Superficial Mycoses

Glenn S. Bulmer, Ph.D.

Prof. Medical Mycology

Superficial Mycoses

1) Mycotic keratitis

2) Otomycosis

3) Piedras

4) Tinea nigra

5) Pityriasis versicolor

6) Rhinosporidiosis

7) Malassezia folliculitis

1) Mycotic Keratitis

Fungus infection of the cornea of the eye. It may be caused by one of numerous filamentous fungi which are found in our environment. Normal flora yeasts are also implicated. Under severe conditions it can lead to blindness and fatal invasion of the brain.

This is a rather typical case of mycotic keratitis. The patient reported that several months previously some foreign matter had lodged in his eye.

In this case of mycotic keratitis the lesion is very obvious. Scrapings from this eye were examined in KOH preparations, and septate hyphae were observed. Additional material was cultured, and the etiologic agent was identified as a Fusarium. The patient was given treatment with topical amphotericin B and responded in a satisfactory fashion.

This is what one sees in cases of mycotic keratitis when infected tissue is observed microscopically under direct examination procedures. Note the presence of hyphae (A,B). This particular organism was cultured on Sabourauds medium and identified as an Aspergillus species.

This, like the previous slide, is a direct examination preparation from a case of mycotic keratitis. Note the abundance of clear, septate hyphae (A,B). When structures of this nature are observed, there is no doubt that the etiologic agent is a fungus.

This is a photomicrograph of Penicillium. Here we see the brushes (A) with a few spores (B) attached to them.

This is the fungus Rhizopus, another etiologic agent of mycotic keratitis. There are 3 important features of species found in the genus Rhizopus: the hyphae (A) are relatively large (8-10 microns in diameter) and are coenocytic; the larger, spherical, dark blue structure in this photograph is a sporangium (B), and, under high magnification, one would see that it contains dozens of spores (sporangiospores); at the end of a piece of hypha, one can see a mass of finger-like projections, the so called rhizoids from which the genus name is derived. The purpose of the rhizoids is probably to hold the fungus to the subtrate and absorb nutrients.

This fungus, Fusarium, is another etiologic agent of mycotic keratitis. This organism produces clear septate hyphae which are not particularly characteristic. The large macroconidia, shown here, are septate, new-moon/banana-shaped spores. Fusarium spp. also produce small spores called microconidia.

This is a typical picture of an Aspergillus species. This fungus produces clear septate hyphae. Note the way the spores are borne. On the ends of the specialized pieces of hyphae (conidiophores) (A) is a swollen tip (vesicle) (B). On these vesicles, phialides (or sterigma) are present, and long strands of small spores (C ) are borne at the end of the sterigma. Aspergillus species cause otomycosis, mycotic keratitis and aspergillosis.

Therapy

1) A 5 % solution of natamycin applied topically.

2) Topically applied Amphotericin B, oral Sporanox (1:50 dilution of Sporanox in ophthalmic solution) and ketoconazole in suspension have been used in difficult cases.

3) If thermophilic Aspergillus spp. are involved the organism may invade the brain. Few drugs are successful in such cases.

2) Otomycosis

Fungus and yeast infection of the external auditory canal of the ear. Numerous common fungi have been implicated.

Some investigators believe this is not a true disease because tissue invasion and destruction has not been demonstrated.

Otomycosis (con’t.)

All of the etiologic agents of this disease are common soil and airborne fungi. Over 40 species have been isolated from infected ears.

The disease is more common in tropical climates.

The disease is usually treated by cleaning the ear canal. Topical antibacterial and antifungal agents may be applied.

3) Piedras

a) Black Piedra

b) White Piedra

a) Black Piedra

This disease is characterized by small dark nodules seen on the hair shaft. It is found mostly in tropical areas such as South America. I have seen it in school children in Vietnam.

This is a higher magnification photograph of hair with black piedra. The lesion is very discrete, surrounds the hair shaft and is dark brown. Eventually the fungus may weaken the hair shaft to the extent that the hair breaks off.

