Fungal Skin Infections — MCQs

A patient self-diagnosed with athlete's foot (tinea pedis) used an over-the-counter product. While the condition improved, it did not fully resolve. A dermatologist was consulted, and a skin scraping was sent for fungal culture. The culture yielded a slow-growing colony that produced a few small microconidia. This finding is consistent with the isolation of a dermatophyte from which genera?

Q40Medium

A farmer from the sub-Himalayan region presents with multiple leg ulcers. The most likely causative agent is?

Fungal Skin Infections Indian Medical PG Practice Questions and MCQs

Question 31: Dermatophytids are defined as:

A. Fungal hyphae in the skin.
B. Vegetative fungal cells within keratinised tissue.
C. Cutaneous lesions secondary to a hypersensitivity reaction to fungal antigens. (Correct Answer)
D. Dead fungal tissue.

Explanation: **Explanation:** **Dermatophytids** (commonly known as **'id' reactions**) are sterile cutaneous eruptions that occur as a result of a delayed-type hypersensitivity reaction (Type IV) to fungal antigens. These antigens circulate from a primary site of infection (usually an inflammatory dermatophytosis like Tinea pedis or Kerion) and manifest as skin lesions at a distant site. **Why Option C is correct:** The hallmark of an 'id' reaction is that the lesions are **sterile**; they do not contain any fungal elements. The reaction is triggered by the body’s immune response to fungal proteins or toxins released into the bloodstream. The most common presentation is a vesicular eruption on the sides of the fingers and palms in patients with an inflammatory fungal infection elsewhere. **Why other options are incorrect:** * **Options A & B:** These describe the actual presence of the pathogen (hyphae or vegetative cells) within the tissue. In dermatophytids, a KOH mount or fungal culture from the 'id' lesion will always be **negative**. * **Option D:** Dermatophytids are an active immunological phenomenon, not merely a collection of dead fungal debris. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnostic Criteria:** To diagnose an 'id' reaction, there must be a proven fungal infection at a distant site, the 'id' lesion must be sterile, and the eruption should resolve spontaneously once the primary fungal infection is treated. * **Commonest Site:** The hands (pompholyx-like vesicles) are the most frequent site for dermatophytids secondary to Tinea pedis. * **Treatment:** Focus on treating the **primary** fungal site. Topical steroids may be used for symptomatic relief of the 'id' reaction itself.

Question 32: Sclerotic bodies 3-15µ in size, multiseptate, chestnut brown colour are characteristic findings in which of the following conditions?

A. Rhinosporidiosis
B. Chromoblastomycosis (Correct Answer)
C. Phaeohyphomycosis
D. Histoplasmosis

Explanation: ### Explanation **Chromoblastomycosis** is a chronic localized fungal infection of the subcutaneous tissue caused by dematiaceous (pigmented) fungi like *Fonsecaea pedrosoi*. The pathognomonic feature of this condition is the presence of **Sclerotic bodies** (also known as **Medlar bodies** or **Muriform bodies**). These are thick-walled, multiseptate, chestnut-brown structures (3–15 µm) that resemble "copper pennies." They represent an intermediate vegetative stage where the fungus divides by internal septation rather than budding. #### Why the other options are incorrect: * **Rhinosporidiosis:** Caused by *Rhinosporidium seeberi*, it is characterized by massive **sporangia** (up to 300 µm) containing thousands of tiny **endospores**. It typically presents as friable, strawberry-like nasal polyps. * **Phaeohyphomycosis:** While also caused by pigmented fungi, it presents as **pigmented hyphae** or yeast-like cells in tissue, but **never** forms sclerotic bodies. * **Histoplasmosis:** Caused by *Histoplasma capsulatum*, it presents as small (2–4 µm) **intracellular yeast** cells with a characteristic narrow-based bud and a pseudo-capsule, typically found within macrophages. #### NEET-PG High-Yield Pearls: * **Clinical Presentation:** Usually occurs in barefoot agricultural workers following trauma (e.g., thorn prick). Presents as a "verrucous (warty) plaque" or cauliflower-like growth, most commonly on the lower limbs. * **Diagnosis:** KOH mount or histopathology showing "Copper penny" bodies. * **Transepidermal Elimination:** Sclerotic bodies are often eliminated through the epidermis, which can be seen on biopsy. * **Treatment:** Itraconazole is the drug of choice; surgical excision or cryotherapy may be used for small lesions.

