
• Rheumatologist confirms inflammatory musculoskeletal disease 1

Comprehensive Baseline Assessment

Once diagnosed, evaluate all disease domains 1, 2:

Musculoskeletal Examination

• Peripheral joints: Assess 68 joints for tenderness and 66 joints for swelling 1, 2
• Enthesitis: Palpate lateral epicondyle of humerus, medial femoral condyle, and Achilles insertion 4
• Dactylitis: Check for "sausage digit" appearance (entire digit swelling) 2, 5
• Axial disease: Assess for inflammatory back pain (morning stiffness, improves with exercise, worse with rest) 4

Patient-Reported Measures

• Pain assessment using visual analogue scale 1, 2
• Patient global assessment of disease activity 1, 2
• Physical function via Health Assessment Questionnaire (HAQ) 1, 2
• Quality of life using SF-36 or PsA-specific PsAQoL 1, 2
• Fatigue via self-report or FACIT instrument 1, 2

Laboratory Tests

• Mandatory: ESR and CRP to assess inflammation 1, 6, 2
• To exclude RA: Rheumatoid factor and anti-CCP antibodies, especially in polyarticular presentations 6, 2

Imaging

• Baseline X-rays: Hands and feet for all suspected inflammatory arthritis 1, 4
• Additional imaging: Ultrasound or MRI based on clinical judgment 1

Identifying Poor Prognosis

These factors predict progressive joint damage and require aggressive treatment 1, 2:

• Polyarticular disease (multiple actively inflamed joints) 1, 2
• Elevated ESR 1, 2
• Previous treatment failures 1, 2
• Existing joint damage on clinical exam or X-ray 1, 2
• Diminished quality of life on standardized measures 1, 2

Comorbidity Screening

Evaluate these associated conditions that impact treatment decisions 1, 2:

• Cardiovascular risk factors (hypertension, hyperlipidemia, diabetes) 1, 2
• Metabolic syndrome 1, 2
• Inflammatory bowel disease 1, 2
• Depression and anxiety 1
• Non-alcoholic fatty liver disease 1
• Osteoporosis 1
• Uveitis 1

Critical Diagnostic Pitfalls

No diagnostic laboratory markers exist for PsA—diagnosis relies on clinical criteria, not blood tests. 6, 2 The presence of rheumatoid factor or anti-CCP antibodies does not exclude PsA but should prompt careful diagnostic scrutiny. 4

Early diagnosis is crucial: 40% of patients develop radiographically detectable joint destruction, and delayed treatment results in irreversible damage. 5, 4 Patients with PsA have 60% higher premature mortality risk and lose approximately 3 years of life expectancy compared to the general population. 4

Psoriasis may follow arthritis: 20% of patients develop PsA before skin manifestations, sometimes years before. 4 Don't dismiss inflammatory arthritis simply because psoriasis isn't currently visible.

Treatment Approach

Initial Management

For peripheral arthritis, use this stepwise approach 1:

• Mild disease: NSAIDs and intra-articular glucocorticoid injections 1
• Moderate-severe disease: Disease-modifying antirheumatic drugs (DMARDs) such as methotrexate, leflunomide, or sulfasalazine 1
• Refractory or aggressive disease: TNF inhibitors (etanercept, infliximab, adalimumab, golimumab, certolizumab) 1, 7

Avoid systemic corticosteroids for chronic use due to risk of psoriasis flare upon withdrawal. 1

Emerging Therapies

For patients failing traditional DMARDs or TNF inhibitors 7:

• IL-23/IL-17 pathway inhibitors (secukinumab, brodalumab, ixekizumab, ustekinumab) 7
• Phosphodiesterase 4 inhibitor (apremilast) 7
• JAK inhibitor (tofacitinib) 7

Treatment Goals and Monitoring

Target remission or low disease activity through regular assessment and prompt treatment adjustment. 1 Early diagnosis and treatment prevents irreversible joint damage and improves long-term prognosis. 1, 4

Assess treatment response using 1, 2:

• DAS28 and EULAR response criteria for peripheral arthritis 1, 2
• ACR20/50/70 criteria 1
• BASDAI for axial disease 2
• Radiographic progression on serial X-rays 1

Shared Decision-Making

Treatment decisions must be individualized based on 1:

• Disease activity across all domains 1
• Prognostic factors (structural damage, polyarticular disease) 1
• Comorbid conditions 1
• Patient preferences regarding cost, convenience, and route of administration 1