Basic mycology concepts superficial, subcutaneous and cutaneous mycoses

Dermatophytes general characteristics

Fungi that infect keratinized tissues (skin, hair, nails) using keratinase to degrade keratin

Dermatophyte growth temperature limitation

Cannot grow well at 37°C, so infections remain superficial

Dermatophyte infection response

Causes inflammation and immune response due to metabolic products

Dermatophyte transmission

Spread by direct contact with humans, animals, or soil

Dermatophyte infection process

Spores attach to keratinized tissue, germinate, invade stratum corneum, and spread outward

Ringworm lesion appearance

Circular, erythematous lesion with raised borders and central clearing

Dermatophyte genera

Microsporum, Trichophyton, Epidermophyton

Microsporum characteristics

Thick-walled, spindle-shaped macroconidia; infect skin and hair

Trichophyton characteristics

Thin-walled, pencil-shaped macroconidia; infect skin, hair, and nails

Epidermophyton characteristics

Club-shaped macroconidia; infect skin and nails but not hair

Superficial mycoses definition

Infections limited to outermost keratin layer with minimal inflammation

Malassezia furfur characteristics

Lipophilic yeast, part of normal flora, causes superficial infections

Pityriasis versicolor

Hypo/hyperpigmented macules on chest and back caused by Malassezia

Malassezia microscopy appearance

"Spaghetti and meatballs" (hyphae + yeast cells)

Wood's lamp finding in Malassezia

Yellow or copper-orange fluorescence

Trichosporon beigelii disease

White piedra affecting hair shaft

White piedra appearance

Soft, white nodules on hair

Piedraia hortae disease

Black piedra affecting hair

Black piedra appearance

Hard, dark nodules on hair shaft

Hortaea werneckii disease

Tinea nigra causing dark macules on palms/soles

Superficial mycoses diagnosis

KOH prep, Wood's lamp, and microscopy

Dermatophyte classification by reservoir

Anthropophilic (human), zoophilic (animal), geophilic (soil)

Tinea pedis

Athlete's foot affecting toes and feet

Tinea capitis

Infection of scalp and hair

Tinea corporis

Ringworm of body skin

Tinea cruris

Infection of groin area

Tinea unguium

Fungal infection of nails (onychomycosis)

Ectothrix infection

Arthroconidia on outside of hair shaft; fluoresces under Wood's lamp

Endothrix infection

Arthroconidia inside hair shaft; no fluorescence

Favus

Severe inflammatory scalp infection with crust formation

Samples for superficial/cutaneous mycoses

Skin scrapings, hair, nail clippings

KOH test purpose

Dissolves keratin to visualize fungal elements

Culture media for dermatophytes

Sabouraud dextrose agar and dermatophyte test medium

Dermatophyte test medium function

Selective and differential medium that changes color with fungal growth

Subcutaneous mycoses general characteristics

Chronic infections of dermis and subcutaneous tissue caused by environmental fungi

Source of subcutaneous mycoses

Soil and decaying vegetation (saprophytes)

Mode of transmission (subcutaneous)

Traumatic implantation (splinters, thorns, wounds)

Common sites of subcutaneous infections

Feet, legs, hands, arms

Subcutaneous infection progression

Slow, chronic growth with nodules and possible spread along lymphatics

Sporotrichosis cause

Sporothrix schenckii

Sporotrichosis nickname

"Rose gardener's disease"

Sporotrichosis infection process

Entry through trauma → nodules → spread along lymphatic vessels

Sporotrichosis lesion type

Nodular, ulcerative lesions along lymphatics

Sporotrichosis morphology

Dimorphic (mold at 25°C, yeast at 37°C)

Sporotrichosis microscopic appearance

Cigar-shaped yeast cells

Chromoblastomycosis cause

Dematiaceous (melanin-producing) fungi

Chromoblastomycosis lesion

Verrucous, wart-like lesions

Chromoblastomycosis hallmark cells

Sclerotic (Medlar) bodies ("copper pennies")

Mycetoma definition

Chronic infection with swelling, sinus tracts, and discharge of granules

Mycetoma common location

Foot ("Madura foot")

Eumycetoma vs actinomycetoma

Fungal vs bacterial cause; distinguished by culture and granule appearance

Mycetoma granules

Colored grains in pus containing fungal hyphae

Subcutaneous mycoses samples

Biopsy, pus, tissue, synovial fluid

Subcutaneous diagnosis methods

KOH, histopathology (PAS, GMS), culture

Culture conditions for Sporothrix

SDA at 25°C (mold) and BHIA at 37°C (yeast conversion)

Chromoblastomycosis diagnosis

KOH or biopsy showing pigmented sclerotic bodies

Mycetoma diagnosis

Identification of granules in pus and culture

Antifungal drugs for dermatophytes

Azoles and terbinafine

Antifungal drugs for superficial infections

Topical azoles (clotrimazole, ketoconazole)

Antifungal treatment for sporotrichosis

Itraconazole or potassium iodide

Antifungal treatment for chromoblastomycosis

Itraconazole or terbinafine

Antifungal treatment for mycetoma

Long-term antifungals or surgery