Mycetoma — MCQs
A farmer presents with a subcutaneous wound on his foot with discharge. Microscopy of a white granule from the wound shows Gram-positive filamentous rods. What is the most likely organism?
A patient presents with sinus tracts on the foot, and a smear reveals filamentous organisms.
A farmer has an ulcer on leg with indurated margin and multiple sinuses with discharging granules. The likely diagnosis is -
Skin scraping and KOH mounting is done for what condition?
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?
Dhobi's itch is:
Brown, spherical, septate bodies found in pus are diagnostic of which condition?
Scutula is classically seen in which of the following conditions?
Tinea unguium affects which part of the nail?
Which dermatophyte species does not involve the nail?
Mycetoma Indian Medical PG Practice Questions and MCQs
Question 1: A farmer presents with a subcutaneous wound on his foot with discharge. Microscopy of a white granule from the wound shows Gram-positive filamentous rods. What is the most likely organism?
- A. Staphylococcus aureus
- B. Histoplasma
- C. Nocardia (Correct Answer)
- D. Sporothrix
Explanation: ***Nocardia*** - The presence of **white granules** in the discharge, along with **Gram-positive, filamentous rods**, is highly characteristic of *Nocardia* infection, often forming **sulfur granules** (though not always yellow). - *Nocardia* is a common soil bacterium, making it a likely pathogen in a **farmer with a subcutaneous wound** related to environmental exposure. *Staphylococcus aureus* - While *Staphylococcus aureus* can cause skin infections and abscesses, it presents as **Gram-positive cocci in clusters**, not filamentous rods. - It does not typically form **granules** in the discharge in the same manner as *Nocardia*. *Histoplasma* - *Histoplasma* is a **dimorphic fungus** that causes systemic infections, often acquired by inhaling spores. - It would appear as **yeast forms** in tissue or cultures, not Gram-positive filamentous rods, and is not typically associated with subcutaneous wounds forming granules. *Sporothrix* - *Sporothrix schenckii* causes **sporotrichosis**, characterized by a **subcutaneous nodule** that progresses along lymphatic channels. - It is a **dimorphic fungus** (yeast in tissue, mold in culture) and would not appear as Gram-positive filamentous rods on microscopy.
Question 2: A patient presents with sinus tracts on the foot, and a smear reveals filamentous organisms.
- A. Sporothrix
- B. Nocardia (Correct Answer)
- C. Dermatophytes
- D. Candida
Explanation: ***Correct: Nocardia*** - **Nocardia species** cause **actinomycetoma**, a chronic infection characterized by **sinus tracts** discharging purulent material with sulfur granules - Smear shows **branching filamentous organisms** that are gram-positive and partially acid-fast - Classic presentation: sinus tracts on foot with filamentous organisms on direct microscopy - Key features: aerobic actinomycetes, branching at acute angles (45°) *Incorrect: Sporothrix* - Causes **sporotrichosis** (lymphocutaneous nodules along lymphatics), not sinus tracts - **Dimorphic fungus** diagnosed primarily by culture, not direct smear - Clinical presentation: nodular lesions following trauma (rose gardener's disease) - Does not show filamentous organisms on direct smear *Incorrect: Dermatophytes* - Cause **superficial infections** of skin, hair, and nails (tinea pedis, ringworm) - Do not form **deep sinus tracts** or involve subcutaneous tissue - Microscopy shows septate hyphae in skin scrapings, not in discharge from sinus tracts - Clinical presentation completely different from actinomycetoma *Incorrect: Candida* - **Yeast** causing mucocutaneous infections (thrush, vaginitis) or systemic candidiasis - Does not cause **sinus tracts** on the foot - Microscopy reveals **budding yeasts and pseudohyphae**, not true branching filaments - Not associated with actinomycetoma-type presentations
