During winter, the outbreaks of the most common skin conditions return, such as psoriasis and atopic dermatitis. In our previous post you can find some tips to reduce the appearance and severity of these outbreaks.
However, although they may seem the same, atopic dermatitis and psoriasis differ both in origin and in their symptoms. Here we detail the differences and similarities of these two dermatoses:
1. Atopic dermatitis affects mainly children
Atopic dermatitis and psoriasis are both chronic diseases characterised by inflammation of the skin. It is estimated that between 1% and 3% of the world population suffers from one of these disorders (1). However, psoriasis affects mostly adults between 20 and 50 years of age and atopic dermatitis is more common in children. Thus, 90% of people with atopic dermatitis develop this disease within the first 5 years of life, while in the case of psoriasis, this percentage is reduced to 33% (2).
2. Atopic dermatitis, a family history
Family history plays an important role as a risk factor. It is estimated that 70% of people with atopic dermatitis have a family history of this disease (3). In case of psoriasis, the genetic component is much reduced since only 14% of patients have a parent suffering from psoriasis (4).
3. Psoriasis affects the extension while dermatitis alters the flexion of the elbows
The psoriatic plaques appear preferentially on the palms of the hands and nails, in addition to the extensor (external) part of the elbow, while atopic dermatitis acts more frequently on the flexor (internal) part of the elbow and face. Although they may look the same, the lesions produced by atopic dermatitis are different from those produced by psoriasis.
Psoriatic lesions are characterised by the appearance of reddish plaques accompanied by whitish desquamation that erupt repeatedly over time.
What causes and triggers psoriasis hasn’t been completely defined yet. However, it is known to have an autoimmune component; the cells of the immune system are activated abnormally, accumulating in the dermis and causing inflammation. All this leads to an increase of the thickness of the epidermis and the formation of plaques due to the excessive growth of the keratinocytes on the external layer of the skin.
The lesions of atopic dermatitis leads to exudation and large areas of dry skin as well as frequent bacterial infections. Like psoriasis, there is a dysregulation of the immune response, but there is also a complex interaction between defects in the barrier function of the skin, allergens and infectious agents.
4. Alterations in the barrier function of the skin
The skin has the function of protecting the body against external agents and environmental dryness. The epidermis acts as a true boundary; the stratum corneum develops a barrier function preventing access to particles from the outside, such as bacteria or allergens, and keeping the skin hydrated by preventing loss of water molecules.
The epidermis and its barrier function are disturbed in both psoriasis and atopic dermatitis, although in a different way.
Deficiencies in the skin barrier function in atopic dermatitis are due to a reduced production of the filaggrin protein (5), which gives structure and stability to the stratum granulosum of the epidermis. The reduction of filaggrin, together with deficiencies in other structural proteins, lipids (6) and cathelicidins (a protein with antimicrobial action), results in the damage of the barrier function with a consequent loss of transepidermal water and an increased penetration of allergens and microbes on the skin. Among microbes, the bacterium Staphylococcus aureus stands out, which colonises the skin of 90% of patients suffering from atopic dermatitis. All these mechanism increase the immune response in the skin which leads to inflammation and the activation of the sensory neurons. These neurons are in the end responsible for causing itchy sensations (7).
On the other hand, in psoriasis, the barrier function of the skin is being disturbed due to an increased expression of the involucrin protein. This increase in expression causes a protein overproduction of involucrin in the entire stratum spinosum (8), whereas in healthy skin, it is restricted only in the stratum granulosum.
5. Diseases associated with psoriasis and atopic dermatitis
As mentioned above, both psoriasis and atopic dermatitis have an autoimmune origin. Thus, chronic diseases with an inflammatory component may occur in addition when having psoriasis or atopic dermatitis.
In the case of psoriasis, it has been associated with diseases such as psoriatic arthritis (9), diabetes mellitus, the metabolic syndrome or several cardiovascular diseases (8).
Atopic dermatitis, in contrast, is associated with the development of various allergies; 35% of children with atopic dermatitis develop some type of food allergy (10), and half of the children who develop dermatitis before two years of age will suffer from asthma in the following years (11). In the case of environmental allergies, it has been shown that exposure to allergens such as dust mites, pollen and mold can aggravate atopic dermatitis (7).
Treatments: the common denominator
Treatments for psoriasis are based on reducing inflammation by using topical corticosteroids, retinoids and vitamin D analogues; or in reducing the formation of plaques through the use of anthralin that slows down the growth of keratinocytes.
The treatment of atopic dermatitis is aimed mainly to restore the skin barrier function, which involves skin hydration and repair as well as a reduction of inflammation with the application of corticosteroids and topical calcineurin inhibitors. Being a multifactorial disease, the treatment of atopic dermatitis requires a broader approach which involves teaching the patient in optimal skin care practices and the use of topical treatments that reduce inflammation to treat both skin infections and itch (11,12,13,14).
Both atopic dermatitis and psoriasis require a guideline of hygiene for the proper care of the skin. In general terms, it is recommended to wash the skin with warm water for 10 or 15 minutes to moisturize and clean it, but avoiding soaps with fragrances and alcohols. After the bath, it is advisable to use lotions or moisturizers.
As mentioned, psoriasis and atopic dermatitis are different in their origin, genetic component and cutaneous manifestations, but the sensation of associated continuous itching occurs in both diseases. This itching (or pruritus) lasts throughout the day and worsens during the night which leads to lack of sleep and, thus, reduced quality of life (13).
Furthermore, the itch associated with dermatitis also usually leads to skin trauma. To control and treat itch, frequent applications of lotions that moisturize the skin as well as topical medications to reduce chronic itch are necessary (6).
Chronic itch is mediated by the sensory neurons which are present in the skin. At AntalGenics, we have been working on this biotechnological challenge. We have developed special molecules which are reducing the activation of these neurons through the intermediation with their receptors. With this approach, we will be able to efficiently treat chronic itch. Our innovative molecules prevent the transmission of the sensation of itch from the origin to the central nervous system.
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