Atopic dermatitis is associated with type (I/II/III) hypersensitivity.
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An 8-month-old infant is brought to the family doctor by her mother who has noticed a red rash developing on her daughter’s face. According to the mother, this rash appeared a few weeks ago and is worsening. She thinks it may have appeared after her daughter opened her aunt’s makeup box and smeared mascara over her face. She has also noticed her daughter scratching at the red areas intermittently. Vital signs are all within normal range. Examination shows multiple small papules, pustules, and vesicles around the daughter’s mouth, and scattered lesions near the nostrils.
Which of following is the most appropriate initial treatment?
“Atopic” refers to an allergy, “derm” refers to the skin, and “itis” refers to inflammation.
So atopic dermatitis describes skin inflammation that results from an allergy, more specifically, it happens when the immune system attacks the skin causing a dry, itchy rash on flexor surfaces of the body, areas like the creases of the wrists, the insides of the elbows, and the backs of the knees, as well as exposed skin surfaces like on the face, the hands, and the feet.
When the immune system inappropriately starts attacking itself, we call that a hypersensitivity reaction, and there are four types.
The pollen is able to travel through the slightly porous skin, where it gets picked up by an immune cell in the tissue just below.
Those IgE antibodies bind to the surface of other immune cells called mast cells, as well as basophils, which can be found in the tissue layer just below the surface of the skin, and this process called “sensitization”.
Now, let’s say that there’s a second exposure to pollen that makes it’s way into the skin tissue.
Now, the allergen can cross-link the IgE on these sensitized cells, resulting in degranulation or release of a number of proinflammatory molecules like histamine, leukotrienes, and proteases.
The combined effect of these molecules is to cause nearby blood vessels to dilate and become leaky as well as attract even more immune cells to the area creating inflammation of the skin tissue.
Ultimately, the inflammation makes the skin barrier more “leaky”, potentially allowing in more of the allergen, while at the same time allowing water to escape, leaving the skin dry and scaly.
Dry skin is very itchy, and scratching further damages the skin barrier, worsening the process and setting up a vicious cycle of allergy-mediated inflammation, dry skin, and itching which characterizes atopic dermatitis.
Occasionally, bacteria can invade the damaged skin causing even more inflammation.
In infants, the rash is most often on the face and scalp, and in children, the rash is usually on flexor surfaces of extremities.