Fungal Skin Infections Practice Questions

Q: Which sign is indicative of Pityriasis versicolor?

Spaghetti and meatball appearance on KOH examination. ***Spaghetti and meatball appearance on KOH examination*** - This characteristic microscopic finding on a **potassium hydroxide (KOH) preparation** is diagnostic for Pityriasis versicolor, revealing clusters of round yeast cells (meatballs) and short hyphae filaments (spaghetti) of *Malassezia* species. - The examination directly visualizes the fungal elements responsible for the infection, confirming the diagnosis. *Nikolsky sign (associated with pemphigus)* - The Nikolsky sign is positive when the outermost layer of the **epidermis** can be dislodged with lateral pressure, indicating a loss of cell-to-cell adhesion typically seen in **pemphigus vulgaris** and other blistering disorders. - It is not associated with fungal infections like Pityriasis versicolor, which primarily affects the stratum corneum without significant blistering. *Koebner phenomenon (associated with psoriasis)* - The Koebner phenomenon (isomorphic response) refers to the development of new skin lesions at sites of **trauma** in individuals with pre-existing skin conditions like **psoriasis** or lichen planus. - It is a reaction pattern of the skin to injury and does not indicate a fungal infection. *Wickham's striae (associated with lichen planus)* - Wickham's striae are characteristic **fine, lacy white lines** or reticular patterns typically seen on the surface of **papules** and plaques in patients with **lichen planus**. - These are hyperkeratotic manifestations of lichen planus and are not seen in or indicative of Pityriasis versicolor.

Q: A washerman presents with thick erosion and discolouration of the web spaces of the toes. What is the most likely diagnosis?

Tinea Pedis. ***Tinea Pedis*** - This patient's occupation as a **washerman** exposes his feet to constant **dampness and maceration**, which creates an ideal environment for **dermatophyte infections** like tinea pedis (athlete's foot). - The symptoms of **thick erosion** and **discoloration** in the **web spaces of the toes** are classic presentations of interdigital tinea pedis. *Psoriasis* - Psoriasis typically presents with **well-demarcated erythematous plaques** covered with silvery scales, which are not described here. - While it can affect the feet, it usually involves the soles and dorsal aspects rather than primarily the interdigital web spaces with erosion. *Candidiasis* - Cutaneous candidiasis often presents with **erythematous patches** with **satellite lesions** and is common in moist areas, but the description of thick erosion and discoloration in the web spaces is more characteristic of tinea pedis. - While *Candida* can cause interdigital infections, the description points more strongly towards dermatophytes. *Tinea Unguium* - Tinea unguium (onychomycosis) is a **fungal infection of the nails**, causing thickening, discoloration, and crumbling of the nail plate. - The symptoms described are focused on the **skin of the web spaces of the toes**, not the nails themselves.

Q: Which of the following tests is used in the diagnosis of tinea faciei?

KOH mount. ***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 1

Which sign is indicative of Pityriasis versicolor?

Accepted Answer

Spaghetti and meatball appearance on KOH examination

Answer

Nikolsky sign (associated with pemphigus)

Answer

Wickham's striae (associated with lichen planus)

Answer

Koebner phenomenon (associated with psoriasis)

Question 2

A washerman presents with thick erosion and discolouration of the web spaces of the toes. What is the most likely diagnosis?

Accepted Answer

Tinea Pedis

Answer

Tinea Unguium

Answer

Candidiasis

Answer

Psoriasis

Question 3

Which of the following tests is used in the diagnosis of tinea faciei?

Accepted Answer

KOH mount

Answer

Gram's stain

Answer

Tissue smear

Answer

Wood's lamp

Fungal Skin Infections — MCQs

Fungal Skin Infections — MCQs

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