Diagnosis of Fungal Infections — MCQs
What is the approximate pH of Sabouraud dextrose agar?
A 10-year-old boy presented with painful boggy swelling of scalp, multiple sinuses with purulent discharge, easily pluckable hair, and lymph nodes enlarged in occipital region, which of the following would be most helpful for diagnostic evaluation?
A child comes with a circular 3cm x 3cm scaly patchy hair loss with itching in the lesions. The investigation of choice is
Wood lamp is used to diagnose –
A female patient presents with complaints of thick white vaginal secretions. Which of the following can be used to identify the likely species of the causative agent?
An 8-year-old male presents with multiple patches of alopecia and severe pruritus. A bright blue-green fluorescence is seen on examination of the scalp with a Wood's lamp. Pathogen most likely responsible is?
Which of the following tests is used in the diagnosis of tinea faciei?
A 24-year-old male came to OPD with brownish itchy patches in axilla, Wood's lamp examination shows "coral red" fluorescence. Most likely diagnosis is:
A 7 Year old boy with boggy swelling of the scalp with multiple discharging sinuses with cervical lymphadenopathy with easily pluckable hair. What would be done for diagnosis -
A child of 7-8 years of age presents with scalp swelling and alopecia. What is the most appropriate diagnostic investigation?
Diagnosis of Fungal Infections Indian Medical PG Practice Questions and MCQs
Question 1: What is the approximate pH of Sabouraud dextrose agar?
- A. 12
- B. 10
- C. 5.4 (Correct Answer)
- D. 8
Explanation: ***5.4*** - Sabouraud dextrose agar (SDA) is specifically formulated with an **acidic pH** range of approximately 5.0 to 6.0, most commonly cited as 5.4 to 5.6. - This **acidic environment inhibits the growth of most bacteria** while promoting the growth of fungi (yeasts and molds), making it a selective medium for fungal isolation. *12* - A pH of 12 is **highly alkaline**, which would be detrimental to the growth of most microorganisms, including fungi, and is not used for routine microbial culture. - Such a high pH would cause **denaturation of proteins** and essential cellular components, inhibiting cell function. *10* - A pH of 10 is also in the **alkaline range**, which is generally unfavorable for fungal growth as fungi prefer slightly acidic to neutral conditions. - Most fungi optimally grow at pH values **below 7**, and a pH of 10 would suppress their growth. *8* - A pH of 8 is slightly alkaline and would be **more favorable for bacterial growth** than fungal growth. - While some fungi can tolerate this pH, it is **not optimally selective** for fungi over bacteria, which is the primary purpose of SDA.
Question 2: A 10-year-old boy presented with painful boggy swelling of scalp, multiple sinuses with purulent discharge, easily pluckable hair, and lymph nodes enlarged in occipital region, which of the following would be most helpful for diagnostic evaluation?
- A. Bacterial culture
- B. Biopsy and giemsa staining
- C. Patch test, gram staining and Tzank smear
- D. KOH mount (Correct Answer)
Explanation: ***KOH mount*** - The symptoms of **painful boggy scalp swelling**, **purulent discharge**, **easily pluckable hair**, and **occipital lymphadenopathy** in a child are highly suggestive of **Tinea capitis**, specifically **Kerion**. - A **KOH mount** is the most direct and rapid method to identify fungal elements (hyphae and spores) in hair shafts and scales, confirming the diagnosis of a dermatophyte infection. *Bacterial culture* - While there is **purulent discharge**, the primary presentation with **boggy swelling** and **hair loss** is more indicative of a fungal etiology. - A bacterial culture would only be useful to rule out secondary bacterial infection, but not as the initial diagnostic step for the described primary fungal condition. *Biopsy and Giemsa staining* - A **biopsy** is an invasive procedure and generally not the first-line diagnostic test for uncomplicated **Tinea capitis/Kerion**, where a non-invasive KOH mount is sufficient. - **Giemsa staining** is primarily used for identifying certain bacteria, parasites, or cellular morphology, but it is not the standard or most efficient method for diagnosing fungal infections of the hair. *Patch test, Gram staining and Tzank smear* - A **patch test** is used to diagnose **allergic contact dermatitis** and is irrelevant to the presented symptoms. - **Gram staining** is for bacterial identification, and a **Tzank smear** is used for viral infections like herpes, neither of which are indicated by the clinical picture of a fungal scalp infection.