Question 33: Which fungus affects hair?

A. Microsporum
B. Trichophyton
C. Both of the above (Correct Answer)
D. None of the above

Explanation: **Explanation:** The fungi that infect keratinized tissues like skin, hair, and nails are collectively known as **Dermatophytes**. These belong to three main genera: *Trichophyton*, *Microsporum*, and *Epidermophyton*. 1. **Why the answer is "Both of the above":** * **Trichophyton:** This genus is capable of infecting **skin, hair, and nails**. It is the most common cause of Tinea capitis (scalp hair infection) worldwide. * **Microsporum:** This genus infects **skin and hair** but rarely involves the nails. It is a frequent cause of ectothrix hair infections, particularly in children. Since both genera have the enzymatic capability (keratinases) to invade the hair shaft, option C is correct. 2. **Analysis of Options:** * **Option A & B:** While both are correct individually, they are incomplete on their own because both genera are known to cause hair infections (Tinea capitis). * **Option D:** Incorrect, as dermatophytes are the primary pathogens for hair infections. **High-Yield Clinical Pearls for NEET-PG:** * **The "Rule of Three":** * *Trichophyton:* Skin, Hair, Nails (All three). * *Microsporum:* Skin, Hair (No nails). * *Epidermophyton:* Skin, Nails (No hair - **"Epidermophyton excludes hair"**). * **Wood’s Lamp Examination:** *Microsporum* species typically show a bright greenish fluorescence, whereas most *Trichophyton* species (except *T. schoenleinii*) do not fluoresce. * **Endothrix vs. Ectothrix:** *Trichophyton* can cause both, but *Microsporum* is characteristically associated with ectothrix infections (spores outside the hair shaft).

Question 34: Which of the following tests is likely to be helpful in diagnosing a patient presenting with an itchy annular plaque on the face?

A. Gram's stain
B. Tissue smear
C. Wood's lamp examination
D. Potassium hydroxide mount (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Potassium hydroxide (KOH) mount** The clinical presentation of an **itchy annular (ring-shaped) plaque** with central clearing and an active scaling border is a classic description of **Tinea faciei** (Dermatophytosis of the face). **Why KOH Mount is the Gold Standard:** Dermatophytes (such as *Trichophyton*, *Microsporum*, and *Epidermophyton*) invade the keratinized layers of the skin. A KOH mount is the initial investigation of choice because the alkali (10-20% KOH) dissolves the keratinocytes, allowing for the clear visualization of characteristic **translucent, branching, septate hyphae** under a microscope. **Analysis of Incorrect Options:** * **A. Gram's stain:** Primarily used for identifying bacterial infections (Gram-positive vs. Gram-negative). It is not used for diagnosing dermatophytosis. * **B. Tissue smear:** Usually refers to a Tzanck smear (used for Herpes Simplex/Varicella) or a slit-skin smear (used for Leprosy/Leishmaniasis). It does not demonstrate fungal hyphae effectively. * **C. Wood's lamp examination:** While useful for *Tinea capitis* (showing green fluorescence in *Microsporum* species) or *Erythrasma* (coral-red fluorescence), most cases of Tinea corporis/faciei caused by *Trichophyton rubrum* do not fluoresce, making it less reliable than a KOH mount. **Clinical Pearls for NEET-PG:** * **Tinea Incognito:** This occurs when a fungal infection is treated with topical steroids, leading to a loss of the classic annular morphology and making diagnosis difficult. * **Specimen Collection:** Always scrape scales from the **active peripheral margin** of the lesion, as this is where the fungal load is highest. * **Culture:** Sabouraud’s Dextrose Agar (SDA) is the standard culture medium for fungi, but it takes 2–3 weeks, making KOH the preferred rapid diagnostic tool.

