Psoriasis is a chronic inflammatory skin condition that affects near 2-4% of the population. It can start at any age (including childhood), with peaks of onset at 15–25 years and 50–60 years which are usually characterised by clearly defined, red and scaly plaques (thickened skin). It is classified into several subtypes. It is especially more common in Caucasians.

Psoriasis is multifactorial. It is related to overactivity of the immune system which attacks to normal skin. An individual’s genetic profile influences their type of psoriasis and its response to treatment.

Psoriasis usually presents with symmetrically distributed, red, scaly plaques with well-defined edges. The scale is typically silvery white, except in skin folds where the plaques often appear shiny and they may have a moist peeling surface. The most common sites are scalp, elbows, and knees, but any part of the skin can be involved. The plaques are usually very persistent without treatment.

Itch is mostly mild but may be severe in some patients, leading to scratching and lichenification (thickened leathery skin with increased skin markings). Painful skin cracks or fissures may occur.

When psoriatic plaques clear up, they may leave brown or pale marks that can be expected to fade over several months.

Certain features of psoriasis can be categorised to help determine appropriate investigations and treatment pathways. Some overlap may occur.

  • Early age of onset <35 years (75%) vs late age of onset >50 years
  • Acute eg guttate psoriasis vs chronic plaque psoriasis
  • Localised eg scalppalmoplantar psoriasis vs generalised psoriasis
  • Small plaques < 3 cm vs large plaques > 3 cm
  • Thin plaques vs thick plaques
  • Nail involvement vs no nail involvement


Typical patterns of psoriasis

  1. Post-streptococcal acute guttate psoriasis
    • Widespread small plaques
    • Often resolves after several months
  2. Small plaque psoriasis
    • Often late age of onset
    • Plaques <3 cm
  3. Chronic plaque psoriasis
    • Persistent and treatment-resistant
    • Plaques >3 cm
    • Most often affects elbows, knees and lower back
    • Ranges from mild to very extensive
  4.  Unstable plaque psoriasis
    • The rapid extension of existing or new plaques
    • Koebner phenomenon: new plaques at sites of skin injury
    • Induced by infection, stress, drugs, or drug withdrawal
  5. Flexural psoriasis
    • Affects body folds and genitals
    • Smooth, well-defined patches
    • Colonised by candida yeasts
  6. Scalp psoriasis
    • Often the first or only site of psoriasis
  7. Sebopsoriasis
    • Overlap of seborrhoeic dermatitis and psoriasis
    • Affects scalp, face, ears, and chest
    • Colonised by Malassezia
  8. Palmoplantar psoriasis
    • Palms and/or soles
    • Keratoderma
    • Painful fissuring
  9. Nail psoriasis
    • Pitting, onycholysis, yellowing, and ridging
    • Associated with inflammatory arthritis
  10. Erythrodermic psoriasis(rare)
    • May or may not be preceded by another form of psoriasis
    • Acute and chronic forms
    • May result in systemic illness with temperature dysregulation, electrolyte imbalance, cardiac failure


Factors that aggravate psoriasis

  • Streptococcal tonsillitis and other infections
  • Injuries such as cuts, abrasions, sunburn (koebnerised psoriasis)
  • Sun exposure in 10% (sun exposure is more often beneficial)
  • Obesity
  • Smoking
  • Excessive alcohol
  • Stressful event
  • Medications such as lithium, beta blockers, antimalarialsnonsteroidal anti-inflammatories, and others
  • Stopping oral steroids or strong topical corticosteroids.


Health conditions associated with psoriasis

Patients with psoriasis are more likely than other people to have other health conditions listed here.

  • Inflammatory arthritis “psoriatic arthritis” and spondyloarthropathy (in up to 40% of patients with early onset chronic plaque psoriasis)
  • Inflammatory bowel disease (Crohn disease and ulcerative colitis)
  • Uveitis (inflammation of the eye)
  • Coeliac disease
  • Metabolic syndrome: obesity, hypertension, hyperlipidemia, gout, cardiovascular disease, type 2 diabetes
  • Localised palmoplantar pustulosisgeneralised pustulosis, and acute generalised exanthematous pustulosis


Treatment of psoriasis

General advice

Patients with psoriasis should ensure they are well informed about their skin condition and its treatment. There are benefits from not smoking, avoiding excessive alcohol and maintaining optimal weight.

Topical therapy

Mild psoriasis is generally treated with topical agents alone. Which treatment is selected may depend on body site, extent, and severity of the psoriasis.

  • Emollients
  • Coal tar preparations
  • Dithranol
  • Salicylic acid
  • Vitamin D analogue (calcipotriol)
  • Topical corticosteroids
  • Calcineurin inhibitor (tacrolimuspimecrolimus)


Most psoriasis centres offer phototherapy with ultraviolet (UV) radiation, often in combination with topical or systemic agents. Types of phototherapy include

  • Narrowband UVB
  • Broadband UVB
  • Photochemotherapy (PUVA)
  • Targeted phototherapy

Systemic therapy

Moderate to severe psoriasis warrants treatment with a systemic agent and/or phototherapy. The most common treatments are:

  • Methotrexate
  • Ciclosporin
  • Acitretin

Other medicines occasionally used for psoriasis include:

  • Mycophenolate
  • Apremilast
  • Hydroxyurea
  • Azathioprine
  • 6-mercaptopurine

Systemic corticosteroids are best avoided due to the risk of severe withdrawal flare of psoriasis and adverse effects.


Biologics or targeted therapies are reserved for conventional treatment-resistant severe psoriasis, mainly because of expense, as side effects compare favourably with other systemic agents. These include:

  • Anti-tumour necrosis factor-alpha antagonists (anti-TNFα) infliximabadalimumab and etanercept
  • The interleukin (IL)-12/23 antagonist ustekinumab
  • IL-17 antagonists such as secukinumab


  2. Clinical Dermatology by Thomas Habif