Infectious Diseases of the Skin — MCQs
A 35-year-old professional businesswoman notices the appearance of several hyperkeratotic, well-demarcated growths on the palmar surface of her index finger and on her toe. They do not change in size and cause her only minimal discomfort. A biopsy of one of the lesions, viewed at 40x magnification, is shown. Which of the following viruses is the most likely etiologic agent?
Which of the following disorders would be more likely associated with Staphylococcus saprophyticus rather than Staphylococcus aureus?
An 18-year-old man has facial and upper back lesions that have waxed and waned for the past 6 years. On physical examination, there are 0.3- to 0.9-cm comedones, erythematous papules, nodules, and pustules most numerous on the lower face and posterior upper trunk. Other family members have been affected by this condition at a similar age. The lesions worsen during a 5-day cruise to the Adriatic. Which of the following organisms is most likely to play a key role in the pathogenesis of these lesions?
False about Tinea versicolor
Best diagnostic test for fungal skin infection –
A child presents with grouped vesicles on the lips. What is the bedside investigation that you would like to do?
Which of the following conditions does NOT exhibit dyskeratosis?
Rhinophyma is associated with-
A patient from Himachal Pradesh gets a thorn prick and subsequently presents with a verrucous lesion on feet which on microscopy revealed "Copper penny bodies". The diagnosis is
A patient presents with a gingival lesion as shown in the image. What is the most likely diagnosis?
Infectious Diseases of the Skin Indian Medical PG Practice Questions and MCQs
Question 1: A 35-year-old professional businesswoman notices the appearance of several hyperkeratotic, well-demarcated growths on the palmar surface of her index finger and on her toe. They do not change in size and cause her only minimal discomfort. A biopsy of one of the lesions, viewed at 40x magnification, is shown. Which of the following viruses is the most likely etiologic agent?
- A. Adenovirus
- B. HPV (Correct Answer)
- C. Molluscum contagiosum virus
- D. Echovirus
Explanation: ***HPV*** - The clinical description of **hyperkeratotic**, **well-demarcated growths** on the palmar surface and toe is highly characteristic of **warts** (verrucae), which are caused by **Human Papillomavirus (HPV)**. - The biopsy likely shows **koilocytes** (HPV-infected keratinocytes with perinuclear vacuolization), which are pathognomonic for HPV infection in the skin. *Adenovirus* - Adenovirus typically causes **respiratory tract infections**, **conjunctivitis**, or **gastroenteritis**, and less commonly skin lesions. - Skin manifestations from adenovirus are usually non-specific rashes, not hyperkeratotic growths like those described. *Molluscum contagiosum virus* - **Molluscum contagiosum** is caused by the **Molluscum contagiosum virus (MCV)** and presents as **umbilicated papules**, differing morphologically from the described hyperkeratotic warts. - Histologically, molluscum contagiosum lesions are characterized by **Molluscum bodies** (large eosinophilic cytoplasmic inclusions), which are different from koilocytes. *Echovirus* - Echoviruses are enteroviruses primarily associated with a wide range of syndromes including **aseptic meningitis**, **exanthems (rashes)**, and **respiratory illnesses**. - They do not typically cause localized, hyperkeratotic skin growths like warts.
Question 2: Which of the following disorders would be more likely associated with Staphylococcus saprophyticus rather than Staphylococcus aureus?
- A. Burns
- B. Tension pneumothorax
- C. Osteomyelitis
- D. Acute cystitis (Correct Answer)
Explanation: ***Acute cystitis*** - **Staphylococcus saprophyticus** is a common cause of **urinary tract infections (UTIs)**, particularly acute cystitis, in young sexually active women. - This bacterium has a high affinity for **uroepithelial cells**, facilitating its colonization and subsequent infection of the bladder. *Tension pneumothorax* - A **tension pneumothorax** is a medical emergency characterized by air accumulation in the pleural space, leading to lung collapse and mediastinal shift. - It is typically caused by trauma or iatrogenic factors, not directly by bacterial infection from either *Staphylococcus saprophyticus* or *Staphylococcus aureus*. *Burns* - Burn wounds are highly susceptible to bacterial colonization and infection, with **Staphylococcus aureus** being a primary pathogen in this context. - *Staphylococcus saprophyticus* is rarely associated with burn wound infections. *Osteomyelitis* - **Osteomyelitis**, an infection of the bone, is most frequently caused by **Staphylococcus aureus** via hematogenous spread or direct inoculation. - *Staphylococcus saprophyticus* is not a common pathogen in osteomyelitis.
