What are the steps to diagnose and treat psoriatic arthritis?

Diagnosing and Treating Psoriatic Arthritis

The diagnosis of psoriatic arthritis should follow the CASPAR (Classification Criteria for Psoriatic Arthritis) criteria, which requires evidence of inflammatory articular disease plus at least 3 points from specific diagnostic features, followed by a treatment approach based on disease severity and pattern of involvement. 1

Diagnostic Steps

1. Clinical Assessment

• Joint Assessment:

  • Examine 68 joints for tenderness and 66 joints for swelling 1
  • Document distribution pattern (asymmetric oligoarthritis, symmetric polyarthritis, distal interphalangeal predominant, arthritis mutilans, or axial) 1
  • Look for dactylitis ("sausage digits") - diffuse swelling of fingers or toes 1
  • Assess for enthesitis (inflammation at tendon/ligament insertion sites) - particularly at Achilles tendon, plantar fascia, and lateral epicondyles 1

• Skin and Nail Examination:

  • Document extent and severity of psoriatic lesions 1
  • Assess for nail changes: pitting, onycholysis, hyperkeratosis, oil spots 1
  • Note: Around 20% of patients develop PsA before psoriasis, often many years before skin or nail changes 2

• Axial Disease Assessment:

  • Evaluate spine and sacroiliac joints for pain, stiffness, and limited range of motion 1
  • Morning stiffness lasting >30 minutes is characteristic of inflammatory back pain 1

2. Laboratory Tests

• Acute phase reactants: C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) 3, 1
• Rheumatoid factor (typically negative in PsA) 1
• Anti-citrullinated protein antibodies (typically negative in PsA) 1
• Note: There are no diagnostic blood tests for PsA, but these help rule out other conditions 2

3. Imaging Studies

• Radiographic assessment of hands, wrists, feet, and affected joints 3, 1
• Look for characteristic findings:
  • Asymmetric distribution
  • Distal interphalangeal joint involvement
  • Pencil-in-cup deformities
  • Periostitis and new bone formation 1

4. Formal Diagnosis

• Apply CASPAR criteria (requires inflammatory articular disease plus ≥3 points from: current psoriasis, psoriatic nail dystrophy, negative rheumatoid factor, radiographic evidence of juxta-articular new bone formation) 3, 1

Treatment Algorithm

1. Initial Assessment

• Evaluate disease severity across domains:
  • Peripheral joint assessment (68 joints for tenderness; 66 joints for swelling)
  • Pain (using visual analog or category rating scale)
  • Patient global assessment of disease activity
  • Physical function (using Health Assessment Questionnaire - HAQ)
  • Health-related quality of life
  • Fatigue
  • Acute phase reactants 3

2. Identify Poor Prognostic Factors

• Polyarticular disease (vs. oligoarticular)
• Elevated ESR/CRP
• Previous treatment failures
• Presence of joint damage
• Diminished quality of life 3, 1

3. Treatment Approach Based on Disease Pattern

For Peripheral Arthritis:

1. First-line therapy:

   • NSAIDs for mild disease
   • For moderate-severe disease: conventional DMARDs (methotrexate preferred)

2. For inadequate response (treatment failure defined as lack of acceptable clinical improvement after appropriate duration and dosing):

   • Switch to or add TNF antagonists (e.g., etanercept) 4
   • Monitor response using validated measures:
     • 28-joint Disease Activity Score (DAS28)
     • American College of Rheumatology (ACR) response criteria
     • European League Against Rheumatism (EULAR) response criteria 3, 1

For Axial Disease:

1. First-line therapy:

   • NSAIDs

2. For inadequate response:

   • TNF antagonists (e.g., etanercept) 4

For Enthesitis:

1. First-line therapy:

   • NSAIDs
   • Local corticosteroid injections

2. For inadequate response:

   • TNF antagonists

For Skin Disease:

• Coordinate with dermatology for optimal management of skin manifestations
• Consider agents effective for both skin and joint disease (e.g., TNF antagonists) 4

4. Monitoring and Follow-up

• Regular assessment of disease activity using validated measures
• Monitor for treatment-related adverse effects
• Screen for and manage comorbidities (cardiovascular disease, metabolic syndrome, depression) 1
• Radiographic assessment to monitor for disease progression

Important Considerations

• Early Diagnosis and Treatment: Aggressive treatment of early stage PsA can substantially improve long-term prognosis 2
• Multidisciplinary Approach: Collaboration between rheumatology and dermatology is essential for optimal management 1
• Treatment Cautions: Before starting TNF antagonists like etanercept, screen for infections (particularly TB), hepatitis B, and other contraindications 4
• Comorbidity Management: PsA patients have a 60% higher risk of premature mortality than the general population, with life expectancy approximately three years shorter 2

Treatment Response Assessment

• Response to peripheral arthritis treatment can be assessed using:
  • DAS28 (reliable and discriminative in PsA)
  • EULAR response criteria
  • ACR percentage response criteria (ACR20/50/70) 3
• Treatment is considered inadequate if there is evidence of progression of joint damage on radiographs despite therapy 3