Makindo Medical Notes

Related Subjects: |Monoarticular arthritis |Polyarticular arthritis |Seronegative Spondyloarthropathies |Ankylosing spondylitis |Enteropathic Spondyloarthritis |Reactive Arthritis

Psoriatic arthritis (PsA) is a chronic inflammatory arthritis associated with psoriasis. It belongs to the seronegative spondyloarthropathies (negative for rheumatoid factor) and can present with a wide range of symptoms, from mild joint involvement to severe, deforming arthritis. PsA can develop in patients with or without a history of psoriasis, and a severe form is more common in HIV-positive patients.

About

• PsA is a seronegative spondyloarthritis (negative for rheumatoid factor and anti-CCP).
• The condition can develop years after the onset of psoriasis or, less commonly, before the appearance of skin lesions.
• It is characterized by a chronic, inflammatory arthritis that may affect the peripheral and axial skeleton.

Aetiology

• PsA affects men and women equally, typically between ages 30-55, though it can present at any age.
• Genetic Factors: Genetic predisposition plays a significant role, with links to HLA-B27 and other HLA alleles like HLA-Cw6.
• Immune-mediated: Thought to involve immune dysregulation, with T-cells and pro-inflammatory cytokines like TNF-alpha and IL-17 driving joint and skin inflammation.
• Exogenous Triggers: Infections, physical trauma (Koebner phenomenon), and environmental factors may trigger or exacerbate PsA in genetically predisposed individuals.

Key Radiological Finding: Pencil-in-Cup Deformity

This characteristic deformity is often seen in advanced psoriatic arthritis, where the ends of the bone are eroded, giving a tapering appearance that resembles a pencil fitting into a cup.

Clinical Features

• Skin Involvement: Look for classic erythematous, scaly plaques of psoriasis, often present in:
  • Scalp, elbows, knees (extensor surfaces)
  • Umbilicus, natal cleft
  • Palms, soles, and lower back
• Nail Changes: Common in PsA and can include:
  • Nail pitting
  • Onycholysis (nail lifting from the nail bed)
  • Oil drop sign (yellow-brown discoloration under the nail)
• Joint Involvement: Various patterns, including:
  • Asymmetrical oligoarthritis (affecting fewer than 5 joints)
  • Symmetrical polyarthritis, resembling rheumatoid arthritis
  • Distal interphalangeal (DIP) arthritis, often with nail changes
  • Dactylitis ("sausage digits")—diffuse swelling of entire fingers or toes
  • Arthritis mutilans (severe, destructive arthritis)
  • Sacroiliitis and axial involvement with spinal stiffness
• Extra-articular Manifestations:
  • Lungs: Pulmonary fibrosis may occur, particularly with severe disease.
  • Cardiac: Aortic regurgitation can be a complication in patients with long-standing PsA.
  • Eyes: Conjunctivitis and anterior uveitis, especially in those with spinal involvement.

Typical Patterns of Joint Involvement in Psoriatic Arthritis

• Distal Interphalangeal (DIP) Predominant: Often seen with nail changes.
• Asymmetrical Oligoarthritis: Less than 5 joints, often large joints, such as the knees.
• Symmetrical Polyarthritis: Resembles rheumatoid arthritis with involvement of MCPs and PIPs.
• Arthritis Mutilans: Severe form with bone resorption leading to deformity.
• Axial Arthritis: Spinal involvement, including sacroiliitis, similar to ankylosing spondylitis.

CASPAR (Classification Criteria for Psoriatic Arthritis)

Inflammatory joint, spine, or entheseal disease with at least 3 points from the criteria below:

• Current or previous psoriasis (+2 if current, +1 if family history or past).
• Nail dystrophy (pitting, onycholysis) (+1).
• Dactylitis (present or past) (+1).
• Negative rheumatoid factor (+1).
• Juxta-articular new bone formation on X-rays (+1).

Investigations

• Blood Tests:
  • FBC: May show anemia of chronic disease.
  • ESR/CRP: Typically elevated during active inflammation.
  • Seronegative for RF and anti-CCP (helps differentiate from RA).
• Radiographic Studies:
  • X-rays of hands, feet, and symptomatic joints to identify:
    • Joint erosions and narrowing
    • Bony proliferation and periostitis
    • Pencil-in-cup deformity in advanced cases
  • MRI may help evaluate sacroiliitis and axial involvement.

Management

• Conservative Management:
  • Patient education about the nature of the disease.
  • Encourage smoking cessation.
  • Exercise and physiotherapy to maintain joint mobility and strength.
  • Use of splints for joint protection.
• Pharmacological Management:
  • NSAIDs: Provide symptomatic relief for pain and stiffness.
  • DMARDs: Methotrexate or sulfasalazine for moderate to severe cases.
  • Biologics: Anti-TNF agents (e.g., etanercept, infliximab), IL-17 inhibitors (e.g., secukinumab), and IL-23 inhibitors (e.g., guselkumab) for refractory or severe cases.
  • Systemic Steroids: Generally avoided due to risk of skin flare-ups but may be used in low doses for acute flares.
• Surgical Intervention: Joint replacement or synovectomy in severe cases to alleviate pain and restore function.

References

• Psoriatic Arthritis: A Review