Psoriasis is a common (prevalence around 2%) and chronic skin disorder. It generally presents with red, scaly patches on the skin although it is now recognised that patients with psoriasis are at increased risk of arthritis and cardiovascular disease.

Chronic plaque psoriasis is the most common form of psoriasis seen in clinical practice, accounting for around 80% of presentations.


  • Incidence: 80.00 cases per 100,000 person-years
  • Peak incidence: 20-30 years
  • Sex ratio: 1:1
<1 1-5 6+ 16+ 30+ 40+ 50+ 60+ 70+ 80+


  • Multifactorial and not yet fully understood
  • Genetic:
    • Associated HLA-B13, -B17, and -Cw6
    • Strong concordance (70%) in identical twins
  • Immunological:
    • Abnormal T cell activity stimulates keratinocyte proliferation
    • There is increasing evidence this may be mediated by a novel group of T helper cells producing IL-17, designated Th17
    • These cells seem to be a third T-effector cell subset in addition to Th1 and Th2
  • Environmental:
    • It is recognised that psoriasis may be worsened (e.g. Skin trauma, stress), triggered (e.g. Streptococcal infection) or improved (e.g. Sunlight) by environmental factors

Clinical features

  • Erythematous plaques covered with a silvery-white scale
    • Typically on the extensor surfaces such as the elbows and knees. Also common on the scalp, trunk, buttocks and periumbilical area
    • Clear delineation between normal and affected skin
    • Plaques typically range from 1 to 10 cm in size
    • If the scale is removed, a red membrane with pinpoint bleeding points may be seen (Auspitz's sign)

© Image used on license from DermNet NZ

© Image used on license from DermNet NZ

© Image used on license from DermNet NZ

© Image used on license from DermNet NZ


Management of chronic plaque psoriasis
  • Regular emollients may help to reduce scale loss and reduce pruritus
  • First-line: NICE recommend a potent corticosteroid applied once daily plus vitamin D analogue applied once daily for up to 4 weeks as initial treatment
    • These should be applied separately, one in the morning and the other in the evening
  • Second-line: if no improvement after 8 weeks then offer a vitamin D analogue twice daily
  • Third-line: if no improvement after 8-12 weeks then offer either:
    • A potent corticosteroid applied twice daily for up to 4 weeks or
    • A coal tar preparation applied once or twice daily
  • Short-acting dithranol can also be used


  • Psoriatic arthropathy (around 10%)
  • Increased incidence of metabolic syndrome
  • Increased incidence of cardiovascular disease
  • Increased incidence of venous thromboembolism
  • Psychological distress