Parasitic Skin Infections Practice Questions

Q: A 2-year-old child presents with a 4-day history of a rash limited to the feet and ankles. The papular rash is both pruritic and erythematous. The 3-month-old sibling of this patient has similar lesions also involving the head and neck. What is the most appropriate treatment for this condition?

Permethrin. **Explanation:** The clinical presentation is classic for **Scabies**, a contagious infestation caused by the mite *Sarcoptes scabiei*. In children, the presentation is often characterized by intensely pruritic, erythematous papules. A key diagnostic clue in this scenario is the involvement of the **head and neck in the 3-month-old sibling**; while adults typically spare the head, in infants and young children, the rash frequently involves the face, scalp, palms, and soles. **1. Why Permethrin is correct:** **5% Permethrin cream** is the first-line treatment (Gold Standard) for scabies. It acts by disrupting the sodium channel currents in the neurons of the parasites, leading to paralysis and death. It is preferred due to its high efficacy and low mammalian toxicity. It should be applied from the neck down in adults, but **from head to toe** in infants and young children. **2. Why other options are incorrect:** * **Coal-tar soap:** Used primarily in chronic plaque psoriasis or seborrheic dermatitis; it has no role in treating parasitic infestations. * **Hydrocortisone cream:** A low-potency steroid that might temporarily reduce itching but will not treat the underlying infestation. In fact, using steroids alone can lead to *Scabies Incognito*, masking the classic symptoms while the infestation worsens. * **Emollients:** These are moisturizing agents used for barrier repair in atopic dermatitis or xerosis; they are ineffective against mites. **Clinical Pearls for NEET-PG:** * **Pathognomonic sign:** The **Burrow** (a short, wavy, grayish line). * **Treatment Protocol:** Apply at night, leave for 8–12 hours, and repeat after 7–14 days to kill newly hatched nymphs. * **Family Treatment:** All close contacts must be treated simultaneously, even if asymptomatic, to prevent re-infestation. * **Nodular Scabies:** Persistent itchy nodules in the axilla or genitalia, common in children even after successful treatment.

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

Bed bug. ### 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.

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.

Question 1

A 2-year-old child presents with a 4-day history of a rash limited to the feet and ankles. The papular rash is both pruritic and erythematous. The 3-month-old sibling of this patient has similar lesions also involving the head and neck. What is the most appropriate treatment for this condition?

Accepted Answer

Permethrin

Answer

Coal-tar soap

Answer

Hydrocortisone cream

Answer

Emollients

Question 2

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

Accepted Answer

Bed bug

Answer

Mite

Answer

Ant

Answer

Tick

Question 3

What is the drug of choice for cutaneous larva migrans?

Accepted Answer

Thiabendazole

Answer

Mebendazole

Answer

Niridazole

Answer

Hetrazan

Question 4

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 5

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 6

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 7

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 8

What is the drug of choice for treating scabies?

Accepted Answer

Permethrin

Answer

Ivermectin

Answer

Albendazole

Answer

Fluconazole

Question 9

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 10

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)

Parasitic Skin Infections — MCQs

Parasitic Skin Infections — MCQs

On this page

Practice by Chapter

Want unlimited practice?