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Psoriasis

SNOMED: 90140021005 words•Updated 03/03/2026

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Exam Tips

In OSCEs, always ask about joint symptoms, heel pain, dactylitis, and morning stiffness; missing psoriatic arthritis loses marks.
Red flags needing urgent same-day dermatology/medical assessment: generalized erythema, widespread pustules, fever, tachycardia, hypotension, dehydration, or hypothermia.
Severity is not just body surface area: include quality-of-life burden (DLQI/CDLQI) and patient global severity.
Drug-history stations commonly test triggers (lithium, beta-blockers, antimalarials, NSAIDs) and rebound after abrupt steroid withdrawal.
For visual recognition practice, compare classic extensor plaque morphology, guttate lesions, and nail pitting in a dermatology atlas figure set.

Definition

Psoriasis is a chronic, systemic, immune-mediated inflammatory disorder that primarily affects skin but can also involve nails and joints (psoriatic arthritis). It classically causes relapsing-remitting, well-demarcated erythematous plaques with scale, most often on extensor surfaces and scalp, with potential progression to severe forms such as erythrodermic or generalized pustular psoriasis.

Pathophysiology

Genetic susceptibility (notably HLA-C*06:02 and other immune/skin-barrier loci) interacts with environmental triggers to activate innate and adaptive immunity. Dendritic-cell and T-cell pathways (especially TNF-alpha, IL-23/Th17 and IL-17 signalling) drive keratinocyte hyperproliferation, abnormal differentiation, and dermal inflammation; epidermal turnover accelerates from about 4 weeks to only a few days, producing thick scale and sharply marginated plaques. Neutrophilic and lymphocytic infiltrates, vascular dilation, and cytokine amplification explain erythema, scale, and recurrence after triggers such as infection or trauma (Koebner phenomenon).

Risk Factors

Family history of psoriasis or psoriatic arthritis (common; stronger with early-onset disease)
Genetic predisposition (including HLA-C*06:02)
Streptococcal upper respiratory infection (strongly linked to guttate flares)
Drugs: lithium, antimalarials (for example chloroquine), beta-blockers, NSAIDs, ACE inhibitors, tetracyclines, penicillins, trazodone
Sudden withdrawal of oral or potent topical corticosteroids
Skin trauma (scratching, tattoos, piercings, burns, surgery) causing Koebnerization
Smoking (particularly linked to palmoplantar pustular psoriasis)
Excess alcohol intake
Obesity and metabolic syndrome
Psychological stress
HIV infection (associated with more severe disease)
Hormonal change (puberty, postpartum, menopause)

Clinical Features

Symptoms

Itch, irritation, burning or soreness of plaques
Visible scaling with intermittent cracking or bleeding
Relapsing-remitting course with flares and partial remissions
Joint pain, morning stiffness, swelling, heel pain, or dactylitis suggesting psoriatic arthritis
Systemic upset (fever, malaise, weight loss) in severe pustular/erythrodermic disease

Signs

Well-demarcated erythematous plaques with silvery-white scale, classically on elbows, knees, scalp, and lumbosacral area
Nail pitting, onycholysis, subungual hyperkeratosis, and 'oil-drop' discoloration
Guttate lesions: numerous small droplet-like papules on trunk/limbs, often after sore throat
Flexural psoriasis: smooth, shiny erythema with less scale in skin folds
Palmoplantar pustulosis: sterile pustules on palms/soles
Erythroderma or generalized pustulation with tachycardia, dehydration, or temperature instability (medical emergency)

Investigations

Clinical assessment (distribution, morphology, nail and joint review):Typical plaque pattern usually confirms diagnosis without biopsy

Psoriasis Epidemiology Screening Tool (PEST):Score >=3/5 suggests psoriatic arthritis risk and need for rheumatology referral

Severity and impact tools (BSA/PASI with DLQI or CDLQI):Objective extent and patient-reported burden guide escalation of therapy

Skin biopsy (if diagnostic uncertainty):Acanthosis/parakeratosis with inflammatory infiltrate supports psoriasis and excludes mimics

Baseline bloods before systemic treatment (FBC, U&Es, LFTs, lipids, glucose/HbA1c; pregnancy test where relevant):Detects contraindications and provides monitoring baseline for methotrexate, ciclosporin, acitretin, or biologics

Screening before biologics (TB, hepatitis B/C, HIV as indicated):Identifies latent infection/reactivation risk prior to immunosuppression

