Overview
The Inflammatory Pattern
Psoriatic arthritis (PsA) is an immune mediated inflammatory disease that links psoriasis with arthritis, enthesitis, dactylitis, and sometimes axial inflammation.
Psoriatic arthritis (PsA) is an immune-mediated inflammatory disease that links psoriasis with arthritis, enthesitis, dactylitis, and sometimes axial inflammation. Skin disease may appear first, at the same time, or after the joint disease; its absence does not exclude PsA. The inflammatory network includes tumour necrosis factor and the IL-23/IL-17 pathway. These cytokines activate synovial tissue, recruit inflammatory cells, and stimulate osteoclasts, producing pain, swelling, cartilage loss, and erosions. The same network promotes keratinocyte proliferation in psoriatic plaques. At entheses—the sites where tendons and ligaments attach to bone—repeated inflammatory signalling causes focal pain and may eventually produce new bone formation. That combination is characteristic: PsA can cause erosion and abnormal new bone at the same time. Rheumatoid arthritis (RA) more typically produces symmetric synovitis and marginal erosions without the same pattern of enthesophytes or periostitis. The disease can affect several clinical domains: - Peripheral arthritis: swollen, tender joints, often with an asymmetric or uneven distribution. - Enthesitis: pain at sites such as the Achilles tendon, plantar fascia, or elbow attachments. - Dactylitis: diffuse swelling of an entire finger or toe, producing...