DermatologyTier 1Disease (DEADMAN)

Psoriasis

Description

Chronic immune-mediated inflammatory disease of skin, nails and joints
- Systemic, not cutaneous - shares inflammatory burden with metabolic and cardiovascular disease

Morphological patterns

Pattern	Features
Chronic plaque (~90%)	Well-demarcated salmon-pink plaques, silvery scale; extensor knees/elbows, scalp, natal cleft, umbilicus
Guttate	Abrupt "raindrop" papules, trunk; 2-3 weeks after streptococcal pharyngitis; young; often self-limiting
Inverse (flexural)	Shiny, non-scaly, glistening red; axilla, groin, submammary - mistaken for candida/intertrigo
Pustular - generalised (von Zumbusch)	Dermatological emergency: fever, sheets of sterile pustules, systemic upset, hypocalcaemia, high-output failure. Classically precipitated by steroid withdrawal
Palmoplantar pustulosis	Palms/soles; strong smoking association; treatment-resistant
Erythrodermic	>90% BSA; thermoregulatory and fluid failure; emergency
Nail	Pitting, onycholysis, oil-drop sign, subungual hyperkeratosis

Signs

Auspitz sign - pinpoint bleeding on scale removal
Koebner phenomenon - lesions at sites of trauma
Nail disease predicts psoriatic arthritis, particularly DIP disease

Epidemiology

2-3% of Australians
Bimodal onset: 16-22 yrs (type I, HLA-Cw6, family history, more severe) and 55-60 yrs (type II)
M=F
Uncommon in Aboriginal and Torres Strait Islander and East Asian populations
Psoriatic arthritis in ~20-30% of psoriasis patients; skin usually precedes joints by ~10 yrs

Aetiopathogenesis

IL-23 / Th17 axis - the entire modern drug pipeline
- Dendritic cell -> IL-23 -> Th17 differentiation
- Th17 -> IL-17A, IL-17F, IL-22, TNF-alpha
- -> keratinocyte hyperproliferation (turnover 3-5 days vs 28) + neutrophil recruitment (Munro microabscesses) + angiogenesis
Cathelicidin LL-37 + self-DNA -> pDC -> type I interferon (initiation)
*Genetics: PSORS1 / HLA-C06:02* - strongest; predicts early onset, guttate pattern, and better ustekinumab response*
- IL23R, IL12B, CARD14 (pustular), IL36RN (generalised pustular - DITRA)

Triggers

Infection - streptococcal (guttate), HIV (severe, paradoxically with low CD4)
Drugs - beta blockers, lithium, antimalarials, ACE inhibitors, interferon, checkpoint inhibitors, terbinafine
- *Systemic corticosteroid withdrawal -> pustular or erythrodermic flare - never treat psoriasis with oral prednisolone*
Smoking (palmoplantar), alcohol, obesity
Trauma (Koebner), stress

Diagnosis

Clinical diagnosis - biopsy only when atypical
Histology: parakeratosis, acanthosis with regular elongation of rete ridges, loss of granular layer, suprapapillary thinning, Munro microabscesses, dilated dermal capillaries

Examine beyond the presenting rash

Scalp (hairline, behind ears), natal cleft, umbilicus, extensor surfaces - hidden sites confirm the diagnosis
Nails - pitting, onycholysis, oil-drop
Joints and spine - DIP, dactylitis, enthesitis, sacroiliac tenderness and spinal movement
Eyes - uveitis; cardiac - aortic regurgitation (with axial disease)

Screen for psoriatic arthritis at every visit

PEST questionnaire (score >=3 -> rheumatology referral)
Joint damage in PsA is early and irreversible - the skin clinic is where it is caught

Severity

BSA (patient's palm+digits = 1%), PASI, DLQI
PBS biologic access in Australia requires severe disease: PASI >10 (or PASI >8 on the face, hands or feet) after failing >=3 systemic agents including phototherapy
Severity is not BSA alone - genital, palmoplantar, scalp and nail disease are disproportionately disabling

Differential

	Discriminator
Eczema	Ill-defined, flexural, weeping, intensely itchy
Tinea corporis	Asymmetric, active scaly edge with central clearing; scrape it
Mycosis fungoides	Fixed atypical patches, buttocks, poor treatment response - biopsy the plaque that will not clear
Seborrhoeic dermatitis	Greasy yellow scale, nasolabial folds, less demarcated
Pityriasis rubra pilaris	Orange hue, islands of sparing, follicular plugging

Management

Tiered by severity and by the sites involved. Treat the comorbidities alongside the skin.

