Vitiligo

Vitiligo


Learning medicine is hard work! Osmosis makes it easy. It takes your lectures and notes to create
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much more. Try it free today! Vitiligo, likely meaning blemish, is a non-contagious
skin condition that is defined by patches of discoloration, or depigmentation. Though vitiligo can affect any race or ethnicity,
it tends to be most noticeable in people with darker skin, like Canadian fashion model Winnie
Harlow. Given the effect on a person’s appearance,
pigment loss can really impact a person’s quality of life. The skin is divided into three layers–the
epidermis, dermis, and hypodermis. The hypodermis is made of fat and connective
tissue that anchors the skin to the underlying muscle. Just above is the dermis, which contains hair
follicles, nerves and blood vessels. And just above, the outermost layer of skin,
is the epidermis. The epidermis itself has multiple cell layers
that are mostly keratinocytes – which are named for the keratin protein that they’re
filled with. Keratin is a strong, fibrous protein that
allows keratinocytes to protect themselves from getting destroyed when you rub your hands
through the sand at the beach. Keratinocytes start their life at the deepest
layer of the epidermis called the stratum basale, or basal layer, which is made of a
single layer of small, cuboidal to low columnar stem cells that continually divide and produce
new keratinocytes that continue to mature as they migrate up through the epidermal layers. But the stratum basale also contains another
group of cells – melanocytes, which secrete a protein pigment, or coloring substance,
called melanin. Melanin is actually a broad term that constitutes
several types of melanin found in people of differing skin color. These subtypes of melanin range in color from
black to reddish yellow and their relative quantity and rate at which they are metabolized
define a person’s skin color. When keratinocytes are exposed to the sun,
they send a chemical signal to the melanocytes, which stimulates the melanocytes into making
more melanin. The melanocytes move the melanin into small
sacs called melanosomes, and these get taken up by newly formed keratinocytes, which will
later metabolize the melanin as they migrate into higher layers of the epidermis. Melanin then acts as a natural sunscreen,
because its protein structure dissipates, or scatters, UVB light–which if left unchecked
can damage the DNA in the skin cells and lead to skin cancer. Melanocytes can also be found in the dermis,
at the base of the hair follicle, and in the eye where they help color hair and the iris. In vitiligo, there’s a loss of melanocytes
or an absence of their function. Histologically, having less melanin in the
epidermis results in white depigmented patches. These patches are classified by type. There’s non-segmental vitiligo which is
the more common type that affects any age group, and it occurs at various locations
that are mirrored on both sides of the body. There’s also segmental vitiligo which mostly
affects children, and occurs in segments along a single spinal nerve typically on only one
side of the body without crossing the midline. The exact cause of melanocyte destruction
isn’t known, but it does seem to be linked to both genetic and environmental triggers. In non-segmental vitiligo, there seems to
be an autoimmune element – where immune cells attack the melanocytes. In segmental vitiligo, there seem to be neural
factors, where nerves release neurochemicals that damage the melanocytes. Other causes may be that the melanocytes get
damaged by a buildup of toxic metabolites as they make melanin or in other metabolic
pathways. One interesting observation is called the
Koebner phenomenon, and it’s when vitiligo develops in skin soon after there has been
a trauma, like a cut, abrasion, or burn. The main symptom of vitiligo is the irregular,
round or oval shaped patches of depigmentation appearing within normally pigmented skin. The patches can range in size from millimeters
to centimeters and can sometimes expand and merge with other patches over time. The body hair and the iris may also be depigmented
in affected areas. Non-segmental vitiligo tends to affect the
hands, forearms, neck, scalp, feet, and face; while segmental vitiligo, tends to affect
areas of skin near dorsal roots from the spinal cord, particular in the face following the
trigeminal nerve. The diagnosis of vitiligo is based on the
appearance of depigmented patches, but a skin biopsy can also be done. There are two main treatments. When the affected area is small, cosmetic
cover up and topical immune-suppressants can be applied directly to skin. When the affected area is large, systemic
immune-suppressants, UV phototherapy, skin-bleaching, and in severe cases, skin grafts, can all
be tried. Whatever the course of therapy, sunscreen
is recommended to prevent darkening of the skin areas immediately surrounding and contrasting
the depigmentation areas, and to reduce the risk of skin cancer. So, to recap: Vitiligo is a non-contagious
condition where destruction of melanocytes and loss of melanin production leads to areas
of depigmentation on the skin. Non-segmental vitiligo tends to affect the
hands, forearms, neck, scalp, feet, and face; while segmental vitiligo tends to affect areas
of skin near dorsal roots from the spinal cord, particularly in the face following the
trigeminal nerve. For small areas, cosmetic cover up and topical
immune-suppressants can be used. For large areas, systemic immune-suppressants,
UV phototherapy, skin-bleaching, and even skin grafts, can be used.

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