Fungal Skin Infections Practice Questions

Q: A laboratory technician develops a pruritic rash and fever after handling soil samples. A skin biopsy reveals septate hyphae. What is the likely organism involved?

Trichophyton rubrum. ***Correct: Trichophyton rubrum*** - **_Trichophyton rubrum_** is the **most common dermatophyte** causing cutaneous mycoses worldwide - Demonstrates **septate hyphae** on histopathology with KOH preparation or biopsy - Primarily **anthropophilic** (human-to-human transmission), causing chronic tinea infections (tinea pedis, cruris, corporis, unguium) - Among the options given, it is the most likely dermatophyte to present with septate hyphae on skin biopsy *Incorrect: Candida albicans* - Typically appears as **budding yeast with pseudohyphae**, not true septate hyphae - Causes mucocutaneous candidiasis (thrush, intertrigo, vulvovaginitis) - Not typically associated with soil exposure or significant systemic symptoms in immunocompetent hosts *Incorrect: Aspergillus niger* - Forms **septate hyphae with acute angle branching** but primarily causes **respiratory infections** (aspergilloma, invasive pulmonary aspergillosis) - **Primary cutaneous aspergillosis** is rare, typically occurring at sites of trauma in immunocompromised patients - Would not be the first consideration for a pruritic rash in an immunocompetent individual *Incorrect: Microsporum canis* - A **zoophilic dermatophyte** acquired primarily from cats and dogs - Causes tinea capitis (especially in children) and tinea corporis - Also shows septate hyphae, but **soil exposure is not the typical epidemiological link** - animal contact is key - Less common than _T. rubrum_ in adults for cutaneous infections **Clinical Note:** While the soil exposure history might initially suggest a geophilic organism like _Microsporum gypseum_ or _Sporothrix schenckii_ (not listed), among the given options, _T. rubrum_ remains the most common dermatophyte encountered in clinical practice that presents with septate hyphae on biopsy.

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 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 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.

Q: A patient presents with a red, itchy, annular rash with central clearing on the upper arm. Identify the most likely causative organism.

Trichophyton rubrum. ***Trichophyton rubrum*** - This dermatophyte is a **common cause** of fungal skin infections, such as tinea corporis (ringworm), which presents as a red, itchy rash. - It can infect the **skin, hair, and nails**, leading to characteristic skin lesions. *Malassezia furfur* - This yeast is responsible for **tinea versicolor**, characterized by hypopigmented or hyperpigmented patches, not typically a classic red, itchy rash on the upper arm. - It primarily affects areas rich in **sebaceous glands** like the chest and back. *Candida albicans* - While it can cause skin infections (e.g., **candidiasis**), it typically presents as bright red, often weeping patches with satellite lesions in intertriginous areas (skin folds), rather than a general red, itchy rash on the upper arm. - Predisposing factors include **diabetes, obesity, and immunosuppression**. *Aspergillus niger* - This fungus is more commonly associated with **invasive pulmonary aspergillosis** in immunocompromised individuals or external otitis, rather than superficial skin infections. - It primarily affects the **respiratory tract** and, in rare cases, can cause disseminated disease.

Q: A 40-year-old male patient presents with multiple erythematous annular lesions with peripheral scales arranged predominantly on the trunk. What is the most appropriate treatment option?

Topical antifungal. ***Topical antifungal*** - The description of **erythematous annular lesions** with **peripheral scales** predominantly on the **trunk** is highly suggestive of **tinea corporis** (ringworm), a superficial fungal infection. - **Topical antifungals** (clotrimazole, miconazole, terbinafine) are first-line treatment for localized tinea corporis. - **Clinical Note**: While this patient has **multiple lesions**, which would typically favor **systemic antifungals** (oral terbinafine or itraconazole) for better coverage and compliance, topical antifungal is the most appropriate option among the choices provided. - Treatment duration: 2-4 weeks, extending 1-2 weeks beyond clinical clearance. *Topical steroids* - While steroids can reduce inflammation and erythema, they **do not treat the underlying fungal infection**. - Using topical steroids alone on a fungal infection can lead to **tinea incognito**, where the infection spreads and changes its clinical appearance, making diagnosis more difficult. - Steroids may be used **in combination** with antifungals for symptomatic relief in highly inflamed cases, but never as monotherapy. *Systemic steroids* - **Completely inappropriate** for superficial fungal infections due to immunosuppressive effects. - Would worsen the fungal infection by suppressing the immune response. - Reserved for severe inflammatory dermatoses (pemphigus, severe eczema) or autoimmune conditions, not infections. *Systemic Azathioprine* - **Azathioprine** is an **immunosuppressant** used for autoimmune conditions (lupus, pemphigus) or organ transplantation. - Completely unsuitable and potentially harmful for fungal infections, as it would suppress cell-mediated immunity and worsen the infection. - No role in infectious dermatoses.

Q: What is the primary cause of jock itch?

Trichophyton rubrum. ***Trichophyton rubrum*** - *Trichophyton rubrum* is the most common **dermatophyte** species responsible for **tinea cruris**, commonly known as jock itch. - This fungus thrives in warm, moist environments, making the groin area an ideal site for infection. *Candida albicans* - While *Candida albicans* can cause skin infections, particularly in warm and moist areas (e.g., **candidal intertrigo**), it is typically not the primary cause of classical jock itch (*tinea cruris*). - Candidal infections often present with distinct satellite lesions and a more intensely red, eroded appearance compared to dermatophyte infections. *Trichophyton tonsurans* - *Trichophyton tonsurans* is primarily known for causing **tinea capitis** (ringworm of the scalp), especially in children. - It is not a common cause of jock itch. *Malassezia furfur* - *Malassezia furfur* is a yeast species responsible for **tinea versicolor**, a superficial fungal infection characterized by discolored patches on the skin. - It is not a typical cause of jock itch, which is usually caused by dermatophytes like *Trichophyton rubrum*.

