Fungal Skin Infections Practice Questions

Q: Dermatophytes affect -

Keratin. ***Keratin*** - **Dermatophytes** are a group of fungi that have a unique ability to digest **keratin**, a protein found in **skin, hair, and nails**. - This characteristic allows them to colonize and thrive in these superficial tissues, causing infections like **tinea corporis** (ringworm) or **tinea pedis** (athlete's foot). *Dermis of skin* - The **dermis** is the layer of skin beneath the epidermis, rich in **collagen, elastin, blood vessels, and nerves**. - Dermatophytes do not typically invade the dermis; their infections are generally limited to the **stratum corneum** and other keratinized structures. *Stratum spongiosum* - **Stratum spongiosum** is a term sometimes used to describe an edematous (swollen) epidermis, often seen in **eczema** and **dermatitis**. - Dermatophytes do not target this specific architectural change in the epidermis but rather feed on the keratin present in the more superficial layers. *Stratum basal* - The **stratum basale** (also called stratum germinativum) is the deepest layer of the **epidermis**, responsible for cell division and producing new skin cells. - Dermatophytes primarily infect the **dead keratinized cells** of the stratum corneum rather than the metabolically active cells of the stratum basale.

Q: In Wood's lamp examination, Tinea versicolor looks like

Yellow fluorescence. ***Yellow fluorescence*** - **Tinea versicolor** (Pityriasis versicolor) caused by *Malassezia* species characteristically shows **golden-yellow to yellow-green fluorescence** under Wood's lamp examination. - This fluorescence is due to **pityriacitrin**, a fluorescent substance produced by the fungus. - This finding helps confirm the diagnosis and distinguish it from other skin conditions. *Non-fluorescent (appears dark)* - This is incorrect for Tinea versicolor, which does show fluorescence. - Conditions that appear non-fluorescent include vitiligo (appears bright white due to lack of melanin but doesn't fluoresce). *Blue-green fluorescence* - This is characteristic of **Pseudomonas aeruginosa** infections due to pyocyanin production. - Seen in wound infections, ecthyma gangrenosum, and folliculitis. - Not associated with Tinea versicolor. *Coral-red fluorescence* - This is pathognomonic for **Erythrasma**, caused by *Corynebacterium minutissimum*. - The coral-red color is due to coproporphyrin III production by the bacteria. - This bright fluorescence easily distinguishes Erythrasma from fungal infections.

Q: Tinea versicolor is caused by:

Malassezia furfur. ***Malassezia furfur*** - **Tinea versicolor** is a superficial fungal infection caused by **Malassezia species**, primarily *Malassezia furfur*. - These fungi are part of the normal skin flora but can become pathogenic under certain conditions, leading to characteristic **hypopigmented or hyperpigmented patches**. *Candida* - **Candida species** are yeasts that typically cause infections like **oral thrush**, **vaginal candidiasis**, and **diaper rash**, not tinea versicolor. - While they can cause skin infections, their clinical presentation differs significantly from the **pigmentation changes** seen in tinea versicolor. *Trichophyton rubra* - **Trichophyton rubra** is a common dermatophyte responsible for various **tinea infections** such as **tinea pedis (athlete's foot)** and **tinea unguium (onychomycosis)**. - It does not cause tinea versicolor, which is caused by a different genus of fungi. *Trichophyton mentagrophytes* - **Trichophyton mentagrophytes** is another dermatophyte that causes common **ringworm infections** like **tinea corporis** and **tinea barbae**. - Its infections are characterized by **erythematous, scaly, and pruritic lesions**, distinct from the macular lesions of tinea versicolor.

Q: An 8-year-old male presents with multiple patches of alopecia and severe pruritus. A bright blue-green fluorescence is seen on examination of the scalp with a Wood's lamp. Pathogen most likely responsible is?

