PHD - Superficial and Subcutaneous Mycoses (Steed) Flashcards
What is tinea corporis and which 2 fungi typically cause this disease?
Tinea corporis is fungal infection of the skin of the body
Typically caused by: Trichophyton rubrum or Microsporum canis
An immunocompetent, outdoorsy, older man who lives on the beach and wears sandals all the time presents with a chronic friable lesion on his lower leg. The lesion has been slowly growing for over a year. An aspirate of this lesion shows the organism in the image below. Which of the following organisms is most likely the cause?
A. Ponsecaea pedrosi
B. Malassezia furfur
C. Microsporum canis
D. Pseudoallescheria boydii
E. Trichophyton ronsurans
A. Ponsecaea pedreosi
The question stem indicates infection with a fungi leading to chromomycosis (tropical climate, sandals, lesion of lower leg). The figure in the slide is called a sclerotic (medlar or copper) body.
Incorrect answers:
B causes altered pigmentation
C causes tinea corporis and ectothrix
D causes mycetoma
E causes tinea and endothrix
What is the name for a fungal infection of the groin and which two fungi are most likely to cause this?
Tinea cruris
Typically caused by: Epidermophyton floccosum or Trichophyton rubrum
Your patient is a 65-year-old male who complains of redness and itching on his hands and scalp. When asked about his social history, he states that he is an avid gardner and works out in the yard multiple times a week. Upon inspection with a woods lamp, you notice some patches of green fluorescence. Based on his history and symptoms, what type of infection does your patient have?
Microsporum infection
Indicated by:
Soil-human transmission
Scalp infection
Positive Wood’s Lamp
True or False: Pathogenic fungi are resistant to active oxygen radicals, making them viable after ingestion by phagocytes?
True
Fungi have special capsules that make them resistant to mammalian enzymes and reactive oxygen species, which prevents them from being degraded by macrophages.
Your patient is a 33-year-old male from Hawaii who complains of wart-like growths on his legs and feet. He tells you that he frequently hikes on the Hawaiian islands and that he often wears sandals because it is so hot there. He says that the warts have been slowly growing for many years, and that his current girlfriend finds them hideous. What condition does this patient have?
Chromomycosis
This disease presents as slow-growing warts of the feet and legs. This is very common in tropical climates, and is caused by implantation of saprophytic fungi into wounds.
What is an endothrix and which organism typically causes it?
An endothrix is a fungal infection within the hair shaft
Caused by: Trichophyton tonsurans
What is a sulfur granule and which disease is characterized by the presence of sulfur granules in a tissue biopsy or drainage sample?
Sulfur granules are compact masses of fungal cells in the tissue or fluid drained from a lesion.
Occurs in mycetoma
True or False: Fungi can alter their metabolic rate and metabolic pathways to aid in invasion of tissues.
True
On your heme/onc rotation you encounter a patient with a neutrophil count of 50. He is clearly immunocompromised, and has patches of skin that are hypopigmented (see below). What is the name of this hypopigmentation and what organism causes it?
Pityriasis (tinea versicolor, hypopigmentation)
Caused by: Malassezia furfur
Remember that Malassezia furfur produces lipids that inhibit the enzyme tyrosinase, which inhibits melanin production in the skin.
Below is a histologic section of a wart from a patient’s foot. What is the name of the structure with the blue arrow pointing to it and what disease does this indicate?
The arrow is pointing to Sclerotic bodies (aka Medlar or copper bodies)
These indicate that the patient suffers from chromomycosis
Sclerotic bodies are reproductive forms of the fungus
What are the 3 main mechanisms that fungi cause disease?
- Mycotoxins
- Hypersensitivity reactions to fungal antigens
- Direct invasion of tissues/organs
What are two things to consider when trying to determine which fungus is infecting your patient?
- Endemic area - certain fungi only grow in certain parts of the world
- Ecological niche - each patient is exposed to different forms of fungi based on what they do:
- Ex: gardeners work with soil that has lots of fungi
- Ex: people who are around lots of bird guano tend to get cryptococcus
Which race most commonly becomes infected with tinea capitis?
African American
African americans account for over 90% of tinea capitis infections
Why does treatment for tinea infections typically take longer to treat than bacterial infections or other fungal infections?
Tinea involves fungal damage of skin and other structures that tend to take 4-12 weeks to regrow.
