Genital psoriasis

What is genital psoriasis?

Psoriasis is a common, long-term scaly skin condition that affects approximately 2% of the population. Genital psoriasis affects the genital skin, which includes the pubic area, vulva or penis, skin folds including natal cleft, and buttocks. It is known as anogenital psoriasis when psoriasis also affects perianal skin. Psoriasis does not affect mucosal surfaces.

Psoriasis is one of the most common diseases affecting anogenital skin. It can be part of more generalised plaque psoriasis, but it may also be the only affected area in 2–5% of cases. Rarely, generalised and localised pustular psoriasis can also affect the genital skin.

Genital skin can also be affected in inverse or flexural psoriasis, psoriasis that mainly affects the skin folds. Genital psoriasis may be associated with considerable discomfort and embarrassment, and may severely impair the quality of life and sexual well-being of those affected.

Who gets genital psoriasis?

Genital psoriasis affects males and females, children and adults. In children, genital psoriasis is most common under the age of 2, when it presents as psoriatic napkin eruption.

What are the clinical features of genital psoriasis?

Psoriasis of the external genitalia and perianal area often presents as well-demarcated, bright red, thin plaques. These usually lack scale, as friction between the skin surfaces rubs it off. Scales may be seen on the outer parts of the genital skin. Scales can be easily scraped off, leaving pinpoint bleeding.

In women, vulval psoriasis appears symmetrical. It can vary from silvery, scaly patches adjacent to the labia majora to moist, greyish plaques or glossy red plaques without scaling in the skin folds.

In men, the penis and scrotum may be involved. The glans penis, the bulbous part of the end of the penis, and the corona (the base or "crown" of the glans) are most commonly affected. In circumcised men, plaques can be more scaly than on the rest of the genital skin. In uncircumcised men, nonscaling plaques are more common.

Psoriatic napkin eruption presents as red and sometimes silvery plaques with well-defined borders in the nappy area of children under the age of 2 years. It usually clears up after a few months to a year, but may later generalise into plaque psoriasis.

Psoriasis in genital areas can be very itchy at times. The plaques may also be fissured and painful.

Psoriasis does not lead to scarring. The skin can return to a normal appearance with treatment or spontaneously.

See images of genital psoriasis.

What causes genital psoriasis?

Genital or anogenital psoriasis may be part of more generalised psoriasis. Psoriasis has multifactorial genetic and environmental causes. These are not fully understood. In the anogenital area, specific factors to consider include:

• Colonisation by bacteria and yeasts (Candida albicans)
• Injury to the skin, causing new plaques of psoriasis to develop (Koebner phenomenon)

Psoriasis in the genital area may also be worsened by contact with irritants such as:

• Urine
• Faeces
• Tight-fitting clothes
• Friction associated with sexual intercourse.

How is the diagnosis of psoriasis made?

The diagnosis of psoriasis is usually made by its clinical appearance, with symmetrical, circumscribed erythematous plaques. Laboratory tests such as swabs and skin biopsies are rarely necessary.

Histologically, there is no apparent difference between ano and non-genital psoriasis.

What is the treatment of genital psoriasis?

Treatment of genital psoriasis is individualised. There is limited published data for efficacy and safety of treatment options. The following suggestions for treatment of genital psoriasis are based on expert opinions and case reports.

Topical corticosteroid cream

• A weak or moderate-potency topical steroid cream may be used as required.
• Short-term intermittent use of moderate-to potent corticosteroids may be necessary but should be followed by a return to use of a weaker preparation.
• Intensive, short-term, intermittent use of potent corticosteroids should be limited to a few weeks under the supervision of a medical practitioner.
• There is increased absorption of topical steroids in genital skin, which can cause skin thinning.

Coal-tar derivatives

• Mild topical coal tar preparations can be used alone or when treatment with a weak topical steroid is insufficient. Tar or ichthammol may be used, with zinc oxide, for napkin psoriasis.
• Tar preparations can irritate. Mixing a tar with a steroid cream may reduce irritation.

Vitamin D analogues

Vitamin D analogues such as calcipotriol cream can be cautiously used alone or in combination with topical steroids. However, they may irritate genital skin.

Immunomodulators

• There are limited data to support the use of the immunomodulators pimecrolimus cream and tacrolimus ointment in genital or anogenital psoriasis. They may cause local irritation and stinging, contact dermatitis, reactivation of herpes simplex, and increase the risk of thrush (Candida albicans infection).

Other

• Bland emollients can be used as required to reduce skin irritation and act as a barrier cream.
• Genital skin infections should be treated promptly.
• Oral agents such as methotrexate, ciclosporin and acitretin are rarely necessary for genital psoriasis alone. They may be required in severe cases that fail to respond to topical treatments or for severe psoriasis on the rest of the body.

Therapy-resistant penile and vulval plaques should be re-evaluated clinically and histologically to rule out malignancy (penile intraepithelial neoplasia and vulval intraepithelial neoplasia).

Treatments to avoid in the genital area

Dithranol, tazarotene, UV rays (UVB phototherapy and photochemotherapy) and laser therapy should be avoided in the genital area.