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Psoriasis is a a common chronic inflammatory skin condition, characterised by raised, red, itchy, scaly plaques on the skin. With treatment, it often follows a relapsing and remitting course, although in more severe cases it may never fully remit.

There is a strong genetic component to the inheritance of the disorder, and there are thought to be environmental triggers that bring on the condition in a genetically susceptible individual.

Pathologically, it is caused by a T-cell mediated abnormal immune response. The T cells release cytokines, resulting in keratinocyte proliferation.

Dermatologists may classify psoriasis into various subtypes, such as guttate psoriasis or palmar-pustular. 

In about 10-15% cases it is associated with psoriatic arthritis.


  • Affects 2-4% of the population
  • Can start at any age, but has two peaks of incidence:
    • 15-25 years
    • 50-60 years
  • 1/3 of patients have a relative with the condition
  • More common in caucasians
  • Usually life-long


Risk factors include:

  • Genetic susceptibility
  • Smoking
  • Obesity
  • Psychological stressors


Keratinocyte hyperproliferation: differentiation.
Histopathological features on skin biopsy:
  • Parakeratosis: retained nuclei
  • Acanthosis: thick epidermis
  • Absent granular layer
  • Lengthened rete ridges
  • Thin dermal papillae
  • Dilated, tortuous capillaries
  • Munro’s micro-abscesses
  • T-cells in upper dermis

Clinical features

Example of widespread psoriasis on a patient's back
Example of widespread psoriasis on a patient’s back
Note that psoriasis is generally a clinical diagnosis.
In unusual cases a skin biopsy may be taken to investigate the cause in which case, it can be diagnosed histologically.
General features
  • Symmetrical
  • Red scaly plaques
    • Scale is usually white or silvery coloured
  • Often extensor surfaces – e.g. front of knees, backs of elbows
    • As opposed to eczema which is commonly the flexor surfaces
  • Common locations:
    • Scalp (particularly behind ears)
      • Sometimes only the scalp is affected
    • Elbows
    • Knees
    • Can affect any part of the body
  • Itchy (!)
    • Often accompanied by excoriation, or in longer term more severe cases – lichenification (thick leathery skin)
  • Resolving patches of psoriasis often leave brown coloured marks that generally fade over a period of months
  • Classical [or typical or chronic plaque psoriasis]
    • The most common type of psoriasis – approx 90% of cases
    • Plaques: Well-circumscribed erythematous plaques with silver scaling
      • Usually plaques >3cm diameter
    • Distribution: Esp. on extensor surfaces [elbow, knee], scalp/hairline, sacral
    • Features: Pain, itch [but less than eczema/dermatitis]
    • Nail changes – e.g. pits or ridges on nails
    • Auspitzs sign: Bleeding on scale removal
  • Guttate psoriasis
    • Age: Young
    • Onset: often follows streptococcal tonsillitis (acute guttate psoriasis)
    • Plaques: Multiple discoid erythematous and scaly macules and plaques on trunk
      • Tend to be smaller than the plaques of typical psoriasis and not in the typical locations (trunk rather than flexor surfaces)
      • Plaques usually <3cm diameter
    • Good prognosis – cases of acute guttate psoriasis often resolve spontaneously after several months
    • In some instances it can become chronic, and chronic guttate psoriasis can often be much more resistant to treatment than classical psoriasis
Example of guttate psoriasis. Note the small plaque size and distribution on the trunk. Guttate psoriasis can often be more resistant to treatment.
Example of guttate psoriasis. Note the small plaque size and distribution on the trunk. Guttate psoriasis can often be more resistant to treatment.
  • Palmoplanar pustular
    • Plaques: Yellow-brown pustules on palms and soles
  • Flexoral
    • Plaques: Erythematous, but not scaly
    • Distribution: Submammary, axillary, anogenital, umbilical
    • Epidemiology: Esp. women; also the elderly and HIV +ve
    • Can be difficult to tell apart from eczema or difficult to tell that it is psoriasis due to its unusual distribution
  • Erythrodermic [emergency!]
    • Features: Acute onset of erythroderma and pustular plaques
    • Management: Methotrexate
    • Others: only scales; only nails; and napkin


  • Features: Pitting, onycholysis [nail lifting off the bed]; subungal hyperkeratosis; Beaus lines [horizontal, across the nail]
  • Differential diagnosis: fungal infection, alopecia areata

Psoriatic arthropathy

  • Patterns: [1] AnkSpond-like/spondylitis; [2] RA-like/symmetrical; [3] Asymmetrical, <3 joints;[4] DIP joints, hands; [5] Arthritis multilans

Differential diagnosis

  • Dermatitis/eczema: discoid or seborrhoeic
  • Lichen planus
  • Pityriasis rosea [esp. guttate psoriasis]
  • 2o stage of syphilis
  • Reiter’s syndrome [Esp. palmoplanar psoriasis]
  • Discoid lupus
  • Syphilis

