Clinicians prefer a classification scheme that is based on clinical relevance for identifying medically important fungi. The five major categories of fungal disease based on clinical presentation are as follows: (1) superficial mycoses; (2) cutaneous mycoses; (3) subcutaneous mycoses; (4) systemic mycoses; (5) opportunistic mycoses.

Superficial Mycoses are diseases that affect 8.9 million Americans and account for 5% of all diseases with skin manifestations or skin discolorations. Superficial Mycoses may be defined as mycotic infections of the dead cornified layers of the epidermis or skin and suprafollicular portion of the hair. The organisms involved in these infections are morphologically diverse and are transmitted to man from other humans, non-human animals, and soil. Some examples of superficial mycoses are piedra, tinea, and ringworm.

Disease Causative organisms Incidence

Black piedra Piedraia hortae   Rare

White piedra Trichosporon beigelii Common

Tinea nigra Exophiala werneckii     Rare

Pityriasis versicolorMalassezia furfur (a lipophilic yeast)

Common

BACKGROUND: Piedra means “stone” in Spanish, and the word is an asymptomatic superficial fungal infection of the hair shaft. In 1911, Horta classified piedra into two types, black and white piedra. The two types of piedra occur in different climatic conditions and affect the hair in different body locations. In both types of piedra hair breakage ultimately occurs because the shaft is weakened by cuticular penetration.

BLACK PIEDRA: Black piedra may also be referred to as tinea nodosa, Chignon disease, and Trichomycosis nodularis. It is a superficial fungal infection of the hair shaft caused by Piedra hortae, a fungus that forms hard black nodules on the shafts of the scalp, beard, mustache and pubic hair. It is common in Central and South America and in South-East Asia. Black piedra usually affects young adults and epidemics in families have been reported following the sharing of combs and hairbrushes. Infected hairs generally have numerous hard black nodules on the shaft. The nodules can vary in size from microscopic to a few millimeters in diameter.

The usual treatment involves shaving or cutting the hairs short, but this is often not considered acceptable, particularly by women. In-vitro susceptibility tests have demonstrated that Piedra hortae is sensitive to an antifungal drug called oral terbinafine and it has been successfully used, at a dose of 250 mg a day for 6 weeks, to treat a 23 year old Swedish Caucasian man following a 4 month visit to India.

CULTURE: Hair fragments should be implanted onto primary isolation media, such as Sabouraud's dextrose agar. Colonies of Piedra hortae are dark, brown-black and take around 2-3 weeks to appear.

WHITE PIEDRA: White piedra may also be referred to as Beigel Disease, Trichomycosis nodularis, and Trichomycosis nodosi. It is a superficial cosmetic fungal infection of the hair shaft caused by an agent known as Trichosporon beigelii. Infected hairs develop pale yellow to soft greyish-white nodules along the shaft. The nodules may be discrete and usually form an irregular sheath. White piedra is common in young adults and is found worldwide, but generally occurs in tropical or subtropical regions, such as South America and the Orient.

The simplest method of treatment involves shaving the hairs. Topical application of an imidazole agent may be used to prevent reinfection of the condition.

CULTURE: Hair fragments should be implanted onto primary isolation media, such as Sabouraud's dextrose agar. The colonies of Trichosporon beigelii are white or yellowish to beige in color, smooth, wrinkled, dull colonies with a mycelial fringe.

TINEA NIGRA: Tinea nigra has also been referred to as tinea nigra palmaris. Tinea nigra is a rare superficial fungal infection of the stratum corneum Tinea nigra is due to infection with a brown mold, Exophiala phaeoannellomyces, which usually inhabits soil. The disease is usually asymptomatic in most cases, but it may be associated with pruritus. Patients usually consult their physician for the new appearance of brown to black non-scaly macules with well-defined borders that resemble silver nitrate stains.

The palmar surfaces are generally affected, but lesions can also occur on the soles and other surfaces of the skin. Tinea nigra occurs most commonly in tropical climates within Central and South America, Africa, Asia, and North America.

Treatment involving therapies as simple as shaving or striping have reported to be successful. A more conservative approach using the combination of keratolytic preparations with topical antifungals have been found to be equally effective. The topical use of the antiparasitic drug, thiabendazol, has also been reported to be a useful remedy. Systemic antifungal agents like itraconazole and terbinafine may also be used and have been found to be curative but may not be required.

CULTURE: Clinical specimens should be inoculated onto primary isolation media, such as Sabouraud's dextrose agar. Scrapings taken from the edge of the scaly lesion demonstrate mycelium (a group of branched filaments or hyphae). The hyphae may be a clear, yellow or brown, and have septate. KOH preparations of skin scrapings will show light to dark septate with branching hyphae as well as budding cells.

PITYRIASIS VERSICOLOR: Pityriasis versicolor is sometimes referred to as tinea versicolor. It is a common skin complaint caused by the lipophilic fungi Malassezia furfur. In this condition, flaky discolored patches or macules appear mainly on the

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patient’s chest and back. The patches may be pink, coppery brown or paler than surrounding skin. The patches or macules may be mildly itchy, round or irregular shaped, and they may also be hypopigmented or hyperpigmented. They tend to fluoresce yellow under Wood’s lamp.

Pale patches may be more common in persons with darker skin; this appearance is known as pityriasis versicolor and is less likely to itch. Sometimes the patches begin scaly and brown, and then resolve through a non-scaly and white stage.

Pityriasis versicolor is classically a disease affecting young people around puberty and the condition is probably related to hormonal changes. High or elevated temperatures and humidity favor the occurrence of pityriasis versicolor. Tropical areas can generally have a prevalence as high as 40% and the frequency is higher during summer months in temperate climates. The yeast has also been isolated from patients with IV catheters.

CULTURE: Malassezia furfur is not usually cultured since it is lipophilic agent (oil loving); however, it can be cultured by using Sabarauds Dextrose Agar (SDA) with antibiotics overlaid with sterile olive oil.  The yeast will usually grow in 3-7 days at 37°C.

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