Psoriasis
A chronic immune-mediated disease in which a self-sustaining T-cell/keratinocyte loop drives massive epidermal overproliferation, producing well-demarcated scaly plaques that respond to therapies aimed at that loop.
In a nutshell
A self-sustaining dendritic-cell, Th17 and keratinocyte loop drives epidermal turnover far faster than keratinocytes can mature. Every feature of the plaque follows from that. Treatment climbs a ladder that targets the loop ever more precisely.
Classic presentation
Chronic, well-demarcated red plaques with silvery scale over the extensor surfaces, scalp and sacrum, with nail pitting and onycholysis.
Key points
- Cells reach the surface before keratinising, so they keep their nuclei (parakeratosis) and pile up as thick silvery scale, while dilated dermal capillaries loop close to the surface, giving the erythema and the Auspitz sign.
- Koebner phenomenon: new plaques seed along lines of skin trauma.
- Triggers worth knowing: streptococcal infection (guttate psoriasis), beta-blockers, lithium, and abrupt withdrawal of systemic corticosteroids.
- It is a clinical diagnosis, made on morphology, distribution and nail changes. Biopsy is rarely needed.
- Screen for psoriatic arthritis: the driving cytokines are systemic and joint damage is irreversible.
- Psoriasis is an independent cardiovascular risk factor through systemic inflammation, so review blood pressure, lipids and glucose.
- The ladder: emollients with a topical vitamin D analogue and/or corticosteroid, then narrowband UVB, then methotrexate or ciclosporin, then biologics against TNF-alpha, IL-17 or IL-23.
First-line investigation
None: the diagnosis is clinical. Screen for psoriatic arthritis (for example with the PEST tool) and review cardiovascular and metabolic risk.
First-line management
Generous emollients plus a topical vitamin D analogue and/or a topical corticosteroid: the analogue slows keratinocyte proliferation while the steroid damps inflammation.
Exam traps
- Systemic corticosteroids are not a psoriasis treatment. Withdrawing them can precipitate unstable or pustular disease.
- Guttate psoriasis after a sore throat in a young person is the streptococcal trigger, not a drug reaction.
- New inflammatory joint pain and stiffness in a patient with psoriasis is psoriatic arthritis until proven otherwise.
Educational content pending clinical review. Not medical advice.