Question 3: A farmer has an ulcer on leg with indurated margin and multiple sinuses with discharging granules. The likely diagnosis is -
- A. Lupus vulgaris
- B. Actinomycosis
- C. Scrofuloderma
- D. Mycetoma (Correct Answer)
Explanation: ***Mycetoma*** - This is the **correct diagnosis** characterized by the classic triad: **tumefaction** (swelling with indurated margin), multiple **draining sinuses**, and discharge of **granules**. - The **occupational history** (farmer with soil exposure) and **location on the leg** are highly suggestive of mycetoma, particularly common in agricultural workers. - The granules are **colonies of microorganisms** (either fungi [eumycetoma] or bacteria [actinomycetoma]) aggregated and encased in a cement-like matrix, a distinctive feature of this chronic infection. - **Key distinguisher**: Mycetoma has a predilection for the **lower extremities**, especially the foot and leg, in individuals with occupational soil exposure. *Actinomycosis* - Actinomycosis is a bacterial infection caused by *Actinomyces* species, which also forms abscesses and draining sinuses with characteristic **"sulfur granules."** - **Why incorrect**: While actinomycosis shares features of sinuses and granules, it most commonly affects the **cervicofacial (50-60%)**, **thoracic**, or **abdominal** regions. - **Leg involvement is rare** for actinomycosis, making mycetoma the more likely diagnosis in this clinical scenario. - The occupational history and typical location favor mycetoma over actinomycosis. *Lupus vulgaris* - This is a form of **cutaneous tuberculosis** presenting as red-brown plaques or nodules, often with an **"apple-jelly" appearance** on diascopy. - While it can cause ulcers, it typically does **not present with deep-seated sinuses and discharging granules**, which are pathognomonic for mycetoma. *Scrofuloderma* - This is a form of cutaneous tuberculosis that develops from the direct extension of underlying **tuberculous adenitis** or **osteomyelitis** to the skin. - It presents as cold abscesses that eventually rupture, forming irregular ulcers and sinuses, but typically **lacks the distinct discharging granules** of mycetoma. - The clinical presentation with granular discharge clearly differentiates mycetoma from scrofuloderma.
Question 4: Skin scraping and KOH mounting is done for what condition?
- A. Leprosy
- B. Varicella
- C. Fungal infections (Correct Answer)
- D. Herpes Simplex Virus (HSV)
Explanation: **Explanation:** **1. Why Fungal Infections is Correct:** Potassium Hydroxide (KOH) mounting is the **gold standard bedside diagnostic test** for superficial fungal infections (Dermatophytosis, Candidiasis, and Tinea versicolor). The medical principle relies on the fact that KOH is a strong alkali that digests keratin, epithelial cells, and debris in skin scrapings, hair, or nails. Since fungal cell walls contain **chitin**, they remain resistant to KOH. This allows the clinician to clearly visualize fungal elements like hyphae, spores, or budding yeast under a microscope. **2. Why Other Options are Incorrect:** * **Leprosy (A):** Diagnosis is primarily clinical, supported by **Slit Skin Smear (SSS)** using Modified Ziehl-Neelsen staining to identify *Mycobacterium leprae* (acid-fast bacilli). * **Varicella (B) & HSV (D):** These are viral infections. The classic bedside test for these is the **Tzanck Smear**, where a scraping from the base of a vesicle is stained (Giemsa/Wright) to look for **multinucleated giant cells** (Acantholytic cells). **3. High-Yield Clinical Pearls for NEET-PG:** * **Concentration:** 10% KOH is used for skin/hair; 20% KOH is used for thicker nail clippings. * **Classic Morphologies:** * **Dermatophytes:** Translucent, branching, septate hyphae. * **Tinea Versicolor:** "Spaghetti and meatballs" appearance (short hyphae and spores). * **Candidiasis:** Pseudohyphae and budding yeast cells. * **Modification:** **DMSO (Dimethyl sulfoxide)** can be added to KOH to speed up the clearing of keratin without requiring heat.
Question 5: 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?
