Psoriatic arthritis

PsA is a chronic, systemic inflammatory disorder that occurs in patients with psoriasis and is associated with multiple musculoskeletal manifestations.

The pathogenesis of PsA is multifactorial and involves polygenic inheritance, environmental factors, and patient-specific risk factors, including obesity. These various factors initiate an auto-inflammatory loop with amplification of the IL-23/IL-17 pathway that leads to a diverse array of associated pathologies at distant body sites.

In the US, the prevalence of PsA is estimated at 50-250 persons per 100,000 population. PsA is prevalent in 6-41% of patients with psoriasis.

Key clinical manifestations include arthritis, enthesitis, spondylitis, nail disease, dactylitis, and uveitis. Five disease phenotypes have been described. The oligoarticular subtype affects ≤ 4 joints, and typically occurs in an asymmetric distribution. The polyarticular subtype affects ≥ 5 joints; the involvement may be symmetric and resemble rheumatoid arthritis. The distal subtype affects distal interphalangeal joints of the hands, feet, or both. The axial or spondyloarthritis subtype primarily involves the spine and sacroiliac joints. Finally, a subtype known as arthritis mutilans is characterized by deforming and destructive arthritis that involves marked bone resorption or osteolysis, with telescoping and flail digits.

Articular damage develops in a large number of patients with PsA, with up to 47% of patients developing bony erosions within 2 years of diagnosis, despite the use of disease-modifying medications. Spontaneous remission is extremely rare. Treatment with biologics leads to partial remission in over 50% of patients.