Q: Which of the following is not a clinical feature of candidal intertrigo?

Central scaling. ***Central scaling*** - **Central scaling** is **NOT a typical feature** of candidal intertrigo, making this the correct answer. - Candidal intertrigo presents with **moist, erythematous patches** in skin folds, not with prominent central scaling. - Central scaling is more characteristic of **dermatophyte infections** like **tinea corporis** (ringworm), which shows an active, scaly border with central clearing. *Satellite lesions* - **Satellite lesions** are a **pathognomonic feature** of candidal intertrigo. - These small papules and pustules surrounding the main erythematous plaque result from yeast spread beyond the primary lesion borders. - Their presence helps distinguish candidal from bacterial intertrigo. *Maceration* - **Maceration** (softening and whitening of skin due to moisture) is a **classic feature** of candidal intertrigo. - Occurs in intertriginous areas (groin, axillae, under breasts) where skin-on-skin contact traps moisture. - The moist environment favors Candida growth and contributes to the characteristic appearance. *Pustular lesions* - **Pustules** are commonly seen in candidal intertrigo, often as satellite lesions or within the main plaque. - These pustules indicate active inflammatory response to the fungal infection. - Their presence, along with erythema and satellite lesions, supports the diagnosis of candidal intertrigo.

Q: Most common pattern of onychomycosis is?

Distal and lateral subungual. ***Distal and lateral subungual*** - This pattern, often caused by dermatophytes like *Trichophyton rubrum*, accounts for the **majority of onychomycosis cases** (80-90%). - It begins at the **distal nail plate** or **lateral nail folds** and spreads proximally under the nail. *Proximal subungual* - This pattern is less common and often indicative of **immunosuppression**, such as in HIV/AIDS patients. - The infection starts at the **proximal nail fold** and spreads distally. *White superficial* - This type of onychomycosis is characterized by **white, powdery patches** on the surface of the nail plate. - It is caused by superficial fungal invasion and can be **scraped off easily**. *Total dystrophic* - This pattern represents the most **advanced and severe form** of onychomycosis, often developing from other types. - The entire nail unit is affected, leading to gross **thickening, discoloration, and crumbling** of the nail.

Q: Onychomycosis is most commonly caused by which of the following fungi?

1) Trichophyton rubrum. **1) Trichophyton rubrum** - **Trichophyton rubrum** is the most common dermatophyte causing **onychomycosis**, responsible for up to 80-90% of cases. - It typically causes **distal and lateral subungual onychomycosis**, leading to nail thickening and discoloration. *2) Trichophyton mentagrophytes* - **Trichophyton mentagrophytes** is another common dermatophyte but is less frequently implicated in onychomycosis compared to *T. rubrum*. - It is more commonly associated with **tinea pedis (athlete's foot)** and **tinea corporis (ringworm)**. *3) Epidermophyton floccosum* - **Epidermophyton floccosum** can cause various dermatophytoses, including **tinea cruris (jock itch)** and **tinea pedis**. - While it can occasionally affect nails, it is not a primary or common cause of onychomycosis. *4) Candida* - **Candida** species, particularly *Candida albicans*, can cause onychomycosis, especially in individuals with **chronic mucocutaneous candidiasis** or those whose hands are frequently wet. - However, **Candida** is a yeast and is less common as a cause of onychomycosis than dermatophytes like *Trichophyton rubrum*, which are molds.

Question 1

A laboratory technician develops a pruritic rash and fever after handling soil samples. A skin biopsy reveals septate hyphae. What is the likely organism involved?

Accepted Answer

Trichophyton rubrum

Answer

Candida albicans

Answer

Aspergillus niger

Answer

Microsporum canis

Question 2

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 3

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 4

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

Question 5

A patient presents with a red, itchy, annular rash with central clearing on the upper arm. Identify the most likely causative organism.

Accepted Answer

Trichophyton rubrum

Answer

Candida albicans

Answer

Malassezia furfur

Answer

Aspergillus niger

Question 6

A 40-year-old male patient presents with multiple erythematous annular lesions with peripheral scales arranged predominantly on the trunk. What is the most appropriate treatment option?

Accepted Answer

Topical antifungal

Answer

Systemic steroids

Answer

Systemic Azathioprine

Answer

Topical steroids

Question 7

What is the primary cause of jock itch?

Accepted Answer

Trichophyton rubrum

Answer

Candida albicans

Answer

Trichophyton tonsurans

Answer

Malassezia furfur

Question 8

Which of the following is not a clinical feature of candidal intertrigo?

Accepted Answer

Central scaling

Answer

Satellite lesions

Answer

Maceration

Answer

Pustular lesions

Question 9

Most common pattern of onychomycosis is?

Accepted Answer

Distal and lateral subungual

Answer

Proximal subungual

Answer

White superficial

Answer

Total dystrophic

Question 10

Onychomycosis is most commonly caused by which of the following fungi?

Accepted Answer

1) Trichophyton rubrum

Answer

2) Trichophyton mentagrophytes

Answer

3) Epidermophyton floccosum

Answer

4) Candida

Fungal Skin Infections — MCQs

Fungal Skin Infections — MCQs

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