What is the workup for psoriatic arthritis (PsA)?

Workup for Psoriatic Arthritis

The workup for psoriatic arthritis centers on clinical diagnosis using CASPAR criteria, comprehensive joint examination, inflammatory markers (ESR/CRP), and baseline imaging—not on diagnostic laboratory tests, which do not exist for PsA. 1, 2

Diagnostic Criteria

Apply CASPAR criteria as the gold standard for diagnosis, which requires established inflammatory articular disease (joint, spine, or entheseal) plus ≥3 points from: current psoriasis (2 points), history of psoriasis (1 point), family history of psoriasis (1 point), dactylitis (1 point), juxta-articular new bone formation on radiographs (1 point), rheumatoid factor negativity (1 point), and nail dystrophy (1 point). 1, 2 This demonstrates 98.7% specificity and 91.4% sensitivity. 2

Confirm psoriasis with dermatology and inflammatory musculoskeletal disease with rheumatology when possible, though either can be confirmed by an appropriately qualified health professional. 1

Clinical Assessment

Perform a comprehensive 68-joint tenderness and 66-joint swelling assessment as the foundation of your examination. 1, 2 Look specifically for:

• Asymmetric oligoarthritis (≤4 joints) or symmetric polyarthritis (≥5 joints), with particular attention to distal interphalangeal joint involvement which is characteristic. 1
• Dactylitis (sausage digits) affecting fingers or toes. 1, 3
• Enthesitis by palpating lateral epicondyle of humerus, medial femoral condyle, and Achilles tendon insertion. 1, 3
• Inflammatory back pain features: early morning stiffness, pain relieved by exercise and worsened by rest, suggesting axial involvement. 3
• Nail changes: pitting and onycholysis occur in 80-90% of PsA patients. 1

Laboratory Testing

Order ESR and CRP as the only mandatory baseline laboratory tests—these assess inflammation severity, not diagnosis. 1, 2, 4 Recognize that ESR/CRP are elevated in only 50% of PsA patients, so normal values do not exclude disease. 5

Check rheumatoid factor (RF) and anti-CCP antibodies to exclude rheumatoid arthritis, especially in polyarticular presentations. 2, 4, 3 While RF is found in 5-13% of PsA patients and anti-CCP in similar percentages, their presence should prompt careful diagnostic scrutiny. 5, 3

There are no true diagnostic laboratory markers for PsA—diagnosis relies on clinical criteria, not blood tests. 2, 4, 5

Patient-Reported Outcomes

Document the following baseline measures:

• Pain severity using visual analogue scale (0-10). 1
• Patient global assessment of disease activity. 1
• Physical function using Health Assessment Questionnaire (HAQ). 1
• Quality of life via SF-36 or PsA-specific PsAQoL. 1
• Fatigue by patient self-report or FACIT instrument. 1

Imaging

Obtain baseline radiographs of hands and feet for all suspected inflammatory arthritis cases. 1, 3 Look for juxta-articular new bone formation, joint space narrowing, erosions, and pencil-in-cup deformities characteristic of PsA. 1

Consider MRI or ultrasound when radiographs are normal but clinical suspicion remains high, as early PsA may not show radiographic changes. 6 Additional imaging should be guided by clinical manifestations and physician judgment. 1

Prognostic Assessment

Identify poor prognostic factors at baseline that predict progressive joint damage and warrant more aggressive treatment: 1, 4

• Polyarticular disease (≥5 actively inflamed joints)
• Elevated ESR (>15 mm/h is associated with increased mortality)
• Failure of previous medication trials
• Presence of existing joint damage clinically or radiographically
• Impaired physical function (elevated HAQ score)
• Diminished quality of life (low SF-36, DLQI, or PsAQoL scores)

Elevated ESR at baseline is one of the best predictors of damage progression and should trigger consideration for earlier biologic therapy. 1, 4, 5

Common Pitfalls

Do not delay referral waiting for laboratory confirmation—any patient with suspected inflammatory arthritis and six weeks of painful, swollen joints requires specialist assessment. 3 Early diagnosis and treatment substantially improve long-term prognosis. 3

Do not dismiss PsA based on normal inflammatory markers—half of PsA patients have normal ESR/CRP. 5, 6

Remember that 20% of patients develop arthritis before psoriasis, often years before skin changes appear, so absence of current psoriasis does not exclude PsA. 3

Avoid using gold salts, chloroquine, or hydroxychloroquine in PsA patients as these are not recommended. 1