A chronic immune-mediated disease of rapid keratinocyte turnover producing well-demarcated red plaques with silvery scale on extensor surfaces.
How it's asked: Auspitz sign, Koebner phenomenon, Munro microabscesses, drugs that aggravate it, and why systemic steroids are avoided.
Why this is true
Dendritic cells drive an IL-23/Th17 response that releases IL-17 and TNF, making keratinocytes proliferate so fast that a cell reaches the surface in about 4 days instead of 28. Cells arrive still holding their nuclei (parakeratosis) and the granular layer is lost, so the surface flakes as silvery scale. Elongated dermal papillae carry dilated, tortuous capillaries close to a thinned suprapapillary epidermis — scratch the scale off and they bleed in pinpoints (Auspitz sign).
Key points
Common traps
- Koebner phenomenon also occurs in lichen planus, vitiligo and warts — it isn't specific to psoriasis.
- Guttate psoriasis follows a streptococcal sore throat in young people — a frequent vignette.
Clinical case
A 30-year-old has well-defined red plaques with silvery scales on both elbows and knees. Removing the scale causes pinpoint bleeding; his nails are pitted.
High-yield
Auspitz sign, Koebner, nail pitting. Munro microabscess (stratum corneum). Aggravators: lithium, β-blockers, antimalarials. Avoid systemic steroids.
Quick check
Q1.Munro microabscesses are found in the:
Q2.Drug known to aggravate psoriasis: