Dermatophytes

CASE 1

• A 25 year old medical student on an elective rotation from Germany complains of a recurrence of itching in the interdigital spaces between several toes. He has had this problem several times in the past and it has been successfully treated with a topical antifungal medication. He believes that it has recurred in Ghana because he has been wearing the same pair of shoes consistently and his feet remain moist throughout the day. The appearance of one interdigitial lesion is shown below.

• Examination of the patient's toenails show the changes in the photograph below.

• A scraping from under the nails was placed on a clean microscopic slide, a drop of 10% potassium hydroxide was added, a coverslip was placed, and the slide was heated just to boiling over a flame. The appearance of the scraping is shown below.

• A diagnosis of tinea pedis with onychomycosis was made. The interdigital rash was treated with miconazole cream applied twice daily.

Questions:

1. What is the structure seen on the 10% KOH preparation of the nail scraping?
2. Why did this fungus recur when this student came to Ghana? What was the source of the interdigital infections?
3. Will the topical treatment also cure the infection of the toenails? Why not?
4. Which fungal species are the most common causes of this type of infection?
5. What other sites of the body can become infected in this way? By are these sites preferred?
6. If there were a reason to culture this fungus in the laboratory, what medium would you use?

CASE 2

• A 45 year old woman developed an itchy rash under the right arm. The rash began as a small round, plaque-like lesion (below left). Without any specific treatment, the rash enlarged in all directions and began to clear at the center, giving the impression of a ring. Three months later, the rash has the appearance shown at the bottom right.

• A scraping of the leading edge of the rash was obtained, and a 10% KOH preparation was examined. Numerous fungal hyphae were seen.

• The patient was treated with topical ketoconazole cream for two weeks, and the rash slowly disappeared.

Questions:

1. What is this form of dermatophyte infection called?
2. What is "ringworm"? Is it caused by a worm?
3. How might this woman have acquired this infection?

CASE 3

• A 12 year old American boy has developed a round, slightly raised, enlarging rash on his scalp. The hair within the bounds of the rash became brittle and began to break off a few centimeters above the scalp.

• The boy lives with his parents and two older siblings. The family recently acquired two puppies from a neighbor, and the boy has been training and feeding them. No one else in his household has a rash.

• One of the short, broken hairs is plucked and stained for fungal organisms. Fungal hyphae were seen to be growing on the exterior surface of the hair shaft (see below).

Questions:

1. What was the likely source of the pathogen in this case? What species is/are likely involved?
2. Invasion of the hair shaft from the exterior is called "ectothrix" infection. What would you call an infection that penetrated and grew in the interior of the hair shaft?
3. What is favus?
4. Will this boy's infection cause permanent hair loss? Are there other forms of tinea capitis that can cause permanent loss of hair?