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164 PSORIATIC ARTHRITIS

164 PSORIATIC ARTHRITIS
Harrison’s Manual of Medicine

164

PSORIATIC ARTHRITIS

Definition
Patterns of Joint Involvement
Evaluation
Diagnosis
Bibliography

Definition
Psoriatic arthritis is a chronic inflammatory arthritis that affects 5–42% of people 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% of pts develop arthritis prior to onset of skin disease.
Patterns of Joint Involvement

Asymmetric oligoarthritis: most common pattern affecting 16–70% (mean 47%); often involve DIP/PIP of hands and feet, knees, wrists, ankles; “sausage digits” may be present, reflecting tendon sheath inflammation.

Symmetric polyarthritis (25%) resembles rheumatoid arthritis except rheumatoid factor is negative, absence of rheumatoid nodules.

Predominantly distal interphalangeal joint involvement (10%): 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 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
Suggested by: pattern of arthritis and inflammatory nature, absence of rheumatoid factor, radiographic characteristics, presence of skin and nail changes of psoriasis (Fig. 161-1).

TREATMENT

Pt education, physical and occupational therapy.

NSAIDs.

Intraarticular steroid injections—useful in some settings. Systemic glucocorticoids should rarely be used as may induce rebound flare of skin disease upon tapering.

Gold salts IM or PO—helpful in some pts, significant side-effect profile.

Methotrexate (5–25 mg PO weekly)—in advanced cases, especially with severe skin involvement, significant side-effect profile.

Bibliography

For a more detailed discussion, see Schur PH: Psoriatic Arthritis and Arthritis Associated with Gastrointestinal Disease, Chap. 324, p. 2003, in HPIM-15.

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