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This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
Key points
- Chronic plaque psoriasis ~90% of cases — well-demarcated, salmon-pink plaques with silvery scale on extensor surfaces
- Auspitz sign (pinpoint bleeding on scraping), Koebner phenomenon (lesions at sites of trauma)
- First-line topical: potent corticosteroid + vitamin D analogue (calcipotriol) for trunk/limbs
- Step-up: phototherapy (NB-UVB) then systemic (methotrexate, ciclosporin) then biologics
- Screen for psoriatic arthritis (PEST tool) and cardiovascular risk in severe disease
Overview
Psoriasis is a chronic, immune-mediated inflammatory skin disease driven by Th1/Th17 pathways leading to accelerated epidermal turnover (transit time ~4 days vs normal ~28 days). Chronic plaque psoriasis is the commonest subtype (~90%). Other variants include guttate, pustular, erythrodermic, flexural (inverse), and scalp psoriasis. Significant associations with psoriatic arthritis, cardiovascular disease, metabolic syndrome, and depression.
Epidemiology
Affects ~2-3% of the UK population. Bimodal onset: 15-25 years (type I, HLA-Cw6+) and 50-60 years (type II). Equal sex distribution. ~70% concordance in monozygotic twins. Triggers include streptococcal throat infection (guttate), stress, drugs (lithium, beta-blockers, antimalarials, NSAID withdrawal), alcohol, smoking, and Koebner phenomenon.
Clinical Features
Symptoms
Well-demarcated, salmon-pink/red raised plaques with silvery-white scale
Extensor surfaces: elbows, knees, sacrum, scalp
Variable pruritus (less intense than eczema)
Nail changes: pitting, onycholysis, subungual hyperkeratosis, oil-drop sign
Joint pain/stiffness suggesting psoriatic arthritis
Rapid onset widespread erythema >90% BSA (erythrodermic psoriasis)
Widespread sterile pustules on erythematous skin (generalised pustular psoriasis)
Signs
Well-demarcated erythematous plaques with silvery scale on extensor surfaces
Auspitz sign: pinpoint bleeding when scale is scraped off
Koebner phenomenon: new plaques at sites of skin trauma
Scalp psoriasis extending beyond hairline
Nail pitting, oil-drop sign, onycholysis
Erythroderma: generalised erythema >90% BSA with systemic upset
Investigations
First-line
Clinical diagnosisBased on appearance and distribution
PASI / DLQI scoreGuides treatment decisions and biologic eligibility
Second-line
Skin biopsyIf uncertain — parakeratosis, Munro microabscesses, regular acanthosis
Throat swab / ASO titreIf guttate psoriasis — confirm streptococcal trigger
Specialist
PEST questionnaireScreen for psoriatic arthritis in all patients
CV risk assessmentOffer to patients with severe psoriasis (NICE CG153)
Baseline bloods before systemicsFBC, U&E, LFT, hep B/C, TB screen before methotrexate/biologics
1
Step 1 — Topical therapy
- Trunk/limbs: potent corticosteroid (betamethasone 0.1%) OD + vitamin D analogue (calcipotriol) OD for up to 4 weeks
- Scalp: potent corticosteroid then vitamin D analogue maintenance
- Face/flexures: mild-moderate TCS or calcineurin inhibitor short-term
2
Step 2 — Phototherapy
- NB-UVB first-line for extensive disease unresponsive to topicals
- PUVA second-line — higher skin cancer risk
- 2-3 sessions per week for 6-10 weeks
3
Step 3 — Systemic non-biologic
- Methotrexate 7.5-25 mg ONCE WEEKLY (+ folic acid): first-line systemic
- Ciclosporin 2.5-5 mg/kg/day: rapid onset, max ~1 year due to nephrotoxicity
- Acitretin: particularly for pustular psoriasis. Teratogenic
4
Step 4 — Biologic therapy
- Anti-TNF: adalimumab, etanercept, infliximab
- Anti-IL-17: secukinumab, ixekizumab
- Anti-IL-23: guselkumab, risankizumab
- Indicated for severe psoriasis (PASI >=10, DLQI >=10) failing systemics
Complications
- Psoriatic arthritis: ~20-30% — DIP joints, dactylitis, enthesitis, sacroiliitis
- Cardiovascular disease: Independent CV risk factor in severe disease
- Metabolic syndrome: Obesity, diabetes, dyslipidaemia
- Psychological morbidity: Depression, anxiety, social stigma
- Erythrodermic psoriasis: Life-threatening — thermoregulatory failure
UKMLA Exam Tips
- 1EXTENSOR surfaces + silvery scale + well-demarcated = psoriasis. FLEXURAL + ill-defined = eczema
- 2Guttate psoriasis: teardrop lesions on trunk 2-3 weeks after streptococcal sore throat
- 3Auspitz sign = pinpoint bleeding on scraping — pathognomonic
- 4Drug triggers: lithium, beta-blockers, antimalarials, NSAID withdrawal
- 5Methotrexate ONCE WEEKLY — daily dosing is a fatal prescribing error
- 6Always screen for psoriatic arthritis with PEST questionnaire and CV risk in severe disease
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regional clinical guidance
Psoriasis: guidance by region
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