DERMATOPHYTOSES
Dermatophytes are classified in many ways by mycologists and physicians. One of the simplest classification systems is based on the natural living conditions of the studied fungi. Fungi can be classified as zoophilic (affecting mammals only), anthropophilic (affecting predominantly humans with little transference to other mammals), or geophilic (predominantly soil fungi that are capable of affecting mammals under the correct living conditions). This classification is widely used by physicians, because more complicated categorizations have minimal impact on the overall therapy and prognosis. Most of these infections are treated with topical antifungal agents that can be purchased over the counter, which have very high success rates. Fungal infections of the hair shaft and nails require systemic therapy for the highest efficacy of treatment. Topical antifungal agents do not penetrate the deeper layers of the stratum corneum, the nail plate, or the hair shaft, and in these cases systemic antifungals are required for therapy.
Clinical Findings: Superficial fungal infections have been around for millennia and have
been reported in the literature under various names and descriptions. Most of
the terms used for these infections are based on the location of the disease.
An individual may be affected by more than one of these types concurrently.
Immunocompetent individuals are less likely than those who are immunosuppressed
to develop widespread disease.
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| TINEA FACIEI AND TINEA CORPORIS |
Tinea corporis (ringworm) is a superficial dermatophyte
infection of the skin of the trunk or extremities. It begins as a small red
macule or papule and, over time, spreads out in an annular or polycyclic
nature. The primary morphology of tinea infections is the scaly patch with a
leading trail of scale. On close examination, one can observe a random amount
of hair loss within the affected area. Most cases are mild and affect only one
or two areas, but some can be widespread and can be associated with other forms
of tinea such as tinea unguium. If tinea corporis is left untreated, the fungus
will continue to spread out from the center of each lesion; lesions can merge
into very large patches that may envelop almost the entire trunk or extremity.
Tinea faciei, as the name implies, occurs on the face.
It appears as annular patches with a leading edge of scale. The scale is easily
scraped off. In adult men, the term tinea faciei is used to describe
disease in regions of the face other than terminal hair–bearing skin, such as
the beard and scalp. The lesions may converge into polycyclic patches and are
typically pruritic. This form of superficial fungal infection is commonly seen
in children. Sleeping in the same bed as pets may increase the risk of exposure
to the causative fungus and the chance of acquiring any of the superficial
fungal infections. Trichophyton tonsurans is the most likely etiological
agent in North America.
Tinea barbae is a fungal infection in the beard region
of postpubertal men. This infection often affects the skin as well as the hair
follicles, and it can appear as red patches with follicle-based pustules. Many
fungal species have been shown to cause this condition, with the zoophilic
agents being more commonly responsible. Trichophyton verrucosum has been
frequently reported, along with
other Trichophyton species. The infection may form boggy, crusted
plaques identical to a kerion of the scalp. If the lesions are plaque-like and
affect the hair follicles, systemic therapy is needed.
Tinea cruris (jock itch) is one of the most easily recognized
and prevalent forms of superficial fungal infections. The fungus prefers to
live in dark, moist regions of the skin that stay at body temperature. The groin a perfect location for fungal infections. The
disease is often very pruritic, and this is what gives it the vernacular name,
“jock itch.” It is seen frequently in athletes but is by no means limited to
them. Trichophyton rubrum and Epidermophyton floccosum are the
most commonly reported etiological agents.
Tinea pedis (athlete’s foot) is probably the
superficial fungal infection that is best known to members of the general public, because of personal involvement or
that of someone they know. This fungal infection is seen in two predominant
types, the interdigital type and the moccasin type. The interdigital subtype
forms macerated, red patches in the toe web spaces. The areas can become
pruritic and can lead to onychomycosis. Moccasin-type tinea pedis involves the
entire foot and is the less common of the two types. T. rubrum is the most
frequent isolate in these cases.
Tinea manuum, also most frequently caused by T.
rubrum, predominantly affects one hand only. It is commonly seen in
association with bilateral tinea pedis and therefore has been called “one hand
two feet disease.” The reason that it affects only one hand is unknown. The
most frequent complaint is itching and the appearance of the red annular
patches.
Majocchi’s granuloma is a form of fungal folliculitis
caused by one of the dermatophyte species. It is universally seen in patients
who have been treated with corticosteroids for a presumed form of dermatitis.
As the patient continues to apply the steroid cream to the patch of fungal
infection, the redness spreads, and pustules may form within the affected
region. The pustules are based on a hair follicle, and the hair may be absent
or easily pulled from the region with minimal or no discomfort. Removal of the
hair and use of a potassium hydroxide (KOH) preparation allows the fungus to be
seen. This form of folliculitis must be treated with a systemic agent, because
the topical antifungals do not penetrate deep enough into the depths of the
hair follicle or into the hair shaft, as would be required to treat an
endothrix fungus. Fungal species are designated as endothrix or ectothrix
species based on their ability to penetrate the hair shaft epithelium.
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| TINEA CRURIS AND TINEA CAPITIS |
Tinea capitis is seen almost exclusively in children
and is most commonly caused by T. tonsurans. This infection begins as a
small, pruritic patch in the scalp that slowly expands outward. Hair loss is
prominent because the fungus invades the hair shaft and can cause the hair to
break. A frequent clinical sign is “black dot” tinea. This is the clinical
finding of tiny, broken-off hairs that appear as black dots just at the level
of the scalp. Posterior occipital adenopathy is always seen in cases of tinea
capitis, and its absence should make one reconsider the diagnosis. If a child
presents with a scaly patch in the scalp and associated hair loss, it should be
treated as tinea capitis until proven otherwise. A KOH examination of the hair
or of a scalp scraping often, but not always, shows evidence of a dermatophyte.