Precipitating factors

  • Trauma [known as Koebner’s phenomena]
  • Infection
  • Drugs: β-blockers, lithium, anti-malarials; NSAIDs and ACE-Is
  • Emotional stress
  • Sunlight
  • Puberty
  • Menopause
  • Alcohol
  • Obesity (insulin resistance)
  • Smoking

Associated Disorders


Lifestyle advice
Minimisation of risk factors
  • Explain the diagnosis and advise about reducing the severity through management of lifestyle factors
  • Smoking cessation
  • Reduction of alcohol intake
  • Weight loss
  • Avoidance of sun exposure
  • Management of stress / mental health
Topical Agents
  • Emollients
  • Corticosteroids
    • The mainstay of treatment
    • In the past associated with “rebound psoriasis” on cessation of treatment – but this is thought to be rare. Higher risk when used alone and not in combination with vitamin D analogies – and as such are almost always prescribed with vitamin D analogues
    • Start with potent agent – e.g. betamethasone 0.1% (betnovate)
    • Dosing regimen recommends morning application of steroid and evening application of vitamin D analogue
    • Sometimes comes as a combined agent with a vitamin D analogue – such as daivobet or Enstillar Foam (betamethasone + Vit D) – which can greatly improve compliance!
    • If not responsding to steroids, or steroids + Vit D used separately, consider swapping to daivobet +/- adding coal tar preparations
    • Be aware of side effects of long term use of topical steroid agents – include stretch marks (striae) and skin atrophy / thinning of the skin
    • For the face, advise steroid only, not a combination – e.g. hydrocortisone 1%
  • Vit. D analogues
    • Calcipotriol, tacalcitol and calcitriol
    • Mechanism: ↓ cell proliferation
    • Side-effects: Skin irritation, hypercalaemia if overuse
  • Coal tar preparations
    • Mechanism: Inhibit DNA synthesis
    • Problems: Smelly, messy
    • Less concentrate version are less messy and just as effective (1-5% coal tar)
    • Scalp psoriasis is particualyl difficult to treat and is the most commonly used location for coal tar
  • Dithranol
    • Anthralin
    • Mechanism: ↓ cell proliferation
    • Side-effects: Irritates neighbouring normal skin, stains clothes purple
  • Keratolytics
    • Salicylic acid
  • Retinoids
    • Tazarotene


Usually only initiated in a secondary care setting

  • Phototherapy
    • UVB for classic/plaque and especially for guttate psoriasis
      • Narrow band UVB therapy has a low risk of burning and ow risk of long-term sun damage. It is used before UVA
    • PUVA
      • Used in cases not responsive to UVA
      • Stands for “photochemotherapy UVA”
      • More likely to cause long-term skin damage and increases risk of skin cancer
      • Often used in combination with retinoids to reduce the dose of PUVA
  • Retinoids
    • Acitretin
    • Note: Therapeutic effect after 4-6 weeks; used for <6 months
    • Side-effects
      • Teratogenic for up to 3 years
      • Dry mucous membranes: skin, eyes, lips [may cause epistaxis]
      • Others: hepatotoxicity; deranged lipid profile
  •  Immunosuppressants
    • Methotrexate
    • Also ciclosporin, azathioprine, and hydroxyurea
    • Often used when all the above have failed
    • usually used in short-courses of 4-12 weeks and repeated in case of relapse
  • Biological agents
    • Used when treatment to all else has failed or is contraindicated
    • Examples: etanercept, adalimumab, infliximab

Complicated regains of various topical agents lead to poor compliance and often then poor response to treatment.

Typical Regimen

Treating classic/typical psoriasis

  • 1st line: Vit. D analogues +/- topical steroids + tar or salicylic acid ± UVB
  • 2nd line: Retinoids, PUVA, UVB, immunosuppressants
  • 3rd line: Dithranol
  • Goekerman regime = Tar + UVB
  • Ingram regime = Goekerman + dithranol

Indications for referral

The majority of cases of psoriasis is managed in primary care. Possible indications for referral to dermatology include:

  • >10% body surface area affected
  • Psoriasis not responding to topical treatment
  • Psoriasis in children
  • Psoriasis having a major impact on psychological health


  • Mental health disorders – e.g. depression or anxiety, secondary to their skin condition
  • There is an associated with psoriasis and reduced rates of employment


  • Course is very variable
  • Often relapses
  • Poor prognostic factors include strong family history and early age of onset
  • Over-use of steroids can cause pustular flares – which can cause serious systemic infection



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Dr Tom Leach

Dr Tom Leach MBChB DCH EMCert(ACEM) FRACGP currently works as a GP and an Emergency Department CMO in Australia. He is also a Clinical Associate Lecturer at the Australian National University, and is studying for a Masters of Sports Medicine at the University of Queensland. After graduating from his medical degree at the University of Manchester in 2011, Tom completed his Foundation Training at Bolton Royal Hospital, before moving to Australia in 2013. He started almostadoctor whilst a third year medical student in 2009. Read full bio

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