Fungal Skin Infections Practice Questions

Q: A patient presents with lesions on the axilla, groin, and trunk. The lesions are characterized by central clearing and a surrounding papulovesicular margin that progressively increases at the borders. Which of the following investigations would be preferred?

10% KOH mount. **Explanation:** The clinical presentation described—lesions with **central clearing** and an **active papulovesicular margin** spreading centrifugally—is the classic hallmark of **Tinea Corporis** (Dermatophytosis). **Why 10% KOH mount is the correct answer:** The 10% Potassium Hydroxide (KOH) mount is the **gold standard bedside investigation** for diagnosing fungal skin infections. KOH acts as a keratolytic agent, dissolving keratinocytes and debris, which allows for the clear visualization of fungal elements under a light microscope. In dermatophytosis, one typically observes **branching, septate hyaline hyphae**. **Analysis of Incorrect Options:** * **A. Wood’s lamp examination:** While useful for Tinea Capitis (e.g., *Microsporum* species) or Erythrasma (coral-red fluorescence), most species causing Tinea Corporis (like *T. rubrum*) do not fluoresce. * **C. Skin biopsy:** This is an invasive procedure generally reserved for atypical presentations or deep fungal infections. It is not the first-line investigation for superficial dermatophytosis. * **D. Patch testing:** This is the investigation of choice for **Allergic Contact Dermatitis**, not fungal infections. **High-Yield 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. * **Culture Medium:** If KOH is inconclusive but suspicion is high, the gold standard culture medium is **Sabouraud’s Dextrose Agar (SDA)**. * **Erythrasma vs. Tinea:** Erythrasma (caused by *Corynebacterium minutissimum*) lacks the active border and central clearing seen in Tinea and shows coral-red fluorescence under Wood's lamp.

Q: Scutula is classically seen in which of the following conditions?

Favus. **Explanation:** **Favus** (Option A) is a chronic inflammatory form of Tinea Capitis, most commonly caused by the anthropophilic fungus *Trichophyton schoenleinii*. The hallmark clinical feature of Favus is the **Scutulum**. A scutulum is a yellowish, cup-shaped crust composed of dense masses of fungal mycelia, epithelial debris, and inflammatory cells. These crusts often have a characteristic "mousy odor" and, if left untreated, lead to extensive scarring (cicatricial) alopecia. **Analysis of Incorrect Options:** * **Small spore ectothrix (Option B):** Characterized by fungal spores forming a sheath around the hair shaft. It typically presents as "Gray Patch" tinea capitis with brittle, broken hairs, but does not form scutula. * **Endothrix (Option C):** Spores are found inside the hair shaft (e.g., *T. violaceum*). This leads to the "Black Dot" appearance due to hair breaking at the level of the scalp. * **Kerion (Option D):** An exaggerated inflammatory host response to zoophilic fungi (e.g., *T. verrucosum*). It presents as a painful, boggy, inflammatory mass with pustules and sinus tracts, rather than the dry, cup-shaped crusts of Favus. **High-Yield Clinical Pearls for NEET-PG:** * **Favus Triad:** Scutula, mousy odor, and cicatricial alopecia. * **Wood’s Lamp:** Favus (*T. schoenleinii*) shows a characteristic **dull green** fluorescence. * **Microscopy:** On KOH mount, Favus shows **"Godet" or "Favic chandeliers"** (antler-like branching hyphae) and air bubbles within the hair shaft. * **Treatment:** Oral Griseofulvin remains the traditional gold standard, though Terbinafine is frequently used.

Q: A 24-year-old man presents with multiple small hypopigmented macules around hair follicles on the upper chest and back. Scratching of the lesions with a glass slide reveals fine scaling. What is the investigation of choice for diagnosing this condition?

KOH preparation of scales. ### Explanation The clinical presentation of small hypopigmented macules around hair follicles with fine scaling (evoked by scratching, known as **Besnier’s sign** or the "coup d'ongle" sign) is classic for **Pityriasis versicolor** (Tinea versicolor), caused by the yeast *Malassezia furfur*. **1. Why Option A is Correct:** The investigation of choice for any superficial fungal infection is a **KOH (Potassium Hydroxide) preparation**. When scales from Pityriasis versicolor are treated with 10% KOH, microscopy reveals a characteristic **"Spaghetti and Meatballs" appearance** (or "Banana and Curd" appearance). This represents a mixture of short, thick fungal hyphae and clusters of round yeast cells. **2. Why Other Options are Incorrect:** * **Option B (Tzank test):** Used for diagnosing viral infections (e.g., Herpes Simplex, Varicella) by identifying multinucleated giant cells. * **Option C (Slit Skin Smear):** Primarily used for diagnosing Leprosy (to look for Acid Fast Bacilli) and Leishmaniasis. * **Option D (Skin biopsy):** While it would show fungal elements in the stratum corneum, it is an invasive procedure and unnecessary for a superficial infection that can be diagnosed bedside. **3. High-Yield Clinical Pearls for NEET-PG:** * **Wood’s Lamp Examination:** Lesions show a characteristic **Golden Yellow fluorescence**. * **Culture:** *Malassezia* is lipophilic; it requires the addition of **olive oil** to the culture medium (e.g., Dixon’s agar) for growth. * **Treatment:** Topical antifungals (Ketoconazole shampoo, Selenium sulfide) are first-line. Oral Fluconazole or Itraconazole is used for extensive cases. * **Besnier’s Sign:** The accentuation of fine scales upon scratching the lesion is a pathognomonic clinical sign.

