Parasitic Skin Infections — MCQs

Parasitic Skin Infections Indian Medical PG Practice Questions and MCQs

Question 21: Regarding cutaneous amoebiasis, which statement is NOT true?

A. It is a spreading necrotizing inflammation of the skin and cutaneous tissue.
B. Rapid improvement with anti-amoebic treatment occurs.
C. It can occur in the perianal region.
D. The infection reaches the skin through the bloodstream. (Correct Answer)

Explanation: **Explanation:** Cutaneous amoebiasis is a rare but severe manifestation of *Entamoeba histolytica* infection. The correct answer is **D** because the infection typically reaches the skin through **direct inoculation or contiguous spread**, rather than the bloodstream. **1. Why Option D is the correct answer (False statement):** Cutaneous amoebiasis is almost always secondary to an underlying intestinal or hepatic infection. It occurs via **direct extension** (e.g., perianal involvement from intestinal amoebiasis) or **external inoculation** (e.g., through contaminated dressings or sexual contact). Hematogenous (bloodstream) spread to the skin is extremely rare compared to direct spread. **2. Analysis of other options:** * **Option A:** It is characterized by a **spreading necrotizing inflammation**. The lesions typically present as painful, rapidly enlarging ulcers with "punched-out" or undermined edges and a necrotic base covered in foul-smelling slough. * **Option B:** One of the diagnostic hallmarks is the **dramatic response to anti-amoebic therapy** (like Metronidazole or Emetine). If the lesion does not improve rapidly with treatment, the diagnosis should be reconsidered. * **Option C:** The **perianal region** is the most common site due to direct spread from the rectum in patients with amoebic dysentery. It can also occur around surgical drainage sites (e.g., after drainage of a liver abscess). **High-Yield Clinical Pearls for NEET-PG:** * **Diagnostic Gold Standard:** Identification of **trophozoites** of *E. histolytica* on a skin biopsy or a smear from the ulcer base (look for ingested RBCs within the trophozoite). * **Differential Diagnosis:** Must be differentiated from Pyoderma Gangrenosum and Squamous Cell Carcinoma. * **Key Feature:** The ulcers are exquisitely **painful**, which helps distinguish them from many other chronic skin ulcers.

Question 22: A patient presents with a rash characterized by the "breakfast, lunch, and dinner" sign. Which of the following is the most likely cause?

A. Bed bug (Correct Answer)
B. Mite
C. Ant
D. Tick

Explanation: ### Explanation **Correct Option: A. Bed bug (*Cimex lectularius*)** The "breakfast, lunch, and dinner" sign is a classic clinical descriptor for the linear or zigzag arrangement of three or more pruritic wheals or papules. This pattern occurs because bed bugs are interrupted during feeding or probe multiple sites to find a capillary. The lesions are typically found on exposed areas of skin (face, neck, arms) and are most prominent in the morning, as these insects are nocturnal. **Analysis of Incorrect Options:** * **B. Mite (*Sarcoptes scabiei*):** Causes Scabies, characterized by nocturnal pruritus and **burrows** (pathognomonic) in web spaces, wrists, and genitals. It does not follow a linear "meal" pattern. * **C. Ant:** Ant bites usually result in immediate pain and the formation of sterile pustules (especially Fire Ants) or localized urticaria, often in a clustered but non-linear distribution. * **D. Tick:** Tick bites are usually solitary. The most characteristic rash associated with ticks is **Erythema Chronicum Migrans** (target lesion) seen in Lyme disease, not a linear sequence of papules. **High-Yield Clinical Pearls for NEET-PG:** * **Causative Agent:** *Cimex lectularius* (common bed bug). * **Histopathology:** Shows a superficial and deep perivascular eosinophilic infiltrate (typical of arthropod bite reactions). * **Management:** Primarily symptomatic with topical corticosteroids and oral antihistamines. Eradication requires professional pest control of the environment (mattresses/crevices). * **Key Identifier:** Look for "rusty spots" on bedsheets (fecal spots/crushed bugs) as a diagnostic clue in history.

Question 23: What is the drug of choice for cutaneous larva migrans?