Question 3: A child comes with a circular 3cm x 3cm scaly patchy hair loss with itching in the lesions. The investigation of choice is
- A. Tzanck smear
- B. Gram stain
- C. KOH mount (Correct Answer)
- D. Split skin smear
Explanation: ***Correct: KOH mount (Potassium Hydroxide mount)*** - A **KOH mount** is the investigation of choice for suspected **dermatophyte infections** (tinea capitis), which commonly present as circular, scaly patches of hair loss with itching in children. - It involves dissolving keratinous material to visualize **fungal hyphae** and spores directly under a microscope. - This is a quick, cost-effective, and highly specific first-line diagnostic test. *Incorrect: Tzanck smear* - A **Tzanck smear** is primarily used to diagnose **viral infections** like herpes simplex or varicella-zoster by identifying multinucleated giant cells. - It is not effective for detecting fungal elements responsible for scaly hair loss. *Incorrect: Gram stain* - A **Gram stain** is a technique used to classify **bacteria** based on their cell wall properties. - It would not reveal fungal hyphae or spores relevant to the described condition. *Incorrect: Split skin smear* - A **split skin smear** (or slit-skin smear) is typically used in the diagnosis of **leprosy** to identify acid-fast bacilli. - This technique involves scraping the dermis and is not suitable for diagnosing superficial fungal infections.
Question 4: Wood lamp is used to diagnose –
- A. Erysipelas
- B. Pityriasis rosea
- C. Psoriasis
- D. Tinea versicolor (Correct Answer)
Explanation: ***Tinea versicolor*** - A Wood lamp is used to diagnose **tinea versicolor** by revealing a characteristic **yellow-green fluorescence** of the affected areas due to the production of **porphyrins** by the causative yeast, *Malassezia*. - This specific fluorescence helps differentiate **tinea versicolor** from other skin conditions that may have a similar appearance. *Erysipelas* - **Erysipelas** is a superficial bacterial skin infection, typically diagnosed based on its **clinical presentation** of a rapidly spreading, fiery red, tender, and sharply demarcated rash. - A Wood lamp is **not used** in the diagnosis of erysipelas, as it does not cause any specific fluorescence under UV light. *Pityriasis rosea* - **Pityriasis rosea** is a self-limiting inflammatory skin rash, usually diagnosed clinically by its distinctive morphology, including a **herald patch** followed by smaller, oval, fawn-colored lesions in a "Christmas tree" pattern. - A Wood lamp examination would **not show any specific fluorescence** indicative of pityriasis rosea. *Psoriasis* - **Psoriasis** is a chronic autoimmune skin condition characterized by well-demarcated, erythematous plaques covered with silvery scales, typically diagnosed through **clinical examination** and sometimes a skin biopsy. - A Wood lamp is **not a diagnostic tool** for psoriasis, as psoriatic lesions do not fluoresce in a characteristic manner under UV light.
Question 5: A female patient presents with complaints of thick white vaginal secretions. Which of the following can be used to identify the likely species of the causative agent?