This is a still higher magnification of hair infected with Piedraia hortai. Close observation reveals that the nodule appears to be composed of hundreds of spherical cells. These cells are the asci, which contains ascospores. Such structures can be seen more clearly when one places infected hair in 1-2 drops of 10-20% KOH on a microscope slide, adds a coverslip, heats the preparation gently and the presses down very firmly on the coverslip. In such preparations the piedra nodules break open, and one sees many individual asci containing ascospores and, occasionally, groups of ascospores which have been squeezed out of individual asci.

This is a culture of the fungus Piedraia hortai. This fungus was cultured on Sabourauds medium and incubated at room temperature. It normally takes 4-6 weeks incubation weeks incubation for a colony to reach this size. The gross features of this colony are that it is slow-growing, is heaped up in the center, is a dark brown-black to metallic green and is surrounded by a clear ring where the young growing mycelium has not yet produced the dark pigment. Microscopically, there are few characteristic features. The fungus produces dermatiaceous hyphae which may contain numerous chlamydospores. No characteristic spores are produced.

b) White Piedra

In this disease we also see nodules on the hair. However, differing from black piedra, the nodules are softer, pale in color and are only found on hair in the groin and axillae.

In this picture we see hair with white piedra (Trichosporon beigelii). Note that, when this module is compared with that seen in black piedra, it is not as discrete and lacks the dark coloration. Additionally, this fungus does not produce ascospores. When cultured on Sabouraud’s agar and incubated for 2-4 weeks at room temperature, this fungus produces a rough, membranous, white to light tan colony. Microscopically, the organism produces no characteristic spores.

This is a 4-5 week old culture of Trichosporon beigelii (T. cutaneum) grown on Sabourauds medium at room temperature. This is the etiologic agent of white piedra.

Therapy

The piedras are treated by removal of the hair and application of topical antifungal agents.

Note: White piedra must be differentiated from trichomycosis axillaris which is bacterial in etiology.

4) Tinea Nigra

This is a superficial infection caused by a black yeast variously known as Cladosporium or Hortaea werneckii. It is usually found in tropical areas of the world. It is seen as circumscribe areas of hyperpigmentation usually on the palms or soles. Lesions are dark brown to black with little scaling.

This is a photograph of tissue prepared for direct examination with 10% KOH. Throughout the field one can readily observe strongly septate dematiaceous hyphae. Note: No coloring agent has been added to this slide; the dark brown color is produced in the fungus. This is how the etiologic agent of tinea nigra appears in tissue.

An unusual case from the Philippines. Now you know why this disease is no longer called tinea nigra palmaris! A small portion scrapped skin, placed in 10% KOH on a microscope slide will reveal the dematiaceous, septate hyphae.

Therapy

Topical antifungal agents as well as Whitefield’s ointment have been used successfully.

5) Pityriasis (Tinea)Versicolor

This is a very common superficial mycoses caused by a lipophilic yeast Malassezia spp. It is seen in all countries but is particularly common in the tropics with more than 60 % of the population infected.

The lesions are hypo or hyper pigmented. The etiologic agent is normal flora of man so the disease re-occurs.

Recent evidence suggest that seborrheic dermatitis is also caused, or triggered by, Malassezia yeast.

There also is Malassezia folliculitis. This is seen in patients who are usually severely ill or in patients after sun exposure.

This is pityriasis versicolor. Note the larger area of hypopigmentation in the center. In this disease there is no erythema, the infected areas are not elevated, and aside from some itching the patient feels no discomfort.

This is a patient with pityriasis versicolor. Again, note the blotchiness of the skin pigmentation.

This is a poster of the once famous rock star Peter Frampton. Note the excellent example of tinea versicolor on his shoulders. I wrote to him and asked permission to use his picture but all I got back was a membership card in his Fan Club; probably the last thing in the world I was looking for!!!

Note the areas of hypopigmentation on the back of this Chinese patient. This again is tinea versicolor.