Question 3: An 18-year-old man has facial and upper back lesions that have waxed and waned for the past 6 years. On physical examination, there are 0.3- to 0.9-cm comedones, erythematous papules, nodules, and pustules most numerous on the lower face and posterior upper trunk. Other family members have been affected by this condition at a similar age. The lesions worsen during a 5-day cruise to the Adriatic. Which of the following organisms is most likely to play a key role in the pathogenesis of these lesions?
- A. Propionibacterium acnes (Correct Answer)
- B. Herpes simplex virus type 1
- C. Group A β-hemolytic streptococcus
- D. Mycobacterium leprae
Explanation: ***Propionibacterium acnes*** (now *Cutibacterium acnes*) - The presence of **comedones, papules, nodules, and pustules** on the face and upper back in an 18-year-old is classic for **acne vulgaris**. - **_P. acnes_** is a commensal bacterium that proliferates in clogged hair follicles, contributing to inflammation and lesion formation in acne due to its lipolytic activity and immune-activating properties. *Herpes simplex virus type 1* - **HSV-1** typically causes **oral herpes (cold sores)** or **genital herpes**, characterized by painful vesicles and ulcers. - The described lesions (comedones, papules, nodules, pustules) are not characteristic of HSV-1 infection. *Group A β-hemolytic streptococcus* - **Group A Strep** causes infections like **pharyngitis (strep throat)**, **impetigo**, or **cellulitis**, which are typically acute and rapidly spreading. - Its presence is not associated with chronic, polymorphic lesions characteristic of acne. *Mycobacterium leprae* - **_M. leprae_** is the causative agent of **leprosy**, presenting with skin lesions, nerve damage, and other systemic effects. - The skin lesions of leprosy are typically macules, papules, or nodules with sensory loss, not the comedones and pustules seen in acne.
Question 4: False about Tinea versicolor
- A. Lesions can be both hypo & hyperpigmented
- B. It is superficial fungal infection caused by Malassezia
- C. Scratch sign is positive
- D. Wood's lamp examination gives Apple green Fluorescence (Correct Answer)
Explanation: ***Wood's lamp examination gives Apple green Fluorescence*** - **Tinea versicolor** typically exhibits a **yellow-green or yellowish-orange fluorescence** under Wood's lamp, not an apple-green fluorescence. - **Apple-green fluorescence** is characteristic of certain bacterial infections, such as those caused by *Pseudomonas aeruginosa*, but not for *Malassezia* species in Tinea versicolor. *Lesions can be both hypo & hyperpigmented* - This statement is true; **Tinea versicolor** lesions can indeed present as **hypopigmented (lighter)** or **hyperpigmented (darker)** patches. - The color variation is due to *Malassezia's* interference with melanin production or its direct pigment production. *It is superficial fungal infection caused by Malassezia* - This statement is true; **Tinea versicolor** is a **superficial fungal infection** of the skin caused by species of the yeast **Malassezia**. - The most common causative agent is **Malassezia globosa**, which is a normal commensal of the skin but can become pathogenic under certain conditions. *Scratch sign is positive* - This statement is true; the **scratch sign** (also known as the Besnier's sign) is positive in **Tinea versicolor**. - When the lesions are gently scraped, fine, **powdery scales** become more apparent, which is a characteristic finding.
