Fungal Skin Infections Practice Questions

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: 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 60-year-old male with a history of diabetes presents with painful urination and white patches on the glans penis. Which condition is most likely responsible?

Candidiasis. ***Candidiasis*** - **Painful urination** and **white patches on the glans penis** in a diabetic patient are classic symptoms of **candidal balanitis**. - Patients with **diabetes mellitus** are at higher risk for fungal infections due to immunocompromise and elevated glucose levels. *Herpes simplex virus* - Characterized by **painful vesicles** that rupture to form ulcers, not typically white patches [1]. - While it can cause painful urination due to urethritis, the appearance of the lesions is different [1]. *Human papillomavirus* - Causes **genital warts**, which are typically flesh-colored, cauliflower-like growths, not white patches or painful urination. - These warts are usually asymptomatic or cause mild itching. *Syphilis* - Presents initially as a **painless chancre** (a firm, round, solitary ulcer) at the site of infection [1]. - Later stages involve rash, fever, and other systemic symptoms, which do not match this presentation.

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.

Q: A 25-year-old female presents with hypopigmented, scaly patches on the upper back and chest. KOH preparation shows a spaghetti and meatball appearance. What is the diagnosis?

Pityriasis versicolor. ***Pityriasis versicolor*** - This diagnosis is indicated by **hypopigmented, scaly patches** on the trunk and the classic "spaghetti and meatballs" appearance on **KOH preparation**, which represents **hyphae and spores** of *Malassezia furfur*. - *Malassezia furfur* is a **dimorphic yeast** that is part of the normal skin flora but can become pathogenic under certain conditions like heat and humidity. *Vitiligo* - Characterized by **well-demarcated, depigmented patches** due to melanocyte destruction; these patches are typically **not scaly**. - **KOH preparation** would show no fungal elements as it is an autoimmune condition, not a fungal infection. *Tinea corporis* - This fungal infection usually presents as **annular (ring-shaped) lesions** with an erythematous, scaly border and central clearing. - While it is a dermatophyte infection, the **KOH preparation** would show only hyphae, not the characteristic "spaghetti and meatballs" pattern of *Malassezia*. *Lichen sclerosus* - This is a chronic inflammatory skin condition that primarily affects the **genital and perianal areas**, causing thin, white, wrinkled patches. - It would not typically present on the upper back and chest, nor would **KOH preparation** reveal fungal elements.

Q: A 45-year-old man presents with thickened, discolored nails and onycholysis. What is the most likely diagnosis?

Onychomycosis. ***Onychomycosis*** - This is a common fungal infection of the nails, typically presenting as **thickened, discolored (yellow, brown, or white) nails** and **onycholysis** (separation of the nail plate from the nail bed). - Risk factors include older age, diabetes, immunosuppression, and trauma to the nails. *Psoriasis* - While psoriasis can cause nail changes such as **pitting, onycholysis, subungual hyperkeratosis**, and discoloration, the primary symptoms are usually skin lesions. - The description of solely thickened and discolored nails with onycholysis is less specific for psoriasis without accompanying skin findings. *Lichen planus* - Nail lichen planus often presents with **longitudinal ridging, thinning, and pterygium formation** (scarring that fuses the nail fold to the nail bed). - Gross thickening and discoloration as the primary features are less typical for lichen planus of the nails. *Eczema* - Nail changes due to eczema usually involve the **nail folds (paronychia)**, leading to secondary nail plate abnormalities like **roughness, pitting, or ridging**. - Direct thickening and discoloration of the nail plate with onycholysis, without significant involvement of the surrounding skin, is not the most common presentation of nail eczema.

Q: A 6-year-old boy presents with multiple annular scaly plaques with central clearing on his trunk. A KOH test is positive. What is the most likely diagnosis?

Tinea corporis. ***Tinea corporis*** - The combination of **annular scaly plaques** with **central clearing** and a **positive KOH test** is classic for tinea corporis, a fungal infection. - The disease is also known as **ringworm** and is caused by dermatophytes which thrive in warm, moist environments. *Psoriasis* - Characterized by well-demarcated, **erythematous plaques** with silvery scales, typically on extensor surfaces like elbows and knees. - **KOH test** is negative as it is not a fungal infection. *Pityriasis rosea* - Presents with an initial **"herald patch"**, followed by smaller, oval, scaly patches oriented along **skin cleavage lines** (Christmas tree pattern). - A **KOH test** would be negative as it is believed to be viral in origin. *Eczema* - Typically presents as **pruritic, erythematous patches** that can be dry, crusted, or lichenified, but usually lack the distinct annular shape and central clearing characteristic of tinea corporis. - **KOH test** would be negative as it is an inflammatory skin condition, not a fungal infection.

Question 1

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 2

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 3

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 4

A 60-year-old male with a history of diabetes presents with painful urination and white patches on the glans penis. Which condition is most likely responsible?

Accepted Answer

Candidiasis

Answer

Herpes simplex virus

Answer

Human papillomavirus

Answer

Syphilis

Question 5

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 6

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 7

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

Question 8

A 25-year-old female presents with hypopigmented, scaly patches on the upper back and chest. KOH preparation shows a spaghetti and meatball appearance. What is the diagnosis?

Accepted Answer

Pityriasis versicolor

Answer

Vitiligo

Answer

Tinea corporis

Answer

Lichen sclerosus

Question 9

A 45-year-old man presents with thickened, discolored nails and onycholysis. What is the most likely diagnosis?

Accepted Answer

Onychomycosis

Answer

Psoriasis

Answer

Lichen planus

Answer

Eczema

Question 10

A 6-year-old boy presents with multiple annular scaly plaques with central clearing on his trunk. A KOH test is positive. What is the most likely diagnosis?

Accepted Answer

Tinea corporis

Answer

Psoriasis

Answer

Pityriasis rosea

Answer

Eczema

Fungal Skin Infections — MCQs

Fungal Skin Infections — MCQs

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