View source for Dermatitis contacta allergica

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'' 'Allergic contact dermatitis' '' is a manifestation of [[immunopathological reaction type IV.]] to substances coming into direct contact with the skin (usually [[haptens]] ).

== Etiology and pathogenesis ==

The development of contact allergic eczema takes place in two phases: '''sensitizing''' and '''equipment'''.
Due to their size, haptens acquire antigenic properties only after binding to epidermal protein carriers. [[Antigen]] is recognized and processed by [[Langerhans cells]], which present it to T-lymphocytes. Langerhans cells then migrate to the regional lymph nodes, changing their phenotype. They elute "IL-1", "IL-6" and "TNF-α", leading to the proliferation of T cell clones that have receptors for the respective antigen. T-lymphocytes then migrate to various organs, including the skin (10-20%). The sensitization process spreads throughout the body, requiring at least 5-7 days to fully sensitize. The onset of sensitization is influenced by a number of factors such as the time and intensity of action of [[allergen]], its allergenic properties, the state of immunity and the disposition of the individual. The resulting hypersensitivity is usually permanent.

:''Common sensitisers:''
::* metals (Ni, Co – jewelry, watches);
::* cosmetics ingredients;
::* chemicals from the work environment;
::* local anesthetics;
::* dyes, etc.

After leaving the vessels, the T-lymphocytes can be activated by contact with the appropriate antigen and [[macrophages]], [[mast cells]] and possibly [[keratinocytes]] are used as the '''accessory phase'''. Each new contact between the allergen and the sensitized T-lymphocytes triggers the immediate release of [[cytokines]], that direct the immune response to remove the allergen from the body as quickly as possible.

If contact eczema is caused by a single substance, it is a so-called monovalent hypersensitivity , more than 1 and less than 5 substances produce oligovalent hypersensitivity , and more causative agents are polyvalent hypersensitivity . Group hypersensitivity refers to a specific part of the primary antigen molecule, resulting in hypersensitivity to a number of chemicals that contain this structure in their molecule. Combined hypersensitivity is caused by the simultaneous or sequential action of two allergens in one substance.

== Clinical picture ==

Manifestations 24-48 h. after contact with the [[allergen]] and are limited to the point of contact. In the '''acute''' phase, a strongly reddish edematous deposit with rapidly eroding papulovesicles and wetting on the surface is formed, rarely with the formation of bul. '''Microscopically''',[[spongiosis]] and intracellular edema are visible , intraepidermal blisters form. Later, crusts form. In the chronic phase, the surface becomes hyperkeratotic and ragads form on it, or lichenification predominates.

'''The hematogenous form''' caused by a substance to which the patient is sensitized by blood to the skin, where it causes [[urticaria]]. Chematically or lymphogenically, chronic contact eczema may also spread beyond the primary site of contact.

== Diagnostics ==
In addition to a careful history, the basic examination is [[epicutaneous test]]. The principle is the application of the test substance under standard conditions and in the correct concentration on healthy skin at a time interval of 2-3 weeks from the healing of skin manifestations. The following is an evaluation and interpretation.
{{Details | Epicutaneous test}}

== Differential diagnosis ==
It is necessary to distinguish:
* [[Irritative contact dermatitis | toxic dermatitis]],
* [[atopic eczema]],
* [[dermatophytosis | superficial dermatophytosis]],
* [[erysipelas]].
We distinguish between chronic manifestations
* [[psoriasis | psoriasis]],
* [[lichen ruber planus | lichen planus]],
* [[Paget's disease]],
* [[Bowen's disease]].

== Therapy ==
The basic premise is to remove the antigen and prevent its further action.
In the acute phase, we apply drying compresses, later solutions of organic dyes, creams, ointments. Topical [[corticosteroids]] are effective, in chronic forms of eczema they are combined with ichtamol or tar preparations. In resistant forms, X-ray irradiation with a "Bucky lamp" is sometimes effective.

== Links ==
==== Související články ====
* [[Allergens]]
* [[Treatment of allergies]]
* [[Urticaria]]
* [[Erythroderma]]
==== Used literature ====
* {{Cite
| type = book
| surname1 = Štork
| name1 = Jiří
| othrs = yes
| title = Dermatovenerologie
| edition = 1
| location = Praha
| publisher = Galén, Karolinum
| year = 2008
| isbn = 978-80-7262-371-6
}}
* {{Cite 
|type = book
|surname1 = Klener
|name1 = P
|others = yes
|title = Vnitřní lékařství
|edition = 3
|location = Praha
|publisher = Galén
|year = 2006
|isbn = 80-7262-430-X
}}

[[Category:Immunology]]
[[Category:Pathology]]
[[Category:internal medicine]]
[[Category:Dermatovenerology]]
[[Category:Pracovní lékařství]]