A. Mebendazole
B. Niridazole
C. Hetrazan
D. Thiabendazole (Correct Answer)

Explanation: **Explanation:** **Cutaneous Larva Migrans (CLM)**, also known as "creeping eruption," is most commonly caused by the larvae of the dog or cat hookworm (*Ancylostoma braziliense*). Humans are accidental hosts; the larvae penetrate the skin but lack the enzymes to penetrate the basement membrane, resulting in characteristic serpiginous, erythematous, pruritic tracks. **Why Thiabendazole is the Correct Answer:** **Thiabendazole** is traditionally considered the drug of choice for CLM. It can be administered orally or applied topically (10–15% cream). It works by inhibiting the helminth-specific enzyme fumarate reductase, effectively killing the migrating larvae. While **Albendazole** (400 mg for 3–7 days) and **Ivermectin** (200 µg/kg single dose) are now more commonly used in modern clinical practice due to better tolerability, Thiabendazole remains the classic textbook answer for NEET-PG. **Analysis of Incorrect Options:** * **A. Mebendazole:** Primarily used for intestinal helminths (like pinworm or roundworm). It has poor systemic absorption, making it ineffective for larvae migrating within the skin. * **B. Niridazole:** An older antischistosomal agent rarely used today due to significant toxicity (CNS and GI side effects). * **C. Hetrazan (Diethylcarbamazine/DEC):** The drug of choice for lymphatic filariasis and tropical pulmonary eosinophilia, but it is not effective against the hookworm larvae causing CLM. **Clinical Pearls for NEET-PG:** * **Most common site:** Feet (due to walking barefoot on contaminated sand/soil). * **Löffler’s Syndrome:** Can occur if larvae reach the lungs (rare in CLM, more common in *A. duodenale*). * **Key Clinical Feature:** "Serpiginous" or "Snake-like" migratory tracks that move a few millimeters to centimeters per day.

Question 24: What is the most common cause of cutaneous larva migrans?

A. Ankylostoma caninum (Correct Answer)
B. Toxocara canis
C. Toxocara cati
D. Gnathostoma

Explanation: **Explanation:** **Cutaneous Larva Migrans (CLM)**, also known as "creeping eruption," is a zoonotic infestation caused by the larvae of animal hookworms. 1. **Why Option A is Correct:** **Ankylostoma caninum** (the dog hookworm) is the **most common** cause of CLM worldwide. **Ankylostoma braziliense** (found in both dogs and cats) is another frequent cause. Humans are accidental "dead-end" hosts; the larvae penetrate the skin (usually through contact with contaminated soil or sand) but lack the enzymes necessary to penetrate the basement membrane and reach the circulation. Consequently, they remain confined to the epidermis, migrating aimlessly and creating the characteristic serpiginous, erythematous, pruritic tracks. 2. **Why Other Options are Incorrect:** * **Options B & C (Toxocara canis/cati):** These are the causative agents of **Visceral Larva Migrans (VLM)** and Ocular Larva Migrans. Unlike CLM, these larvae migrate through internal organs rather than the skin. * **Option D (Gnathostoma):** This causes **Larva Migrans Profunda**. Unlike the superficial tracks of CLM, Gnathostomiasis typically presents as deep, migratory subcutaneous swellings (panniculitis). **High-Yield Clinical Pearls for NEET-PG:** * **Classic Presentation:** Intensely pruritic, linear or serpiginous tracks, most commonly on the feet (ground itch). * **Rate of Migration:** The larvae move at a rate of roughly **1–2 cm per day**. * **Löffler’s Syndrome:** Rare systemic involvement where larvae reach the lungs, causing transient pulmonary infiltrates and peripheral eosinophilia. * **Treatment of Choice:** **Oral Albendazole** (400 mg for 3–7 days) or **Ivermectin** (200 µg/kg single dose). Topical Thiabendazole is also an option.

Question 25: What is the characteristic lesion in scabies?