For this reason, tinea treatment must last for as long as it takes to regrow the afflicted area.
Patients with neutrophil and CD4+ T-cell counts below what number are at high risk for developing fungal infections?
Below 100
Malassezia furfur tends to grow on patients who are on prolonged supplementation with what?
Lipids
Malassezia furfur thrives on oily skin
What is an ectothrix and which 2 organisms typically cause it?
An ectothrix is a hypha formation from the sheath on the hair shaft surface
Commonly caused by: Microsporum canis and Microsporum audouinii
Ectothrix is another term for mold growing on the surface of the hair shaft
What are some predisposing factors to fungal infection?
- Immune compromise - most important
- Severe burns
- IV drug use
- Certain therapeutic procedures - antibiotics, catheters, valve replacements, radiation
True or False: Fungi can infect hair.
True
Below is a fungal specimen that has been stained and placed on a slide. Based on its morphology, what type of fungus is this?
Trichophyton
Few cylindrical or “club-shapped” macroconidia with thin-walled septae and numerous microconidia
A 26-year-old male presents to your clinic complaining of an itchy and red rash along the groin and inner portion of his thighs. Examination with a wood’s lamp showed no changes in fluorescence on the rash. What fungus is infecting this patient and what is its mode of transmission?
Epidermophyton floccosum
Mode of transmission: human-human contact
Key factors:
Infection of skin of groin
Woods Lamp negative
How are exogenous sources of fungi acquired by humans?
Inhalation, ingestion, or traumatic implantation (wounds)
Which fungal infection typically presents as folliculitis in neutropenic patients?
Malassezia furfur
Remember that low neutrophil counts increase risk of fungal infection AND that malassezia furfur loves oily areas.
Because the hair follicles contain lots of oil and sebaceous glands are attached, this fungus thrives in the hair follicles
A 42-year-old female comes into the office complaining of rough and oddly shaped fingernails (seen below). Which organism is primarily responsible for this condidition and what is the condition called?
Trichophyton rubrum
This condition is called onychomycosis (tinea unguium)
A relative of yours asks your advice about an odd rash on her back. The flat, hyperpigmented rash has well defined margins, without itching, pain, or pirulence. You recommend an OTC antifungal medication. She wants you to explain where she got the rash:
A. Eating a wild mushroom that was poisonous
B. From her own skin
C. From her poodle, Duchess
D. It is a hypersensitivity reaction to fungi in her environment
E. Working in her garden
B. From her own skin
The characteristics of this rash point to Malassezia furfur infection of the skin. This causes hyperpigmentation with well-defined margins without any itching or pain.
Malassezia furfur is a commensal organism that resides on the skin. So it was not transmitted to her, she has always had it.
On examination of a patient specimen under the microscope, you see the following structures. Based on the characteristic appearance of this structure, what organism is present on the slide?
Epidermophyton floccosum
This slide demonstrates the characteristic “baseball bat” or “club” appearance of the macroconidia.
Also note that there are no microconidia present.
What is mycetoma and what is one defining characteristic of this disease?
Mycetoma is a type of phaehyphomycosis in which a wound is infected with fungal spores.
Defining characteristic: draining lesions of skin
Below is a microscope image of a fungus that was cultured from a patient. Based on its morphology, what type of fungus is this?
Microsporum
Microsporum contain rough/spiny macroconidia with multiple, thick-walled septae
These also contain few microconidia
What is the standard treatment for onychomycosis?
Oral Itraconazole or terbinafine
What is chromomycosis?
Chromomycosis is implantation of soil saprophytes or plant pathogens in wounds that leads to chronic granulomatous disease and warts.
A patient with a suspected fungal infection is swabbed and the specimen is sent to the lab. On examination under the microscope, you see what is on the slide below. What organism is infecting the patient and what characteristic appearance tells you that it is this organism?
Malassezia furfur
This fungus has a characteristic “spaghetti and meatball” appearance.
Spaghetti = hyphae
Meatball = conidia
True or False: Chromomycosis is typically caused by dematiaceous fungi?
True
Remember that dematiaceous fungi are fungi that produce melanin in their cell walls (aka black mold)
What are mycotoxins?