Microsporum canis. ***Microsporum canis*** - This dermatophyte species is a common cause of **tinea capitis** in children, characterized by **patches of alopecia** and **pruritus**. - **Microsporum** species are known to exhibit **bright blue-green fluorescence** under a Wood's lamp due to the production of pteridine, which aids in diagnosis. *Epidermophyton floccosum* - This fungus primarily causes **tinea pedis**, **tinea cruris**, and **tinea corporis**, but rarely **tinea capitis**. - Infections caused by *Epidermophyton floccosum* typically do **not fluoresce** under a Wood's lamp. *Candida albicans* - *Candida albicans* is a yeast that causes superficial infections like **oral thrush**, **diaper rash**, and **vaginitis**, but it is **not a common cause of tinea capitis**. - *Candida* infections do **not show fluorescence** with a Wood's lamp. *Trichophyton tonsurans* - This is a common cause of **tinea capitis** (especially in the US), often presenting as **"black dot" tinea capitis** due to hair shaft breakage at the scalp surface. - Infections by *Trichophyton tonsurans* typically do **not fluoresce** under a Wood's lamp, differentiating it from *Microsporum* infections.

Q: Wood lamp is used to diagnose –

Tinea versicolor. ***Tinea versicolor*** - A Wood lamp is used to diagnose **tinea versicolor** by revealing a characteristic **yellow-green fluorescence** of the affected areas due to the production of **porphyrins** by the causative yeast, *Malassezia*. - This specific fluorescence helps differentiate **tinea versicolor** from other skin conditions that may have a similar appearance. *Erysipelas* - **Erysipelas** is a superficial bacterial skin infection, typically diagnosed based on its **clinical presentation** of a rapidly spreading, fiery red, tender, and sharply demarcated rash. - A Wood lamp is **not used** in the diagnosis of erysipelas, as it does not cause any specific fluorescence under UV light. *Pityriasis rosea* - **Pityriasis rosea** is a self-limiting inflammatory skin rash, usually diagnosed clinically by its distinctive morphology, including a **herald patch** followed by smaller, oval, fawn-colored lesions in a "Christmas tree" pattern. - A Wood lamp examination would **not show any specific fluorescence** indicative of pityriasis rosea. *Psoriasis* - **Psoriasis** is a chronic autoimmune skin condition characterized by well-demarcated, erythematous plaques covered with silvery scales, typically diagnosed through **clinical examination** and sometimes a skin biopsy. - A Wood lamp is **not a diagnostic tool** for psoriasis, as psoriatic lesions do not fluoresce in a characteristic manner under UV light.

Q: A patient presents with tinea corporis showing minimal response to terbinafine. What is the most likely cause?

Microsporum canis. ***Microsporum canis*** - *Microsporum canis* is a **zoophilic dermatophyte** (acquired from animals, especially cats and dogs) that shows **reduced susceptibility to terbinafine** compared to *Trichophyton* species. - The *Microsporum* genus has inherently **lower response rates to terbinafine** due to differences in fungal cell wall composition and drug target affinity. - Treatment of *M. canis* infections typically requires **griseofulvin or azole antifungals** (itraconazole, fluconazole) rather than terbinafine for optimal outcomes. - Minimal response to terbinafine in tinea corporis should prompt consideration of *Microsporum* infection. *Trichophyton rubrum* - *Trichophyton rubrum* is the **most common cause of tinea corporis** and shows **excellent response to terbinafine**. - This is typically the most terbinafine-susceptible dermatophyte, making treatment failure with adequate therapy highly unlikely. - Minimal response would only occur with poor compliance, incorrect diagnosis, or very rare resistance. *Trichophyton mentagrophytes* - *Trichophyton mentagrophytes* is a common cause of tinea corporis with **good susceptibility to terbinafine**. - This species typically responds well to standard terbinafine therapy. - Treatment failure would be uncommon with proper dosing and compliance. *Trichophyton tonsurans* - *Trichophyton tonsurans* primarily causes **tinea capitis** but can also cause tinea corporis. - Shows **good response to terbinafine** and would not typically present with treatment resistance. - Not the most likely explanation for terbinafine failure in tinea corporis.

