Psoriasis is a chronic inflammatory disease of the skin that can also affect other tissues such as joint surfaces or the eye. There is no single form of psoriasis, but a whole range of different pathologies that can manifest themselves in different ways and result from inflammatory or autoimmune phenomena. This essentially cutaneous disease manifests itself by an attack on the skin in the form of cutaneous patches that may be accompanied by significant desquamation. It is a chronic disease that lasts for several weeks, months or even a lifetime and in some cases can be systemic, i.e. affect the entire body.
This disease generally affects young adults, more often in their thirties and rarely children. According to various studies, the frequency of this disease can reach 8 to 11% of the population in certain regions of the world. The cause or rather the many causes are not very clear and associate genetic and environmental factors. A family association of this disease can be seen in up to 40% of cases.
Psoriasis appears due to an infiltration of the superficial skin layers by activated T lymphocytes which in turn stimulate a particular group of skin cells called keratinocytes. It is this exaggerated and poorly controlled stimulation of keratinocytes that causes the reddish patches that are visible on the skin of patients.
Psoriasis is also classified into two types: type I in which there is a family history and which occurs before the age of 40 and type 2 in which there is no family history and which occurs later.
Any skin injury in a psoriasis patient can induce the appearance of psoriasis lesions. This phenomenon is called Koebner’s phenomenon and is a sign of the disease activity.
Although the general form of the disease consists of skin involvement with erythematous plaques and the presence of abundant scales, from a clinical point of view, this disease can be classified into different subgroups such as plaque psoriasis (majority of cases), guttate psoriasis (occurs after an ENT infectious episode), pustular psoriasis, etc.
In 7% of cases, patients may also have joint involvement. In this case, we speak of psoriatic arthritis or psoriatic rheumatism.
Skin involvement very often concerns the scalp, but also the hands and feet, the skin folds and the nails (ungual form).
This inflammatory disease has a rather chronic profile and can evolve in flare-ups that are unpredictable and very variable over time. The cutaneous attacks can remain visible for many months or even years or evolve by relapses with sometimes a momentary disappearance.
This disease can have a definite impact on the quality of life of patients, who often experience depression and a diminished quality of life.
Up to 10% of patients (mainly women) may present with uveitis, which is an inflammation of the uvea, an internal part of the eye.
To measure the severity of the disease, the physician can either assess the extent of skin involvement by measuring the body surface area (BSA) of the skin lesions or use an international measure called the Psoriasis Area and Severity Index (PASI). The PASI is the most commonly used tool in the clinic to assess disease severity and to measure the effectiveness of patient treatment. PASI takes into account the extent of the lesions (as with the BSA) but also considers the degree of inflammation of the lesions (skin redness), the thickness of the plaques and the amount of associated scaling.
Treatments
There are two types of treatments: local and per os medications.
Local treatments :
The main treatments that are applied locally are corticosteroid-based creams. When used topically, this treatment may decrease the localized skin inflammation and skin itching.
Other types of creams containing vitamin D analogues will act on the multiplication of keratinocytes. Creams containing vitamin D3 analogues can reduce the extent of skin lesions.
There are also other products such as tazarotene or salicylic acid.
Oral (systemic) treatments:
The drug of choice is methotrexate, which is a potent anti-inflammatory and anti-proliferative agent. Other drugs such as cyclosporine may also be used.
Recently, new molecules have come onto the market: these are the so-called biological products (anti-TNF, anti-IL17, etc.).
Phototherapy (use of certain types of light) also has a role in the management of psoriasis. The administration of ultraviolet light type A (PUVA therapy) is combined with the administration of psoralen.
References:
Yun Liang, Mrinal K Sarkar et ali. Psoriasis: a mixed autoimmune and autoinflammatory disease. Curr Opin Immunol. 2017; 49:1-8
Chayada Chaiyabutr, Patompong Ungprasert et ali. Psoriasis and risk of uveitis: a systematic review and metaanalysis. BioMed Research Int. 2020. Article ID 9308341; 1-8
Erica B Lee, Mina Amin et ali. Emerging therapies in psoriasis: a systematic review. Cutis. 2018. Mar;101(3S):5-9
Rosa Parisi, Deborah Symmons et ali. Global epidemiology of psoriasis: a systematic review of incidence and prevalence. J Invest Dermatol. 2013 Feb; 133(2):377-85
