Parasitic Skin Infections — MCQs

Q: Adult scabies is characterized by which of the following?

Involvement of palms and soles. **Explanation:** Scabies is a contagious skin infestation caused by the mite *Sarcoptes scabiei var. hominis*. The distribution of lesions is the most critical diagnostic feature in NEET-PG questions. **1. Why Option A is Correct:** In **adult scabies**, the "Circle of Hebra" defines the classic distribution. This includes the interdigital spaces, wrists, elbows, axillae, periumbilical area, and genitalia. While traditionally taught that palms and soles are spared in adults compared to infants, modern clinical dermatology (and standard textbooks like IADVL) recognizes that **palms and soles** are frequently involved in adults, especially in cases of high mite burden or crusted scabies. Among the given options, it is the most characteristic site of involvement. **2. Why Options B and C are Incorrect:** * **Option B (Face):** The face and scalp are characteristically **spared** in adult scabies. This is because adults have a higher density of sebaceous glands; the sebum is thought to be inhibitory to the mites. Facial involvement is a hallmark of **infantile scabies** or **crusted (Norwegian) scabies**. * **Option C (Anterior Abdomen):** While the periumbilical area is involved, "anterior abdomen" is too broad and less specific than the involvement of the palms/soles or the web spaces. **Clinical Pearls for NEET-PG:** * **Infantile Scabies:** Unlike adults, infants show involvement of the **face, scalp, palms, and soles** with common secondary vesicopustules. * **Pathognomonic Sign:** The **Burrow** (a S-shaped track) is the clinical hallmark, most commonly found on the finger webs and wrists. * **Nocturnal Pruritus:** Itching is worst at night due to a Type IV hypersensitivity reaction to the mite, its eggs, and scybala (feces). * **Treatment of Choice:** Topical **Permethrin (5%)** is the gold standard. Oral Ivermectin (200 µg/kg) is an alternative or adjunct for crusted scabies.

Q: An infant presents with papulovesicular lesions on the palms, soles, face, and trunk. What is the most likely diagnosis?

Scabies. ### Explanation **Correct Answer: A. Scabies** The clinical presentation of papulovesicular lesions involving the **palms, soles, and face** in an infant is classic for **Infantile Scabies**. While scabies in adults typically spares the head and neck (due to the distribution of sebaceous glands), infants are an exception. In this age group, the infestation is often generalized, frequently involving the face, scalp, palms, and soles. The lesions are often inflammatory, presenting as vesicles, pustules, or nodules rather than the classic burrows seen in adults. **Why other options are incorrect:** * **Atopic Dermatitis:** While common in infants, it typically presents as erythematous, itchy, scaly patches on the cheeks and extensor surfaces. It rarely involves the palms and soles. * **Urticaria:** Presents as transient, evanescent wheals (hives) that migrate. It does not present as persistent papulovesicular lesions. * **Seborrheic Dermatitis:** Characterized by "cradle cap" (greasy yellow scales) on the scalp and involvement of skin folds (intertriginous areas). It is generally non-pruritic and does not affect the palms and soles. **High-Yield Clinical Pearls for NEET-PG:** * **Pathogen:** *Sarcoptes scabiei var. hominis*. * **Hallmark Sign:** The **Burrow** (S-shaped track), most commonly found in finger webs and wrist creases. * **Infantile Scabies Key Difference:** Involvement of the **face, scalp, palms, and soles** is a high-yield diagnostic pointer. * **Treatment of Choice:** Topical **Permethrin (5%)** cream. For infants under 2 months, **Precipitated Sulfur (6-10%)** is often preferred due to safety profiles. * **Nodular Scabies:** Persistent itchy nodules in the axilla or genitalia, representing a hypersensitivity reaction.

