Psoriatic Arthritis

PsA Overview - Rash's Arthritic Kin

• Definition: Psoriatic Arthritis (PsA) is a chronic, inflammatory spondyloarthropathy occurring in individuals with psoriasis.
• Link to Psoriasis: Skin or nail psoriasis usually precedes PsA onset, often by years.
• Prevalence: Affects ~0.3-1% of the general population.
• Age of Onset: Typically between 30-50 years.
• Sex Ratio: M:F is approximately 1:1.

⭐ A significant proportion, up to 30%, of psoriasis patients eventually develop PsA.

Pathogenesis & Clinical Types - Immune Mayhem & Joint Tales

• Immunopathogenesis: Key cytokines TNF-α, IL-17, IL-23 drive inflammation. Genetics: HLA-B27 (axial), HLA-Cw6 (psoriasis).
• Clinical Patterns (📌 Mnemonic: "A DAMP S" - Asymmetric, DIP, Arthritis Mutilans, Polyarthritis, Spondylitis):
  • Asymmetric Oligoarthritis: Affects ≤4 joints, often large, asymmetrically.

    ⭐ Most common PsA pattern, affects ~50%.

  • Symmetric Polyarthritis: ≥5 joints symmetrically, RA-like, RF-neg.
  • DIP Predominant: Primarily Distal Interphalangeal joints; nail changes common.
  • Arthritis Mutilans: Rare (<5%), severe, deforming; marked osteolysis ('pencil-in-cup').
  • Spondylitis/Axial: Sacroiliitis and/or spondylitis; HLA-B27 positive. May occur alone.
• Key Features:
  • Dactylitis: 'Sausage digits' - diffuse swelling of entire finger/toe.
  • Enthesitis: Inflammation at tendon/ligament insertions (Achilles, plantar fascia).
  • Nail Changes: Pitting, onycholysis, oil drop sign, subungual hyperkeratosis (in ~80%).

Diagnosis & Investigations - PsA Detective Kit

• CASPAR Criteria: Requires inflammatory articular disease + ≥3 points from:
  • Psoriasis: Current skin/scalp (2 pts); OR Personal history (1 pt); OR Family history (1st/2nd degree) (1 pt)
  • Nail lesions (pitting, onycholysis, hyperkeratosis): 1 pt
  • Dactylitis (current/history): 1 pt
  • RF negativity (non-latex method, < lab ULN): 1 pt
  • Juxta-articular new bone (X-ray hands/feet, not osteophytes): 1 pt
• Lab Findings:
  • ↑ ESR, ↑ CRP (non-specific)
  • RF usually negative (distinguishes from RA)
  • Anti-CCP usually negative

⭐ RF negativity is a key feature distinguishing PsA (a seronegative spondyloarthropathy) from Rheumatoid Arthritis.

• Imaging:
  • X-ray: "Pencil-in-cup" deformity, erosions, ankylosis, periostitis, asymmetric sacroiliitis.
  • MRI/US: Early enthesitis, synovitis detection.

Treatment Strategies - Inflammation Takedown

• Goals: ↓ Inflammation, prevent joint damage, ↑ function & QoL.
• Non-Pharmacological: Patient education, physiotherapy, occupational therapy, weight management.
• Pharmacological Approach:
  • NSAIDs: Initial for mild pain/stiffness.
  • csDMARDs (Methotrexate, Sulfasalazine, Leflunomide):
    • Key for peripheral arthritis. MTX often anchor drug.
  • bDMARDs: For moderate-severe PsA, axial disease, enthesitis, or dactylitis.
    • TNF inhibitors (e.g., Adalimumab, Infliximab): Often 1st line biologic.
    • IL-17 inhibitors (e.g., Secukinumab, Ixekizumab).
    • IL-12/23 inhibitors (e.g., Ustekinumab).
  • tsDMARDs (JAK inhibitors, e.g., Tofacitinib, Upadacitinib): If bDMARDs inadequate/contraindicated.
• Domain-Specific Notes:
  • Axial Disease: NSAIDs → bDMARDs (TNF-i, IL-17i). csDMARDs generally ineffective.
  • Enthesitis/Dactylitis: NSAIDs, local steroid injections → bDMARDs.

⭐ TNF inhibitors are frequently the first-line biologic agents for severe Psoriatic Arthritis, especially if other systemic therapies are insufficient or contraindicated.

High‑Yield Points - ⚡ Biggest Takeaways

• Psoriatic Arthritis (PsA) is a seronegative spondyloarthropathy often linked with HLA-B27, especially in axial disease.
• Hallmark features include dactylitis (sausage digits) and enthesitis (inflammation at tendon/ligament insertion).
• Classic X-ray finding: "pencil-in-cup" deformity, often at DIP joints, alongside erosions and new bone formation.
• Most common pattern is asymmetric oligoarthritis; Distal Interphalangeal (DIP) joint involvement is characteristic.
• Skin and nail psoriasis (e.g., pitting, onycholysis) usually precedes arthritis, sometimes by years.
• Management includes NSAIDs, DMARDs (methotrexate is a cornerstone), and biologics (e.g., anti-TNF agents) for moderate-severe disease.