Question 5: Best diagnostic test for fungal skin infection –
- A. KOH test (Correct Answer)
- B. Diascopy
- C. Patch test
- D. Wood's lamp
Explanation: ***Correct: KOH test*** - The **potassium hydroxide (KOH) test** is the **most common and rapid method** for diagnosing dermatophyte infections. - It involves dissolving keratinous material to visualize **fungal hyphae** and **spores** under a microscope. - KOH test is **quick, inexpensive, and can be performed in any outpatient setting**, making it the best first-line diagnostic test. *Incorrect: Diascopy* - **Diascopy** is used to determine if a lesion is **vascular** (erythematous and blanches) or **non-vascular** (purpuric and does not blanch). - It involves pressing a glass slide against the lesion and observing color changes. - This test is not relevant for fungal identification. *Incorrect: Patch test* - A **patch test** is used to identify **allergic contact dermatitis** by applying specific allergens to the skin and observing for a delayed hypersensitivity reaction. - It is not designed to detect or diagnose fungal infections. *Incorrect: Wood's lamp* - A **Wood's lamp** emits ultraviolet light and is used to detect certain skin conditions that fluoresce. - While it can help diagnose some fungal infections like **Tinea capitis** caused by *Microsporum* species (which fluoresces green), it is **not a definitive diagnostic test** for all fungal infections. - Many common dermatophytes do not fluoresce, leading to false negatives.
Question 6: A child presents with grouped vesicles on the lips. What is the bedside investigation that you would like to do?
- A. Wood's lamp
- B. Slit skin smear
- C. Tzanck smear (Correct Answer)
- D. KOH
Explanation: ***Tzanck smear*** - A **Tzanck smear** is a rapid bedside test that can identify **multinucleated giant cells**, which are seen in herpes simplex virus infections. - The presence of **grouped vesicles on the lips** is highly suggestive of **herpes labialis** (HSV-1), which is primarily a **clinical diagnosis**. - Among the options provided, Tzanck smear is the only relevant bedside investigation, though it has **limited sensitivity and specificity** and **cannot distinguish between HSV and VZV**. - In modern practice, **PCR or direct immunofluorescence** are preferred when laboratory confirmation is needed, but Tzanck smear remains a low-cost option in resource-limited settings. *Wood's lamp* - A Wood's lamp uses **ultraviolet light** to detect certain fungal or bacterial infections by revealing characteristic fluorescence. - It is useful for conditions like **tinea capitis** (green fluorescence) and **erythrasma** (coral-red fluorescence), but has no role in diagnosing viral vesicular lesions. *Slit skin smear* - A **slit skin smear** is used to detect **acid-fast bacilli** in the diagnosis of **leprosy**. - It is not indicated for vesicular lesions and is irrelevant to herpes simplex infection. *KOH* - A **KOH (potassium hydroxide) mount** is used to diagnose **fungal infections** by dissolving keratinocytes and revealing fungal hyphae or spores. - It has no utility in diagnosing viral infections such as herpes simplex.
Question 7: Which of the following conditions does NOT exhibit dyskeratosis?
- A. Bowen's disease
- B. Squamous cell carcinoma
- C. Darier's disease
- D. Lichen planus (Correct Answer)
Explanation: ***Lichen planus*** - This is an **inflammatory skin condition** characterized by **puritic, polygonal, planar, purple papules and plaques** [1]. - Histologically, it shows a **sawtooth pattern of rete ridges**, basal cell liquefaction degeneration, and a band-like lymphocytic infiltrate, but **no dyskeratosis**. *Squamous cell carcinoma* - This is a **malignant tumor** of keratinocytes that frequently exhibits **dyskeratosis** (premature keratinization of individual cells) [2]. - Dyskeratosis is a key feature indicating abnormal keratinocyte maturation and cellular atypia. *Bowen's disease* - Also known as **squamous cell carcinoma in situ**, Bowen's disease is a full-thickness atypia of the epidermis [2]. - It frequently demonstrates **dyskeratosis** among other features of keratinocyte atypia, such as nuclear pleomorphism and mitotic figures. *Darier's disease* - This is an **autosomal dominant genodermatosis** characterized by abnormal keratinization. - Histologically, it classically presents with **dyskeratosis** in the form of corps ronds and grains, along with suprabasal acantholysis. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Skin, pp. 1168-1170. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Disorders Involving Inflammatory And Haemopoietic Cells, pp. 644-645.
