Superficial fungal infections

Question 1

What are Dermatophytes?

Answer 1

Moulds. Superficial and cutaneous infections. Like keratin (skin, nails, hair).

Question 2

Genera of dermatophytes

Answer 2

Trichophyton, microsporum, epidermophyton

Question 3

Other agents that could be part of superficial infection DDX

Answer 3

Staphylococcus aureus, Streptococcus pyogenes; Endemic fungi like Histoplasma, Blastomyces, and Coccidioides; Parasitic or viral rash; Allergy and other non-infectious etiologies

Question 4

Tinea - what’s it mean?

Answer 4

Latin for worm, refers to the lesions (no worms involved). Tania is genus for tapeworm

Question 5

Tinea classification

Answer 5

Tinea capitis - head. Tinea corporis – trunk. Tinea cruris - groin. Tinea pedis - feet. Tinea unguium – nails. This is not genus-species setup

Question 6

Sources of dermatophytes

Answer 6

Human, animal, soil

Question 7

Pathogenesis of dermatophytes

Answer 7

Enter via skin breaks (groin and toes prone due to use, moisture). Bind keratinocytes and invade with keratinases, germinate and infect. Usually restricted by temp (prefer 30C).

Question 8

Pathogenesis of dermatophyte in skin infection

Answer 8

Spread through stratum corneum. Growth outward in centrifugal pattern (ring). Viable fungi are at margin or leading edge. No viable organisms in centre of lesions

Question 9

Pathogenesis of dermatophyte in nail infection

Answer 9

Invasion of lateral or superficial nail plates. Spreads throughout nail

Question 10

Pathogenesis of dermatophyte in hair

Answer 10

Ectothrix (infects outside of hair shaft) and Endothrix (infects inside of hair shaft)

Question 11

Acute and chronic dermatophyte infection

Answer 11

Acute has inflammatory lesions due to immune system, sometimes pustules (often from non human), Chronic is less severe and is usually human-human

Question 12

Tinea capitis

Answer 12

Scalp ringworm, Hair shafts infected. M. canis, M. audouinii. Often from dogs and cats. Children predisposed (Poor hygiene, prolonged moist skin). Scaling of scalp, hair loss, itching. Quite transmissible. Resembles dandruff

Question 13

Tinea corporis

Answer 13

Aka Ringworm on body; trunk and legs. Trichophyton spp. Most lesions have prominent edge + pustules. Centre of lesion less inflammed and scaly. Uncommon in temperate climates.

Question 14

Tinea pedis

Answer 14

aka Athlete’s foot. Interdigital spaces between toes, soles. Itching, erythema, scaling. Causes: E. floccosum, T. mentagrophytes. Poor hygiene, sports, wet occupation, Gym class and teenagers

Question 15

Tinea cruris

Answer 15

aka Jock itch. Causes: T. rubrum, E. floccosum. Scaling and irritation of groin, rash migrates to inner thigh, pustules uncommon. Disease of young men. Anthropophilic (ie human-human) (military and institutionalized)

Question 16

Tinea unguium

Answer 16

Nail infections, Aka – onychomycosis. Causes: T. rubrum, Candida spp (a yeast!). Nail invasion leads to thickening and discolouration (White, yellow, or brown)

Question 17

Micro diagnosis of dermaophyte disease

Answer 17

Skin/nail scraping, hair stubs. Look under direct microscopy, fungal culture

Question 18

Tinea versicolour

Answer 18

Superficial infection caused by yeast. Not related to poor hygeine, mostly cosmetic. Malassezia sp. (Lipophilic yeast that colonizes normal skin, Most adults colonized, Not a dermatophyte). Lesions on Trunk and limbs, Hypo- or hyperpigmented skin patches. Versicolor – variable changes in skin pigmentation. May be macular. Scaling is mild. Not in nail bed or hair

Question 19

Opportunistic infections of Malassezia

Answer 19

Catheter-related fungemia, Neonates, Inntavenous lipids for parenteral nutrition (High triglyceride content). More serious, not just limited to superficial

Question 20

Sporotrichosis

Answer 20

Thermally dimorphic fungus. Yeast at 37ºC and mould at 25ºC!! Not restricted geographically like ‘Endemics’. Subcutaneous infection, Deep, ulcerated skin lesions; can track up lymphatic tract; Rarely invade deeper tissues.

Question 21

DDX of tracking skin lesions

Answer 21

Nocardia (bac in dirt), Atypical mycobacteria (M. marinum - often in fish tanks), Leishmania species (in middle east)

Question 22

Pathogenesis of sporothrix

Answer 22

Thorn, barb, pine needle injury introduces Conidia (from mould phase). Localized infection (several days). Fungal spread along lymphatic channels (Chain of nodular lesions). Lesions are suppurating granulomas: Hystiocytes and giant cells (Surrounded by neutrophils, lymphocytes, and plasma cells)