Q: A 29-year-old male presents with annular plaques featuring central clearing and peripheral scaling in the groin. A KOH preparation shows hyphae. What is the most likely diagnosis?

Tinea cruris. ***Tinea cruris*** - The presence of **annular plaques** with **central clearing** and **peripheral scaling** in the groin, combined with **hyphae** on KOH preparation, is classic for **tinea cruris** (jock itch). - This dermatophyte infection is characterized by its **itchy**, often **red-brown** border, and is common in warm, moist areas. *Erythrasma* - Caused by *Corynebacterium minutissimum*, **erythrasma** typically presents as **reddish-brown patches** with fine scales in intertriginous areas. - It would show **coral-red fluorescence** under a Wood's lamp and *not* hyphae on KOH prep. *Pityriasis rosea* - Characterized by a **"herald patch"** followed by smaller, oval, salmon-pink patches with fine scales, often in a **"Christmas tree" pattern** on the trunk. - It is *not* typically found in the groin and is a viral rash, so no hyphae would be present. *Lichen planus* - Presents as **pruritic, polygonal, planar, purple papules and plaques** (the "6 P's"), often with fine white lines (Wickham's striae). - It is an inflammatory condition and would *not* show hyphae on KOH preparation.

Q: A patient presents with onychomycosis involving the toenails. What is the first-line systemic treatment for this condition?

Oral terbinafine. ***Oral terbinafine*** - **Oral terbinafine** is the **first-line systemic treatment** for onychomycosis due to its high efficacy (cure rates 70-80%), excellent safety profile, and relatively short treatment duration (12-16 weeks for toenails) - Works by inhibiting **squalene epoxidase**, an enzyme essential for fungal ergosterol synthesis, leading to **fungicidal action** - Superior to other oral antifungals in terms of mycological and clinical cure rates *Topical terbinafine* - Not effective for **toenail onychomycosis** due to poor penetration through the nail plate to reach the infection site - Reserved for **cutaneous fungal infections** like tinea pedis (athlete's foot) or very mild superficial nail involvement - Cannot achieve adequate drug concentration in the nail bed for established onychomycosis *Oral griseofulvin* - Older antifungal agent largely replaced by terbinafine and itraconazole for onychomycosis - **Fungistatic** rather than fungicidal, requiring **longer treatment duration** (12-18 months for toenails) with **lower cure rates** (30-40%) - Higher relapse rates and requires prolonged therapy make it a second-line option *Oral ketoconazole* - **Not recommended** for onychomycosis due to significant risk of **hepatotoxicity** and drug interactions - Reserved for severe systemic fungal infections when other therapies fail or are not tolerated - Risk-benefit profile unfavorable for a condition like onychomycosis that has safer alternatives

Q: A 30-year-old woman presents with an itchy, annular lesion featuring central clearing and raised, scaly borders on her right arm. What is the most likely diagnosis?

Tinea corporis. ***Tinea corporis*** - This presentation, characterized by an **itchy**, **annular lesion** with **central clearing** and **raised, scaly borders**, is classic for **tinea corporis**, also known as ringworm. - It is a **dermatophyte infection** that typically grows outwards in a centrifugal pattern, leading to the characteristic ring-like appearance. *Pityriasis rosea* - This condition often starts with a single large "**herald patch**" followed by smaller, oval lesions in a "Christmas tree" distribution on the trunk. - It does not typically present with the same prominent annular shape, central clearing, and raised scaly borders as described. *Nummular eczema* - Characterized by **coin-shaped (nummular)**, intensely itchy, erythematous, and sometimes weeping or crusted plaques. - It does not typically feature central clearing or raised, scaly borders but rather presents as well-demarcated patches of eczema. *Granuloma annulare* - Typically presents as **smooth, firm, flesh-colored to erythematous papules** that coalesce into **annular rings** without scaling or significant itching. - It lacks the characteristic **scaly borders** and itchiness seen in this patient's presentation.