Management

Lifestyle Modifications

Explain chronic relapsing nature and set realistic control goals
Daily emollients and soap substitutes to reduce scale, itch, and fissuring
Stop smoking, reduce alcohol, and support weight reduction if overweight
Identify/avoid triggers (trauma, infections, culprit medicines where feasible)
Screen and manage cardiometabolic risk; assess mood, stigma, and quality-of-life impact

Pharmacological Treatment

Topical vitamin D analogue

Calcipotriol 50 micrograms/g ointment or scalp solution, usually twice daily (max 100 g/week)
Calcitriol 3 micrograms/g ointment, usually twice daily

First-line for many plaque sites; avoid exceeding maximum weekly amount due to hypercalcaemia risk; avoid on face/flexures if irritant.

Topical corticosteroids

Betamethasone valerate 0.025% to 0.1% once daily (potency/site matched)
Clobetasol propionate 0.05% once daily short course for very thick plaques/scalp
Hydrocortisone 1% once or twice daily for face/flexures (short courses)

Use shortest effective course; adverse effects include skin atrophy, striae, telangiectasia, and rebound on abrupt withdrawal. Avoid prolonged potent/very potent steroid use, especially on face/genitals/flexures.

Fixed-combination topical

Calcipotriol 50 micrograms/g plus betamethasone dipropionate 0.5 mg/g gel/ointment once daily (typically up to 4 weeks, then review)

Useful when monotherapy inadequate; follow product-specific weekly dose limits and duration warnings.

Keratolytic/adjunctive topical therapy

Salicylic acid 2% to 6% preparations for thick scale
Coal tar shampoos/ointments as adjunct in scalp or chronic plaque disease

Improves scale removal and penetration of active treatments; avoid extensive salicylic acid in young children and caution in renal impairment.

Phototherapy

Narrowband UVB delivered in supervised dermatology units

Indicated for widespread disease not controlled with topicals; counsel on erythema/photoaging and cumulative skin-cancer risk; avoid if photosensitive disorders.

Conventional systemic therapy (specialist use)

Methotrexate 7.5-15 mg once weekly orally/subcutaneously, titrated (with folic acid 5 mg once weekly on a different day)
Ciclosporin 2.5 mg/kg/day in 2 divided doses, up-titrate to max 5 mg/kg/day if needed
Acitretin 25-50 mg once daily with food

Methotrexate: contraindicated in pregnancy, severe liver disease, significant renal impairment, blood dyscrasias; monitor FBC/LFT/U&Es and avoid trimethoprim due to marrow toxicity risk. Ciclosporin: avoid in uncontrolled hypertension, renal dysfunction, or malignancy risk; monitor BP and renal function. Acitretin: highly teratogenic (strict pregnancy prevention; avoid pregnancy during treatment and for 3 years after), caution with liver disease/alcohol and dyslipidaemia.

Biologic/targeted therapies (moderate-severe disease, specialist criteria)

Adalimumab 80 mg then 40 mg every 2 weeks
Ustekinumab 45 mg at weeks 0 and 4 then every 12 weeks (90 mg if higher body weight)
Secukinumab 300 mg weekly for 5 doses then monthly

Screen for TB/hepatitis before initiation; increased infection risk, avoid live vaccines, and pause during serious infection. Choice depends on comorbidity profile (for example IBD, psoriatic arthritis), prior response, and local commissioning.

Complications

Psoriatic arthritis with peripheral, axial, or entheseal disease
Severe psoriasis emergencies: erythrodermic psoriasis and generalized pustular psoriasis with fluid/temperature/hemodynamic instability
Psychological morbidity (anxiety, depression, social withdrawal, impaired self-image)
Cardiometabolic disease (obesity, hypertension, dyslipidaemia, type 2 diabetes, ischaemic heart disease)
Associated inflammatory and systemic disease (IBD, NAFLD, venous thromboembolism)
Ocular disease (blepharitis, conjunctivitis, uveitis, dry eye)
Pregnancy risks in moderate-severe disease (miscarriage, preterm birth, low birth weight; higher risk in pustular disease)

Prognosis

Most plaque psoriasis follows a lifelong relapsing-remitting course, though spontaneous remission can occur and may last months. Guttate psoriasis often settles within 3-4 months, but around one-third later develop chronic plaque psoriasis. Earlier-onset disease and positive family history are associated with greater long-term severity and instability.