What is the updated protocol for diagnosing and managing psoriatic arthritis (PSA), including differentiating between axial and peripheral PSA?

Updated Protocol for Diagnosis and Management of Psoriatic Arthritis

Diagnose PsA using the CASPAR criteria (≥3 points from established inflammatory arthritis plus psoriasis features), then classify as peripheral, axial, or mixed based on clinical presentation and imaging, with peripheral disease showing asymmetric joint involvement, DIP joints, dactylitis, and enthesitis, while axial disease presents with asymmetric sacroiliitis and "skip" pattern spinal involvement that is typically less symptomatic than ankylosing spondylitis. 1

Diagnostic Protocol

CASPAR Classification Criteria

• Established inflammatory arthritis (tender/swollen joints with prolonged morning stiffness) PLUS ≥3 points from: current psoriasis (2 points), personal/family history of psoriasis (1 point each), nail dystrophy, negative rheumatoid factor, dactylitis (current or history), and radiographic evidence of juxta-articular new bone formation 1
• These criteria have 98.7% specificity and 91.4% sensitivity for diagnosing PsA 1

Essential Baseline Assessment Domains

• Peripheral joint examination: 68 joints for tenderness, 66 joints for swelling (must include DIP joints of hands and feet, which distinguishes PsA from RA) 1, 2
• Pain assessment: Visual analogue or category rating scale 1, 2
• Patient and physician global assessment of disease activity 1, 2
• Physical function: Health Assessment Questionnaire (HAQ) or similar validated tool 1, 2
• Laboratory tests: ESR, CRP (elevated in active disease), rheumatoid factor (should be negative) 1, 2
• Imaging: Radiographs for baseline damage assessment; MRI or CT for detecting asymptomatic axial disease 1, 3

Differentiating Axial from Peripheral PsA

Peripheral PsA Features

• Joint distribution: Asymmetric involvement, less tender and swollen than RA, commonly affects DIP joints (uncommon in RA) 1, 4
• Pathognomonic features: Dactylitis ("sausage digits") and enthesitis (plantar fascia, Achilles tendon insertion sites) are hallmarks that distinguish from RA 1, 4, 2
• Nail involvement: Pitting, onycholysis, oil spots strongly associated with DIP joint disease 4, 2
• Skin findings: Psoriatic plaques or nail changes confirm PsA diagnosis 1, 4

Axial PsA Features

• Prevalence: 5% have exclusively axial involvement; 20-50% have both spine and peripheral joint involvement 1
• Clinical presentation: Often less symptomatic than ankylosing spondylitis, with asymmetric sacroiliitis (often asymptomatic) 1
• Spinal involvement: "Skip" pattern affecting any spinal level (not continuous like AS), rarely progresses to complete ankylosis 1
• Imaging characteristics: Asymmetric sacroiliitis on radiographs/MRI; CT or MRI needed to detect asymptomatic disease 1
• Distinguishing from AS: Presence of psoriatic plaques/nail changes (absent in AS), less severe disease, preserved mobility 1

Assessment Tools for Axial Disease

• BASDAI (Bath Ankylosing Spondylitis Disease Activity Index): Can measure axial disease activity and treatment response, though 75.7-78.7% agreement among experts (lower than other measures) 1, 2
• Imaging: MRI superior for axial assessment; US not useful for spine/sacroiliac joints 3

Disease Severity Classification and Management

Mild Disease

• Definition: Responds to NSAIDs 1
• Treatment: NSAIDs as initial therapy 1

Moderate Disease

• Definition: Requires DMARDs or TNF blockers 1
• Treatment: Initiate conventional DMARDs (methotrexate, sulfasalazine) or TNF inhibitors 1, 5, 6

Severe Disease

• Definition: Requires DMARDs plus TNF blockers or other biologic therapies 1
• Treatment: Combination therapy with DMARDs plus biologics (TNF inhibitors, IL-17 inhibitors, IL-23 inhibitors, JAK inhibitors, or PDE4 inhibitors) 1, 5

Poor Prognostic Factors Requiring Aggressive Treatment

• Polyarticular disease with high number of actively inflamed joints 2
• Elevated ESR at presentation 2
• Previous treatment failures 2
• Existing joint damage (clinical or radiographic) 2
• Diminished quality of life on standardized measures 2

Treatment Response Monitoring

Peripheral Arthritis

• ACR20/50/70 criteria: Primary endpoint in clinical trials; 20% reduction in tender/swollen joint counts plus 20% improvement in 3 of 5 measures (pain, patient/physician global, HAQ disability, acute phase reactants) 1, 2
• DAS28 and EULAR response criteria: Can be used but ensure DIP joints are included in assessment 2

Axial Disease

• BASDAI: Monitor disease activity over time, though evidence for this is less robust than peripheral measures 1, 2
• ASAS response criteria: 20% improvement in assessment measures 7

Critical Pitfalls to Avoid

Diagnostic Errors

• Do not diagnose PsA if rheumatoid nodules, extra-articular RA features, or high-titer rheumatoid factor present—this indicates seronegative RA with coincidental psoriasis 1
• Do not miss axial involvement: 20-50% have asymptomatic spine/sacroiliac disease requiring imaging for detection 1
• Distinguish from osteoarthritis: DIP involvement in PsA shows joint inflammation, not Heberden's nodes (bone spurs); morning stiffness improves with activity in PsA but worsens with activity in OA 1

Assessment Errors

• Always examine skin and nails: Psoriasis precedes arthritis in 80% of cases; nail disease strongly correlates with DIP involvement 4, 2, 6, 8
• Include DIP joints in counts: Standard RA joint counts miss these critical PsA-affected joints 1
• Screen for enthesitis and dactylitis: These are pathognomonic for PsA and commonly missed 1, 4

Management Errors

• Early treatment is critical: Progressive joint destruction occurs within the first year if untreated, leading to irreversible disability 4, 8
• Treating skin alone does not impact joint disease: Joint and skin manifestations require separate therapeutic consideration 6
• Radiographic progression inhibition: Only TNF inhibitors and newer biologics have demonstrated ability to slow radiographic progression; traditional DMARDs lack this evidence 7, 5, 6

Comorbidity Screening Requirements

• Cardiovascular risk factors: Hypertension, hyperlipidemia, diabetes 2, 9
• Metabolic syndrome components 2
• Inflammatory bowel disease 2, 9
• Depression and anxiety 2
• Liver disease (especially before methotrexate) 2, 9