Q: A 30-year-old male presents with a scaly, annular rash on his groin that has spread to the thighs. What is the most likely causative organism?

Trichophyton rubrum. ***Trichophyton rubrum*** - This dermatophyte is a very common cause of **tinea cruris** (jock itch), which presents as a **scaly, annular rash** in the groin and thigh regions. - Its ability to infect keratinized tissues makes it a frequent culprit in superficial fungal infections of the skin. *Candida albicans* - While *Candida albicans* can cause skin infections, particularly in moist areas (intertrigo), its lesions are typically **erythematous patches with satellite lesions**, rather than annular and scaly. - Genital candidiasis more commonly presents as pruritic papules and pustules or erosions, differing from the described rash. *Malassezia furfur* - This yeast is responsible for **tinea versicolor**, which typically presents as discolored, **faintly scaly patches** on the trunk and upper extremities, not typically in the groin as an annular rash. - The characteristic appearance and location are different from the described case. *Epidermophyton floccosum* - *Epidermophyton floccosum* is a dermatophyte that can cause tinea cruris and tinea pedis, presenting with **scaly patches and occasional vesiculation**. - While it causes a similar presentation to *Trichophyton rubrum*, *Trichophyton rubrum* is statistically a more common cause of tinea cruris.

Question 1

Dermatophytes affect -

Accepted Answer

Keratin

Answer

Dermis of skin

Answer

Stratum spongiosum

Answer

Stratum basale

Question 2

In Wood's lamp examination, Tinea versicolor looks like

Accepted Answer

Yellow fluorescence

Answer

Non-fluorescent (appears dark)

Answer

Blue-green fluorescence

Answer

Coral-red fluorescence

Question 3

Tinea versicolor is caused by:

Accepted Answer

Malassezia furfur

Answer

Candida

Answer

Trichophyton rubra

Answer

Trichophyton mentagrophytes

Question 4

An 8-year-old male presents with multiple patches of alopecia and severe pruritus. A bright blue-green fluorescence is seen on examination of the scalp with a Wood's lamp. Pathogen most likely responsible is?

Accepted Answer

Microsporum canis

Answer

Epidermophyton floccosum

Answer

Candida albicans

Answer

Trichophyton tonsurans

Question 5

Wood lamp is used to diagnose –

Accepted Answer

Tinea versicolor

Answer

Erysipelas

Answer

Pityriasis rosea

Answer

Psoriasis

Question 6

A patient presents with tinea corporis showing minimal response to terbinafine. What is the most likely cause?

Accepted Answer

Microsporum canis

Answer

Trichophyton mentagrophytes

Answer

Trichophyton tonsurans

Answer

Trichophyton rubrum

Question 7

A 29-year-old male presents with annular plaques featuring central clearing and peripheral scaling in the groin. A KOH preparation shows hyphae. What is the most likely diagnosis?

Accepted Answer

Tinea cruris

Answer

Erythrasma

Answer

Pityriasis rosea

Answer

Lichen planus

Question 8

A patient presents with onychomycosis involving the toenails. What is the first-line systemic treatment for this condition?

Accepted Answer

Oral terbinafine

Answer

Topical terbinafine

Answer

Oral griseofulvin

Answer

Oral ketoconazole

Question 9

A 30-year-old woman presents with an itchy, annular lesion featuring central clearing and raised, scaly borders on her right arm. What is the most likely diagnosis?

Accepted Answer

Tinea corporis

Answer

Pityriasis rosea

Answer

Nummular eczema

Answer

Granuloma annulare

Question 10

A 30-year-old male presents with a scaly, annular rash on his groin that has spread to the thighs. What is the most likely causative organism?

Accepted Answer

Trichophyton rubrum

Answer

Candida albicans

Answer

Malassezia furfur

Answer

Epidermophyton floccosum

Fungal Skin Infections — MCQs

Fungal Skin Infections — MCQs

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