A. Burrows (Correct Answer)
B. Vesicle
C. Papule
D. Pustule

Explanation: **Explanation:** **1. Why Burrows are the Correct Answer:** The **burrow** is the pathognomonic (diagnostic) clinical sign of scabies. It is a short, wavy, greyish-white thread-like line (usually 5–15 mm long) created by the female mite (*Sarcoptes scabiei var. hominis*) as it tunnels through the **stratum corneum** to lay eggs and deposit scybala (feces). These are most commonly found in areas with thin skin and few hair follicles, such as the interdigital webs of the fingers, flexor aspects of the wrists, and the penis. **2. Why Other Options are Incorrect:** * **Vesicles:** While "pearl-like" vesicles can be found at the advancing end of a burrow (containing the mite), they are non-specific and can occur in many inflammatory dermatoses. * **Papules:** These are the most common clinical finding in scabies due to a Type IV hypersensitivity reaction to the mite's proteins, but they are not the *characteristic* or pathognomonic lesion. * **Pustules:** These usually indicate a secondary bacterial infection (typically *Staphylococcus aureus* or *Streptococcus pyogenes*), a common complication of scabies due to scratching. **3. NEET-PG High-Yield Clinical Pearls:** * **Nocturnal Pruritus:** The hallmark symptom is itching that worsens at night (due to increased mite activity with warmth). * **Circle of Hebra:** An imaginary line connecting the axillae, elbow, wrists, and groin, representing the classic distribution of lesions. Note: The face and scalp are typically spared in adults but involved in infants. * **Norwegian (Crusted) Scabies:** A hyperkeratotic variant seen in immunocompromised patients; it is highly contagious due to millions of mites but often lacks the characteristic itch. * **Treatment of Choice:** Topical **Permethrin (5%)** cream is the gold standard. Oral **Ivermectin** is an alternative, especially for institutional outbreaks or crusted scabies.

Question 26: A 6-month-old infant presented with multiple papules and exudative lesions on the face, scalp, and trunk, along with a few vesicles on the palms and soles, for 2 weeks. The infant's mother had a history of itchy lesions. What is the most likely diagnosis?

A. Scabies (Correct Answer)
B. Infantile eczema
C. Infantile seborrheic dermatitis
D. Impetigo contagiosa

Explanation: ### Explanation **Correct Answer: A. Scabies** The clinical presentation is classic for **Infantile Scabies**. Unlike adults, where lesions are typically restricted to the "Circle of Hebra" (sparing the face and scalp), infants frequently present with involvement of the **face, scalp, palms, and soles**. The presence of **vesicles and pustules** on the palms and soles is a hallmark sign in this age group. The history of itchy lesions in the mother is a crucial diagnostic clue, indicating a contagious infestation within the household. **Why other options are incorrect:** * **Infantile Eczema (Atopic Dermatitis):** While it involves the face and trunk, it typically spares the diaper area and rarely presents with isolated vesicles on the palms and soles. There is usually no history of similar lesions in the mother. * **Infantile Seborrheic Dermatitis:** Characterized by greasy, yellowish scales (cradle cap) on the scalp and flexures. It is generally non-itchy and does not present with palmoplantar vesicles. * **Impetigo Contagiosa:** This is a primary bacterial infection presenting with honey-colored crusts. While exudative lesions occur, it would not explain the generalized distribution or the maternal history of pruritus. **Clinical Pearls for NEET-PG:** * **Pathognomonic Sign:** The **Burrow** (S-shaped track) is the most specific sign of scabies, though often difficult to find in infants due to secondary eczematization or infection. * **Nodular Scabies:** Common in infants; reddish-brown pruritic nodules found in the axilla and groin that persist even after successful treatment. * **Treatment of Choice:** **Permethrin 5% cream** is the gold standard. In infants, it must be applied from head to toe (including face/scalp), unlike adults where the head is spared. * **Modified Circle of Hebra:** In infants, the "circle" expands to include the face, scalp, palms, and soles.

Question 27: A 7-year-old boy presents with itchy, excoriated papules on his forehead and exposed areas of the arms and legs that have been present for 3 years. The condition is most severe during the rainy season and improves completely in winter. What is the most likely diagnosis?

