Allergic dermatitis

Introduction Allergic dermatitis is a skin allergic reaction caused by exposure to allergic antigens, which is mainly caused by IgE-mediated type I allergy. Anyone who is genetically or physically susceptible to a specific antigen may cause immediate or delayed atopic dermatitis when exposed to this antigen, mainly because the human body is exposed to certain allergens and causes redness and swelling of the skin. Itchy skin, wheal, peeling and other skin conditions. Specific allergens can be divided into four categories: contact allergens, inhaled allergens, ingested allergens, and injected into allergens. Each type of allergen can cause a corresponding allergic reaction, the main manifestations are a variety of dermatitis, eczema, urticaria, when allergic dermatitis occurs, the cause should be found as soon as possible, good care, and early treatment.

Cause

1. Primary irritation: mainly caused by strong acid, strong alkali, cantharidin and some chemicals with strong irritancy or concentration. This type of individual is non-selective and has no incubation period, and any person's exposure can immediately cause acute inflammation of the skin.

2, allergic reaction (allergic reaction): This type is mainly delayed allergic reaction (v1 type allergic reaction). It is caused by exposure to certain stimulating factors (allergens) on the skin and mucous membranes, and only a few people with specific allergies develop symptoms. They do not immediately develop after initial contact, but often have an incubation period of 4-20 days (average 7 8 days) Make the body sensitized first. If you touch the substance again, dermatitis can occur in about 12 hours (generally no more than 72 hours). This type of allergic reaction is the most common in contact dermatitis.

3, often use a certain kind of cosmetics, once stopped or used again, allergic reactions will occur, or allergic reactions will occur in the back of the first use, and some will react after exposure to sunlight.

an examination

Related inspection

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1. Peripheral blood:

Eosinophils are often significantly elevated. The number of T lymphocytes was reduced, with CD8 being significantly lower. The number of B lymphocytes is usually increased. Most of the serum IgE was significantly increased. IgG, IgM may have a slight increase, and most may have a low IgA.

2. Skin test:

(1) Type I: The quick-acting skin test reaction is often positive. Nowadays, the provocative or scratch method is commonly used, and the commonly used original fungi, pollen, house dust, dust mites, and dander are used. However, it should be noted that positivity is not necessarily a sensitizer for AD.

(2) Type IV: delayed type allergy test, often low. Intradermal testing is generally performed on the forearm flexion. Commonly used antigens include tuberculin, Mycobacterium tuberculosis pure protein derivative (PPD), double-stranded enzyme (SD-SK), chymectin, candida, mumps vaccine, and the like. There are also phytohemagglutinin (PHA) for intradermal testing. In addition, there is a DNCB patch test. Patients with AD are often negative or weakly positive.

3. Pathophysiological skin test:

(1) Skin white scratch test: The scratch was pressed at the normal or skin lesion with a blunt stick, and a white line was formed after 15 s instead of the red line.

(2) Delayed whitening reaction of acetylcholine: The concentration of acetylcholine is in the range of 1:100 to 1:100, and the usual concentration is 1:10000. After intradermal injection of 0.1 ml, local flushing, sweating and chicken skin disease occurred in normal people for 15 s, and disappeared after 3 to 4 minutes. The patient usually has a white reaction 3 to 5 minutes after the skin test, and the elderly can last for 15 to 30 minutes.

(3) Histamine test: the commonly used concentration is 1:10000, 30s after intradermal injection of 0.1ml, the redness is not obvious or the lack is negative.

All of the above tests are prone to abnormal reactions in the skin lesions and normal skin of AD patients, especially in the skin lesions, but the significance of abnormal reactions on normal skin is large.

Histopathology: no specificity. In the acute phase, acanthosis can be seen in the epidermis, intercellular edema or sponge formation, lymphocyte and histiocyte infiltration in the epidermal sponge formation zone and upper dermis, neutrophils and eosinophils, and dermal edema. As the eczema inflammation subsides, the mossy lesions appear, and the tissue image also changes accordingly, showing a marked epidermal hyperplasia with little or no sponge formation. The dermal papillary thickening is accompanied by moderately intensive inflammatory cell infiltration, with an increased number of LCs, sometimes accompanied by more EOS. Staining with anti-lymphocyte surface antigen monoclonal immunoenzyme labeling confirmed that the dermal infiltration was mainly T lymphocytes (CD4) and HLA-DR antigen, suggesting activation characteristics. In addition, there have been reports of a large number of mast cells and phagocytic cells. The LC in the epidermis of the mossy lesions increased significantly.

Differential diagnosis

The disease should be differentiated from the following diseases:

Contact dermatitis:

It is due to the acute skin inflammatory reaction at the contact site after exposure of certain substances to the skin and mucous membranes. The causes can be divided into primary stimuli and allergic reactions. Clinical manifestations include erythema, blisters, bullae, and even necrosis. The course of the disease is self-limiting.

Neurodermatitis:

Neurodermatitis, also known as chronic moss, is believed by Chinese medicine to be caused by cortical inhibition and excitatory dysfunction. Emotional local irritation and spicy alcohol can aggravate and induce the disease. Healing all year round, it is easy to relapse afterwards. Clinical manifestations are characterized by intense itching or skin lichen.

Solar dermatitis:

Solar dermatitis is a delayed photoallergic skin disease induced by sunlight. Some people think that it is mainly caused by UVB, and some people think that it is mainly caused by long-wave ultraviolet rays. The clinical manifestations are pleomorphic rash, which may have erythema, papules, blisters, erosions, scales, and mossy changes, often with a certain rash. Mainly manifested in the following types: plaque, erythema, eczema, pruritic and urticaria.

Seborrheic dermatitis:

Seborrheic dermatitis occurs in areas with a large distribution of sebaceous glands, such as the scalp, face, chest and wrinkles. Occurred in the scalp, began with mild flushing patches, covered with grayish white scaly scales, with mild itching, rash spread, visible greasy scaly map-like patches; severe with exudation, thick sputum, stinky Flavor can invade the entire head. Hair can fall off and be sparse. Facial damage is more common in the nose, nasolabial folds and eyebrows, with reddish spots, oily yellow scales, often full of shine. The chest and shoulders are initially small reddish-brown hair follicle papules with greasy scales. Later, they gradually become ring-shaped patches with fine scales on the center, dark red papules on the edges and large oiliness. Wrinkles are more common in the armpits, under the breasts, umbilicus and groin. They are clear erythema, less scum, and moist, often accompanied by erosion and exudation. More common in 30 to 50 years old, especially obese middle-aged people. The disease is chronic, easy to recurrent, often accompanied by folliculitis, blepharitis, facial often with hemorrhoids, rosacea, sputum dermatitis.

Hormone-dependent dermatitis:

Hormone-dependent dermatitis is an abbreviation for corticosteroid-dependent dermatitis, which is caused by dermatitis caused by long-term repeated inappropriate external use of hormones. In recent years, the incidence has been increasing year by year, and it is stubborn and difficult to cure. It has become the focus of medical experts.

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