Parasitic Skin Infections Practice Questions

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

Thiabendazole. **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.

Q: 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?

Scabies. ### 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.

Q: 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?

Scabies. **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.

Q: What is the drug of choice for treating scabies?

Permethrin. **Explanation:** **Permethrin (5% cream)** is the current **drug of choice** for the treatment of scabies caused by the mite *Sarcoptes scabiei*. It acts by disrupting the sodium channel conductance in the neuronal membranes of the parasite, leading to delayed repolarization, paralysis, and death. It is preferred due to its high efficacy (ovocidal activity), low systemic toxicity, and superior safety profile compared to older agents like Lindane. **Analysis of Options:** * **Permethrin (A):** Correct. It is applied from the neck down to the toes, left for 8–12 hours, and then washed off. A single application is usually curative, though a second dose after 1–2 weeks is often recommended to kill newly hatched mites. * **Ivermectin (B):** This is an oral alternative and is the **drug of choice for Crusted (Norwegian) Scabies** or for managing outbreaks in institutional settings. However, it is generally considered second-line to topical Permethrin for classic scabies. * **Albendazole (C):** An anthelmintic used primarily for intestinal worms (roundworms, hookworms) and Neurocysticercosis. It has no role in treating scabies. * **Fluconazole (D):** An antifungal agent used for candidiasis and other fungal infections; it is ineffective against ectoparasites like mites. **High-Yield Clinical Pearls for NEET-PG:** * **Safe in Pregnancy:** Permethrin is the safest choice for pregnant/lactating women and infants (>2 months). * **Treatment Strategy:** Always treat all close household contacts simultaneously, even if asymptomatic, to prevent re-infestation. * **Lindane Warning:** No longer first-line due to risk of neurotoxicity (seizures), especially in children and patients with skin breakdown.

Q: Which of the following drugs is NOT used in the management of scabies?

Tacrolimus. **Explanation:** The management of scabies, caused by the mite *Sarcoptes scabiei*, requires **scabicidal agents**—drugs that directly kill the mites and their eggs. **Why Tacrolimus is the correct answer:** **Tacrolimus** is a **calcineurin inhibitor** and an immunosuppressant. It is used primarily in the management of atopic dermatitis and vitiligo to modulate the immune response. It has **no scabicidal properties**. In fact, applying topical steroids or immunosuppressants like tacrolimus to an undiagnosed scabies infestation can lead to "Scabies Incognito," where the typical inflammatory signs are masked while the infestation worsens. **Analysis of other options:** * **Permethrin (5%):** The current **drug of choice** for scabies. It acts by disrupting the sodium channel currents in the neurons of the mites, leading to paralysis and death. * **Gamma-benzene hexachloride (Lindane):** An organochlorine insecticide that was once a first-line treatment. Its use has declined due to potential neurotoxicity (seizures), especially in children and patients with damaged skin. * **Crotamiton (10%):** A scabicidal and antipruritic agent. While less effective than permethrin, it is useful in pediatric cases or when itching persists. **High-Yield Clinical Pearls for NEET-PG:** * **Ivermectin:** The oral drug of choice (200 μg/kg). It is particularly useful in institutional outbreaks and **Crusted (Norwegian) Scabies**. * **Treatment Protocol:** Scabicides must be applied from the **neck down to the toes** and left overnight. * **Nodular Scabies:** Characterized by itchy nodules on the genitalia/axilla; these are hypersensitivity reactions and may require topical steroids *after* the mites are eradicated. * **Safety:** Permethrin is considered safe in pregnancy and for infants over 2 months of age.

Q: What is considered the most severe form of scabies?

Norwegian scabies. **Explanation:** **Norwegian Scabies (Crusted Scabies)** is the correct answer because it represents a hyperkeratotic, highly contagious infestation characterized by millions of *Sarcoptes scabiei* mites. Unlike classical scabies (where a patient hosts 10–15 mites), Norwegian scabies occurs in immunocompromised individuals (HIV, leprosy), those with neurological deficits (Down syndrome), or the elderly. The lack of an effective cell-mediated immune response allows for uncontrolled mite proliferation, leading to thick, "oyster-shell" crusts, particularly on the palms, soles, and scalp. **Analysis of Incorrect Options:** * **Nodular Scabies:** A hypersensitivity reaction to mite antigens. It presents as persistent, itchy reddish-brown nodules (often on genitalia or axillae) that remain even after the mites are eradicated. It is not "severe" in terms of mite burden. * **Animal Scabies:** Caused by mites from pets (e.g., *Sarcoptes scabiei var. canis*). It is self-limiting in humans because the mites cannot complete their life cycle on human skin; no burrows are formed. * **Genital Scabies:** Simply refers to the site of involvement. While distressing, it follows the clinical course of classical scabies and is not a distinct severe variant. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Oral **Ivermectin** (200 µg/kg) combined with topical **Permethrin (5%)** is the gold standard for Crusted Scabies. * **Key Feature:** It is often **non-pruritic** or minimally itchy despite the massive infestation. * **Sign:** The "Circle of Hebra" refers to the characteristic distribution of classical scabies (interdigital webs, wrists, elbows, axillae, areola, and umbilicus).