Q: A 6-month-old infant presented with multiple erythematous papules and exudative lesions on the face, scalp, trunk, and a few vesicles on palms and soles for 2 weeks. The infant's mother has 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 scabies typically spares the head and neck, infants frequently present with involvement of the **face, scalp, palms, and soles**. The presence of **vesicles** on the palms and soles is a high-yield diagnostic clue in this age group. Furthermore, the history of itchy lesions in the mother (a close contact) strongly points toward a contagious parasitic infestation. **Why other options are incorrect:** * **Infantile Eczema (Atopic Dermatitis):** While it involves the face and trunk with exudative lesions, it typically **spares the diaper area** and rarely presents with discrete vesicles on the palms and soles. There is usually a family history of atopy rather than a history of acute contagious itching. * **Infantile Seborrheic Dermatitis:** This presents with greasy, yellow 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 superficial bacterial infection characterized by honey-colored crusts. While it can complicate scabies (secondary infection), it would not explain the widespread distribution and the mother’s symptoms. **NEET-PG High-Yield Pearls:** * **Pathognomonic sign:** The **Burrow** (S-shaped track), though often difficult to find in infants due to secondary eczematization or infection. * **Nodular Scabies:** Common in infants; occurs on the axillae and groin as a hypersensitivity reaction. * **Treatment of Choice:** **Permethrin 5% cream** (applied from head to toe in infants). * **Alternative:** Oral Ivermectin (only for children >15 kg or >5 years old). * **Key Rule:** Always treat all close household contacts simultaneously to prevent re-infestation.

Q: Vagabond disease is transmitted by which of the following?

Louse. **Explanation:** **Vagabond disease** (also known as Parasitophobia or Vagabond's Melanoderma) is a skin condition caused by a chronic infestation of **Body Lice (*Pediculus humanus corporis*)**. 1. **Why Louse is correct:** The disease typically occurs in individuals with poor hygiene, such as the homeless or "vagabonds." Chronic scratching due to persistent body lice infestation leads to post-inflammatory hyperpigmentation and thickening (lichenification) of the skin. The skin becomes dark, dry, and scaly, resembling a "melanoderma." Unlike head lice, body lice live in the seams of clothing and only move to the skin to feed. 2. **Why other options are incorrect:** * **Mite:** *Sarcoptes scabiei* causes Scabies, characterized by nocturnal itching and burrows in web spaces, but it does not cause the generalized melanoderma seen in Vagabond disease. * **Tick:** Ticks are vectors for systemic diseases like Rocky Mountain Spotted Fever or Lyme disease, but they do not cause chronic infestation-related skin pigmentation. * **Black Fly:** These are vectors for Onchocerciasis (River Blindness) and do not cause Vagabond disease. **High-Yield Clinical Pearls for NEET-PG:** * **Vector Potential:** Body lice are significant because they transmit **Epidemic Typhus** (*Rickettsia prowazekii*), **Trench Fever** (*Bartonella quintana*), and **Epidemic Relapsing Fever** (*Borrelia recurrentis*). * **Diagnosis:** Look for lice or nits in the **seams of the patient's clothing**, rather than on the body itself. * **Treatment:** The primary treatment is laundering clothing in hot water (>60°C) and improving personal hygiene; topical pediculicides (e.g., Permethrin) are secondary.

Q: Prurigo of Hebra is most probably caused by which of the following?

Allergy to insect bites. **Explanation:** **Prurigo of Hebra** (also known as Prurigo Ferox) is a chronic, severely pruritic skin disorder primarily seen in children and young adults. **1. Why Option B is Correct:** The underlying medical concept is a **hypersensitivity reaction (Type I and Type IV)** to antigens introduced by **insect bites** (most commonly mosquitoes, fleas, or bedbugs). It is considered a severe, chronic variant of papular urticaria. The condition is characterized by extremely itchy, firm, dome-shaped papules, often with a central crust or "pitting," predominantly affecting the extensor surfaces of the limbs. **2. Why Other Options are Incorrect:** * **Option A (Autoimmune):** While some pruritic conditions like Pemphigoid are autoimmune, Prurigo of Hebra is strictly an inflammatory response to external parasitic stimuli. * **Option C (Papova virus):** Papovaviruses (like HPV) cause warts. There is no viral etiology associated with Prurigo of Hebra. * **Option D (Focal infection):** While secondary bacterial infection (impetiginization) is a common complication due to intense scratching, a focal internal infection is not the primary cause of the disease. **3. NEET-PG High-Yield Pearls:** * **Clinical Presentation:** Look for the "Hard Papules of Hebra" on the legs, associated with **post-inflammatory hyperpigmentation** and **lymphadenopathy** (Prurigo buboes). * **Epidemiology:** More common in lower socioeconomic groups and tropical climates where insect exposure is high. * **Management:** Focuses on insect bite prevention (nets/repellents), topical steroids, and antihistamines. In refractory cases, phototherapy (PUVA) may be used. * **Differential Diagnosis:** Must be distinguished from Atopic Dermatitis; however, Hebra's lacks the typical flexural involvement.

