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Arthritis, Psoriatic (PsA)

Basics

  • Chronic, destructive seronegative arthropathy in patients with psoriasis.
  • Five clinical patterns:
  • Asymmetric oligoarthritis (<5 joints)
  • Distal interphalangeal (DIP) predominant (with nail psoriasis)
  • Symmetric polyarthritis (may mimic RA, milder)
  • Spondyloarthritis (asymmetric, discontinuous)

  • Arthritis mutilans (destructive β€œopera-glass” digits)

  • Psoriasis extent does not correlate with arthritis severity.

  • RF and anti-CCP usually negative; HLA-B27 positive in spondylitis subtype.

Epidemiology

  • Peak onset 30–50 years.
  • Equal gender distribution; polyarthritis more common in women, spondylitis more common in men.
  • Psoriasis precedes arthritis by ~12 years on average.
  • PsA prevalence 1–2/1000 population.
  • 6–42% of patients with psoriasis develop PsA.

Etiology & Pathophysiology

  • Inflammatory cytokines: TNF-Ξ±, IL-1, IL-6, IL-8, IL-10, IL-17, IL-23.
  • Osteoclast precursor upregulation.
  • Multifactorial: genetic, immunologic, environmental.
  • Genetics: 30–40% twin concordance; HLA-B27 (15–50% with axial disease), other HLA types.

Risk Factors

  • Psoriasis.
  • Family history of PsA.
  • Obesity.

Commonly Associated Conditions

  • Psoriasis.

Diagnosis

History

  • Long-standing psoriasis.
  • Morning stiffness >30 minutes.
  • Joint pain, swelling, low back/buttock/heel pain.
  • Dactylitis (uniform swelling of digit).

Physical Exam

  • Peripheral joint erythema, warmth, swelling.
  • Synovitis, dactylitis.
  • Enthesitis (Achilles tendon, calcaneus).
  • Limited axial range of motion, SI joint tenderness.
  • Psoriatic skin plaques and nail changes (pitting, onycholysis, oil spots).

Differential Diagnosis

  • Reactive arthritis.
  • Psoriasis + RA, OA, gout.
  • Psoriasis + ankylosing spondylitis.

Diagnostic Criteria: CASPAR

  • Inflammatory articular disease + β‰₯3 points from:
  • Current psoriasis or history/family psoriasis (2 points).
  • Psoriatic nail dystrophy (1 point).
  • Negative RF (1 point).
  • Dactylitis (1 point).
  • Radiologic new bone formation excluding osteophytes (1 point).

Tests

  • Seronegative for RF and anti-CCP.
  • Elevated ESR, CRP.
  • HLA-B27 positive in 50–70% axial disease; <15% peripheral.
  • X-rays: "pencil-in-cup" erosions, periostitis.
  • Ultrasound: enthesitis.
  • Diagnosis clinical; biopsy rarely needed.

Treatment

General Measures

  • Physical and occupational therapy.
  • Lifestyle: smoking cessation, weight loss, joint protection, exercise, stress coping.

Medications

  • First line: NSAIDs for symptom control.
  • Second line: DMARDs β€” methotrexate, sulfasalazine, leflunomide.
  • Avoid systemic steroids if possible; short-term use in severe flares.

Biologics

  • Anti-TNF agents: adalimumab, etanercept, infliximab, certolizumab, golimumab.
  • Anti-IL-17: secukinumab, ixekizumab, brodalumab.
  • Anti-IL-12/23: ustekinumab.
  • IL-23 selective: risankizumab, guselkumab.
  • PDE4 inhibitor: apremilast.
  • JAK inhibitors: tofacitinib, upadacitinib.

  • T-cell costimulation blocker: abatacept.

  • Avoid biologics in active infections, malignancy, live vaccines.

  • Pregnancy: avoid teratogenic meds (methotrexate, leflunomide).

Issues for Referral

  • Rheumatology.
  • Dermatology.

Surgery

  • Joint fusion or replacement for advanced damage.

Ongoing Care

  • Control cardiovascular and metabolic risk factors.
  • Monitor disease activity and medication toxicity.

Patient Education

  • National Psoriasis Foundation, Arthritis Foundation, ACR resources.

Prognosis

  • Typically chronic insidious course with relapsing-remitting skin and joint disease.
  • Prognosis better than RA except in arthritis mutilans.

Complications

  • Disability.
  • Anxiety and depression related to psychosocial impact.

ICD10 Codes

  • L40.50 Arthropathic psoriasis, unspecified
  • L40.51 Distal interphalangeal psoriatic arthropathy
  • L40.53 Psoriatic spondylitis

Clinical Pearls

  • 25% of psoriasis patients develop PsA.
  • Severity of psoriasis correlates with arthritis risk, not arthritis severity.
  • Look for psoriasis in scalp, ears, umbilicus, gluteal cleft.
  • Polyarticular PsA mimics RA; presence of enthesitis and psoriasis help differentiate.
  • Rapidly evolving therapies include NSAIDs, DMARDs, biologics, and JAK inhibitors.