Superficial, Cutaneous, & Subcutaneous Mycoses

Question 1

Fungal Structure

Answer 1

• Eukaryotic
• Cell wall w/ chitin and glucans
• Fungal membrane w/ ergosterol (non-human)
• No endotoxin
• Unicellular form: yeast
  
  • Budding reproduction
• Filamentous multicellular form: mold
  
  • Hyphae w/ apical growth
  • Spores: mitosis or meiosis
    
    • Dispersal and dormancy
• Dimorphic: both yeast

Question 2

Microscopic diagnosis

Answer 2

• KOH solution: disolves tissue and visualizes hyphae
  
  • Used to see dermatophytes & candida
• India Ink stains background leaving organism clear
  
  • used to determine if a cell has a gelatinous capsule
  • encapsulated yeast Cryptococcus spp

Question 3

Culture diagnosis

Answer 3

• More sensitive than microscopy
• ID by appearance of mycelium and asexual spores
• Sabouraud’s agar: inhibits bacterial growth
• Standard blood culture bottles

Question 4

Antifungals: Azoles

Answer 4

• Inhibit ergosterol synthesis
• Imidazoles: topical candidasis dermatophytes
  
  • Clotrimazole, miconazole
• Triazoles: systemic and broad spectrum
  
  • Fluconazole itraconazole, voriconazole

Question 5

Antifungals: Polyenes

Answer 5

• Bind ergosterol- pore causing osmotic death
• Amphotericin B (IV systemic) broad specturm
  
  • Renal toxicity
• Nystatin: topical

Question 6

Antifungals: Echinocandins

Answer 6

• inhibit b-glucan synthesis; blocks cell wall
• caspofungin, anidulafungin, micafungin
  
  • broad spectrum

Question 7

Antifungals: Allylamines

Answer 7

• Ergosterol inhibitor
• Terbinafine: topical, oral: onychymycosis
  
  • used for dermatophytes
• Butenafine: topical for dermatophytes

Question 8

Immune response to fungi

Answer 8

• Endothelial cells: recognize fungi
  
  • Dectin-1 of B-glucan binds definsins
• Neutrophils activated against mold such as aspergillus
• Th1 response to intracellular fungi

Question 9

Superficial Mycoses

Answer 9

• Colonize outer keratinized surface
  
  • Skin, hair, nails
• little to no immune response
  
  • non-destructive
• mainly yeasts

Question 10

Tinea (pityriasis) veriscolor

Answer 10

-Superficial Mycose
-Caused by yeast
-Malassezia furfur
-patches of skin w/ hyper- or hypo-pigmentation
-Wood’s lamp exam shows yellow-green fluorescence
-Spaghetti & meat ball appearance on microscope
*yeast-like cells w/ short pseudohyphae
-growth enhanced by adding olive oil
-Persistant & rarely self cures
Tx: topical therapy (azoles) or oral azoles if widespread

Question 11

Tinea nigra

Answer 11

• Superficial Mycose
• dark brown spots on palms
• Hortaea werneckii
• Mold

Question 12

White piedra

Answer 12

• Superficial mycose
• soft nodules composed of yeast cells and arthroconidia that encompass hair shafts.
• Trichosporon sp.
• Yeast

Question 13

Cutaneous Mycoses

Answer 13

• Invasion of epidermis w/ inflammation
• Primarily caused by dermatophytes
• Breakdown keratin
• Invade skin, hair, nails
• Invade outermost layer of epidermis
  
  • Stratum corneum

Question 14

Tinea Infections

Answer 14

• Tinea capitus: ringworm on head
• Tinea corporis: ring worm of the body
• Tinea barbae: ringworm of the beard
• tinea cruris: ringworm of the groin
  
  • Jock itch
• Tinea pedis: athlete’s foot
• Tinea unguium: onychomycosis: in nails
  
  • Very hard to treat
• Transmission by direct or indirect contact
• TX: topical agents for most
  
  • Oral azoles, terbiafine for hair or nail

Question 15

Subcutaneous Mycoses

Answer 15

• Invasion of subcutaneous tissues
• Slow progression may req surgery
• All rare: trauma, rarely spread, hard to tx

Question 16

Sporotrichosis

Answer 16

-Sporothrix schenckii
-Dimorphic, in soil and dead vegetation
*Pricked skin of gardener
-Primary lesion at site of injury
*Nodule grows, ulcerates and becomes painful
-Secondary lesions weeks later along lymphatics progress proximally
*Growing in macrophages
-Biopsy shows starburst pattern: eosinophilic granulomatous structure w/ radiating pattern
-Dx: culture
Tx: intraconazole for several weeks

Question 17

Chromomycosis

Answer 17

• Chronic local infection causing warty/nodular outgrowths
• granulomatous inflammation
• Soil fungi after traumatic inoculation
• Tx: intraconazole or terbinafine + 5FC
  
  • heat or cryotherapy to shrink lesions

Question 18

Eumycotic mycetoma

Answer 18

• deep subcutaneous infection seen as swellings in sinus tracts
• Granulomas develop
• Pus and granules drain thru skin
• Caused by madurella, fusarium
• Dx: black granules in biopsy
• Tx: antifungal agents and local surgery can be tried
  
  • Often ineffective
  • frequent cure is amputation