Q: Scabies can be effectively treated systemically by:

Ivermectin. ### Explanation **Correct Answer: B. Ivermectin** **Why Ivermectin is correct:** Ivermectin is the only **systemic (oral)** treatment option listed for Scabies. It is an anthelmintic agent that works by binding to glutamate-gated chloride channels in the invertebrate nerve and muscle cells, leading to paralysis and death of the *Sarcoptes scabiei* mite. * **Dosage:** 200 μg/kg body weight as a single oral dose, repeated after 1–2 weeks (to kill mites that hatched from eggs after the first dose). * **Indications:** It is particularly useful for institutional outbreaks, bedridden patients, and is the drug of choice for **Crusted (Norwegian) Scabies** (used in combination with topical agents). **Why other options are incorrect:** * **A. Psoralens:** These are photosensitizing agents used in PUVA therapy for conditions like Psoriasis and Vitiligo; they have no role in treating parasitic infections. * **C. Permethrin (5%):** While Permethrin is the **overall drug of choice** for scabies, it is a **topical** cream, not a systemic treatment. * **D. Cotrimoxazole:** This is an antibiotic used for bacterial infections or *Pneumocystis jirovecii*. While it has been studied for head lice, it is not a standard treatment for scabies. **High-Yield Clinical Pearls for NEET-PG:** 1. **Drug of Choice (Topical):** 5% Permethrin (apply neck down, leave for 8–12 hours). 2. **Drug of Choice (Systemic/Crusted Scabies):** Oral Ivermectin. 3. **Nodular Scabies:** Treated with intralesional or potent topical steroids (it is a hypersensitivity reaction, not active infestation). 4. **Contraindication:** Oral Ivermectin is generally avoided in children weighing <15 kg and pregnant/lactating women. 5. **The "Seven Year Itch":** Itching is typically worse at night (nocturnal exacerbation).

Q: A 7-month-old infant presents with itchy erythematous papules and vesicles on the palms and soles. Examination reveals serpentine, thread-like lesions and eczematous, crusted lesions on the face and trunk. The mother reports similar lesions in other family members. What is the most probable diagnosis?

Scabies. **Explanation:** The clinical presentation is classic for **Infantile Scabies**, caused by the mite *Sarcoptes scabiei*. Unlike adults, where lesions are typically restricted to the "Circle of Hebra," infants frequently show involvement of the **palms, soles, face, and scalp**. The presence of **serpentine, thread-like lesions (burrows)** is pathognomonic. The history of similar symptoms in family members strongly suggests a contagious parasitic infestation rather than an endogenous dermatitis. **Why other options are incorrect:** * **Atopic Dermatitis:** While it causes itchy eczematous lesions on the face and trunk, it typically spares the diaper area and does not present with burrows or a strong family history of acute contagion. * **Papular Urticaria:** This is a hypersensitivity reaction to insect bites. It presents as recurrent, grouped erythematous papules (often with a central punctum), but it does not feature burrows or widespread palm/sole involvement. * **Seborrheic Dermatitis:** This presents as "cradle cap" (greasy yellow scales) on the scalp and flexures. It is generally non-pruritic and does not involve the palms and soles with vesicles. **High-Yield Clinical Pearls for NEET-PG:** * **Pathognomonic sign:** The Burrow (linear track representing the female mite's tunnel). * **Nodular Scabies:** Often seen in children on the axillae and genitalia; represents a hypersensitivity reaction. * **Drug of Choice:** **Permethrin 5% cream** (applied neck-down in adults; head-to-toe in infants). * **Alternative:** Oral Ivermectin (200 µg/kg), but it is generally avoided in children weighing <15 kg. * **Treatment Rule:** Always treat all close contacts simultaneously to prevent re-infection.

