The CPSA gratefully acknowledges Nadia Kashetsky, MSc, MD candidate, Memorial University of Newfoundland, and Cheryl F. Rosen, MD, FRCPC, for assistance in the preparation of this report. October 2021.
Psoriasis is a common chronic inflammatory skin disorder causing areas of the skin to become thickened and often covered with silvery scales.1 In individuals with darker skin tones, areas with psoriasis may look purple, dark brown, dark gray, or red as compared to red in individuals with lighter skin tones.2–4
Psoriasis occurs mainly in adults, however children and adolescents can develop psoriasis too.1 Females and males are equally affected, and psoriasis is not contagious or an infection.1 Psoriasis affects between 0.2% to 4.8% of the population.5 There are several types of psoriasis as described below.3
- The most common type of psoriasis, 80-90% of cases.1
- Skin plaques are usually 1-10cm in diameter but may be larger.
- It can occur at any age but tends to begin in young to middle aged adults.
- The severity varies between individuals and over time from mild, moderate, to severe.
- It may occur in a few small areas or may cover a large part of the body.
- The most commonly affected locations include the back of the elbow, the front of the knee (extensor surfaces), and the lower back.
- Psoriasis may or may not be itchy.
- Plaques of psoriasis may occur on the scalp. Psoriasis does not cause hair loss.
Further anatomical classification of plaque psoriasis6
- Named “inverse” because the presentation is on the flexor surfaces or skin folds.1
- Can occur in the armpits, groin, genitals, buttocks and under the breasts.
- May cause tiny pits in the nails, brown or salmon-coloured spots, or cause the nails to separate from the nailbed.
- If severe, nails may thicken and crumble.
- Seen in 60-80% of patients with psoriasis.
Palmoplantar psoriasis 3
- Occurs on the palms of the hands and soles of the feet.
- Like other types of psoriasis, the skin can crack, bleed and be painful.
- There is also a variant of palmoplantar psoriasis that results in pus-filled bumps, called palmoplantar pustulosis.
- A sudden eruption of small scaly papules primarily on the trunk.
- Tends to affect children or young adults.
- May occur after a recent streptococcal infection.
Other Types of Psoriasis
- May be generalised (spread out over the body) or localised (on smaller, specific areas of the body).
- The generalized type is rare and may be severe with a rapid onset of multiple small pustules (pus-filled bumps) which may join to form larger pustules.
- With generalized pustular psoriasis, people may have fever, chills, malaise, and enlarged lymph nodes.
- Palmoplantar pustulosis is a localised form of pustular psoriasis located on the palms of the hands and soles of the feet.
- The entire skin surface becomes red (erythematous) and scaly.
- People may have fever, chills, malaise, enlarged lymph nodes, joint pain, and a faster heart rate.
Comorbidities (conditions associated with psoriasis)
- An inflammatory arthritis (joint pain and swelling).
- About 1 in 3 people who have psoriasis will develop psoriatic arthritis.
- Psoriasis develops first in 85% of people, however 15% of people experience arthritis first.
- About 80-90% of people with psoriatic arthritis may have nail involvement
The prevalence of depression is higher in people with psoriasis.
Obesity, heart disease, diabetes, and metabolic syndrome
There is an increased incidence of these conditions in people with psoriasis.
What is the cause of psoriasis?
The exact cause of psoriasis has not yet been identified. However, psoriasis is thought to develop from a combination of genetic, immune, and environmental factors.1
Although there is no genetic test to tell you whether you will develop psoriasis, about 40% of individuals with psoriasis or psoriatic arthritis have family members with the disorder.
In psoriasis, immune cells produce molecules (Interleukin 23, interleukin 12/23, TNF) that contribute to inflammation. These molecules enter the skin through blood vessels, and cause the outer layer of skin (the epidermis) to become thicker, growing very fast without time to develop correctly, leading to surface scaling. Blood vessels in the middle layer of skin (the dermis), dilate which causes redness.
Environmental factors that have been linked to psoriasis include:
- Bacterial and viral infections
- Certain medications (beta blockers, lithium, antimalarial drugs)