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Chapter 161: Psoriatic Arthritis

DEFINITION

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.

PATTERNS OF JOINT INVOLVEMENT

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.

EVALUATION

  • 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.

DIAGNOSIS

(Table 161-1)

TABLE 161-1THE CASPAR (CLASSIFICATION CRITERIA FOR PSORIATIC ARTHRITIS) CRITERIAa
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TABLE 161-1THE CASPAR (CLASSIFICATION CRITERIA FOR PSORIATIC ARTHRITIS) CRITERIAa
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.

TREATMENT: PSORIATIC ARTHRITIS

  • Coordinated therapy is directed at the skin and joints.

    ...

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