- A. Wood's lamp examination
- B. 10% KOH mount (Correct Answer)
- C. Skin biopsy
- D. Patch testing
Explanation: **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.
Question 6: Dhobi's itch is:
- A. Tinea corporis
- B. Tinea cruris (Correct Answer)
- C. Tinea barbae
- D. Tinea capitis
Explanation: **Explanation:** **Tinea cruris**, commonly known as **Dhobi’s itch**, is a dermatophyte infection of the groin, perineum, and perianal regions. The term "Dhobi’s itch" originates from the historical association with laundry workers (dhobis) who often wore damp clothes for long periods, creating the warm, humid environment that favors fungal growth. It typically presents as an erythematous, pruritic rash with a well-demarcated, scaly, elevated border and central clearing. **Analysis of Options:** * **Tinea cruris (Correct):** Specifically refers to the fungal infection of the groin. It is most commonly caused by *Trichophyton rubrum* or *Epidermophyton floccosum*. * **Tinea corporis:** Refers to infection of the glabrous skin (trunk and limbs), often called "ringworm." * **Tinea barbae:** A fungal infection of the beard and mustache area, seen primarily in adult males. * **Tinea capitis:** Fungal infection of the scalp and hair shafts, most common in children. **High-Yield Clinical Pearls for NEET-PG:** * **Most common causative agent:** *Trichophyton rubrum* is the most frequent isolate globally for most Tinea infections. * **Sparing of Scrotum:** A key clinical differentiator is that Tinea cruris typically **spares the scrotum and penis**, whereas Candidiasis (Intertrigo) frequently involves the scrotum and presents with "satellite lesions." * **Autoinoculation:** Patients often have concurrent **Tinea pedis** (Athlete's foot); the fungus is transferred to the groin while putting on underwear (feet first). * **Diagnosis:** Confirmed by **KOH mount** showing septate branching hyphae. * **Treatment:** Topical antifungals (e.g., Terbinafine, Clotrimazole) are first-line. Avoid topical steroids as they lead to **Tinea incognito**.
Question 7: Brown, spherical, septate bodies found in pus are diagnostic of which condition?
- A. Geotrichosis
- B. Chromomycosis (Correct Answer)
- C. Mucormycosis
- D. Sporotrichosis
Explanation: **Explanation:** The presence of **brown, spherical, thick-walled, septate bodies** (also known as **Sclerotic bodies**, **Medlar bodies**, or **Copper-penny bodies**) in pus or tissue sections is the pathognomonic hallmark of **Chromomycosis** (Chromoblastomycosis). These structures represent the vegetative fungal form and are naturally pigmented due to melanin in their cell walls (dematiaceous fungi). **Why the other options are incorrect:** * **Geotrichosis:** Caused by *Geotrichum candidum*, it typically shows rectangular arthroconidia and true hyphae, not pigmented spherical bodies. * **Mucormycosis:** Characterized by broad, **non-septate (coenocytic)**, ribbon-like hyphae with right-angle (90°) branching. * **Sporotrichosis:** Caused by *Sporothrix schenckii*, it typically presents as **cigar-shaped yeast** cells in tissue. The characteristic clinical finding is "sporotrichoid spread" (nodules along lymphatic drainage). **High-Yield Clinical Pearls for NEET-PG:** * **Causative Agents:** Most commonly *Fonsecaea pedrosoi* and *Phialophora verrucosa*. * **Clinical Presentation:** Usually occurs in barefoot agricultural workers following traumatic inoculation. It presents as slow-growing, **verrucous (warty) plaques** or cauliflower-like lesions, most commonly on the lower limbs. * **Diagnosis:** KOH mount of "black dots" on the lesion surface or biopsy reveals the characteristic **Sclerotic bodies**. * **Treatment:** Itraconazole is the drug of choice; surgical excision or cryotherapy may be used for small lesions.
Question 8: Scutula is classically seen in which of the following conditions?