Q: A 19-year-old man develops a rash in the groin area. On examination, it is a large, well-demarcated area of tan-brown discoloration around his left inguinal area. There is some scaling of the lesion when brushed with a tongue depressor. What is the most appropriate initial diagnostic test?

Potassium hydroxide (KOH) preparation of scrapings. **Explanation:** The clinical presentation of a well-demarcated, tan-brown, scaly rash in the inguinal area is highly suggestive of a superficial fungal infection, most likely **Tinea cruris** (jock itch). In any patient presenting with a scaly, erythematous, or pigmented skin lesion suspicious of a fungal etiology, the **Potassium Hydroxide (KOH) preparation** is the gold standard initial diagnostic test. * **Why KOH is correct:** KOH dissolves keratin in skin scrapings, allowing for the clear visualization of fungal elements (septate hyphae and spores) under a microscope. It is rapid, cost-effective, and provides immediate bedside confirmation. * **Why other options are incorrect:** * **Punch biopsy:** This is an invasive procedure reserved for atypical presentations, suspected malignancies, or inflammatory dermatoses that do not respond to treatment. It is not a first-line test for superficial infections. * **Tzanck smear:** This is used for the diagnosis of **herpetic infections** (HSV/VZV) to look for multinucleated giant cells, not fungal infections. * **Blood culture:** This is indicated for systemic/disseminated fungal infections (e.g., Candidemia) in immunocompromised patients, not for localized cutaneous rashes. **NEET-PG High-Yield Pearls:** * **Differential Diagnosis:** If the lesion shows a "coral red" fluorescence under **Wood’s lamp**, the diagnosis is **Erythrasma** (caused by *Corynebacterium minutissimum*), which can mimic Tinea cruris but lacks hyphae on KOH. * **Tinea Cruris:** Usually spares the scrotum (unlike Candidiasis, which involves the scrotum and presents with satellite lesions). * **KOH Findings:** Look for "branching hyphae" in Dermatophytosis and "spaghetti and meatballs" appearance in Tinea versicolor.

Q: What is the recommended treatment for tinea unguium?

Itraconazole. **Explanation:** **Tinea unguium** (a form of onychomycosis) refers to a fungal infection of the nail plate caused by dermatophytes. Because the infection resides deep within the nail bed and the keratinized nail plate, topical antifungal agents often fail to penetrate effectively. Therefore, **systemic (oral) antifungal therapy** is the gold standard for treatment. **Why Itraconazole is correct:** Itraconazole is a broad-spectrum triazole that inhibits the enzyme lanosterol 14-α-demethylase, disrupting fungal cell membrane synthesis. It is highly lipophilic and keratophilic, allowing it to persist in the nail for months even after the drug is discontinued. In clinical practice, it is often administered as **"Pulse Therapy"** (200 mg twice daily for 7 days a month; 2 pulses for fingernails and 3 pulses for toenails) to minimize side effects while maintaining efficacy. **Why other options are incorrect:** * **Fluticasone:** This is a potent topical corticosteroid used for inflammatory conditions (like eczema or psoriasis). Using steroids on a fungal infection can lead to *Tinea incognito*, worsening the infection by suppressing the local immune response. * **Oleamine oil:** This is not a recognized antifungal treatment. While some oils have mild emollient properties, they have no role in eradicating dermatophyte infections of the nail. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** While Itraconazole is a standard option, **Terbinafine** (an allylamine) is often considered the first-line drug of choice for dermatophyte onychomycosis due to higher cure rates. * **Diagnosis:** The most sensitive test for diagnosis is **PAS (Periodic Acid-Schiff) stain** of nail clippings, though KOH mount is more commonly used in clinics. * **Monitoring:** When prescribing systemic antifungals (especially Itraconazole or Terbinafine), baseline **Liver Function Tests (LFTs)** should be monitored due to the risk of hepatotoxicity.

Question 1

A patient presents with lesions on the axilla, groin, and trunk. The lesions are characterized by central clearing and a surrounding papulovesicular margin that progressively increases at the borders. Which of the following investigations would be preferred?

Accepted Answer

10% KOH mount

Answer

Wood's lamp examination

Answer

Skin biopsy

Answer

Patch testing

Question 2

Scutula is classically seen in which of the following conditions?

Accepted Answer

Favus

Answer

Small spore ectothrix

Answer

Endothrix

Answer

Kerion

Question 3

A 24-year-old man presents with multiple small hypopigmented macules around hair follicles on the upper chest and back. Scratching of the lesions with a glass slide reveals fine scaling. What is the investigation of choice for diagnosing this condition?

Accepted Answer

KOH preparation of scales

Answer

Tzank test

Answer

Slit Skin Smear Examination

Answer

Skin biopsy of lesion

Question 4

A 19-year-old man develops a rash in the groin area. On examination, it is a large, well-demarcated area of tan-brown discoloration around his left inguinal area. There is some scaling of the lesion when brushed with a tongue depressor. What is the most appropriate initial diagnostic test?

Accepted Answer

Potassium hydroxide (KOH) preparation of scrapings

Answer

Punch biopsy of skin

Answer

Tzanck smear

Answer

Blood culture for fungi

Question 5

What is the recommended treatment for tinea unguium?

Accepted Answer

Itraconazole

Answer

Fluticasone

Answer

Oleamine oil

Answer

All of the above

Fungal Skin Infections — MCQs

Fungal Skin Infections — MCQs

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