Week 2 - Antifungal Case Studies

Question 0

What organism causes “cradle cap” or seborrheic dermatitis?

Answer 0

Malassezia

Question 1

What are the three dermatophytes?

Answer 1

Microsporum, Tichophyton, Epidermophyton

Question 2

What organisms cause bacterial folliculitis?

Answer 2

Staphylococcus aureus or Pseudomonas

Question 3

What are the limitations of a KOH test?

Answer 3

It is a fast result but it does’t identify the species and has lower sensitivity.

Question 4

What are the limitations of Wood’s Lamp?

Answer 4

The fungi Trichophyton tonsurans does not fluoresce.

Question 5

When would you take a bacterial culture if you think something is a fungal infection?

Answer 5

If you see inflammation, you want to take a bacterial culture just to rule out secondary infections.

Question 6

What are the pros and cons of culturing fungi on Sabouraud’s agar + antibiotics?

Answer 6

It takes longer (1-4 weeks) but its more sensitive and used for refractory cases. You can follow up with susceptibility tests ad strain identification through PCR.

Question 7

What structures are seen in a KOH scraping of Microsporum?

Answer 7

Spindle shaped Macroconidia

Question 8

What is the most common pediatric dermatophyte infection?

Answer 8

Tinea capitis (age 4-14)

Question 9

What is unique about sebum?

Answer 9

It’s fungistatic

Question 10

What is the most common cause of tinea capitis?

Answer 10

Trichophyton tonsurans (90-95% of cases)
Second most common is Microsporum canis or audouinii which fluoresce blue-green under wood's lamp.

Question 11

What are the three most common morphologies for dermatophytes?

Answer 11

Microsporum canis: spindle-shaped macroconidia and microconidia
Trichophyton tonsurans: Macroconidia are rare, Microconidia - looks like hairs with tiny little dots
Epidermophyton floccosum: Dumbbel-shaped macroconidia - No microconidia

Question 12

What type of organism is Trichophyton tonsurans?

Answer 12

Antropophilic

Question 13

What type of transmission does Microsporum fulvum do?

Answer 13

It is geophilic (loving soil) and causes tinea corporis

Question 14

How does Microsporum canis invade the hair follicle?

Answer 14

It is ectothrix so it penetrates AROUND the hair shaft. It tends to be chronic.

Question 15

How does Trichophyton tonsurans invade the hair follicle?

Answer 15

It can penetrate within the hair shaft (endothrix).

Question 16

What properties of dermatophytes promote cutaneous growth?

Answer 16

Dermatophytes adhere to keratinocytes and produce keritinase. They also have mannans in their cell wall that allows them to evade the host immune response.

Question 17

What makes disseminated disease rare for dermatophytes?

Answer 17

The fungi are unable to grow at body temperature.

Question 18

What treatment would you recommend for a patient with tinea capitis caused by Microsporum canis?

Answer 18

Systemic therapy - oral griseofulvin (microtubule inhibitor) for 8-10 weeks or until the layer of skin is sloughed off. - Griseofulvin needs to be taken with foods high in fat
(2nd choice: terbinafine - inhibits squalene epoxidase - but its not as effective for M. canis)

Question 19

Onychomycoses is also referred to as:

Answer 19

Tinea unguium

Question 20

Which fungi are most often associated with onychomycoses?

Answer 20

Subungal - Trichophyton rubrum, most common for tinea pedis, tinea corporis, and tinea cruris
White superficial - Trichophyton mentagrophytes - more common in children
Bacteria pseudomonas - blue-green nail infection

Question 21

What does Candida albicans do as an onychomycosis?

Answer 21

It’s more common on fingers and causes inflammation.

Question 22

How do you diagnose a tinea pedis/onychomycosis infection?

Answer 22

1. Clean with alcohol to remove bacteria
2. Take a sample from nail bed for KOH test
3. False negative 5-15% of time - hyphae can be rare
4. Beware of Candida contamination

Question 23

What is the pathogensis of Trichophyton rubrum that causes tinea pedis?

Answer 23

1. Conidia adhere to keratinocytes (sebum is inhibitory so they prefer soles of feet) and germinate
2. Chronic infection (slow growing) starts with big toe and spreads
3. Nail thickening may cause pain
4. Subungual hyperkeratosis can cause seperation of nail plate from nail bed
5. Can make individual more prone to secondary infections like gangrene

Question 24

What treatment is used for Trichophyton rubrum?

Answer 24

• Discard exposed footwear and minimize moisture
• Regular trimming of nails
• Some doctors refuse to treat this because they believe its a cosmetic problem
• USE SYSTEMIC: Terbinafine or Itraconazole (for onchyomycoses)
• Need to monitor heptatoxicity - take baseline of liver enzymes
• Recurrance is common so need to treat for a week after symptoms stop - think of it as controllable, rather than curable

Question 25

What drugs are used to treat onchyomycosis?

Answer 25

Terbinafine and Itraconazole