5 Dermatomycoses Flashcards by Hannah Frank

Which species are considered cutaneous fungi?

Malassezia furfur

Hortaea werneckii

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How are dermatophytes different from cutaneous fungi?

Pathogenic fungi
Require keratin for growth (hair, nails, skin)
Do not infect mucosal surfaces
Secrete keratinase (allows for inhabiting keratinized regions of the body)

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Important genera of dermatophytes

Epidermophyton
Microsporum
Trichophyton

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What makes dermatophytes morphologically identifiable?

Hyphae and arthoconidia can be visualized in dead keratinized tissue

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How do you culture dermatophytes for diagnosis?

If onychomycosis, culture material under nails

Sabouraud agar at room temp for 1-3 weeks

DERMATOPHYTES TEST MEDIUM (DTM) allows for early detection

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How does Dermatophytes test medium work?

Selective (cyclohexamide and abx) and differential (color change based on fermentation of sugars)

Dermatophytes utilize nitrogenous compounds preferentially over carbs

Change in pH (alkaline) —> red color change

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What is the infective stage of dermatophyte?

Arthroconidium - can be visualized microscopically in 10% KOH wet mount

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How is the morphology of Trichophytin different?

Galactomannan peptide

Crude antigen of dermatophytes
• CHO component-intermediate response
• Peptide component-delayed response

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How does 10% KOH work?

Digests human tissue, leaves fungal components intact

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What classification of dermatophyte:

Animal pathogens that may be transmitted to people

Zoophilic

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What classification of dermatophyte:

Human transmission

Antrophophilic

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What classification of dermatophyte:

Transmitted through soil to people

Geophilic

Usually invade non-viable keratinized tissue

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What are the favored habitats for dermatophytes?

Moist areas of the body

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What parts of the world will you find dermatophyte infections?

Worldwide, but most prevalent in the tropics

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What are arthrospores?

Fragment hyphal elements in hair, nails, outer skin

Also see infections by microconidia, macroconidia, and sexual spores

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How do dermatophyte infections typically present in people?

Lesions are inflamed at edges, with a central clearing zone

Hair loss with itching, but not debilitating

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Predisposing factors for dermatophytosis?

Nail trauma, HIV, DM, immunosuppressive meds

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Risk factors for dermatophytosis

Communal bathing facilities, immunocompromised status, Cushing syndrome (increased cortisol interferes with inflammation) and some contact sports (ie wrestling)

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Disseminated disease from dermatophytes is possible in …

HIV patients

Typically T. mentagrophytes and M. canis

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What are the different fungal elements you might see on KOH?

Arthrospores (arthroconidia) - the infectious element, survives in environment

Microconidia

Macroconidia (usually multicellular)

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What is Dermatophytid?

“Id reaction”

Allergic dermal reaction to fungal antigens occurring in areas devoid of organisms

Most common in Tinea pedis

Sometimes a result of excessive treatments or pruritis

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How is dermatophytid treated?

As an allergy

Corticosteroids (systemic or topical)
Wet compresses
Antihistamines (systemic or topical)

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How do you treat dermatophyte infections?

Antifungal agents
• Azole creams (miconazole, clotrimazole)
• Systemic antifungals (terbinafine, itraconazole)

Laser and removal of the infected tissue (ie nail)

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How do azoles and terbinafine work in treating fungal infections?

Interfere with sterol synthesis in the cytoplasmic membrane of the fungus

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Control measures to prevent dermatophyte infection

Good personal hygiene Keep skin as dry as possible Spores are shed on skin and hair (regular housecleaning important) Spores are generally susceptible to common disinfectants, chlorine bleach, and detergents

What are the clinically relevant species of Trichophytons?

T. tonsurans T. rubrum T. mentagrophytes****

How are trichophytons distinguishable from other dermatophytes?

Not often fluorescent All make pencil-shaped macroconidia with thin walls Produce hyphae (spindle shaped), microconidia, macroconidia

Most common of cause of tinea capitis

Microsporum canis Can also be due to T. mentagrophytes or T. tonsurans

What makes microsporum species identifiable?

