Psoriasis and Psoriatic Arthritis

Psoriasis is a chronic, immune-mediated skin disease affecting roughly 2–3% of the population. Psoriatic arthritis (PsA) is an inflammatory arthropathy that occurs in a substantial subset of people with psoriasis and targets peripheral joints, the spine, and sites where tendons and ligaments insert (entheses). Shared genetic architecture (notably variants along the IL-23/Th17 pathway) and overlapping environmental risks (obesity, mechanical stress, and metabolic comorbidities) create a biologic continuum from skin to musculoskeletal inflammation. Nail involvement, scalp and intertriginous psoriasis, and higher skin severity are particularly linked with later PsA, likely reflecting the close anatomic and immunologic relationship between the nail unit and entheses. Epidemiologically, about 20–30% of individuals with psoriasis develop PsA, most often years after skin onset, though arthritis can precede skin disease in a minority. Subclinical entheseal and synovial inflammation is detectable by imaging in some patients with cutaneous psoriasis alone, underscoring the need for vigilant screening. Simple questionnaires (PEST, ToPAS, PASE) can flag suspected PsA for rheumatology referral. Early diagnosis matters: persistent inflammation risks irreversible joint damage, disability, and reduced quality of life, while timely treatment can achieve minimal disease activity and prevent progression. Therapies increasingly target the shared IL-23/IL-17–TNF axis, yielding options effective for both skin and joints: TNF inhibitors, IL-17 inhibitors, IL-23 inhibitors, and ustekinumab have strong evidence across domains; apremilast offers oral convenience with moderate efficacy; JAK inhibitors are effective for PsA musculoskeletal domains. Conventional agents (methotrexate, cyclosporine) remain useful, particularly for skin and peripheral arthritis, though effect sizes vary. Lifestyle interventions—weight reduction, exercise, smoking cessation, cardiometabolic risk control—improve症