Clinical meaning
Psoriatic arthritis (PsA) is a chronic inflammatory arthropathy occurring in approximately 30% of patients with psoriasis, characterized by synovitis, enthesitis (inflammation at tendon and ligament insertions), dactylitis (diffuse swelling of entire digits -- 'sausage digits'), and spondylitis. The pathogenesis involves dysregulated immune responses in genetically susceptible individuals (HLA-B27 positive in axial disease) with activation of the IL-23/IL-17 axis, which drives both skin and joint inflammation. IL-23 stimulates Th17 cells to produce IL-17, which activates synovial fibroblasts and osteoclasts, causing synovial inflammation, cartilage destruction, and bone erosion, while also stimulating keratinocyte proliferation in psoriatic skin plaques. A distinctive feature of PsA compared to rheumatoid arthritis is concurrent new bone formation (enthesophytes, periostitis) alongside erosive disease, and nail involvement (pitting, onycholysis) in 80% of patients with PsA. The nurse assesses joint function and range of motion, evaluates skin and nail involvement, administers biologic therapy (TNF inhibitors, IL-17 inhibitors, IL-23 inhibitors, JAK inhibitors) as prescribed, monitors for injection site reactions, screens for latent tuberculosis before initiating biologic therapy, monitors CBC and liver function during treatment, promotes joint protection strategies, and coordinates physiotherapy referrals.