- A. Brain heart infusion agar
- B. Sabouraud dextrose agar
- C. CHROMagar (Correct Answer)
- D. Birdseed agar
Explanation: ***CHROMagar*** - **CHROMagar Candida** is a differential and selective medium used for the isolation and presumptive identification of common yeast species, including *Candida albicans*, *Candida tropicalis*, and *Candida glabrata*, based on chromogenic reactions. - Different *Candida* species produce distinct colonies of varying colors on this medium, aiding in their **presumptive identification** directly from patient samples like vaginal secretions. *Birdseed agar* - This medium (also known as Staib's medium or Niger seed agar) is primarily used for the isolation and identification of **Cryptococcus neoformans**, which produces dark brown to black colonies due to its phenoloxidase activity. - While it's a fungal growth medium, it is not optimized for distinguishing common *Candida* species responsible for vaginal candidiasis. *Brain heart infusion agar* - **Brain heart infusion (BHI) agar** is a general-purpose, enriched non-selective medium used for the cultivation of a wide variety of fastidious bacteria, yeasts, and molds. - It does not contain differential components that would allow for the specific identification or differentiation of *Candida* species based on colony color or morphology. *Sabouraud dextrose agar* - **Sabouraud dextrose agar (SDA)** is a selective medium primarily used for the isolation and cultivation of pathogenic and nonpathogenic fungi, including yeasts and molds. - While *Candida* species will grow well on SDA, it does not provide differential characteristics (like distinct colony colors) to allow for the presumptive identification and differentiation of various *Candida* species.
Question 6: An 8-year-old male presents with multiple patches of alopecia and severe pruritus. A bright blue-green fluorescence is seen on examination of the scalp with a Wood's lamp. Pathogen most likely responsible is?
- A. Microsporum canis (Correct Answer)
- B. Epidermophyton floccosum
- C. Candida albicans
- D. Trichophyton tonsurans
Explanation: ***Microsporum canis*** - This dermatophyte species is a common cause of **tinea capitis** in children, characterized by **patches of alopecia** and **pruritus**. - **Microsporum** species are known to exhibit **bright blue-green fluorescence** under a Wood's lamp due to the production of pteridine, which aids in diagnosis. *Epidermophyton floccosum* - This fungus primarily causes **tinea pedis**, **tinea cruris**, and **tinea corporis**, but rarely **tinea capitis**. - Infections caused by *Epidermophyton floccosum* typically do **not fluoresce** under a Wood's lamp. *Candida albicans* - *Candida albicans* is a yeast that causes superficial infections like **oral thrush**, **diaper rash**, and **vaginitis**, but it is **not a common cause of tinea capitis**. - *Candida* infections do **not show fluorescence** with a Wood's lamp. *Trichophyton tonsurans* - This is a common cause of **tinea capitis** (especially in the US), often presenting as **"black dot" tinea capitis** due to hair shaft breakage at the scalp surface. - Infections by *Trichophyton tonsurans* typically do **not fluoresce** under a Wood's lamp, differentiating it from *Microsporum* infections.
Question 7: Which of the following tests is used in the diagnosis of tinea faciei?
- A. Gram's stain
- B. KOH mount (Correct Answer)
- C. Tissue smear
- D. Wood's lamp
Explanation: ***KOH mount*** - A **KOH (potassium hydroxide) mount** is the gold standard for diagnosing **dermatophyte infections**, including **tinea faciei**. - The KOH solution dissolves keratinocytes, allowing for the visualization of fungal **hyphae and spores** under a microscope. *Gram's stain* - **Gram's stain** is primarily used to differentiate bacterial species based on their cell wall properties. - It does not effectively visualize **fungal elements** and is therefore not used for diagnosing tinea infections. *Tissue smear* - A **tissue smear** involves examining cells from a lesion, typically for conditions like viral infections (e.g., Tzanck smear for herpes) or some cutaneous malignancies. - It is not the standard or preferred method for identifying **dermatophyte fungal structures**. *Wood's lamp* - A **Wood's lamp**, which emits ultraviolet light, is used to detect certain fungal infections (e.g., *Microsporum* species causing tinea capitis) and bacterial conditions (e.g., erythrasma). - Many common dermatophytes causing **tinea faciei** (e.g., *Trichophyton*) do not fluoresce under a Wood's lamp, making it an unreliable diagnostic tool for this specific condition.
