Criterion 1: psoriatic changes in skin and/or nails
Criterion 2: peripheral arthritis (see below)
Criterion 3: central involvement (see below)
The definite diagnosis of psoriatic arthritis involves both of the following:
(1) criterion 1
(2) any finding for criterion 2 or 3
Features of peripheral arthritis:
(1) pain and soft tissue swelling in distal interphalangeal joints with or without limitation of motion for > 4 weeks
(2) pain and soft tissue swelling of peripheral joints in an asymmetrical pattern with or without limitation of motion for > 4 weeks (includes "sausage digit" with diffuse swelling of the entire digit)
(3) symmetrical peripheral arthritis for > 4 weeks in absence of rheumatoid factor or subcutaneous (rheumatoid) nodules
(4) radiographic findings in peripheral joints ("pencil in cup" deformity; "whittling" of terminal phalanges, "fluffy periostitis", "bony ankylosis")
Features of central involvement:
(1) spinal pain, stiffness and restriction motion for > 4 weeks
(2) Grade II symmetrical sacroiliitis (New York criteria)
(3) Grade III or IV unilateral sacroliliitis
