Extrinsic photodermatitis

Introduction to exogenous photoallergic dermatitis Exogenous photoperceptive dermatitis can be divided into two types: photocontacting dermatitis and photolinear drug eruption due to different ways of light-sensitive substances entering the body. Among them, it is divided into phototoxic and photoallergic dermatitis. basic knowledge The proportion of illness: 0.005% Susceptible people: no special people Mode of infection: non-infectious Complications: pruritus, swelling

Causes of exogenous photoallergic dermatitis

(1) Causes of the disease

The disease is caused by skin contact with light-sensitive substances or certain photosensitivity drugs.

(two) pathogenesis

The mechanism is still unclear, mainly related to phototoxicity and photoallergic reactivity, but is known to be limited.

1. Common light-sensitive substances that cause photocontact dermatitis are:

(1) Cosmetics such as spices (bergamot sesame oil, lemon oil, sandalwood oil), impure Vaseline, etc.

(2) Dyes such as ethacridine, methylene blue, eosin and the like.

(3) topical drugs such as sulfonamides, benzocaine and the like.

(4) Industrial products such as asphalt.

(5) An opacifier such as p-aminobenzoic acid and an ester thereof, dicitric acid trioleate.

(6) Soap-halogenated phenols such as hexachlorophenol, tribromosalicylic acid amide, and the like.

(7) Coumarins such as 8-methoxypsoralen, trimethyl psoralen, and quercetin.

(8) Fluorescent whitening agent.

2. Common drugs that cause linear drug eruptions are:

(1) Sulfonamides and their derivatives, oral hypoglycemic agents such as sulfabutamide, chlorpropamide, tolbutamide and the like.

(2) Antibacterial drugs such as tetracycline, griseofulvin, nalidixic acid, and the like.

(3) phenothiazine drugs such as chlorpromazine, promethazine and the like.

(4) Diuretics such as gram uridine, hydrochlorothiazide, furosemide (furosemide).

(5) antihistamines such as diphenhydramine, chlorpheniramine, tropyridine and the like.

(6) Antimalarial drugs such as chloroquine.

(7) tranquilizers such as chloronitrogen-.

(8) Salicylates such as aspirin, sodium salicylate and the like.

(9) Antitumor drugs such as vinblastine sulfate.

(10) Oral contraceptives such as estrogen.

In addition, animals such as mud snails, bamboo snails, plants such as gray cabbage, Chinese milk vetch, cabbage, leeks, leeks, radish leaves, rapeseed, mustard greens, beets, malan head, spinach, sauerkraut, scallions, thorns Vegetables, purslane, lettuce, buckwheat, sassafras, medlar, safflower, fungus, fig, bamboo shoots, etc. all contain light-sensitive substances, Chinese herbal medicines such as schizonepeta, wind, sand ginseng, solitary, anterior, cumin , Agrimony, bamboo yellow, white sable, white peony, psoralen, musk, edulis, dragon buds, etc. have caused reports of photodermatitis.

Exogenous photoperceptive dermatitis prevention

First of all, you should not touch the light-sensitive substances that cause disease and the items that can cause cross-allergy. The related drugs should be banned. Secondly, it should be protected against strong sunlight. Avoid illuminating fluorescent lamps or even reflected light. Acetone, naphthoquinone lotion for external use, 2 ~ 3 times / d, has a good preventive effect.

Exogenous photoreceptive dermatitis complications Complications pruritus swelling

The occurrence of this disease is related to the use of certain drugs. Because this disease may be accompanied by itching and the integrity of the skin is destroyed, it may cause skin bacterial infection or fungal infection due to scratching, usually secondary to low constitution, or long-term use of immunity. Inhibitors and patients with fungal infections such as onychomycosis, such as concurrent bacterial infections may have fever, skin swelling, ulceration and purulent secretion. Severe cases can lead to sepsis, which should be brought to the attention of clinicians.

Exogenous photoreceptive dermatitis symptoms common symptoms skin damage after exposure, papules, eczema, scarlet fever, rash, shock, sleepiness, fatigue, drug eruption, dermatitis, dizziness

1. Photo-contactdermatitis: It is the inflammatory reaction caused by exposure to sun-induced sun exposure after exposure to pathogenic light-sensitive substances. It can be clinically divided into:

(1) Phototoxic contact dermatitis (phototoxic contactdermatitis): It is a phototoxic reaction in contact with light-sensitive substances and local skin irradiated by sunlight. Local skin has sun-like damage, conscious burning and pain, and asphalt or tar workers are easy. see.