Mycotoxins are chemical substances that certain fungi produce that cause disease
Examples:
Psilocybin mushrooms (psychadelics)
Ergot (hallucinations and muscle tics)
Sick building syndrome (reaction to mold infestation in a particular building)
What is the major endogenous source of infecting fungi in humans?
Commensal organisms
Typically appear after immunosuppression or use of antibacterial agents.
What are the two types of mycetoma and what distinguishes them from one another?
- Actinomycotic mycetoma - caused by bacteria (Nocardia)
- Eumycotic mycetoma - caused by black molds
Distinguished by the causative organism: bacteria or fungi
How does Malassezia furfur lead to pityriasis (hypopigmentation) in patients?
Malassezia furfur produces a special lipid that inhibits the enzyme tyrosinase, which is involved in synthesis of melanin.
Lack of melanin –> hypopigmentation of skin
What are the 3 types of dermatophyte infections that are treated with oral antifungals?
Tinea capitis, Tinea corporis, and Tinea unguium (onychomycosis)
What are the clinical manifestations of chromomycosis?
- Unilateral wart-like lesions of the legs and feet
- Secondary lesions develop along lymphatics or from autoinnoculation
- Can invade underlying muscle and bone if patient is immunocompromised
Which bacteria is the causative agent of actinomycotic mycetoma?
Nocardia
Which two types of dermatophytes are transmitted through animal-human interaction?
Microsporum and trichophyton
How is chromomycosis treated?
- Surgical removal of lesions
- Prolonged (1-3 years) treatment with itraconazole
- If very severe, treat with amphotericin B
What is pityriasis (tinea versicolor) and which type of fungus typically causes it?
Caused by Malassezia furfur
Pityriasis (tinea versicolor) is used to indicate hyper- or hypopigmentation of toe skin caused by Malassezia furfur infection.
What is tinea capitis and which organism is usually the cause of it?
Tinea capitis is fungal infection of the scalp
Typically caused by: Trichophyton tonsurans
Fungal culture of hair from an area of ringworm on the scalp of a child grows a mold that makes a few large, club-shaped, smooth-walled spores and numerous much smaller spores. The best antifungal treatment is:
A. Fluconazole for 14 days
B. Fluconazole for 4-12 weeks
C. Griseofulvin for 4-6 weeks
D. Tolnaftate for 7 days
E. Terbinafine for 7 days
B. Fluconazole for 4-12 weeks
The question stem is describing Trichophyton, a fungi that contains few club-like macroconidia with numerous microconidia.
However, the fungus is present on the scalp, indicating that it is tinea capitis.
The recommended treatment for tinea capitis is 4-12 weeks of fluconazole.
What is the common name for tinea pedis and which two types of fungi typically cause it?
Athlete’s Foot
Caused by: Trichophyton rubrum and Epidermophyton floccosum
Which type of fungal infection can be diagnosed using a Woods Lamp (UV light) on the skin?
Malassezia furfur
Causes a yellow-green fluorescence under UV light
Which type of dermatophyte is commonly transmitted through soil-human interaction?
Microsporum
How do clinicians classify fungal infections, and what are the 4 classifications?
Classified by his where the fungus resides
4 Classifications:
- Superficial - confined to epidermis
- Cutaneous - cutaneous layers of hair, skin, nails
- Subcutaneous - confined to subcutaneous tissues
- Systemic - deep viscera and are widespread
Below is a histologic section from a patient who presented to a hand surgeon with a lump on the palm of his hand after he pinched his hand with pliers. Based on the slides below, what condition does this patient have and what is the arrow pointing to?
The patient has chromomycosis
The arrow is pointing to a sclerotic body
Presence of sclerotic bodies, the patient history (trauma to hand) and the presence of dematiaceous fungi (with melanin) in the tissue samples all indicate chromomycosis.
Epidermophyton floccosum typically infects which parts of the body?
Groin and nails
What is the standard treatment for tinea capitis? What is the treatment for resistant infections?
Griseofulvin
For griseofulvin-resistant strains: fluconazole
What are the 2 most critical determinants of the severity of fungal infections?
- Number of neutrophils
- Whether or not cell-mediated immunity is intact
How does a mycetoma cause a draining lesion on the skin?
Mycetomas are subcutaneous abscesses filled with pus. When these abscesses grow to a certain size, they will rupture through the surface of the skin.
Which type of dermatophyte is only transmitted via human-human contact?
Epidermophyton floccosum