This is a photomicrograph of skin infected with Malassezia furfur. Note that in vivo this organism produces clusters or clumps of rather short hyphae and spherical yeast cells. Some authors refer to this overall picture as “spaghetti and meatballs”.

This is a high magnification of tinea versicolor. Note the round clump of yeast cells and the short strands of hyphae. This slide was made with 10% KOH and up to 10% Super Chrome ink or methylene blue stain was added.

Culture

Malassezia furfur can be grown in a laboratory but only when one covers the culture with oil. This leads me to speculate that there is a genetic susceptibility to this disease resulting from qualitative or quantitative differences in the oil content of susceptible persons.

Therapy

1) Tinea versicolor is one of the few places where ketoconazole is used universally ( a single 400 mg. dose or 5 days of 200 mg. is sufficient) for large lesions.

Smaller infected areas can be treated with selenium sulfide in a shampoo or other topical antifungals.

2) Seborrheic dermatitis (dandruff) is treated the same as above.

NOTE: Ketoconazole can be used safely for short term results. For other mycoses, requiring longer therapy, the newer drug Sporanox can be used with greater safety.

This is a chronic infection of the nasal and other mucosal surfaces. Large vegetative outgrowths are seen. Histopathologically one sees structures that look like fungal elements (sporangia). However, the organism has never been cultured. Current opinion is that the organism is not a fungus but is infact a protozoan.

I have seen a few human cases in Vietnam and several cases in horses in the USA.

6) Rhinosporidiosis

This is a stained section from a lesion of rhinosporidiosis. There is one large sporangium (near the center of the field) and 6-8 other small ones scattered throughout the slide. The large sporangium in this slide is about 300 microns in diameter and is filled with numerous sporangiospores.

The large growth coming out of the patient’s nostril is rhinosporidiosis. This young patient was seen and diagnosed in Saigon.

Note the size of the mass. Usually the masses in this disease are much smaller and resemble allergy induced polyps.

7.) Malassezia folliculitis (Pityrosporum folliculitis)

Superficial malassezia folliculitis (Xinjiang Province, Urumqi)

Itchy follicular papules and pustules are seen with erythema, usually on the upper torso of young adults except for the head and scalp. It resembles acne except there are no comedones, no scarring and the organism is a yeast.

During the past decade molecular biology methods have identified a dozen species in the genus Malassezia. They cause or are implicated in pityrosporum folliculitis, seborrheic dermatitis, dandruff, psoriasis and may trigger atopic dermatitidis. Malassezia globosa is frequently implicated as an important etiologic agent of malassezia folliculitis. Read “Update on the genus Malassezia”, by HR Ashbee, a review article in Medical Mycology, 2007, in press.

All these yeasts are normal flora of human and animal skins. Most species are lipophilic (except for one, thus far), making laboratory culture different from all other yeasts.

Since these organisms are lipophilic and normal flora it follows that predisposing factors must be the key. Lipid content, qualitatively and quantatively, may also be important. This is undoubtedly a reason why the disease is seen most often in sebum-rich body areas. In China most cases are seen in young, healthy adults during the summer. However, in the world literature, most reported cases are in immunosuppressed adults.

In order to accurately diagnose malassezia folliculitis clinical material must be taken from lesions and examined microscopically in 10 to 20 % KOH, Parker (i.e., blue) ink or methylene blue dye (3 gm/L). Diagnosis is confirmed with the observation of budding yeast cells.

For many years these organism could not be cultured in the lab. Then, it was discovered that they require certain lipids (fats) in the medium, eg., Sabourauds medium with an overlay of sterile olive oil. Since this is not feasible in the normal clinical lab, culture is not done. In fact even if it is done PCR methods are required to identify to the species level.

In the world literature ketoconazole and itraconazole are most often recommended. Due to cost, many local medicines are used.

This is a relatively common disease seen in dermatology clinics all over China and the Orient. In China it is usually seen in normal, apparently healthy, adults mostly in the summer time.

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