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)
- Evidence of psoriasis (current, past, family): two points if current history of psoriasis, one point others.
- Psoriatic nail dystrophy: one point
- Negative rheumatoid factor: one point.
- Dactylitis (current, past history): one point.
- 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
|
SUBTYPE |
PERCENTAGE |
TYPICAL JOINTS |
|
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 |
5 |
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. |
|
|
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