(2) Photoallergic contact dermatitis: It is considered to be a T cell-mediated immune process, and it begins to cause delayed papules and eczema-like damage on skin that is exposed to light-sensitive substances and sun. Similar to non-photoallergic contact dermatitis, but rash can also occur in untreated areas in the future, showing a manifestation of photoallergic reactions.

2. Actinic drug eruption: It is a photo-sensitive drug that is caused by internal use. At the same time, the skin suffers from inflammatory damage caused by sun exposure. There are many factors affecting the occurrence of skin lesions, such as the nature of the drug, concentration, and dose. The degree of light absorption by the skin, the exposure time, the thickness of the stratum corneum, the presence of melanin and the physical constitution are all related, clinically divided into:

(1) Phototoxic drug eruption: It is because people have applied some sufficient amount of light-sensitive drugs to certain diseases. At the same time, after the skin is exposed to strong sunlight, the drugs in the body absorb certain wavelengths of ultraviolet rays, that is, the drugs become light energy. Receptors, which cause phototoxic reactions, clinical manifestations of redness, fixed rash, wheal, measles-like or scarlet fever-like rash, blisters, purpura, lichen planus rash, nail dark spots, pigmentation, etc. Symptoms such as fever, dizziness, nausea, vomiting, fatigue, etc., often cause phototoxic drug eruption drugs such as sulfa, tetracycline, diuretics, psoralen and so on.

(2) photoallergic drug eruption (photoallergic drug eruption): It is generally believed that it is due to the action of light of a certain wavelength, causing the photochemical effect of the drug itself or its metabolites ingested in the body, combined with the body protein to form a complete antigen. Produces corresponding antibodies in sensitive individuals, exhibits delayed allergic reaction, clinical manifestations of eczema-like rash, wheal, angioedema, exfoliative dermatitis, purpura, blue-gray skin, purple pigmentation, vasculitis or localized skin Itching, etc., sometimes systemic symptoms such as dizziness, fever, lethargy, listlessness, and even anaphylactic shock, such as sulfonamides, antibiotics, chlorpromazine, etc., which often cause photoallergic drug eruptions.

Examination of exogenous photoallergic dermatitis

The spot test is a method for diagnosing exogenous photoreceptive dermatitis and examining sensitizing substances. The most practical S.Epstein method is now introduced.

The suspected photo-sensitized substance was divided into two parts and placed on both sides of the waist without exposure to sunlight. After 48 hours, one test substance was removed, and it was not exposed to light as a contact reaction test, and then another place was taken. Upon exposure to UVA (320 nm), the irradiated site was compared to the previously covered portion for another 48 h.

If the test results are positive in both places, it is a contact allergic reaction; if both are negative, it is non-contact allergy and non-photo contact allergy; if only the irradiated part is positive, it is light contact allergy; More positive than the unirradiated area, it is both contact and photocontact dermatitis.

Diagnosis and identification of exogenous photoperceptive dermatitis

Diagnosis of exogenous photo-sensing dermatitis In addition to a detailed inquiry about whether there is a history of contact with light-sensitive substances or application of light-sensitive drugs, it is possible to apply spot test and ultraviolet light after avoiding the contact of light-sensitive substances or stopping the use of light-sensitive drugs. The erythema reaction test (see the Diagnostic section of the pleomorphic sun rash) is used to confirm the diagnosis.

Exogenous photoperceptive dermatitis should be identified with the following diseases:

1. Polymorphic sun rash: no light-sensitive substance exposure history, long recurrence, rash is significant in summer, the pathogenic spectrum is mainly UVB, the spot test is negative, the ultraviolet erythema reaction test often has abnormal reaction, some patients have light sensation Family history antimalarials such as chloroquine are effective.

2. erythropoiesis : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :

3. Drug rash: only the internal history of the drug has nothing to do with the light sensation, the initial rash is not necessarily exposed to the sun, and has nothing to do with light exposure.

4. Eczema: Irrespective of medication and light exposure, the rash is not necessarily exposed.

5. Contact dermatitis: There is a clear history of exposure to irritating items, and it has nothing to do with light exposure and medication.

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