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Psoriatic arthritis

Psoriatic arthritis is a polygenic disorder. HLA-Cw6 is associated with severe, early-onset skin psoriasis. HLA-B38 and HLA-B39 are associated with psoriatic arthritis and HLA-B27 is associated with sacroiliitis and spondylitis. Notably, only 50% of patients with psoriatic sacroiliitis/spondylitis are HLA-B27 positive.

Clinical features

• Asymmetric joint involvement.

• Absence of rheumatoid factor.

• Significant nail pits (>60 total pits is pathognomonic) or nail dystrophy.

• Involvement of DIP joints in the absence of osteoarthritis.

• “Sausage digits” (dactylitis): seen in 30% to 50%. Due to synovitis and flexor tenosynovitis.

• Enthesitis: seen in 35% to 40%. Most common Achilles and plantar fascia insertion.

• Family history of psoriasis or psoriatic arthritis.

• Axial radiographic evidence of sacroiliitis, paravertebral ossification, and syndesmophytes.

• Peripheral radiographic evidence of erosive arthritis with relative lack of periarticular osteopenia.

• Synovial biopsies show increased vascularity and the presence of macrophages(CD163+), lymphocytes, and neutrophils.

Classification of Psoriatic Arthritis criteria (CASPAR)

  1. Evidence of psoriasis (current, past, family): two points if current history of psoriasis, one point others.
  2. Psoriatic nail dystrophy: one point
  3. Negative rheumatoid factor: one point.
  4. Dactylitis (current, past history): one point.
  5. Radiographic evidence of juxtaarticular new bone formation: one point.

Three or more points have 99% specificity and 92% sensitivity for diagnosis of psoriatic arthritis.

Classification of Joint Involvement in Psoriatic Arthritis




Asymmetric oligoarticular disease

15 to 20

DIP joints and PIP joints of hands and feet. MCP joints, MTP joints, knees, hips, and ankles

Predominant DIP involvement

2 to 5

DIP joints

Arthritis mutilans


DIP joints, PIP joints

Polyarthritis “rheumatoid-like”

50 to 60

MCP joints, PIP joints, and wrists

Axial involvement (isolated)

2 to 5

Sacroiliac, vertebral

DIP, Distal interphalangeal; MCP, metacarpophalangeal; MTP, metatarsophalangeal; PIP, proximal interphalangeal.






Hopkins Arthritis

National Psoriasis Foundation