CLASSIFICATION OF MYCOSES Type Depth of Infection Host Response Examples — — —
MYCOSES — SUPERFICIAL, CUTANEOUS, SUBCUTANEOUS, SYSTEMIC & OPPORTUNISTIC --- CLASSIFICATION OF MYCOSES Type Depth of Infection Host Response Examples --- --- --- --- Superficial Outermost skin layer only None Pityriasis versicolor, Tinea nigra Cutaneous Skin, hair, nails (keratinized tissue) Cellular immune response Dermatophytoses (ringworm) Subcutaneous Skin + subcutaneous tissue Granulomatous Mycetoma, Sporotrichosis Systemic Deep organs Variable Histoplasmosis, Blastomycosis Opportunistic Any site in immunocompromised host Variable Candidiasis, Cryptococcosis, Aspergillosis --- A. SUPERFICIAL MYCOSES Infection restricted to the outermost horny layer of skin, hair and nails. No cellular response, no pathological changes, purely cosmetic. No discomfort to the patient. Predisposing factors: humidity, immunosuppression, poor hygiene --- 1. Pityriasis Versicolor (Tinea Versicolor) Also called: Dermatomycosis furfuracea, Tinea flava Causative agents: Malassezia globosa and Malassezia furfur These are lipophilic yeasts (feed on skin oils/lipids) Part of normal skin flora — only become pathogenic under warm, humid conditions Clinical features: Hypopigmented or hyperpigmented skin patches Usually on trunk, back, underarm Occasionally on face Diagnosis: KOH mount of skin scales → "spaghetti and meatballs" appearance (short curved septate hyphae + budding yeast cells) Under Wood's lamp → fluoresces yellow Culture media must be supplemented with fatty acids (lipophilic organism) Treatment: Topical imidazole --- 2. Tinea Nigra Dark, non-scaly patches on palms Caused by Hortaea werneckii (dematiaceous/dark fungus) Diagnosis: KOH mount showing dark septate hyphae Treatment: Topical azoles or salicylic acid 3. Black Piedra Hard dark nodules on hair shafts Caused by Piedraia hortae Treatment: Shaving affected hair + topical azoles 4. White Piedra Soft white/cream nodules on hair shafts Caused by Trichosporon spp. Treatment: Shaving affected hair + topical azoles --- B. CUTANEOUS MYCOSES (DERMATOPHYTOSES) Involves skin, nails and hair infections. Caused by fungi that invade superficial keratinized tissue . Clinical manifestation = ringworm/tinea . Evoke cellular immune response and may cause hypersensitivity (id reaction). --- Causative Agents — Dermatophytes Dermatophytes are keratinophilic (keratin-loving). They use keratin as nitrogen source and produce keratinases (extracellular enzymes that hydrolyze keratin). Three genera: Genus Sites Infected Age Group Macroconidia Microconidia --- --- --- --- --- Microsporum Hair, skin; rarely nails Children mainly Numerous, thick-walled, rough, spindle-shaped Rare Trichophyton Hair, skin AND nails Both children & adults Rare, thin-walled, smooth, pencil-shaped Abundant Epidermophyton Skin, nails; rarely hair Adults mainly Numerous, smooth, club-shaped in clusters Absent --- Ecology — Sources of Dermatophytes Type Source Transmission Examples --- --- --- --- Anthropophilic Humans only Man to man by close contact or contaminated objects (comb, hat) T. rubrum , E. floccosum , M. audouinii Zoophilic Animals Close contact with animals (cats, dogs, cows) or contaminated products M. canis , M. nanum , T. verrucosum Geophilic Soil Direct exposure to soil M. gypseum --- Clinical Forms of Dermatophytosis Spread peripherally from foci to produce ring-like lesions — hence "ringworm" or "tinea." Named by site affected: Tinea Pedis (Athlete's Foot) Most prevalent of all dermatophytoses Caused by T. rubrum , T. mentagrophytes , E. floccosum (anthropophilic) Starts itchy between toes → small vesicles rupture → skin macerated, peels, cracks Prone to secondary bacterial infection → lymphangitis and lymphadenitis Tinea Corporis (Ringworm of the Body) Also called Tinea circinata, Tinea glabrosa Infection of glabrous (hairless) skin Annular lesions with active border — may be pustular or vesicular Caused by T. rubrum , T. mentagrophytes , M. canis , E. floccosum Often from a pet or another body site Usually resolves in several months Treatment: topical ketoconazole, miconazole Tinea Capitis — scalp and hair; mainly children Tinea Barbae — beard area Tinea Cruris (Jock Itch) — groin area Tinea Unguium (Onychomycosis) — nails Tinea Manum — hands Tinea Faciei — face Tinea Imbricata — concentric ring pattern; tropical regions --- Laboratory Diagnosis of Dermatophytoses Specimen collection: Skin scales, nail scrapings, hair clippings Scrape outwards from the edge of lesion with scalpel Stop antifungals one week before nail specimen collection 1. Wood's Lamp (Macroscopic) Infected hair/scalp lesions fluoresce under UV light Microsporum spp. fluoresce bright green Trichophyton spp. generally do NOT fluoresce 2. Direct Microscopy — KOH Mount (10–20% KOH) KOH digests protein debris and dissolves keratin, leaving fungal elements visible DMSO can be added to hasten clearing In skin/nails → branching hyphae or chains of arthrospores seen In hair → hyphae or spores detected: Ectothrix — spores OUTSIDE the hair s