Question 35: Athlete's foot infection is caused due to which of the following microorganisms?

A. Trichophyton (Correct Answer)
B. Candida
C. Papilloma virus
D. E.coli

Explanation: **Explanation:** **Athlete’s foot**, medically known as **Tinea pedis**, is a common fungal infection of the feet. It is caused by **Dermatophytes**, a group of fungi that require keratin for growth. The most common causative organism is **Trichophyton rubrum**, followed by *Trichophyton mentagrophytes* and *Epidermophyton floccosum*. These fungi thrive in warm, moist environments like locker rooms and showers, leading to scaling, maceration, and itching, particularly in the interdigital spaces. **Analysis of Options:** * **A. Trichophyton (Correct):** As a dermatophyte, it invades the keratinized layer of the skin (stratum corneum), making it the primary cause of Tinea infections. * **B. Candida:** While *Candida albicans* can cause skin infections (Candidiasis), it typically affects intertriginous areas (folds) and presents with satellite lesions. It is a yeast, not a dermatophyte. * **C. Papilloma virus:** Human Papillomavirus (HPV) causes **warts** (Verruca), which are viral proliferations of the epithelium, not fungal infections. * **D. E. coli:** This is a Gram-negative bacterium primarily associated with urinary tract infections and enteric diseases, not superficial fungal skin infections. **High-Yield Clinical Pearls for NEET-PG:** * **The "Two feet, one hand" syndrome:** A common clinical pattern where Tinea pedis involves both feet and the dominant hand (Tinea manuum). * **Diagnosis:** Confirmed by **KOH mount** showing translucent, branching septate hyphae. * **Treatment:** Topical antifungals (Azoles or Terbinafine) are first-line; oral therapy is reserved for resistant or extensive cases. * **Mnemonic:** The three genera of dermatophytes are **M.E.T.** (**M**icrosporum, **E**pidermophyton, **T**richophyton).

Question 36: Which of the following organisms affects only the skin and nails?

A. Microspora gypseum
B. Microspora audovinii
C. Epidermophyton floccosum (Correct Answer)
D. Tricophyton rubrum

Explanation: **Explanation:** The question tests your knowledge of **Dermatophytes**, a group of fungi that require keratin for growth. They are categorized into three genera: *Trichophyton*, *Microsporum*, and *Epidermophyton*. Each genus has a specific predilection for keratinized tissues (skin, hair, and nails). **1. Why Epidermophyton floccosum is correct:** *Epidermophyton* is the only genus among the three that **does not infect hair**. It specifically targets the **skin and nails**. *E. floccosum* is the most clinically significant species in this genus and is a common cause of tinea cruris and tinea pedis. **2. Analysis of Incorrect Options:** * **A & B (Microsporum gypseum & M. audouinii):** The genus *Microsporum* typically affects the **skin and hair**, but rarely involves the nails. * **D (Trichophyton rubrum):** The genus *Trichophyton* is the most versatile; it can affect the **skin, hair, and nails**. *T. rubrum* is the most common cause of dermatophytosis worldwide. **High-Yield NEET-PG Pearls:** To quickly differentiate these for the exam, remember this "Rule of Involvement": * **Trichophyton:** Skin + Hair + Nails (All three) * **Microsporum:** Skin + Hair (No Nails) * **Epidermophyton:** Skin + Nails (No Hair) **Microscopic Identification (High Yield):** * *E. floccosum:* Characterized by **club-shaped (beaver-tail)** macroconidia arranged in clusters, with no microconidia. * *Microsporum:* Spindle-shaped macroconidia. * *Trichophyton:* Pencil-shaped macroconidia (rare) and numerous microconidia.

Question 37: Sclerotic bodies are seen in which of the following conditions?