A. Insect bite hypersensitivity (Correct Answer)
B. Contact dermatitis
C. Varicella zoster
D. Dermatitis herpetiformis

Explanation: **Explanation:** The clinical presentation of chronic, itchy, excoriated papules localized to exposed areas (forehead, arms, legs) with a distinct **seasonal variation** (worsening in rainy/summer seasons and clearing in winter) is classic for **Insect Bite Hypersensitivity**, also known as **Papular Urticaria**. **1. Why Insect Bite Hypersensitivity is correct:** This is a hypersensitivity reaction (Type I and Type IV) to the saliva of biting insects like mosquitoes, fleas, or bedbugs. It primarily affects children (2–10 years). The "exposed area" distribution is a hallmark. The rainy season provides the ideal breeding ground for insects, leading to exacerbations, while the lack of insect activity in winter leads to complete resolution. **2. Why other options are incorrect:** * **Contact Dermatitis:** While it causes itchy papules, it usually follows the pattern of the offending agent (e.g., nickel, footwear) rather than a strict seasonal pattern related to rainfall. * **Varicella Zoster (Chickenpox):** This presents as an acute febrile illness with a "dewdrop on rose petal" rash that evolves rapidly over days, not a chronic 3-year recurring course. * **Dermatitis Herpetiformis:** This is characterized by intensely pruritic, grouped vesicles on extensor surfaces (elbows, knees, buttocks) and is associated with Celiac disease. It does not follow a seasonal pattern related to the rainy season. **Clinical Pearls for NEET-PG:** * **Distribution:** Usually asymmetrical and grouped in clusters (the "breakfast, lunch, and dinner" sign). * **Histopathology:** Shows superficial and deep perivascular eosinophilic infiltrate (characteristic of arthropod bites). * **Management:** Primarily involves prevention (insect nets/repellents), topical steroids for symptomatic relief, and antihistamines. * **Desensitization:** Most children eventually outgrow the hypersensitivity as they develop natural desensitization over several years.

Question 28: Cutaneous larva migrans is caused by which of the following?

A. Ancylostoma braziliense (Correct Answer)
B. Anisakiasis
C. Necator americanus
D. Ancylostoma catifera

Explanation: **Explanation:** **Cutaneous Larva Migrans (CLM)**, also known as "creeping eruption," is a common tropically acquired dermatosis. It is caused by the accidental penetration of human skin by the larvae of **animal hookworms**. 1. **Why Option A is Correct:** The most common causative agent is **Ancylostoma braziliense**, the hookworm of cats and dogs. Humans are accidental "dead-end" hosts. Because the larvae lack the enzymes (collagenases) necessary to penetrate the human basement membrane and enter the circulation, they remain confined to the epidermis. They migrate aimlessly, creating the characteristic **serpiginous, erythematous, pruritic tracks**. 2. **Why the Other Options are Incorrect:** * **B. Anisakiasis:** This is caused by the ingestion of raw or undercooked fish containing *Anisakis* larvae. It primarily affects the gastrointestinal tract, not the skin. * **C. Necator americanus:** This is a **human hookworm**. Unlike animal hookworms, these larvae can penetrate the basement membrane, enter the bloodstream, and complete their life cycle in the human intestine. While they cause a transient "ground itch" at the site of entry, they do not typically cause the prolonged migrating tracks seen in CLM. * **D. Ancylostoma catifera:** This is a distractor; the correct canine hookworm species is *Ancylostoma caninum*. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** Intensely pruritic, linear or serpiginous tracks that move at a rate of **1–2 cm per day**. * **Most Common Site:** Feet (due to walking barefoot on contaminated sand/soil). * **Treatment of Choice:** **Oral Albendazole** (400 mg for 3–7 days) or **Ivermectin** (200 µg/kg single dose). * **Löffler’s Syndrome:** Rare complication where larvae reach the lungs, causing eosinophilic pneumonia.

Question 29: A 9-month-old child presents with multiple itchy papulovesicular lesions on the face, trunk, palms, and soles. Similar lesions are also observed on the younger brother. Which of the following is the most probable diagnosis?

