Inverse Psoriasis: What is it and what are the treatments?

Inverse psoriasis, also known as psoriasis of the folds or flexural psoriasis, is a skin condition that primarily targets areas of the body with folds. The lesions are located in the genital region and the main folds (axillary, inguinal, submammary, intergluteal, retroauricular). The affected areas correspond to the armpits, the skin under the breasts, the space between the fingers or toes, the navel, the intergluteal cleft. When this skin rash reaches the part that touches the nappy in children, it is called "nappy psoriasis".

The factors contributing to the onset of inverse psoriasis are similar to those of plaque psoriasis, such as:

• Stress;

• The intake of certain medications;

• Excessive consumption of tobacco or alcohol;

• Overweight;

• Skin injuries;

• Infections.

Scratching and sweating are factors that exacerbate inverse psoriasis. According to various studies and populations, the prevalence of inverse psoriasis varies greatly, ranging from 3 to 36%, due to the lack of precise diagnostic criteria.

Inverse psoriasis should be distinguished from other forms of psoriasis such as plaque psoriasis or psoriatic arthritis. Its symptoms exhibit some notable differences including:

• Red, inflammatory lesions with smooth, minimally scaly patches accompanied by an itching sensation and distinct from the lesions of other forms of psoriasis;

• Intense itching sensations and burning;

• Patches resembling those of a fungal infection in the folds of the skin.

Located in the skin folds (armpits, spaces between the fingers...), the lesions of inverse psoriasis can cause cracks that are sometimes painful and bleeding.

Inverse psoriasis is a chronic disease for which a permanent cure has not yet been found. However, there are treatments available to alleviate it:

• Use of dermocorticoid-based creams: these are the first treatments used against inverse psoriasis. Dermocorticoids, derivatives of cortisone, should be used over a specified period and not over a long duration. Topically, dermocorticoids help to soothe the skin by fighting against inflammation. They inhibit the transcription factor NF-kB by activating the transcription of the IkB gene, thus conferring anti-inflammatory effects. Dermocorticoids are available in the form of ointment, lotion or cream. These medications require a medical prescription. If they do not work, it is recommended to contact a dermatologist to seek other solutions.

  Class 3 and 4 dermocorticoids are favoured for treating psoriasis. For instance, the use of betamethasone dipropionate (class 3) twice a day has resulted in the disappearance of symptoms in 46-56% of patients after four weeks.

• Biotherapy: this type of treatment often utilises cells of animal origin. These are then cultivated to develop antibodies specifically targeting the elements responsible for the development of psoriasis. This treatment is reserved for severe cases of psoriasis.

• Phototherapy based on UVA and UVB ultraviolet rays: this treatment is sought when psoriasis affects a large part of the body. It is carried out in a dermatological clinic or in a hospital, under the supervision of a dermatologist.

• Use of immuno-modulatory drugs prescribed by a doctor: this solution is aimed at patients suffering from severe psoriasis that is resistant to phototherapy and local treatments.

SAURAT J. & al. Psoriasis. Dermatologie et infections sexuellement transmissibles (2016).

REYNOLDS K. A. & al. Treatments for Inverse Psoriasis: A Systematic Review. Journal of Dermatological Treatment (2019).

MICALI G. & al. Inverse Psoriasis: From Diagnosis to Current Treatment Options. Clinical, Cosmetic and Investigational Dermatology (2019).