What is psoriasis?
Psoriasis is a chronic inflammatory skin condition characterised by clearly defined, red and scaly plaques (thickened skin). It is classified into several subtypes.
Who gets psoriasis?
Psoriasis affects 2–4% of males and females. It can start at any age including childhood, with peaks of onset at 15–25 years and 50–60 years. It tends to persist lifelong, fluctuating in extent and severity. It is particularly common in Caucasians, but may affect people of any race. About one third of patients have family members with psoriasis.
What are the clinical features of psoriasis?
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.
How is psoriasis classified?
Certain features of psoriasis can be categorised to help determine appropriate investigations and treatment pathways. Overlap may occur.
|Early age of onset <35 years (75%)||Late age of onset >50 years|
|Acute eg guttate psoriasis||Chronic plaque psoriasis|
|Localised eg scalp, palmoplantar||Generalised|
|Small plaques <3 cm||Large plaques >3 cm|
|Thin plaques||Thick plaques|
|Nail involvement||No nail involvement|
Types of psoriasis
|Post-streptococcal acute guttate psoriasis||
|Small plaque psoriasis||
|Chronic plaque psoriasis||
|Unstable plaque psoriasis|
|Erythrodermic psoriasis (rare)||
© Dr Ph Abimelec – dermatologue
© Dr Ph Abimelec – dermatologue
- Streptococcal tonsillitis and other infections
- Injuries such as cuts, abrasions, sunburn (koebnerised psoriasis)
- Sun exposure in 10% (sun exposure is more often beneficial)
- Excessive alcohol
- Stressful event
- Medications such as lithium, beta blockers, antimalarials, nonsteroidal anti-inflammatories
- 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)
- Celiac disease
- Metabolic syndrome: obesity, hypertension, hyperlipidaemia, gout, cardiovascular disease, type 2 diabetes
- Localised palmoplantar pustulosis, generalised pustulosis and acute generalised exanthematous pustulosis
What causes psoriasis?
Psoriasis is multifactorial. It is classified as an immune-mediated inflammatory disease (IMID).
Genetic factors are important. An individual's genetic profile influences their type of psoriasis and its response to treatment.
Theories about the causes of psoriasis need to explain why the skin is red, inflamed and thickened. It is clear that immune factors and inflammatory cytokines (messenger proteins) such is IL1β and TNFα are responsible for the clinical features of psoriasis. Current theories are exploring the TH17 pathway and release of the cytokine IL17A.
How is psoriasis diagnosed?
Psoriasis is diagnosed by its clinical features. If necessary, diagnosis is supported by typical skin biopsy findings.
Assessment of psoriasis
Medical assessment entails a careful history, examination, questioning about effect of psoriasis on daily life, and evaluation of comorbid factors.
Validated tools used to evaluate psoriasis include:
- Psoriasis Area and Severity Index (PASI)
- Self-Administered Psoriasis Area and Severity Index (SAPASI)
- Physicians/Patients Global Assessment (PGA)
- Body Surface Area (BSA)
- Psoriasis Log-based Area and Severity Index (PLASI)
- Simplifed Psoriasis Index
- Dermatology Life Quality Index (DLQI)
The severity of psoriasis is classified as mild in 60% of patients, moderate in 30% and severe in 10%.
Evaluation of comorbidities may include:
- Psoriatic Arthritis Screening Evaluation (PASE) or Psoriasis Epidemiology Screening Tool (PEST)
- Body Mass Index (BMI, ie height, weight, waist circumference)
- Blood pressure (BP) and electocardiogram (ECG)
- Blood sugar and glycosylated haemoglobin
- Lipid profile, uric acid
Treatment of psoriasis
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.
Mild psoriasis is generally treated with topical agents alone. Which treatment is selected may depend on body site, extent and severity of the psoriasis.