A. Sporotrichosis
B. Histoplasmosis
C. Chromoblastomycosis (Correct Answer)
D. Rhinosporodiosis

Explanation: **Explanation:** **Chromoblastomycosis** is a chronic subcutaneous fungal infection caused by dematiaceous (pigmented) fungi, most commonly *Fonsecaea pedrosoi*. The hallmark histopathological feature of this condition is the presence of **Sclerotic bodies** (also known as **Medlar bodies**, **Copper-penny bodies**, or **Muriform bodies**). These are thick-walled, dark brown, globe-shaped structures that divide by binary fission (septation) rather than budding. They represent a transition stage of the fungus and are highly diagnostic. **Analysis of Incorrect Options:** * **A. Sporotrichosis:** Characterized by **Asteroid bodies** (a central spore surrounded by a radiating eosinophilic "Splendore-Hoeppli" phenomenon) and cigar-shaped yeast cells. * **B. Histoplasmosis:** Shows small, intracellular yeast cells (2–4 µm) typically found within macrophages, often described as having a "halo" appearance due to artifactual shrinkage. * **C. Rhinosporodiosis:** Caused by *Rhinosporidium seeberi*, it is identified by massive **sporangia** (up to 300 µm) containing thousands of tiny daughter spores (endospores). **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** Chromoblastomycosis typically presents as a slow-growing, "cauliflower-like" verrucous plaque, usually on the lower limbs of agricultural workers. * **Pseudoepitheliomatous Hyperplasia:** This is a common reactive epidermal change seen on histology. * **Transepidermal Elimination:** Sclerotic bodies are often eliminated through the epidermis, appearing as "black dots" on the skin surface. * **Treatment:** Itraconazole is the drug of choice; surgical excision or cryotherapy may be used for small lesions.

Question 38: Which of the following structures is affected by dermatophytes?

A. Skin
B. Hair
C. Nail
D. All of the above (Correct Answer)

Explanation: **Explanation:** Dermatophytes are a unique group of filamentous fungi (molds) that possess the enzyme **keratinase**. This enzyme allows them to digest and metabolize **keratin**, a structural protein found in the cornified layers of the body. Consequently, dermatophytosis (commonly known as Tinea or Ringworm) is restricted to non-living, keratinized tissues. * **Skin:** Dermatophytes colonize the *stratum corneum* (the outermost layer of the epidermis), leading to characteristic annular, erythematous lesions with central clearing (Tinea corporis, Tinea cruris, etc.). * **Hair:** They can invade the hair shaft and follicle (Tinea capitis), leading to hair breakage or alopecia. This occurs via endothrix or ectothrix patterns of invasion. * **Nails:** They infect the nail bed and plate, causing **Onychomycosis** (Tinea unguium), characterized by subungual hyperkeratosis and nail dystrophy. Since all three structures—skin, hair, and nails—contain keratin, they are all susceptible to dermatophyte infection. **Clinical Pearls for NEET-PG:** 1. **The Three Genera:** Dermatophytes belong to three genera: *Trichophyton* (affects skin, hair, and nails), *Microsporum* (affects skin and hair; rarely nails), and *Epidermophyton* (affects skin and nails; never hair). 2. **Most Common Cause:** *Trichophyton rubrum* is the most common cause of dermatophytosis worldwide. 3. **Diagnosis:** The gold standard for screening is **KOH (Potassium Hydroxide) mount**, which reveals translucent, branching hyphae. 4. **Culture:** **Sabouraud’s Dextrose Agar (SDA)** is the standard culture medium used for identification.

Question 39: A patient self-diagnosed with athlete's foot (tinea pedis) used an over-the-counter product. While the condition improved, it did not fully resolve. A dermatologist was consulted, and a skin scraping was sent for fungal culture. The culture yielded a slow-growing colony that produced a few small microconidia. This finding is consistent with the isolation of a dermatophyte from which genera?

