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Dermatophyte infections
are fungal infections
of the skin, hair, and nails,
which are caused by spore-forming,
single-cell, filamentous fungi.
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The three main genera are:
Trichophyton, Microsporum,
and Epidermophyton.
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They metabolize and survive
upon keratin.
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These infections also have
general names including
Tinea, Dermatophytoses,
Ringworm, and Cutaneous mycoses,
as well as site specific names,
which we will describe later.
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Other fungal infections
of the skin include:
Yeast such as Candida,
and nondermatophyte molds
such as Fusarium, and Aspergillus.
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They cause what we call
cutaneous mycoses,
which again is a reference
to the fungal appearance
of mycotic infection.
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But in fact,
the common name for this is
ringworm
or to the dermatologist
these are dermatophytoses.
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So, let us look as you can see,
with a classic picture
on the right side of the slide
at what a ringworm does
a raised red spot
with some scaly nature on top of it.
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Transmission of these organisms
is unfortunately quite common
because they are ubiquitous,
they live everywhere.
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So all of us, at any point in time,
at many parts of our body
are colonized
with these organisms.
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Fortunately, infection only occurs
when there is a disruption
of our normal defenses.
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What is our most
common normal defense?
Our skin.
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And so any breaks in the skin
whether they're microscopic
or even more significant,
such as an abrasion
or a laceration
will allow for these infections
to gain entry,
even to the slight superficial
component of the skin
and begin to start their action.
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The incubation period is unknown,
because we don't exactly know
when to start the clock from ticking
that these organisms,
all of them are on the skin
at any point in time.
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So just imagine that it takes simply
a break in skin of some sort,
and then at
some point in time,
a cutaneous mycoses
will develop.
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The target for these
the pathogenesis
it really has to do with the fact
that these organisms
especially are focusing on getting
access to keratin.
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They actually process keratin.
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So, they will start
at the very surface on top
of the stratum corneum.
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And then once they're given access
to deeper layers of the epidermis
to get access to the keratin
containing layers of that epidermis.
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So side of the inoculation will be
somewhere on
somebody's stratum corneum
and then they'll invade deeper
to pursue the keratin.
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The organisms all produce
keratinase,
an enzyme
which will break down keratin,
and that allows them to feast
if you will on the keratin
as their nutritional source.
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Interestingly, when it's time
for the organisms to replicate,
they will actually be able to place
fungal spores from the cells,
typically onto hair shaft
forming an ecotothrix,
which is in a way
for those of you who study
or have seen lice,
where the eggs of the lice
will also bind
to that bottom of the hair shaft.
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So to with these organisms,
their fungal spores will be attached
to the exterior of the hair shaft.
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So diagnosis.
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Well, if a clinical picture
is not worth a thousand words,
then we have the ability
to look even more specifically
with a Wood's lamp:
a bright fluorescent light,
which when shown on an active
mycotic lesion
due to these organisms
will shine white.
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Now, the picture you see
in front of you
is a Wood's lamp
brightening picture of the ear
and sort of posterior neck
of a patient.
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On top of the picture is the hair,
which normally luminousness.
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But if you look at the ear lobe,
the pinna itself
as well as parts of the neck,
you'll see multiple areas
of these white luminescent areas.
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Those would all be areas
of cutaneous infection
with these organisms.
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In addition, so the picture being
worth a thousand words is great,
but of course we like proof.
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So one can scrape
these lesions gently
with the razor blade
onto a glass slide
and then put a drop
of potassium hydroxide.
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One will then be able to see
the branching septate hyphae
and one could also do
a blue fungal stain
to further identify them.
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So let's now look at the
different types of clinical diseases
related to the different
type of these organisms
which are commonly called tinea.
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The first one is Tinea capitis.
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Capitis for head,
and as you would expect,
this causes skin lesions
on the head and the scalp.
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The picture to the right side
of the slide
shows you that classic appearance
with significant secondary alopecia.
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You can see
bare areas or bare patches
on this patient's scalp.
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And in those bare areas,
you can see scaly lesions
that will be a classic
tinea capitis.
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Now, as an interesting side note,
patients with tinea capitis
will frequently also present
with a kerion,
K-E-R-I-O-N
Kerion is going to be
an extremely swollen nodule
underneath that site
of the tinea capitis infection,
and it represents
a sterile id reaction.
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A sterile hypersensitivity
immunologic reaction
to antigens expressed
by the tinea capitis.
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And those patients
with tinea capitis and a kerion
will frequently also have
very enlarged
occipital lymph nodes.
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So, those three all go together.
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You can make a clinical diagnosis
in a heartbeat
just by visualizing
such a patient.
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Next, tinea corporis.
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Corporis or corpus for body.
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These lesions are found
anywhere in the body,
most often on the extremities
but sometimes on the trunk,
the back, the buttocks, etc.
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The tinea corporis lesions
are slightly more erythematous
and you will see
with the other tinea
that we're talking about,
and they're slightly less
circumscribed.
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The appearance on this picture
is of a somewhat
serpiginous bordered lesion,
which is so scaly
but which also has various discrete
erythematous papules
raised upon its surface.
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Regardless, there will be
areas of some central clearing
such as you also see
expressed on this picture.
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Tinea cruris commonly
called jock itch.
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Now, not just in the inguinal,
or peritoneal regions
but also in the axilla areas
where one typically sees
secondary sexual characteristics
with pubic hair
is where this tinea loves to
hang out, pardon <inaudible>.
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Tinea cruris also is going to be
slightly erythematous
and raised typically though
without the central clearing.
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Now, many patients
will come to you complaining
of a burning, or an irritation
in either the antecubital fossa,
the axilla, or the perinatal region
that the groin
and then that complaint along
with the clinical appearance
should be able to give you
the diagnosis.
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Tinea pedis.
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Pedis for feet, but also
to be seen on the hands
will be typically and most oftenly
seen in the interdigital space.
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So in the hands
between the fingers right there.
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Some might think,
"Oh, it's just skin breakdown
because my hands are dry,
they're cracked, it's cold outside.
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I've been washing
my hands diligently
because I'm a good
health care provider."
But these will...
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in addition to that
cracked appearance
you have erythema and
also that scaly appearance.
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The moccasin distribution,
well, that sort of makes sense
if you happen to wear moccasins,
you know that
they're sort of low slung
and they typically don't cover
the anterior portion
of the foot as well.
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Occasionally, and not all the time,
but occasionally,
tinea pedis lesions also
appear to be somewhat vesicular.
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But trust me,
they're not herpetic,
they're all due to this
cutaneous mycotic infection.
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And then finally,
Tinea unguium
is absolutely to do with the nails
of the the fingers and the toes.
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Another name for this would be
onychomycosis.
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And there again that mycoses there's
that fungally sounding name again,
these all behave very much like a
slow growing fungal infection would.
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Tinea unguium or onychomycosis
can absolutely cause
destruction of the nail itself.
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It frequently looks
brittle or fragile,
very much like
this picture shows
with the appearance that
it could just sort of chip off,
and indeed, that's a scaly
appearance, but of the toenails.
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Occasionally, these lesions
will appear green.
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Other times there appear
yellow, gray, bronze, you name it.
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It depends on the subspecies
of the tinea causing the disease.
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So the cutaneous mycoses caused by
the tinea organisms.
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Location, location, location
is probably your best friend
and identifying
what organisms causing
what where?
But the diagnosis is still the same.
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Clinical, perhaps a skin scraping,
and your good friend
the Wood's lamp.