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U N I T 1 3
Integumentary Function
or ringworm, are confined to the epidermis and its integ-
uments, the hair and nails.
Most of the superficial mycoses are
dermatophytoses—
dermatoses caused by the dermatophytes, a group
of closely related fungi classified into three genera:
Microsporum
,
Epidermophyton
, and
Trichophyton
.
2,4
Some dermatophytes are anthropophilic; that is, they
are parasitic in humans and are spread by other infected
humans. These tend to cause chronic infections that
are difficult to treat.
Zoophilic
species cause parasitic
infections in animals, some of which can be spread to
humans.
Geophilic
species originate in the soil, but may
infect animals, which in turn serves as a source of infec-
tion for humans. These species tend to cause inflamma-
tory lesions that respond well to therapy or may even
resolve spontaneously.
2,4
The fungi that cause superficial mycoses emit an
enzyme that enables them to digest keratin, which
results in superficial skin scaling, nail disintegration, or
hair breakage, depending on the location of the infec-
tion. Deeper reactions involving vesicles, erythema, and
infiltration are caused by the inflammation that results
from exotoxins liberated by the fungus.
Diagnosis of superficial fungal infections is primar-
ily done by microscopic examination of skin scrapings
for fungal spores, the reproducing bodies of fungi.
2
Potassium hydroxide (KOH) preparations are used to
prepare slides of skin scrapings. Potassium hydroxide
disintegrates human tissue and leaves behind the thread-
like filaments, or hyphae, that grow from the fungal
spores. Cultures also may be done using a dermatophyte
test medium or a microculture slide that allows for
direct microscopic identification. The Wood light is an
ultraviolet (UV) light that can assist with the diagnosis
of tinea, as some types of fungi fluoresce yellow-green
when the light is directed onto the affected area.
Topical agents are commonly used in the treatment
of tinea infections; however, success often is limited
because of the lengthy duration of treatment, poor
compliance, and high rates of relapse at specific body
sites. The principal agents are the azoles (ketoconazole,
miconazole, clotrimazole, etc.) and the allylamines (naf-
tifine and terbinafine). Both act by inhibiting the syn-
thesis of ergosterol, which is an essential part of fungal
cell membranes.
2,3
Topical corticosteroids may be used
in conjunction with topical antifungal agents to relieve
itching and erythema secondary to inflammation.
The systemic (i.e., oral) antifungal agents include gris-
eofulvin, the azoles, and the allylamines.
2,3
Griseofulvin
is an antifungal agent derived from a species of penicil-
lium, whose only use is in the systemic treatment of der-
matophytosis. It acts by binding to the keratin of newly
formed skin, protecting the skin from new infection. It
must be administered for 2 to 6 weeks to allow for skin
and hair replacement, and nail infections often require
months of treatment. Systemic azoles and allylamines are
also used. In contrast to griseofulvin, the synthetic agents
are fungicidal (i.e., kill the fungus) and therefore are more
effective over shorter treatment periods. Some of the oral
agents can produce serious side effects, such as hepatic
toxicity, or interact adversely with other medications.
Tinea of the Body or Face.
Tinea corporis
(ringworm
of the body) can be caused by any of the dermatophyte
species. Although it affects all ages, children seem most
prone to infection. Transmission is most commonly
from kittens, puppies, and other children who have
infections. The most common types of lesions are oval
or circular patches on exposed skin surfaces and the
trunk, back, or buttocks (Fig. 46-1). Less common are
foot and groin infections. The lesion begins as a red pap-
ule and enlarges, often with a central clearing. Patches
have raised red borders consisting of vesicles, papules,
or pustules. The borders are sharply defined, but lesions
may coalesce. Pruritus, a mild burning sensation, and
erythema frequently accompany the skin lesion.
Tinea faciale,
or ringworm of the face, is typically
caused by one of the
Trichophyton
species. Tinea faci-
ale may mimic the annular, erythematous, scaling, pru-
ritic lesions characteristic of tinea corporis. It also may
appear as flat erythematous patches.
Topical antifungal agents usually are effective in
treating tinea corporis and tinea faciale. Oral antifungal
agents may be used in resistant cases.
Tinea of the Scalp.
Tinea capitis, the most common
type of fungal infection in children, is an infection of
the scalp and hairshaft. Children between the ages of 3
and 14 years are primarily affected. The primary lesions
vary from grayish, round, hairless patches to balding
spots. The lesions vary in size and are most commonly
seen on the back of the head (Fig. 46-2). Mild erythema,
crust, or scale may be present. The individual usually is
asymptomatic, although pruritus may exist. Treatment
is with oral griseofulvin or synthetic antifungal agents
that penetrate the hair shafts.
5–7
Topical ointments or
shampoos are sometimes indicated.
The inflammatory type of tinea capitis is caused by
virulent strains of
T. mentagrophytes, T. verrucosum,
and
M. gypseum
. The onset is rapid, and inflamed lesions
usually are localized to one area of the head. The inflam-
mation is believed to be a delayed hypersensitivity reac-
tion to the invading fungus. The initial lesion consists
FIGURE 46-1.
Tinea of the arm due to the dermatophytic
fungus trichophyton rubrum. (From the Centers for Disease
Control and Prevention Public Health Image Library. No. 4811.)
