DERMATOLOGY
Etiology
Autoimmune
Genetic predisposition (HLA-Cw6)
Triggered by infections, stress, trauma (Koebner phenomenon), drugs (β-blockers, lithium)
Pathogenesis
Hyperproliferation of keratinocytes driven by T-cell–mediated inflammation
Shortened epidermal turnover → thickened plaques
Clinical Features
Well-demarcated erythematous plaques with silvery scales
Extensor surfaces, scalp
Auspitz sign (pinpoint bleeding)
Nail pitting
Possible psoriatic arthritis
Treatment
Topical steroids, vitamin D analogs
Phototherapy (NB-UVB)
Systemic therapy: methotrexate, cyclosporine, biologics (TNF-α, IL-17, IL-23 inhibitors)