Micro: Mycoses

Question 1

What are the basics of pityriasis (tinea) versicolor?

Answer 1

young people at beginning of puberty, SUPERFICIAL
multiple macules - variable appearance, hypopigmented, surrounded by normal skin, midline and symmetrical
high temp and humidity favors occurrence
inf agent = *malassezia furfur = superficial mold

Question 2

What is tinea nigra?

Answer 2

SUPERFICIAL fungal inf, appears as black spots
usually palms and soles
caused by hortaea werneckii

Question 3

What is piedra?

Answer 3

nodules on outside of hair shafts, SUPERFICIAL ectothrix infections
black piedra from piedraia hortae
white piedra from trichosporon

Question 4

How is pityriasis versicolor diagnosed?

Answer 4

clinical appearance, KOH prep
use Wood’s lamp - yellow to yellow-green fluorescence of scales from active lesions
skin samples have “spaghetti & meatballs” appearance

Question 5

What are the therapeutic options for pityriasis versicolor?

Answer 5

topical agents and oral meds

Question 6

What are the different ways to classify fungi?

Answer 6

mold vs. yeast: mold grow as hyphae, yeast as oval cells
monomorphic vs. dimorphic (yeast at 37 deg C, mold in environment)
imperfect (no sexual form) vs. perfect (sexual form)

Question 7

What are basic features of the dermatophytes?

Answer 7

= cutaneous mycoses, invade stratum corneum only and other keratinized tissues (hair and nails)
lesions are serpentine or annular w raised margins
monomorphic - only mold, colorless spores
arthroconidia = infective form, also macro and micro

Question 8

What are the 3 genera of dermatophytes?

Answer 8

microsporum: hair, skin
epidermophyton: skin, nail
trichophyton: hair, skin, nail

Question 9

What are the basic clinical features of inf w dermatophytes?

Answer 9

skin: circular, dry, erythematous, itchy, scaly lesions
hair: scarring, alopecia
nails: thickened, disformed, discolored, subungual debris

Question 10

Where do zoophilic vs. anthropophilic organisms usually affect?

Answer 10

z - exposed areas (face, neck, arms)

a - occluded areas, areas of trauma

Question 11

What mold is suggested by spindle-shaped macroconidia?

Answer 11

microsporum canis, radial yellow appearance on plate

Question 12

What mold is suggested by dumbbell-shaped macroconidia?

Answer 12

epidermophyton floccosum

Question 13

What are ectothrix vs. endothrix invasions?

Answer 13

arthroconidia outside or inside the hair shaft

Question 14

What are the modes of transmission for dermatophytes?

Answer 14

direct contact w lesions or contact w materials, animals, or soil
person to person, animal to human, or from environment
anthropophilic only humans, zoophilic mostly animals, geophilic in soil

Question 15

Do dermatophytes disseminate? why or why not?

Answer 15

no - can’t grow at body temp (37 C)

Question 16

How do dermatophytes invade keratinized tissues?

Answer 16

produce keratinases and proteinases

Question 17

How are the dermatophytes diagnosed?

Answer 17

growin in Sabouraud’s dextrose agar = acidic pH 5.2 mimics skin

Question 18

What do the following color colonies suggest:
greenish-brown or khaki
pale, yellowish-brown or reddish-brown from under plate
white from top of plate

Answer 18

E. floccosum
Trichophyton
Microsporum

Question 19

What does trichophyton look like?

Answer 19

many spherical microconidia clustering on hyphae

few macroconidia

Question 20

What is an id reaction?

Answer 20

to dermatophytes = a hypersensitivity rxn

rash and vesicles on skin distant from site of inf

Question 21

What is the basic treatment of dermatophyte inf?

Answer 21

topical or systemic
oral agents concentrate in keratinocyts and also found in sweat
usually a couple of weeks
recurrences common after stopping therapy

Question 22

What is the basic treatment of onychomycosis?

