Flexural psoriasis

In some patients, psoriasis localises to the skin folds and genitals:

• Armpits
• Groin
• Under the breasts
• Umbilicus (navel)
• Penis
• Vulva
• Natal cleft (between the buttocks)
• Around the anus

Many patients have typical psoriasis elsewhere.

Flexural psoriasis

Clinical features

Due to the moist nature of the skin folds the appearance of the psoriasis is slightly different. It tends not to have silvery scale, but is shiny and smooth. There may be a crack (fissure) in the depth of the skin crease. The deep red colour and well-defined borders characteristic of psoriasis may still be obvious.

Scaly plaques may sometimes occur however, particularly on the circumcised penis.

Flexural psoriasis can be difficult to tell apart from seborrhoeic dermatitis, or may co-exist. Seborrhoeic dermatitis in skin folds tends to present as thin salmon-pink patches that are less well defined than psoriasis.

Complications of flexural psoriasis include:

• Chaffing and irritation from heat and sweat
• Secondary fungal infections particularly candida (thrush)
• Lichenification (a type of eczema) from rubbing and scratching – this is a particular problem around the anus where faecal material irritates causing increased itching
• Sexual difficulties because of embarrassment and discomfort
• Thinned skin due to long term overuse of strong topical steroid creams

Treatment

Flexural psoriasis responds quite well to topical treatment but often recurs.

Topical steroids
Weak topical steroids (often in combination with an antifungal agent to combat thrush) may clear flexural psoriasis but it will usually recur sometime after discontinuing treatment. Stronger topical steroids need to be used with care and only for a few days, thinly and very accurately applied to the psoriasis. If the psoriasis has cleared, stop the steroid cream. The steroid cream may be used again short-term when the condition recurs.

Overuse of topical steroids in the thin-skinned body folds may cause stretch marks, marked thinning of the skin and can result in long term aggravation of psoriasis (tachyphylaxis).

Vitamin D-like compounds
Calcipotriol cream is an effective and safe treatment for psoriasis in the flexures and should be applied twice daily. If it irritates, it can be applied once daily and hydrocortisone cream 12 hours later.

Topical calcineurin inhibitors
Tacrolimus ointment and pimecrolimus cream may be effective and do not cause skin thinning.

Combinations of the treatments listed above may be used, together with emollients. Antiseptics and topical antifungal agents are often recommended as flexural psoriasis may be complicated by bacteria and yeasts, including Candida albicans and Malassezia.

Strong topical agents
Treatments that are tolerated in other sites are often too irritating to use in skin folds, e.g., dithranol, salicylic acid and coal tar. However, it may be possible to use them by diluting in emollients, or by applying them for short periods and washing off.

Systemic agents are rarely required for limited flexural psoriasis and phototherapy is relatively ineffective because the folds are hidden from light exposure.