Question 8: Rhinophyma is associated with-
- A. Epithelial cell hyperplasia
- B. Endothelial cell hyperplasia
- C. Sweat gland hypertrophy
- D. Sebaceous gland hypertrophy (Correct Answer)
Explanation: ***Sebaceous gland hypertrophy*** - **Rhinophyma** is a severe form of rosacea characterized by marked thickening and enlargement of the nose, [1] primarily due to **hypertrophy of the sebaceous glands**. - This glandular overgrowth leads to a bulbous, erythematous, and often disfigured appearance of the nose [1]. *Epithelial cell hyperplasia* - While there may be some secondary **epidermal hyperplasia** in rhinophyma, it is not the primary defining feature of the condition. - The dominant histological change is related to the **sebaceous glands** and connective tissue, not mainly the surface epithelium. *Endothelial cell hyperplasia* - **Vascular changes** and **telangiectasias** are common in rosacea, including rhinophyma, indicating some proliferation of endothelial cells [1]. - However, the most prominent and characteristic pathological feature of rhinophyma is the enlargement of the **sebaceous glands**, not the endothelial cells. *Sweat gland hypertrophy* - **Sweat glands** (eccrine or apocrine) are generally not primarily affected or undergo hypertrophy in rhinophyma. - The pathology is specifically centered on the sebaceous glands, which are distinct from sweat glands. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Skin, p. 1176.
Question 9: A patient from Himachal Pradesh gets a thorn prick and subsequently presents with a verrucous lesion on feet which on microscopy revealed "Copper penny bodies". The diagnosis is
- A. Sporothrix
- B. Chromoblastomycosis (Correct Answer)
- C. Verruca vulgaris
- D. Eumycetoma
Explanation: ***Chromoblastomycosis*** - The presence of **"copper penny bodies" (sclerotic bodies or Medlar bodies)** on microscopy is pathognomonic for chromoblastomycosis. - This chronic fungal infection typically presents as **verrucous lesions** on the skin, often in exposed areas like the feet, following **traumatic inoculation**, such as a thorn prick. *Eumycetoma* - Characterized by the formation of **grains or granules** composed of fungal hyphae within subcutaneous tissue, usually with **multiple draining sinuses**. - While it can be caused by a thorn prick and affect the feet, it does not typically show "copper penny bodies" on microscopy. *Sporothrix* - Causes **sporotrichosis**, which often presents as **lymphocutaneous nodules** that ulcerate and follow lymphatic drainage, or fixed cutaneous lesions. - Microscopic examination typically reveals **cigar-shaped budding yeasts** in tissue, not copper penny bodies. *Verruca vulgaris* - This is a common **viral wart** caused by the **Human Papillomavirus (HPV)**, presenting as a raised, rough, cauliflower-like papule [1]. - Histologically, it shows **koilocytes** (HPV-infected keratinocytes), but no fungal elements like "copper penny bodies." [1] **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Skin, p. 1178.
Question 10: A patient presents with a gingival lesion as shown in the image. What is the most likely diagnosis?
- A. Carcinoma alveolar margin
- B. Leukoplakia
- C. Hyperplastic candidiasis
- D. Fibrous epulis (Correct Answer)
Explanation: ***Fibrous epulis*** - The image shows a **focal, exophytic, firm, nodular growth** on the gingiva, which is characteristic of a **fibrous epulis** [1]. These are common reactive lesions caused by **chronic irritation or trauma** [1]. - They are typically **pink, well-demarcated**, and may be pedunculated or sessile, composed primarily of **fibrous connective tissue** [1]. *Carcinoma alveolar margin* - Malignant lesions like **carcinoma** often present with irregular, ulcerated, fungating, or infiltrative borders, and may be associated with **bleeding, pain, or rapid growth** [4]. - While it can occur at the alveolar margin, the lesion in the image appears more organized and smooth-surfaced, which is less consistent with a typical malignant presentation. *Leukoplakia* - **Leukoplakia** is characterized by a **white patch or plaque** that cannot be rubbed off and is not diagnosable as any other disease [3]. - The lesion in the image is a clearly defined, **flesh-colored, nodular mass**, not a flat white patch. *Hyperplastic candidiasis* - **Hyperplastic candidiasis** typically presents as **persistent white plaques** that are adherent to the mucosa and may have a **nodular or granular appearance** [2]. - While it can be firm, the overall presentation in the image, particularly the color and distinct fibrous-like texture, is less suggestive of candidal infection. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Lung, pp. 735-736. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Lung, pp. 736-737. [3] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Alimentary System Disease, pp. 344-345. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Lung, pp. 739-741.
Want unlimited practice?
Get full access to all questions, explanations, and performance tracking.
Start For Free