Eczema (atopic dermatitis) – causes, symptoms, diagnosis, treatment, pathology

Atopic dermatitis or atopic eczema is a skin
rash that’s particularly common among young children, but can last into adulthood. “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. Atopic dermatitis is a type 1 hypersensitivity
reaction, and it starts off with something in the environment called an allergen, like
flower pollen. 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. The immune cell is called an antigen presenting
cell because it presents a bit of the allergen to a naive T helper cell, activating it into
a Th2 cell. This Th2 cell then stimulates a nearby B cell
to start producing IgE or immunoglobulin E antibodies specific to that pollen. 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. Atopic dermatitis can worsen in the presence
of allergens like cigarette smoke, mold, and dust mites, as well as changes in the weather,
and even emotional stress. Although it usually causes patches of red
itchy skin that come and go, the skin can occasionally even blister and peel. Over time, the skin can become lichenified,
which literally means turned to leather. Itchiness is often worst at night, perhaps
because there are no distractions, and this is often when young children are most likely
to scratch at their eczema lesions. Because eczema is an autoimmune mediated process,
it cannot be spread to other people, but since it affects the skin and therefore the way
a person looks, there is still a lot of social stigma associated with it. Unfortunately, many individuals especially
teenagers and young adults with atopic dermatitis suffer from depression and social anxiety
as a result. Genetics plays an important role in atopic
dermatitis, and individuals with atopic dermatitis often also have asthma, as well as allergic
rhinitis, making up what’s called the atopic triad. These illnesses also often run in families. Occasionally, atopic dermatitis can be part
of a syndrome like Hyper IgE syndrome, which has an autosomal dominant form commonly called
Job syndrome, phenylketonuria, which is a metabolic disorder that results from a buildup
of the amino acid phenylalanine, and Wiskott-Aldrich syndrome, which is an X-linked recessive disease
characterized by a clinical triad of eczema, thrombocytopenia, and immunodeficiency. Atopic dermatitis is generally a clinical
diagnosis, and there are ways to help break the cycle of allergy-mediated inflammation,
dry skin, and itching. With regard to allergy-mediated inflammation
it’s important to identify and avoid any triggers, as well as avoiding overheating,
dressing in soft fabrics, and managing stress well, which is of course a good life habit
anyway. Dry skin can be managed with frequent moisturization,
which is usually best to apply after a lukewarm bath. And itching can sometimes be managed with
simple measures like keeping fingernails short, and trying to keep children from scratching. But in more extreme cases, there are also
steroids and calcineurin inhibitors both of which aim to dampen the immune reaction, as
well as antihistamines that can help with itching, and antibiotics to help treat infections
if their needed. Alright, as a quick recap, atopic dermatitis
also called atopic eczema, is a type 1 hypersensitivity reaction in the skin, and is characterized
by a cycle of allergy-mediated inflammation, dry skin, and itching that most commonly affects
infants and young children. Atopic dermatitis can be managed by minimizing
exposure to allergens, keeping the skin hydrated, and minimizing itching. Thanks for watching, you can help support
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