1. All patients

Emollients - liberal, ongoing
Smoking cessation, alcohol, weight loss (weight loss improves both psoriasis and biologic response)
Screen and treat cardiovascular risk, metabolic syndrome, depression
Never give systemic corticosteroids for psoriasis

2. Mild-moderate / localised - topical

Potent topical corticosteroid + calcipotriol (combination ointment/foam, once daily) - first-line for plaques
Site-adjusted:
- Face and flexures: mild-moderate steroid, or calcineurin inhibitor (tacrolimus/pimecrolimus) - avoid potent steroids, atrophy
- Scalp: potent steroid lotion/shampoo, calcipotriol/betamethasone gel, coal tar, salicylic acid for thick scale
- Nails: intralesional or potent topical steroid; usually needs systemic therapy
Coal tar, dithranol - effective, cosmetically limiting

3. Moderate-severe - phototherapy

Narrowband UVB - first-line phototherapy, 2-3x/week
- Guttate psoriasis responds especially well
PUVA - more effective, higher cutaneous SCC risk with cumulative dose

4. Moderate-severe - conventional systemic

Drug	Notes
Methotrexate	Weekly + folate. Best if concurrent PsA. Monitor FBE/LFT; hepatic fibrosis - fibroscan
Ciclosporin	Rapid onset - use for crisis control and erythroderma; limit to <1-2 yrs: nephrotoxicity, HTN
Acitretin	Best for pustular and palmoplantar disease; teratogenic - avoid pregnancy for 3 yrs after
Apremilast (PDE4)	Oral, modest efficacy, no monitoring bloods; diarrhoea, weight loss, depression

5. Severe - biologics (PBS-restricted, dermatologist-prescribed)

Class	Agents
IL-23 (p19)	Risankizumab, guselkumab, tildrakizumab - highest sustained clearance and drug survival; 8-12-weekly dosing
IL-17	Secukinumab, ixekizumab, bimekizumab (IL-17A+F) - fastest clearance; candidiasis; avoid/caution in IBD
IL-12/23 (p40)	Ustekinumab
TNF-alpha	Adalimumab, etanercept, certolizumab, infliximab - preferred where uveitis or IBD coexists

Pre-biologic screening: latent TB (QuantiFERON + CXR), hepatitis B/C, HIV, pregnancy, vaccination status
Live vaccines contraindicated on biologics

6. Emergencies

Generalised pustular psoriasis: admit, fluid/electrolytes, temperature, sepsis workup
- Spesolimab (anti-IL-36R) is the targeted agent for GPP flares; otherwise ciclosporin, acitretin or infliximab
Erythrodermic: admit, warm, fluids, ciclosporin or infliximab

Associations

Psoriatic arthritis (~20-30%) - nail disease and scalp/intergluteal involvement predict it
Metabolic syndrome - obesity, T2DM, dyslipidaemia, hypertension
Accelerated cardiovascular disease - independent of traditional risk factors; risk tracks severity
Non-alcoholic fatty liver disease
Inflammatory bowel disease - shared IL-23 biology; relevant to IL-17 inhibitor choice
Depression, anxiety, suicidality - markedly increased
Uveitis; aortic regurgitation with axial disease
Alcohol misuse and smoking
Lymphoma (small absolute increase)

Natural history & complications

Chronic, relapsing-remitting, lifelong; remission is achievable, cure is not
Guttate: ~1/3 resolve completely, ~1/3 recur, ~1/3 evolve to plaque disease
Severe psoriasis: life expectancy reduced ~4-5 years, predominantly cardiovascular
Psychological burden disproportionate to BSA - genital, facial, palmoplantar disease

Monitor

PASI/DLQI response; PEST at each review
Cardiovascular risk annually; weight, BP, lipids, HbA1c
Drug-specific: FBE/LFT/UEC (MTX), BP/creatinine (ciclosporin), lipids/pregnancy (acitretin), infection surveillance (biologics)

Complications

Erythroderma, generalised pustular psoriasis
Irreversible joint erosion and ankylosis if PsA missed
Secondary infection, cutaneous malignancy after cumulative PUVA

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