DR3.1 | Psoriasis Recognition and Differential Diagnosis — Summary & Reflection

KEY TAKEAWAYS

Psoriasis is a common, chronic, immune-mediated papulosquamous disease recognised clinically by well-defined erythematous plaques with silvery-white scale, the candle-grease sign and pinpoint Auspitz bleeding on scraping, and the Koebner phenomenon at sites of trauma. Its four major variants — chronic plaque (commonest), guttate (post-streptococcal), pustular (including the Von Zumbusch emergency), and erythrodermic (>90% BSA) — each carry distinct distribution, triggers, and severity. The disease arises in a genetically predisposed person (HLA-Cw6) through the IL-23/IL-17 axis driving keratinocyte hyperproliferation and capillary dilatation, which explains its signs. A disciplined differential separates psoriasis from seborrhoeic dermatitis (greasy scale), pityriasis rosea (herald patch), lichen planus (violaceous Wickham-striae papules, no Auspitz), tinea corporis (KOH-positive), and secondary syphilis (palms/soles). Accurate recognition selects the management tier and enforces the cardinal safety rule that systemic corticosteroids must never be used, as their withdrawal can precipitate a pustular or erythrodermic flare.

REFLECT

Think back to a scaly rash you have seen — in a relative, a ward patient, or a clinic — that was labelled 'ringworm', 'eczema', or 'dandruff' and treated accordingly. With what you now know, what features would you re-examine to test whether it might actually have been psoriasis: the character of the scale, the symmetry and site, the nails, a recent sore throat, the response to previous treatment? Consider how a single careful examination — lifting a flake of scale, checking for Auspitz, glancing at the nails — could change the diagnosis and the entire treatment trajectory. How will you build this disciplined morphological reading into your own routine examination of every scaly lesion you meet?