- Coal tar preparations
- Salicylic acid
- Vitamin D analogue (calcipotriol)
- Topical corticosteroids
- Calcineurin inhibitor (tacrolimus, pimecrolimus)
Moderate to severe psoriasis warrants treatment with a systemic agent and/or phototherapy. The most common treatments are:
Other medicines occasionally used for psoriasis include:
Most psoriasis centres offer phototherapy with ultraviolet (UV) radiation, often in combination with topical or systemic agents. Types of phototherapy include
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-TNF&dlpha;) infliximab, adalimumab and etanerept
- The IL-12/23 antagonist ustekinumab
- IL-17 antagonists such as secukinumab
- The phosphodiesterase 4 inhibitor, apremilast
- OMIM – Online Mendelian Inheritance in Man (search term Psoriasis)
- Chularojanamontri L, Griffiths CE, Chalmers RJ. The Simplified Psoriasis Index (SPI): a practical tool for assessing psoriasis. J Invest Dermatol. 2013 Aug;133(8):1956-62. doi: 10.1038/jid.2013.138. Epub 2013 Mar 20. PubMed PMID: 23807685.
- Feldman SR, Fleischer AB Jr, Reboussin DM, Rapp SR, Exum ML, Clark AR, Nurre L. The self-administered psoriasis area and severity index is valid and reliable. J Invest Dermatol. 1996 Jan;106(1):183-6. PubMed PMID: 8592072.
On DermNet NZ:
- Chronic plaque psoriasis and images of plaque psoriasis
- Facial psoriasis
- Flexural psoriasis
- Genital psoriasis and images of genital psoriasis
- Scalp psoriasis and images of scalp psoriasis
- Guttate psoriasis and images of guttate psoriasis
- Palmoplantar psoriasis and images of palmoplantar psoriasis
- Nail psoriasis and images of nail psoriasis
- Intraoral psoriasis
- Palmoplantar pustulosis and images of palmoplantar pustulosis (palmoplantar pustular psoriasis)
- Pustular psoriasis
- Paediatric psoriasis. Psoriasis in children
- Erythrodermic psoriasis
- Psoriatic arthritis
- Treatment of psoriasis
- Treatment of psoriasis in pregnancy
- PASI score
- Scaly skin diseases continuing medical education for health professionals
- Guidelines for the management of psoriasis
- Southland Psoriasis Association New Zealand
- International Federation of Psoriasis Associations (IFPA)
- The Psoriasis Association UK
- Psoriasis Society of Canada
- Deutscher Psoriasis Bund
- Associazione per la Difesa degli PSOriasici
- Japan Psoriasis Association
- Accion Psoriasi Spain
- IFPA International Federation of Psoriasis Associations
- Association Pour La Lutte Contre Psoriasis
- The National Psoriasis Foundation USA
- Psoriasis & Psoriatic Arthritis Alliance (PAPAA)
- Asociation for the Psoriatic Patient (AEPSO)
- The Psoriasis PACT
- Psoriasis – American Academy of Dermatology
- Psoriasis – MayoClinic.com USA
- Guttate psoriasis, Nail psoriasis, Plaque psoriasis – Medscape Reference
- Psoriasis – emedicinehealth
- Psoriasis – Healthline
- My Skin's on Fire – documentary about psoriasis and psoriatic arthritis
- Psoriasis – An Overview – British Association of Dermatologists
- Psoriasis – Dr Ph Abmelec patient pamphlet (French)
- Patient information: Psoriasis (Beyond the Basics) – UpToDate (for subscribers)
- Deutschen Psoriasis Bund e.V.
- Asociación de Pacientes de Psoriasis y Familiares
- Schweizerische Psoriasis und Vitiligo Gesellschaft
- MyPsoriasis.co.nz – Information for New Zealand patients with psorasis and psoriatic arthritis, sponsored by AbbVie
- Simplifed Psoriasis Index – DermatologistsBlog
Books about skin diseases:
See the DermNet NZ bookstore