Q: Skin lesions following visceral leishmaniasis typically present as which of the following?

Hypopigmented macules. **Explanation:** The question describes **Post-Kala-Azar Dermal Leishmaniasis (PKDL)**, a non-ulcerative cutaneous manifestation that occurs in patients following the clinical recovery from Visceral Leishmaniasis (Kala-azar), caused by *Leishmania donovani*. **Why Hypopigmented Macules are Correct:** PKDL typically presents in two stages. The earliest and most common presentation is **hypopigmented macules**, which usually start on the face and later spread to the trunk and extremities. These macules are characteristically non-anesthetic (unlike Leprosy). Over time, these may progress into malar erythema, followed by the development of yellowish-pink non-ulcerating nodules or plaques. **Why Other Options are Incorrect:** * **Hyperpigmented Macules:** While Kala-azar itself is known as "Black Fever" due to generalized hyperpigmentation (especially on the hands, feet, and abdomen), the specific dermal sequel (PKDL) is characterized by a loss of pigment (hypopigmentation), not an increase. * **Ecchymosis:** This refers to subcutaneous bleeding/bruising. While Visceral Leishmaniasis can cause thrombocytopenia leading to bleeding tendencies, it is not a characteristic feature of the post-treatment skin lesions (PKDL). **High-Yield Clinical Pearls for NEET-PG:** * **Incidence:** In the Indian subcontinent, PKDL occurs in about 5-10% of cases, usually **2–3 years** after the visceral phase. In Sudan, it occurs in up to 50% of cases, much sooner (weeks to months). * **Diagnosis:** Slit-skin smear or biopsy shows **LD bodies** (Amastigotes), though they are harder to find in macules compared to nodules. * **Treatment:** The drug of choice in India is **Miltefosine** (for 12 weeks) or Amphotericin B. * **Public Health Significance:** Patients with PKDL act as an important **environmental reservoir** for the parasite, as the lesions are highly infectious to sandflies (*Phlebotomus argentipes*).

Question 1

What is the drug of choice for cutaneous larva migrans?

Accepted Answer

Thiabendazole

Answer

Mebendazole

Answer

Niridazole

Answer

Hetrazan

Question 2

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?

Accepted Answer

Scabies

Answer

Infantile eczema

Answer

Infantile seborrheic dermatitis

Answer

Impetigo contagiosa

Question 3

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?

Accepted Answer

Insect bite hypersensitivity

Answer

Contact dermatitis

Answer

Varicella zoster

Answer

Dermatitis herpetiformis

Question 4

What is the most likely diagnosis in a patient with a migratory, pruritic skin eruption?

Accepted Answer

Cutaneous larva migrans

Answer

Contact dermatitis

Answer

Paragonimiasis

Answer

Myiasis

Question 5

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?

Accepted Answer

Scabies

Answer

Papular urticaria

Answer

Atopic dermatitis

Answer

Allergic contact dermatitis

Question 6

What is the drug of choice for treating scabies?

Accepted Answer

Permethrin

Answer

Ivermectin

Answer

Albendazole

Answer

Fluconazole

Question 7

In a child presenting with itchy lesions over the groin and prepuce, which of the following management strategies is NOT indicated?

Accepted Answer

Administer intravenous antibiotics.

Answer

Administer a bath and apply a scabicidal agent.

Answer

Treat all household contacts.

Answer

Boil clothing and bedding.

Question 8

Which of the following drugs is NOT used in the management of scabies?

Accepted Answer

Tacrolimus

Answer

Crotamiton

Answer

Permethrin

Answer

Gamma-benzene hexachloride (BHC)

Question 9

What is considered the most severe form of scabies?

Accepted Answer

Norwegian scabies

Answer

Nodular scabies

Answer

Animal scabies

Answer

Genital scabies

Question 10

Skin lesions following visceral leishmaniasis typically present as which of the following?

Accepted Answer

Hypopigmented macules

Answer

Hyperpigmented macules

Answer

Ecchymosis

Answer

All of the above

Parasitic Skin Infections — MCQs

Parasitic Skin Infections — MCQs

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