Fluorescence when examined with a wood’s lamp Produce hyphae, microconidia, macroconidia (large, spindle shaped; multicellular; thick walled)

Name the area affected: Tinea barbae

Beard

Name the area affected: Tinea capitis

Scalp

Name the area affected: Tinea corporis

Arm, leg, torso

Name the area affected: Tinea cruris

Groin

Name the area affected: Tinea manus

Hand

Name the area affected: Tinea pedis

Foot

Name the area affected: Tinea unguium

Nails

Tinea capitis is mostly a ________ disease

Childhood Involves the hair and scalp

Endothrix ringworm infections are usually from...

Trichophyton

Ectothrix ringworm infections are usually from...

Microsporum

Black dot ringworm gets its appearance from...

Broken hair follicles Infected hair can break off leading to alopecia Intense inflammation, scarring and permanent alopecia can occur

Tinea capitis can be acquired from...

Kittens and puppies (zoonotic)

What is a good systemic treatment for tinea capitis?

Griseofulvin

Agents that cause tinea pedis?

E. floccosum, T. mentagrophytes, T. rubrum

Tinea pedis is characterized by ...

Itching, peeling, and cracking of the skin, usually toe webs and soles

Most prevalent of all dermatophytoses

Tinea pedis

Predisposing factors for tinea corporis and tinea cruris?

Diabetes, obesity, excessive perspiration Transmission can be either direct or indirect (contaminated objects like towels, clothing, bed linens)

What gender is more commonly affected by tinea corporis/cruris?

Men

Tinea unguium is another name for ...

Onychomycosis (ringworm of the nail) Finger and toenails become discolored and thick May be mistaken for psoriasis

Tinea unguium is commonly caused by...

E. floccosum, T. mentgrophytes, T. rubrum

Tinea unguium usually has ______ involvement as well

Fungal (candida)

Preferred treatment for tinea unguium

Systemic antifungals better than topical agents

Most commonly encountered opportunistic mycoses worldwide

Candidiasis Normal flora of the skin, mucous membranes that colonize mucosal surfaces soon after birth

Underlying causes of candidiasis

Absence of competing normal flora Introduction to abnormal site Pathologic change in microenvironment Inborn or acquired immune defect Use of broad-spectrum abx

What factor helps Candida albicans adhere the most?

Germ tube more adhesive than yeast cell Not many virulence factors other than that

How is candida diagnosed?

Direct microscopic exam —> gram stained samples show large G(+) cells Will also see yeast cells, pseudohyphae, and true hyphae

What kind of culture can you do for candida?

Chromagar (will show hyphae and pseudohyphae in addition to germ tubes)

Why is serology difficult for candida?

It’s normal flora Many have had prior exposure Low tigers of antibody

How do you treat candida?

Topical cream (miconazole) or oral fluconazole

Tinea versicolor is caused by...

Malassezia furfur (cutaneous fungi)

What does Malassezia furfur look like?

Microscopically: short, unbranched hyphae and somewhat spherical cells (SPAGHETTI AND MEATBALLS)***

Malassezia furfur has what growth factor?

Lipophilic Requires fat to grow —> likes sebaceous glands

Who is more commonly affected by tinea versicolor?

Young adults Occurs worldwide but more common in the tropics

What does a tinea versicolor infection look like?

Lesions occur as a macular patch of depigmented or hyperpigmented skin that may enlarge Can lead to dandruff as well

Diagnosis of tinea versicolor is via...

Microscopic exam of skin scrapings in KOH

Treatment for tinea versicolor

Topical selenium sulfide, miconazole

Tinea nigra is a cutaneous fungi caused by ...

Hortaea werneckii

What distinguishes Hortaea werneckii from other species?

Dimorphic species (can grow as yeast and/or mold) Can grow in saturated salt solutions (extreme halotolerance)

How does tinea nigra present?

Brownish lesion (fungus produces melanin)

How do you diagnosis tinea nigra?

KOH and microscopy

Treatment for tinea nigra?

Tincture of iodine or azole creams

5 Dermatomycoses Flashcards

(70 cards)