Question 8: A 24-year-old male came to OPD with brownish itchy patches in axilla, Wood's lamp examination shows "coral red" fluorescence. Most likely diagnosis is:
- A. Tinea corporis
- B. Tinea cruris
- C. Hidradenitis suppurativa
- D. Erythrasma (Correct Answer)
Explanation: ***Erythrasma*** - Erythrasma is a superficial bacterial infection caused by *Corynebacterium minutissimum*, presenting as **brownish, itchy patches** in intertriginous areas like the **axilla**. - The pathognomonic finding is a characteristic **"coral red" fluorescence** under Wood's lamp due to the production of porphyrin. *Tinea corporis* - This is a fungal infection (ringworm) of the body, characterized by **annular lesions** with raised, erythematous borders and central clearing. - While it can be itchy, it typically does not produce **coral red fluorescence** under Wood's lamp; instead, a fungal infection might show no fluorescence or a dull green-yellow hue in some cases. *Tinea cruris* - This is a fungal infection of the groin, commonly known as "jock itch," presenting as an **erythematous, scaling rash** with well-demarcated borders. - Similar to tinea corporis, it is caused by dermatophytes and does not exhibit **coral red fluorescence** under Wood's lamp. *Hidradenitis suppurativa* - This is a chronic inflammatory skin condition characterized by **recurrent abscesses, nodules, and sinus tracts** in areas with apocrine sweat glands, such as the axilla and groin. - While it affects the axilla, its presentation with painful nodules and scarring is distinct from the described brownish patches, and it does not demonstrate **coral red fluorescence**.
Question 9: A 7 Year old boy with boggy swelling of the scalp with multiple discharging sinuses with cervical lymphadenopathy with easily pluckable hair. What would be done for diagnosis -
- A. KOH mount (Correct Answer)
- B. Patch test
- C. Pus for culture
- D. Biopsy
Explanation: ***KOH mount*** - A **KOH mount** is the most appropriate initial diagnostic step for suspected **tinea capitis** with a **kerion** (boggy swelling, discharging sinuses, easily pluckable hair), as it allows for rapid visualization of fungal elements. - This test directly identifies **hyphae and spores** in hair shafts and scales, confirming a fungal infection. *Patch test* - A **patch test** is used to identify **contact allergens** in cases of **allergic contact dermatitis**, which presents with eczematous lesions, not boggy swelling and hair loss. - It involves applying small amounts of potential allergens to the skin and observing for a reaction after a period of time, which is irrelevant for a suspected fungal infection. *Pus for culture* - While a **bacterial culture** might be considered if a **secondary bacterial infection** is suspected, the primary diagnosis indicated by the symptoms (boggy swelling, easily pluckable hair) is fungal. - Culturing pus alone would miss the underlying fungal etiology and might lead to inappropriate treatment if bacteria are not the primary pathogen. *Biopsy* - A **skin biopsy** is an invasive procedure usually reserved for when less invasive tests are inconclusive or when conditions like **malignancy** or certain **inflammatory dermatoses** are suspected. - It is not the first-line diagnostic test for a clear case of suspected fungal infection like kerion, where **KOH mount** is rapid and effective.
Question 10: A child of 7-8 years of age presents with scalp swelling and alopecia. What is the most appropriate diagnostic investigation?
- A. KOH staining of the scrapings (Correct Answer)
- B. Blood culture
- C. PAS staining
- D. Gram staining
Explanation: ***KOH staining of the scrapings*** - This presentation is highly suggestive of **tinea capitis**, a fungal infection of the scalp. **Potassium hydroxide (KOH) staining** of hair and scalp scrapings is the primary diagnostic method to identify fungal elements (hyphae and spores). - KOH dissolves keratinous material, making it easier to visualize the **fungal hyphae or spores** under a microscope. *Blood culture* - **Blood culture** is used to diagnose **systemic infections**, particularly bacterial or fungal infections that have entered the bloodstream. - It is **not indicated** for the initial diagnosis of localized skin and hair infections like tinea capitis. *PAS staining* - **Periodic acid–Schiff (PAS) staining** is primarily used for **histopathological examination** of tissue biopsies to detect fungi or other carbohydrates. - While it can identify fungi in tissue sections, it is **not the first-line diagnostic investigation** for tinea capitis, which typically uses direct microscopic examination of scrapings. *Gram staining* - **Gram staining** is a differential staining technique used to classify **bacteria** based on their cell wall properties (Gram-positive or Gram-negative). - It is **not effective** for identifying fungal organisms, which have different cell wall compositions.
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