- A. Favus (Correct Answer)
- B. Small spore ectothrix
- C. Endothrix
- D. Kerion
Explanation: **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.
Question 9: Tinea unguium affects which part of the nail?
- A. Nail fold
- B. Nail plate (Correct Answer)
- C. Joints
- D. Interdigital space
Explanation: **Explanation:** **Tinea unguium** is a dermatophyte infection specifically involving the **nail plate**. The term is often used interchangeably with *onychomycosis*, though the latter technically includes infections caused by non-dermatophyte molds and yeasts (like *Candida*). Dermatophytes are keratinophilic fungi; they thrive on the keratin found in the nail plate, leading to characteristic thickening, discoloration (yellow-white), subungual hyperkeratosis, and onycholysis (separation of the nail plate from the bed). **Analysis of Options:** * **Nail fold (Option A):** Inflammation of the nail folds is termed **Paronychia**. While *Candida* can cause chronic paronychia, dermatophytes (Tinea) primarily target the hard keratin of the plate, not the soft tissue of the folds. * **Joints (Option C):** Fungal infections are superficial or subcutaneous. Joint involvement (Arthritis) is not a feature of Tinea infections. * **Interdigital space (Option D):** Infection of the toe webs is called **Tinea pedis** (Athlete’s foot). While Tinea pedis often coexists with Tinea unguium, they are distinct clinical entities. **High-Yield Clinical Pearls for NEET-PG:** * **Most common organism:** *Trichophyton rubrum* is the leading cause of Tinea unguium worldwide. * **Clinical Patterns:** The most common pattern is **Distal Lateral Subungual Onychomycosis (DLSO)**. * **White Superficial Onychomycosis (WSO):** Characterized by "powdery" white patches on the surface; usually caused by *T. mentagrophytes*. * **Diagnosis:** Potassium hydroxide (KOH) microscopy of nail clippings is the initial screening test; Culture is the gold standard. * **Treatment:** Oral **Terbinafine** is the drug of choice (DOC) for dermatophyte nail infections. Topical lacquers (Ciclopirox/Amorolfine) are used only in mild cases or when systemic drugs are contraindicated.
Question 10: Which dermatophyte species does not involve the nail?
- A. Trichophyton
- B. Microsporum (Correct Answer)
- C. Epidermophyton
- D. None of the above
Explanation: ### Explanation The correct answer is **Microsporum**. The classification of dermatophytes into three genera—*Trichophyton*, *Microsporum*, and *Epidermophyton*—is based on the specific keratinized tissues they can invade (skin, hair, and nails). **1. Why Microsporum is correct:** *Microsporum* species primarily infect the **hair and skin**. They lack the biochemical capability to effectively invade the nail plate. Therefore, it is the only genus among the three that does not cause Onychomycosis (nail infection). **2. Why the other options are incorrect:** * **Trichophyton:** This is the most versatile genus. It can involve all three keratinized structures: **Skin, Hair, and Nails**. *T. rubrum* is the most common cause of Onychomycosis worldwide. * **Epidermophyton:** This genus involves the **Skin and Nails** but notably **does not involve the hair**. *Epidermophyton floccosum* is a common cause of Tinea cruris and Onychomycosis. **3. High-Yield Clinical Pearls for NEET-PG:** To quickly memorize the tissue involvement, use this simple table: | Genus | Skin | Hair | Nails | | :--- | :---: | :---: | :---: | | **Trichophyton** | Yes | Yes | Yes | | **Microsporum** | Yes | Yes | **No** | | **Epidermophyton** | Yes | **No** | Yes | * **Wood’s Lamp Examination:** *Microsporum* species (like *M. audouinii* and *M. canis*) typically show a brilliant greenish fluorescence, whereas most *Trichophyton* species (except *T. schoenleinii*) do not fluoresce. * **Macroconidia Shape:** *Microsporum* has spindle-shaped macroconidia, *Trichophyton* has pencil-shaped, and *Epidermophyton* has club-shaped macroconidia.
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