Key Facts

Psoriasis is a systemic inflammatory disease, not just a skin condition. Cardiovascular risk is independently increased and should be actively managed. Biologic therapies have transformed outcomes for severe disease.

Epidemiology

• UK prevalence: 2–3% (~1.8 million people)
• Bimodal onset: type I (16–22 years, HLA-Cw6+, family history) and type II (55–60 years)
• 30% have first-degree relative with psoriasis
• Increased cardiovascular mortality: severe psoriasis shortens life expectancy by ~5 years

Aetiology

• Genetic: HLA-Cw6 (strongest association), multiple susceptibility loci (PSORS1-9)
• Environmental triggers: streptococcal pharyngitis (guttate), stress, drugs (lithium, beta-blockers, antimalarials, NSAIDs, ACEi withdrawal of steroids), alcohol, smoking, trauma (Koebner)

Pathophysiology

• Dendritic cell activation → IL-23 production → Th17 cell differentiation → IL-17A, IL-22 production
• Keratinocyte hyperproliferation: cell cycle reduced from 28 days to 3–4 days → accumulation of immature keratinocytes → silvery scale
• Angiogenesis: dilated tortuous capillaries in dermal papillae
• TNF-alpha also contributes: targeted by anti-TNF biologics

Chronic Plaque Psoriasis (~90%)

• Well-demarcated, erythematous plaques with silvery-white scale
• Symmetrical; extensor surfaces (elbows, knees), scalp, sacrum, umbilicus
• Pruritus in ~70%

Guttate Psoriasis

• Small (<1cm) drop-like papules over trunk and proximal limbs
• Often triggered by streptococcal pharyngitis (2–4 weeks prior)
• Common in children/young adults; may be first presentation

Other Types

• Flexural (inverse): smooth, glazed erythema in flexures; minimal scale
• Pustular: localised (palmoplantar) or generalised (von Zumbusch — emergency)
• Erythrodermic: >90% BSA; risk of hypothermia, cardiac failure — EMERGENCY

Nail Psoriasis (~50%)

• Pitting, onycholysis, oil drop sign, subungual hyperkeratosis

Red Flags

• Generalised pustular psoriasis (systemic illness, fever)
• Erythrodermic psoriasis (hypothermia, high-output cardiac failure)
• Rapid worsening after systemic steroid withdrawal

Clinical Diagnosis

• Usually clinical; no investigations needed for typical plaque psoriasis

Severity Assessment

• BSA, PASI, DLQI: required for biologic eligibility (PASI ≥10 and DLQI ≥10)
• PEST questionnaire: screen for psoriatic arthritis

Pre-Treatment Bloods (if systemic therapy)

• FBC, U&Es, LFTs: baseline before methotrexate/ciclosporin
• Hepatitis B/C, HIV: before biologics
• TB screening (IGRA): before anti-TNF biologics
• Lipid profile, HbA1c, BP: cardiovascular risk assessment

Special Tests

• Skin biopsy: if diagnostic uncertainty — regular acanthosis, Munro microabscesses, parakeratosis, dilated capillaries
• Throat swab/ASO titre: if guttate (streptococcal trigger)
• Joint imaging: if psoriatic arthritis suspected (X-ray: pencil-in-cup, periostitis)

Topical (Mild-Moderate)

• Vitamin D analogues: calcipotriol (Dovonex) OD-BD; combined with betamethasone (Dovobet/Enstilar)
• Topical corticosteroids: potent (betamethasone valerate 0.1%) for body; moderate for face/flexures
• Coal tar preparations: for chronic stable plaques; messy but effective
• Dithranol: short-contact therapy in specialist settings
• Emollients: adjunctive; descale before active treatment

Phototherapy (Moderate)

• Narrowband UVB: first-line for moderate-extensive disease; 2–3× weekly for 6–8 weeks
• PUVA: psoralen + UVA — more effective but higher skin cancer risk; limited courses

Systemic (Moderate-Severe)

• Methotrexate: 7.5–25mg weekly (PO or SC) + folic acid 5mg weekly (not same day); monitor FBC, LFTs
• Ciclosporin: 2.5–5mg/kg/day; rapid onset; limit to 1–2 years (nephrotoxicity, hypertension)
• Acitretin: 25–50mg OD; retinoid; teratogenic — women must avoid pregnancy for 3 years after stopping
• Apremilast: PDE4 inhibitor; 30mg BD; oral; fewer monitoring requirements

Biologics (Severe — NICE TA)

• Anti-TNF: adalimumab 40mg alternate weeks, etanercept 50mg weekly
• Anti-IL-17: secukinumab 300mg monthly, ixekizumab, bimekizumab
• Anti-IL-23: guselkumab 100mg every 8 weeks, risankizumab
• Anti-IL-12/23: ustekinumab 45mg every 12 weeks
• Entry criteria: PASI ≥10 AND DLQI ≥10, failed standard systemic therapy

Referral Criteria

• Dermatology: moderate-severe psoriasis, diagnostic uncertainty, biologic consideration
• Rheumatology: suspected psoriatic arthritis
• Urgent: generalised pustular or erythrodermic psoriasis

• Chronic condition: no cure; management aims for control
• Guttate psoriasis: ~60% resolve spontaneously; ~30% develop chronic plaque psoriasis
• Biologics: PASI 90 achieved in 60–80% with modern anti-IL-17/IL-23 agents
• Cardiovascular risk: severe psoriasis independently increases CV mortality; manage risk factors actively
• Quality of life: DLQI improvement is a key treatment target

Psoriasis Treatment Ladder

PASI Score