Psoriatic Arthritis

Psoriatic Arthritis is a topic covered in the Harrison's Manual of Medicine.

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Psoriatic arthritis is a chronic inflammatory arthritis that affects 5–42% of persons with psoriasis. Some pts, especially those with spondylitis, will carry the HLA-B27 histocompatibility antigen. Onset of psoriasis usually precedes development of joint disease; approximately 15–20% of pts develop arthritis prior to onset of skin disease. Nail changes are seen in 90% of pts with psoriatic arthritis.


There are five patterns of joint involvement in psoriatic arthritis.

  • Asymmetric oligoarthritis: often involves distal interphalangeal/proximal interphalangeal (DIP/PIP) joints of hands and feet, knees, wrists, ankles; “sausage digits” may be present, reflecting tendon sheath inflammation.
  • Symmetric polyarthritis (40%): resembles rheumatoid arthritis except rheumatoid factor is negative, absence of rheumatoid nodules.
  • Predominantly DIP joint involvement (15%): high frequency of association with psoriatic nail changes.
  • “Arthritis mutilans” (3–5%): aggressive, destructive form of arthritis with severe joint deformities and bony dissolution.
  • Spondylitis and/or sacroiliitis: axial involvement is present in 20–40% of pts with psoriatic arthritis; may occur in absence of peripheral arthritis.


  • Negative tests for rheumatoid factor.
  • Hypoproliferative anemia, elevated ESR.
  • Hyperuricemia may be present.
  • HIV infection should be suspected in fulminant disease.
  • Inflammatory synovial fluid and biopsy without specific findings.
  • Radiographic features include erosion at joint margin, bony ankylosis, tuft resorption of terminal phalanges, “pencil-in-cup” deformity (bone proliferation at base of distal phalanx with tapering of proximal phalanx), axial skeleton with asymmetric sacroiliitis, asymmetric nonmarginal syndesmophytes.


(Table 161-1)

To meet the CASPAR criteria, a pt must have inflammatory articular disease (joint, spine, or entheseal) with ≥3 points from any of the following five categories:
  1. Evidence of current psoriasis,b, c a personal history of psoriasis, or a family history of psoriasisd
  2. Typical psoriatic nail dystrophye observed on current physical examination
  3. A negative test result for rheumatoid factor
  4. Either current dactylitisf or a history of dactylitis recorded by a rheumatologist
  5. Radiographic evidence of juxtaarticular new bone formationg in the hand or foot
aSpecificity of 99% and sensitivity of 91%.
bCurrent psoriasis is assigned 2 points; all other features are assigned 1 point.
cPsoriatic skin or scalp disease present at the time of examination, as judged by a rheumatologist or dermatologist.
dHistory of psoriasis in a first- or second-degree relative.
eOnycholysis, pitting, or hyperkeratosis.
fSwelling of an entire digit.
gIII-defined ossification near joint margins, excluding osteophyte formation.
Source: From Taylor W et al: Classification criteria for psoriatic arthritis. Development of new criteria from a large international study. Arthritis Rheum, 54:2665, 2006.

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