Psoriasis
Summary
Psoriasis is a chronic, immune-mediated inflammatory skin disease characterised by well-demarcated erythematous plaques with silvery-white scale, typically affecting extensor surfaces, scalp, and nails. It affects 2-3% of the population and is associated with significant comorbidities including psoriatic arthritis, cardiovascular disease, and metabolic syndrome. Management follows a stepwise approach: topical therapy for mild disease, phototherapy or systemic agents for moderate disease, and biologics for moderate-to-severe disease. Quality of life impact is substantial, often comparable to major chronic diseases.
Key Facts
- Prevalence: 2-3% worldwide
- Age of Onset: Bimodal — Type 1 (16-22 years, HLA-Cw6+), Type 2 (50-60 years)
- Pathophysiology: T-cell mediated; IL-17, IL-23, TNF-α pathways
- Assessment: PASI (Psoriasis Area and Severity Index), BSA, DLQI
- First-Line (Mild): Topical vitamin D analogues + corticosteroids
- Biologics: Anti-IL-17 (secukinumab), Anti-IL-23 (guselkumab), Anti-TNF (adalimumab)
- Comorbidities: Psoriatic arthritis (30%), CVD, metabolic syndrome, depression
Clinical Pearls
"Auspitz Sign": Removal of scale reveals pinpoint bleeding (dilated capillaries in dermal papillae).
"Nail Changes = Joint Risk": Nail psoriasis strongly predicts psoriatic arthritis development.
"Treat the Patient, Not Just the Skin": Screen for psoriatic arthritis, cardiovascular risk, and depression.
"Koebner Phenomenon": New psoriatic lesions appear at sites of skin trauma.
Why This Matters Clinically
Psoriasis significantly impacts quality of life and is associated with serious comorbidities. Modern biologics can achieve PASI 90-100 (near-complete clearance) and transform patient outcomes. Early treatment of psoriatic arthritis prevents joint destruction.
Incidence & Prevalence
| Measure | Value |
|---|---|
| Prevalence | 2-3% worldwide |
| Incidence | 50-140 per 100,000/year |
| Trend | Increasing |
Demographics
| Factor | Details |
|---|---|
| Age | Bimodal: Type 1 (16-22), Type 2 (50-60) |
| Sex | Equal M:F |
| Ethnicity | Higher in Caucasians; lower in East Asians |
| Geography | Higher in northern latitudes |
Risk Factors
Genetic:
- Family history (30-50% with affected first-degree relative)
- HLA-Cw6 (Type 1, early onset)
- Multiple susceptibility loci
Environmental:
- Streptococcal pharyngitis (guttate trigger)
- Trauma (Koebner phenomenon)
- Stress
- Alcohol
- Smoking
- Obesity
- Medications (lithium, beta-blockers, antimalarials, NSAIDs)
Mechanism
Step 1: Initiation
- Trigger (infection, trauma, stress) activates innate immunity
- Dendritic cells activated, migrate to lymph nodes
Step 2: T-Cell Activation
- IL-23 from dendritic cells drives Th17 differentiation
- IL-12 promotes Th1 cells
Step 3: Cytokine Cascade
- IL-17A, IL-17F from Th17 cells
- TNF-α, IFN-γ from Th1 cells
- Keratinocyte activation
Step 4: Keratinocyte Response
- Hyperproliferation (cell cycle 3-5 days vs normal 28 days)
- Abnormal differentiation
- Parakeratosis (nuclei in stratum corneum)
Step 5: Inflammation
- Neutrophil infiltration (Munro's microabscesses)
- Vascular changes (dilated capillaries in dermal papillae)
Classification
| Type | Features | % of Cases |
|---|---|---|
| Plaque (Vulgaris) | Well-demarcated plaques, silver scale | 80-90% |
| Guttate | Small "raindrop" lesions, post-streptococcal | 2% |
| Inverse | Flexural, minimal scale | 3-7% |
| Pustular | Sterile pustules, localised or generalised | <5% |
| Erythrodermic | >0% BSA, emergency | <3% |
Symptoms
Typical:
Atypical:
Signs
| Sign | Description |
|---|---|
| Plaques | Well-demarcated, erythematous, silver scale |
| Auspitz Sign | Pinpoint bleeding on scale removal |
| Koebner Phenomenon | New lesions at trauma sites |
| Nail Pitting | Small depressions |
| Onycholysis | Nail plate separation |
| Oil-Drop Sign | Yellow-brown discolouration under nail |
Red Flags
[!CAUTION] Red Flags:
- Erythrodermic psoriasis (thermoregulatory failure)
- Generalised pustular psoriasis
- Rapid progression
- Systemic symptoms (fever, malaise)
- Joint symptoms (psoriatic arthritis)
Structured Approach
General:
- Distribution pattern (extensor vs flexural)
- Body surface area estimation
Specific Sites:
- Scalp (hairline extension)
- Ears (external auditory meatus)
- Nails (all 20)
- Umbilicus
- Natal cleft
- Genitalia
Special Tests
| Test | Description | Finding |
|---|---|---|
| Auspitz Sign | Scale removal | Pinpoint bleeding |
| Grattage Test | Scratching plaque | Silver "candle wax" scale |