A. Papular urticaria
B. Scabies (Correct Answer)
C. Atopic dermatitis
D. Allergic contact dermatitis

Explanation: **Explanation:** The clinical presentation of itchy papulovesicular lesions involving the **palms, soles, and face** in an infant, combined with a **history of similar symptoms in a family member**, is a classic hallmark of **Infantile Scabies**. 1. **Why Scabies is correct:** Scabies is caused by the mite *Sarcoptes scabiei*. While adult scabies typically spares the head and neck, infantile scabies (children <2 years) characteristically involves the **face, scalp, palms, and soles**. The presence of lesions on the younger brother indicates a highly contagious infestation, which is a key diagnostic clue in NEET-PG questions. 2. **Why other options are incorrect:** * **Papular Urticaria:** This is a hypersensitivity reaction to insect bites. It typically presents as grouped, firm papules on exposed areas (legs/arms) and is not usually contagious among family members. * **Atopic Dermatitis:** While it causes intense itching and can involve the face, it usually presents with xerosis (dry skin) and poorly defined erythematous patches rather than a contagious papulovesicular eruption involving the palms and soles. * **Allergic Contact Dermatitis:** This is rare in a 9-month-old and would be localized to the site of allergen exposure rather than a generalized distribution. **High-Yield Clinical Pearls for NEET-PG:** * **Pathognomonic Sign:** The **Burrow** (S-shaped track) is the most specific sign, though often difficult to find in infants due to secondary infection or eczematization. * **Nodular Scabies:** Commonly seen in infants on the axillae and groin; these are hypersensitivity reactions to the mite and persist even after treatment. * **Drug of Choice:** **Permethrin 5% cream** is the gold standard. In infants, it must be applied from head to toe (including face/scalp), unlike adults where it is applied neck-down. * **Treatment Rule:** Always treat all close household contacts simultaneously to prevent re-infestation.

Question 30: Cutaneous larva currens is a feature of which of the following?

A. Ancylostoma braziliense
B. Ancylostoma caninum
C. Strongyloides stercoralis (Correct Answer)
D. Loa loa

Explanation: **Explanation:** **Larva currens** is a pathognomonic clinical sign of **Strongyloides stercoralis** infection. It occurs during the autoinfection cycle when filariform larvae penetrate the perianal skin and migrate rapidly through the dermis. The term "currens" (Latin for "running") refers to the exceptionally high speed of migration—up to **5–10 cm per hour**—resulting in a rapidly advancing, pruritic, erythematous, serpiginous wheal. **Analysis of Options:** * **Strongyloides stercoralis (Correct):** Causes Larva currens. It typically presents in the perianal region, buttocks, or trunk. Due to its speed, the lesion changes position visibly within a short period. * **Ancylostoma braziliense & A. caninum (Incorrect):** These are the most common causes of **Cutaneous Larva Migrans (CLM)** or "creeping eruption." Unlike larva currens, CLM moves much slower (about **1–2 cm per day**) and is caused by non-human hookworms that cannot complete their life cycle in humans. * **Loa loa (Incorrect):** This filarial nematode causes **Calabar swellings** (transient localized angioedema) and can be seen migrating across the subconjunctiva of the eye. **High-Yield NEET-PG Pearls:** 1. **Speed is the Key:** Larva currens (cm/hour) vs. Larva migrans (cm/day). 2. **Autoinfection:** *S. stercoralis* is unique because it can complete its entire life cycle within the human host, leading to persistent infections for decades. 3. **Hyperinfection Syndrome:** In immunocompromised patients (especially those on steroids), *S. stercoralis* can lead to fatal disseminated disease. 4. **Treatment:** Ivermectin is the drug of choice for Strongyloidiasis.

Practice by Chapter

Scabies

Practice Questions

Pediculosis

Practice Questions

Cutaneous Larva Migrans

Practice Questions

Leishmaniasis

Practice Questions

Onchocerciasis

Practice Questions

Myiasis

Practice Questions

Tungiasis

Practice Questions

Cutaneous Amebiasis

Practice Questions

Cutaneous Manifestations of Malaria

Practice Questions

Ectoparasitic Infestations

Practice Questions

Diagnosis of Parasitic Infestations

Practice Questions

Antiparasitic Therapy

Practice Questions

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