There is no consensus on the criteria for the diagnosis of psoriatic arthritis (PsA), although the Classification Criteria for Psoriatic Arthritis (CASPAR) criteria publised in 2006 appear to be gaining increasing acceptance for both clinical research and daily usage in clinical practice because of their relatively high specificity (98.7%) and sensitivity (91.4%). The classification of PsA based on the CASPAR criteria requires the presence of inflammatory arthritis (joints, spine, or entheses) with ≥ 3 points from 5 categories. Current psoriasis is assigned 2 points, while all other clinical features are assigned 1 point:
- Current psoriasis, prior history of psoriasis, or family history of psoriasis.
- Nail psoriasis, including onycholysis, pitting, and hyperkeratosis.
- Absence of serum rheumatoid factor.
- Current or prior history of dactylitis.
- Radiographic evidence of periarticular new bone formation (excluding osteophytes) on x-rays of the hand or foot.
Radiographic changes due to PsA, unlike those of rheumatoid arthritis, demonstrate characteristic bony proliferation and erosion. A highly specific finding of erosive arthritis of PsA is the classic “pencil-in-cup” (image below)
deformity in the phalanges, osteolysis, articular ankylosis, sacroiliitis (two images below)
spondylitis (image below), enthesitis and periostitis.
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*Images within this article are from the American College of Rheumatology Slide Collection.