| Woronoff Ring | Blanched halo around plaque | Resolution indicator |
First-Line
- Clinical diagnosis in most cases
- No routine bloods for diagnosis
Pre-Treatment
| Test | Purpose |
|---|---|
| FBC, LFTs, U&E | Baseline before systemics |
| Hepatitis B/C, HIV | Pre-biologic screening |
| TB (IGRA/Mantoux) | Pre-biologic screening |
| Lipids, HbA1c | Metabolic syndrome screening |
| Pregnancy test | Before methotrexate/acitretin |
Biopsy (If Uncertain)
- Parakeratosis
- Munro's microabscesses
- Acanthosis with elongated rete ridges
- Dilated capillaries in dermal papillae
See Management Algorithm above (Section 2)
Summary
| Severity | Treatment |
|---|---|
| Mild | Topical vitamin D + steroid combination |
| Moderate | Phototherapy, methotrexate, ciclosporin |
| Severe | Biologics (anti-IL-17, anti-IL-23, anti-TNF) |
Disease Complications
| Complication | Notes |
|---|---|
| Psoriatic Arthritis | 30%, screen all patients |
| Cardiovascular Disease | Increased risk |
| Metabolic Syndrome | Obesity, diabetes, dyslipidaemia |
| Depression | Common, assess |
| Erythroderma | Rare, emergency |
Treatment Complications
| Treatment | Complication |
|---|---|
| Topical Steroids | Atrophy, striae, tachyphylaxis |
| Methotrexate | Hepatotoxicity, myelosuppression |
| Ciclosporin | Nephrotoxicity, hypertension |
| Biologics | Infection, reactivation TB |
Natural History
- Chronic, relapsing-remitting course
- No cure, but excellent control possible
- Guttate may resolve spontaneously or progress to plaque
With Treatment
| Treatment | PASI 75 | PASI 90 |
|---|---|---|
| Methotrexate | 40-60% | 20-35% |
| Secukinumab | 70-80% | 55-65% |
| Guselkumab | 85-90% | 75-80% |
| Risankizumab | 88-90% | 75-82% |
Prognostic Factors
Good Prognosis:
- Mild disease
- Early treatment
- Good treatment adherence
- No comorbidities
Poor Prognosis:
- Severe, extensive disease
- Psoriatic arthritis
- Obesity
- Smoking
Key Guidelines
-
NICE NG153: Psoriasis — assessment and management (2017, updated 2023)
-
BAD Guidelines: British Association of Dermatologists (2020)
-
AAD-NPF Guidelines: American Academy of Dermatology (2019-2021)
Landmark Trials
ERASURE & FIXTURE (2014) — Secukinumab
- Anti-IL-17A demonstrated superior efficacy to etanercept
- Established IL-17 as key therapeutic target
UltIMMa-1/2 (2019) — Risankizumab
- Anti-IL-23 showed superior PASI 90 vs ustekinumab
- High sustained response rates
IMMhance (2019) — Risankizumab
- Demonstrated durability of response with intermittent dosing
Evidence Strength
| Intervention | Level | Key Evidence |
|---|---|---|
| Topical vitamin D + steroid | 1a | Cochrane review |
| Methotrexate | 1a | Multiple RCTs |
| Anti-IL-17 biologics | 1a | ERASURE, FIXTURE |
| Anti-IL-23 biologics | 1a | UltIMMa |
What is Psoriasis?
Psoriasis is a long-term skin condition where your immune system causes skin cells to grow too fast, creating thick, scaly patches. It's not contagious — you can't catch it from someone else.
Why does it matter?
- It can be uncomfortable (itchy, sore skin)
- It can affect how you feel about yourself
- Some people also get joint problems (psoriatic arthritis)
- There's a slightly higher risk of heart disease
How is it treated?
- Creams and ointments: For mild psoriasis — moisturisers plus vitamin D or steroid creams
- Light therapy: UV light treatment at hospital
- Tablets: If creams don't work — methotrexate or other medications
- Injection treatments (biologics): Newer, very effective treatments for severe psoriasis
What to expect
- There's no cure, but treatments can control symptoms very well
- Some people get nearly clear skin with modern treatments
- It tends to come and go (flares and remissions)
- Regular check-ups help monitor for joint problems
When to seek help
- Psoriasis spreading rapidly
- Joint pain or stiffness
- Creams not working
- Feeling low or depressed about your skin
Primary Guidelines
- National Institute for Health and Care Excellence. Psoriasis: assessment and management (NG153). 2017 (updated 2023). nice.org.uk/guidance/ng153
Key Studies
-
Langley RG, et al. Secukinumab in plaque psoriasis — results of two phase 3 trials (ERASURE and FIXTURE). N Engl J Med. 2014;371(4):326-338. PMID: 25007392
-
Gordon KB, et al. Efficacy and safety of risankizumab in moderate-to-severe plaque psoriasis (UltIMMa-1 and UltIMMa-2). Lancet. 2018;392(10148):650-661. PMID: 30097359
Reviews
- Griffiths CEM, et al. Psoriasis. Lancet. 2021;397(10281):1301-1315. PMID: 33812489
Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances.