What are the diagnostic criteria and treatment options for psoriatic arthritis?

Diagnosis of Psoriatic Arthritis

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. 1, 2

CASPAR Diagnostic Criteria

To meet CASPAR criteria for psoriatic arthritis diagnosis, a patient must have inflammatory articular disease (joint, spine, or entheseal) plus at least 3 points from the following:

• Current psoriasis (2 points), personal history of psoriasis (1 point), or family history of psoriasis (1 point)
• Psoriatic nail dystrophy (1 point)
• Negative rheumatoid factor (1 point)
• Current dactylitis or history of dactylitis documented by a rheumatologist (1 point)
• Radiographic evidence of juxta-articular new bone formation (1 point)

Comprehensive Disease Assessment

Clinical Evaluation

1. Peripheral Joint Assessment

   • Examine 68 joints for tenderness and 66 joints for swelling 1, 2
   • Document distribution pattern (asymmetric oligoarthritis, symmetric polyarthritis, distal interphalangeal predominant, arthritis mutilans, or axial)

2. Axial Disease Assessment

   • Evaluate spine and sacroiliac joints for pain, stiffness, and limited range of motion 2
   • Morning stiffness lasting >30 minutes is characteristic

3. Enthesitis Evaluation

   • Assess inflammation at tendon, ligament, and joint capsule insertion sites 2
   • Common sites: Achilles tendon insertion, plantar fascia insertion, lateral epicondyles

4. Dactylitis Assessment

   • Look for "sausage digits" (diffuse swelling of fingers or toes) 2
   • Document number and location of affected digits

5. Skin and Nail Examination

   • Document extent and severity of psoriatic lesions
   • Assess for nail changes: pitting, onycholysis, hyperkeratosis, oil spots

Laboratory Tests

• Acute phase reactants: C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) 1, 2
• Rheumatoid factor (typically negative in PsA)
• Anti-citrullinated protein antibodies (typically negative in PsA)
• HLA-B27 (may be positive, especially in axial disease)

Imaging Studies

• Radiographic assessment of hands, wrists, feet, and affected joints 1, 2
• Look for characteristic findings:
  • Asymmetric distribution
  • Distal interphalangeal joint involvement
  • Pencil-in-cup deformities
  • Periostitis and new bone formation
  • Joint space narrowing
  • Erosions (often less severe than in rheumatoid arthritis)
  • Sacroiliitis (often asymmetric)

Disease Activity Measurement

Disease activity in psoriatic arthritis can be measured using:

1. 28-joint Disease Activity Score (DAS28) 1

   • Validated for use in PsA despite only counting 28 joints

2. American College of Rheumatology (ACR) response criteria 1, 2

   • ACR20/50/70 measures percentage improvement in tender and swollen joint counts

3. European League Against Rheumatism (EULAR) response criteria 1

   • Categorizes levels of disease and changes to assess response

Patient-Reported Outcomes

Important patient-reported outcomes to assess include:

• Pain (using visual analog or category rating scales) 1, 2
• Patient global assessment of disease activity 1, 2
• Physical function (using Health Assessment Questionnaire - HAQ) 1, 2
• Health-related quality of life (using SF-36 or PsA-specific measures like PsAQoL) 1, 2
• Fatigue (using patient self-report or instruments like FACIT) 1, 2

Prognostic Factors

Factors associated with poor prognosis include:

• Polyarticular disease (multiple inflamed joints) 1
• Elevated ESR 1
• Previous treatment failures 1
• Presence of joint damage 1
• Diminished quality of life 1

Diagnostic Pitfalls and Caveats

1. Delayed Diagnosis

   • PsA is often underdiagnosed or misdiagnosed, leading to delayed treatment and irreversible joint damage 3
   • Skin symptoms typically precede joint symptoms in 80% of cases, making dermatologists crucial for early detection 4, 3

2. Unusual Presentations

   • Temporomandibular joint involvement can be the first articular manifestation 5
   • Axial disease occurs in 25-70% of PsA patients, sometimes as the exclusive manifestation 4

3. Differential Diagnosis

   • Distinguish from rheumatoid arthritis (RF positive, symmetric, less DIP involvement)
   • Rule out osteoarthritis (non-inflammatory, no enthesitis)
   • Consider other spondyloarthropathies (reactive arthritis, ankylosing spondylitis)

4. Multidisciplinary Approach

   • Ideally, diagnosis involves confirmation of psoriasis by a dermatologist and inflammatory musculoskeletal disease by a rheumatologist 1, 2
   • Collaboration between specialties is essential for optimal management 6

By following these diagnostic criteria and comprehensive assessment protocols, clinicians can accurately diagnose psoriatic arthritis and initiate appropriate treatment to prevent joint damage, reduce morbidity, and improve quality of life.