Inverse psoriasis, also known as flexural or intertriginous psoriasis is a rare form of psoriasis that occurs in the flexural skin folds. Plaque psoriasis is most commonly found on the trunk and extensor surfaces of the body, such as the knees, elbows, sacral (lower back) area, and scalp whereas Inverse psoriasis is found in the folds of the axilla (armpits), submammary (breast) folds, and groin (inguinal) and buttock folds. It can occur in any area where two skin surfaces meet. The inguinal fold is the most commonly affected area, followed by the axilla and the external genitalia. The skin at the inverse body sites differs from skin at extensor sites with less epidermal keratinization (thinner skin) and more sweat glands. The most evident difference between classical plaque-type psoriasis and inverse psoriasis is the lack of, or less, scaling. The lesions are usually well demarcated, erythematous (red), and are often shiny, appear moist, weepy and fissured. The irritation may be increased in inverse psoriasis as a result of the rubbing and sweating involved in the skin folds. 1, 2
Approximately 3–7% of psoriasis patients present with inverse psoriasis and patients with palmar psoriasis have a greater chance of having inverse psoriasis as compared with plaque psoriasis. In one study of 170 psoriasis patients with palmar involvement, 5.3 times more patients had inverse psoriasis than patients with plaque psoriasis. Development of inverse psoriasis has been reported as a paradoxical side effect to treatment with infliximab for Crohn’s disease and hidradenitis suppurativa. Inverse psoriasis has been observed to be more common in the obese population possibly due to the rubbing of the skin folds. 1, 2
Inverse psoriasis affecting the genitalia seems to be underreported and undertreated; and approximately 35% patients with genital psoriasis never speak to their physician about their genital lesions. Nearly 70% of Physicians do not offer treatment for genital lesions. 3
A study on the quality of life and sexual life in 487 patients with genital psoriasis concluded that3:
Results of several questionnaire-based surveys show that involvement of the genital skin region occurs in 29–40% of patients with psoriasis. The genital area may frequently be involved in cases of inverse psoriasis. Of 48 patients with inverse psoriasis, the external genitalia were involved in 38 (79.2%). 4
In another report researchers stated that patients with genital psoriasis have significantly worse quality of life (QoL) scores compared with patients without genital lesions. In addition, numerous patients with psoriasis have sexual dysfunction. Between 25–40% of patients reported a decline of sexual activity since the onset of psoriasis, mainly due to diminished sexual desire, embarrassment of physical appearance and inconvenience caused by scaliness of the skin or topical therapy. Particularly in women with genital psoriasis, sexual distress is higher and sexual function is more significantly impaired compared to those without genital lesions. 4
Inverse psoriasis is often misdiagnosed for bacterial or fungal intertrigo. Intertrigo is inflammation of opposed skin folds caused by skin-on-skin friction that presents as erythematous, macerated (moist, broken, soft skin) plaques. Secondary bacterial and fungal infections are common because the moist, denuded skin provides an ideal environment for growth of microorganisms. Candida is the most common fungal organism associated with intertrigo. Intertriginous candidiasis also presents as well demarcated, erythematous patches but with tell tale satellite papules or pustules at the periphery (around the edges). Candida, Staphylococcus aureus and Malassezia furfur have been shown to colonize psoriatic skin lesions so diagnosis for flexural psoriasis is sometimes not easy. Candida species have been isolated from the skin of 15% of psoriasis patients compared to only 4% in the control group. 5, 6 However, some studies have also suggested that Candida is not commonly found in psoriatic lesions of inverse of genital psoriasis.
Application of topical treatment in the intertriginous areas is considered as treatment under occlusion due to enhanced hydration and increased skin absorption. However, the inverse areas are considered more sensitive and prone to side effects from topical steroids (i.e. due to thinner skin at these locations). 2