Answer 22

topical therapy ineffective
systemic therapy for several months
itraconazole and terginafine DOC but potentially hepatotoxic

Question 23

What is sporotrichosis?

Answer 23

subcutaneous inf caused by sporothrix schenckii

dimorphic fungus

Question 24

What is the histological appearance of sporotrichosis?

Answer 24

yeast = cigar shaped budding yeast
mold = thins septate hyphae w daisy-like conidia, darkly pigmented
demo may be difficult because fungi not abundant

Question 25

What is the reservoir and modes of transmission of sporothrichosis?

Answer 25

soil, moss, hay, decaying wood, vegetation
risks = occupational (rose handler’s dz from thorn pricks)
usually direct inoculation, rarely inhalation in alcoholics and COPD

Question 26

What are the dz manifestations of sporotrichosis?

Answer 26

minor trauma and inoculation through skin
subcutaneous lesions - chronic, firm, nonhealing nodules, sometimes ulcerate and ooze serous fluid
spreads along lymphatics - become firm and cordlike –> nodules in LINEAR arrangement, progresses proximally
no constitutional symptoms unless bacterial inf

Question 27

When and how does sporotrichosis spread outside the subcutaneous layer?

Answer 27

osteoarthritis in immunocompetent
disseminated in immunocompromised –> osteoarticular and pulmonary, poor prognosis
rarely subacute pneumonia w inhalation - can look like Tb or histo in immunocompromised

Question 28

What are the lesions of sporotrichosis made of?

Answer 28

suppurating granulomas - histiocytes and giant cells surrounded by neutrophils, lymphocytes and plasma cells

Question 29

What is the general treatment for sporotrichosis?

Answer 29

saturated potassium iodide for most forms
itraconazole and terbinafine effective
amphoterecin B for disseminated

Question 30

What is chromoblastomycosis?

Answer 30

chronic localized inf of skin and subcutaneous tissue

produces raised, warty, scaly lesions, usually on legs (“cauliflower like”)

Question 31

What are the dz manifestations of chromoblastomycosis?

Answer 31

most follow minor traumatic inoculation
small papule at site of trauma - enlarges to form nodule w friable surface - then spread laterally for satellite lesions
lesions usually not painful, but can ulcerate and bleed
can encircle leg and cause lymphatic obstruction
overlying skin becomes hyperkeratotic and pigmented
lesions can be there for yrs, bacterial superinfection common
acute and chronic granulomatous inflammation, microabscesses, reactive fibrosis

Question 32

What cause chromoblastomycoses?

Answer 32

dark walled pigmented fungi = dematiaceous fungi that produce melanin like pigment
*most common cause is Fonsecaea pedrosoi)

Question 33

How are chromoblastomycoses diagnosed?

Answer 33

skin scrapings and punch biopsies
large clusters of fungal cells appearing brown
grow slowly over 4 wks

Question 34

What is the general treatment for chromoblastomycoses?

Answer 34

itraconazole and terbinafine
prolonged therapy (6 mos-1 yr)

Question 35

What is mycetoma?

Answer 35

chronic progressive granulomatous inf of skin and subcutaneous tissue, can progress to bone
usually legs, most often foot
local swelling, draining sinus tracts, production of granules in tracts

Question 36

How does mycetoma infect?

Answer 36

inoculation following minor trauma w thorns, splinters
PMNs cannot destroy –> granulomatous response
incubation 5-10 yrs
spread is rare

Question 37

What is the microbiology of mycetoma?

Answer 37

actinomycotic and eumycotic types

a: caused by filamentous bacteria
e: caused by fungi, white grain or dark grain mycetoma

Question 38

How is mycetoma diagnosed?

Answer 38

clinical hx, long duration of symptoms, painless soft tissue welling, sinus tracts and grains in drainage
culture can identify causative organism

Question 39

What is the treatment for mycetoma?

Answer 39

amphoterecin B not effective for eumycetoma
oral useful, but cure is rare
long durations of therapy, often amputation
antibacterials for bacterial causes