A. Trichophyton (Correct Answer)
B. Microsporum
C. Epidermophyton
D. Trichosporon

Explanation: **Explanation:** The clinical presentation of **tinea pedis** (athlete's foot) and the laboratory findings point directly to the genus **Trichophyton**. 1. **Why Trichophyton is correct:** Dermatophytes are classified into three genera based on their macroconidia and microconidia. *Trichophyton* species (like *T. rubrum*, the most common cause of tinea pedis) are characterized by **abundant microconidia** and **rare, smooth-walled, pencil-shaped macroconidia**. In many cultures, they grow slowly and may only produce a few small microconidia, fitting the description in the question. 2. **Why the other options are incorrect:** * **Microsporum:** These are characterized by **abundant, thick-walled, spindle-shaped macroconidia** with rough surfaces. Microconidia are usually scarce. * **Epidermophyton:** This genus (specifically *E. floccosum*) produces **club-shaped macroconidia** in clusters and is unique because it **never produces microconidia**. * **Trichosporon:** This is a yeast-like fungus responsible for White Piedra. It produces arthroconidia and blastoconidia, not the typical micro/macroconidia structure of dermatophytes. **High-Yield NEET-PG Pearls:** * **Tinea Pedis:** Most commonly caused by *Trichophyton rubrum* (distal subungual) and *Trichophyton mentagrophytes*. * **Macroconidia Mnemonic:** * **M**icrosporum = **M**any (and spindle-shaped). * **T**richophyton = **T**enous (few/rare and pencil-shaped). * **E**pidermophyton = **E**mpty of microconidia (only club-shaped macroconidia). * **Wood’s Lamp:** *Microsporum* species fluoresce (bright green), while most *Trichophyton* species (except *T. schoenleinii*) do not.

Question 40: A farmer from the sub-Himalayan region presents with multiple leg ulcers. The most likely causative agent is?

A. Trichophyton Rubrum
B. Cladosporium species
C. Sporothrix Schenckii (Correct Answer)
D. Aspergillus

Explanation: ### Explanation **Correct Answer: C. Sporothrix schenckii** **Reasoning:** The clinical presentation describes **Sporotrichosis** (Rose Gardener’s Disease). The key diagnostic clues are the patient’s occupation (**farmer**) and the geographic location (**sub-Himalayan region**, which is an endemic belt for this fungus in India). * **Pathogenesis:** *Sporothrix schenckii* is a dimorphic fungus found in soil, hay, and decaying vegetation. Infection occurs via **traumatic inoculation** (e.g., thorn pricks or splinters). * **Clinical Presentation:** It typically presents as a primary nodule at the site of entry which later ulcerates. The classic "sporotrichoid spread" involves secondary nodules developing along the **proximal lymphatic channels**. **Analysis of Incorrect Options:** * **A. Trichophyton rubrum:** This is the most common cause of superficial dermatophytoses (like Tinea corporis). While it causes skin scaling and itching, it does not typically present as deep ulcers or follow a lymphatic distribution. * **B. Cladosporium species:** These are common causes of **Chromoblastomycosis**. While also seen in farmers, the lesions are typically slow-growing, "cauliflower-like" verrucous (warty) plaques rather than simple ulcers. * **D. Aspergillus:** This is an opportunistic fungus. Primary cutaneous aspergillosis is rare and usually occurs in severely immunocompromised patients, presenting as necrotic eschars. **High-Yield Clinical Pearls for NEET-PG:** * **Geographic Belt in India:** Sub-Himalayan regions (Himachal Pradesh, Uttarakhand, Assam). * **Morphology:** It is a **dimorphic fungus**. In tissue (37°C), it appears as **"Cigar-shaped" bodies**. In culture (25°C), it shows a "Daisy petal" appearance. * **Asteroid Bodies:** These are yeast cells surrounded by Splendore-Hoeppli material seen on histology. * **Drug of Choice:** **Itraconazole** is the gold standard. Historically, Saturated Solution of Potassium Iodide (SSKI) was used.

Practice by Chapter

Dermatophytoses

Practice Questions

Tinea Versicolor

Practice Questions

Candidiasis

Practice Questions

Onychomycosis

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Subcutaneous Mycoses

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Systemic Mycoses with Cutaneous Manifestations

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Opportunistic Fungal Infections

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Mycetoma

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Tropical Fungal Infections

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Diagnosis of Fungal Infections

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Antifungal Therapy

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Preventive Strategies

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