A fungal culture can be used in these cases to confirm the diagnosis if the KOH
examination is negative. The culture sample is easily obtained by rubbing the
scaly patch with a toothbrush and collecting the scale that is removed in a
sterile container. The cultures are grown in the laboratory on dermatophyte
test medium (DTM), and growth is often seen in 2 to 4 weeks. Tinea capitis
requires at least 6 weeks of systemic oral therapy to clear, and all the
patients’ pets, especially cats, should be evaluated by a veterinarian for
evidence of disease.
A kerion is a boggy plaque found on occasion in tinea capitis that results from a massive immune inflammatory
response to the causative fungal agent. The fungi most likely to cause this
reaction are in the zoophilic class. The kerion often appears as a large, inflamed, boggy-feeling
plaque with alopecia. Serous drainage and crusting are also present. These
plaques are very tender to palpation, and children complain of pain even when
the lesions are not manipulated. Alopecia overlies the plaque, and if it is
severe, a kerion can lead to permanent scarring alopecia. Posterior occipital
and cervical adenopathy is present and tender to palpation. The kerion often
become impetiginized with bacteria,
especially Staphylococcus species. Treatment is based on the use of
systemic oral antifungals in association with an oral corticosteroid to decrease
the massive inflammatory response. Any bacterial coinfections must be treated
at the same time. Scarring alopecia may be permanent and may lead to morbidity
for the child.
Tinea unguium, or onychomycosis, is clinically recognized
by thick, dystrophic, crumbling nails. One or all the nails on a foot or hand may be involved. Toenail infection is
much more common than infection of the fingernails. Most patients start with
tinea pedis, after which the fungus spreads to infect the nail plate. This
results in thickening and yellowing of the nail. Over time, the nail becomes
thickened with subungual debris that is easily removed with a blunt instrument
such as a curette. The nail may become onycholytic and fall off the nail bed.
Patients are most frequently asymptomatic, but some complain of discomfort and
difficulty clipping their nails. Diabetic patients and those with peripheral
vascular disease are at risk for bacterial cellulitis. The dystrophic nails
serve as a nidus for infection with various bacteria. Nail disease requires the
use of systemic oral medications to get the best therapeutic response. Topical
agents have shown some benefit, but only for very mild nail involvement. A deep
green discoloration under the nail is an indication of Pseudomonas nail
colonization. The bacteria make a bright green pigment that is easily visible.
Soaks in acetic acid (vinegar) diluted 1 : 4 in water are effective in clearing
up the secondary Pseudomonas.
Dermatophytid reactions can occur with any dermatophyte
infection. They are infrequently seen. They manifest as monomorphic, pink-red,
scattered papules. They are typically pruritic and are most commonly seen in
patients with a tinea
capitis or kerion infection. Another manifestation of dermatophytid reactions
is a deep vesicular reaction on the palms or soles. This can closely mimic
dyshidrotic dermatitis. Treatment of the underlying fungal infection clears the
dermatophytid reaction. Topical or oral corticosteroids may be used for relief
until the fungal infection is cured.
The easiest, most sensitive, and most specific means
of diagnosing the infection is by KOH examination. A scraping of the leading
edge of the rash is taken and placed on a slide; KOH is added, and the
preparation is heated for a few seconds. It is then viewed under a micro- scope
for the characteristic branching and septated fungi of a dermatophyte. This
method does not allow speciation of the fungus, which requires growth of
cultures on fungal growth media. Each fungus has characteristic growth
requirements and appears slightly different on microscopic evaluation of the
cultured colonies.
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| TINEA PEDIS AND TINEA UNGUIUM |
Histology: Tinea corporis
infections are rarely biopsied. When they are, one sees on close inspection
fungal hyphae within the stratus corneum. Hyphae can be demonstrated with
various staining methods. Neutrophils are the predominant cell type seen in the
stratum corneum.
Pathogenesis: Dermatophyte
infections are predominantly caused by three fungal genera: Trichophyton,
Microsporum, and Epidermophyton. Multiple species within each of the
first two genera have cutaneous effects; Epidermophyton floccosum is the
only known species in the last genus to cause skin disease. Other genera have
been implicated, but 99% of dermatophyte infections are caused by these three
genera of fungi.
Treatment: Topical
antifungal agents are the mainstay of treatment for tinea corporis, pedis,
manuum, and cruris. Terbinafine is a topical fungicidal agent that has
excellent efficacy against dermatophytes. The topical azoles are used equally as often and also show excellent
therapeutic results. Twice-daily treatment for 2 to 4 weeks usually is an
effective treatment course. The importance of cleaning and drying the involved
skin thoroughly cannot be understated. The fungi do not like to live in dry
environments, and these simple steps can help treat and prevent the disease.
Immunosuppressed individuals with widespread disease are candidates for oral antifungal agents.
Tinea capitis, tinea barbae, Majocchi’s granuloma, and
onychomycosis all require oral systemic treatment. Topical antifungals are
ineffective in these cases because they do not penetrate deeply into the hair
shaft or into the nail plate. Topical antifungals may be used in con- junction
with the oral agents. The two most commonly prescribed oral antifungals are
terbinafine and griseofulvin. The azole antifungal agents have also been used with excellent efficacy rates.
