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DERMATOPHYTOSES

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.

TINEA FACIEI AND TINEA CORPORIS
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.

TINEA CRURIS AND TINEA CAPITIS
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.

TINEA PEDIS AND TINEA UNGUIUM
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.