Psoriatic Arthritis

Psoriatic arthritis (PsA) is a chronic immune-mediated inflammatory disease. It may involve one or several disease domains: peripheral synovitis, the spine and sacroiliac joints, entheses, entire digits through dactylitis, skin, and nails. The pattern is variable, so a patient may have severe enthesitis with little synovitis, or prominent psoriasis with subtle joint disease. Psoriasis supports the diagnosis but is not required at the time of presentation. Joint symptoms can precede recognized skin disease, and psoriasis may be hidden in the scalp, umbilicus, gluteal cleft, or behind the ears. Ask about a personal or family history rather than relying only on what is visible during the examination. Inflammation at an enthesis can cause focal heel, plantar fascia, elbow, or pelvic pain. Dactylitis produces diffuse swelling of an entire finger or toe because the joint, tendon sheath, and surrounding soft tissue are inflamed together. A “sausage digit” is therefore different from isolated swelling of one interphalangeal joint. PsA can erode bone and cartilage, but it can also stimulate abnormal new bone formation. This combination—erosions alongside periostitis or other new bone formation—is a...