Q: Where is nodular scabies typically found?

Scrotum. **Explanation:** **Nodular scabies** is a clinical variant of scabies characterized by persistent, intensely pruritic, reddish-brown nodules. These nodules represent a **hypersensitivity reaction** to the mite, its eggs, or scybala (feces), rather than an active infestation in those specific lesions. **Why Scrotum is the Correct Answer:** The most characteristic and high-yield site for nodular scabies is the **scrotum and penis** in males. Other common sites include the groin and the axillary folds. These nodules are unique because they often persist for weeks or months even after the mites have been successfully eradicated by scabicides (post-scabietic nodules). **Analysis of Incorrect Options:** * **A. Web space of fingers:** This is the most common site for **classic scabies** and the typical location to find "burrows." While common in general scabies, it is not the classic site for the *nodular* variant. * **B. Axilla:** While nodular scabies can occur in the axillary folds, the **scrotum** is considered the most pathognomonic and frequently tested site for this specific presentation. * **C. Abdomen:** The periumbilical area is a common site for the "Circle of Hebra" in classic scabies, but it is less common for the persistent nodular form compared to the genitalia. **Clinical Pearls for NEET-PG:** * **Circle of Hebra:** Refers to the distribution of scabies (axilla, elbow, wrist, finger webs, and genitals). * **Treatment:** Nodular scabies does not respond to repeat scabicides alone. It requires **intralesional or topical corticosteroids** or coal tar to suppress the hypersensitivity reaction. * **Infants:** In infants, scabies can involve the face, scalp, palms, and soles (areas usually spared in adults). * **Norwegian (Crusted) Scabies:** Seen in immunocompromised patients; characterized by thousands of mites and minimal itching.

A 10-year-old girl presents with multiple excoriations on her hands that have appeared over the past week. She reports itching and scratching her hands. Physical examination reveals multiple 0.2- to 0.6-cm linear streaks in the interdigital regions. The condition resolved with topical lindane lotion. Which of the following organisms is most likely responsible for these findings?

Q6Easy

Vagabond disease is transmitted by which of the following?

Q7Easy

Prurigo of Hebra is most probably caused by which of the following?

Q8Medium

Scabies can be effectively treated systemically by:

Q9Medium

A 7-month-old infant presents with itchy erythematous papules and vesicles on the palms and soles. Examination reveals serpentine, thread-like lesions and eczematous, crusted lesions on the face and trunk. The mother reports similar lesions in other family members. What is the most probable diagnosis?

Q10Easy

Where is nodular scabies typically found?

Parasitic Skin Infections Indian Medical PG Practice Questions and MCQs

Question 1: Adult scabies is characterized by which of the following?

A. Involvement of palms and soles (Correct Answer)
B. Involvement of the face
C. Involvement of the anterior abdomen
D. All of the above

Explanation: **Explanation:** Scabies is a contagious skin infestation caused by the mite *Sarcoptes scabiei var. hominis*. The distribution of lesions is the most critical diagnostic feature in NEET-PG questions. **1. Why Option A is Correct:** In **adult scabies**, the "Circle of Hebra" defines the classic distribution. This includes the interdigital spaces, wrists, elbows, axillae, periumbilical area, and genitalia. While traditionally taught that palms and soles are spared in adults compared to infants, modern clinical dermatology (and standard textbooks like IADVL) recognizes that **palms and soles** are frequently involved in adults, especially in cases of high mite burden or crusted scabies. Among the given options, it is the most characteristic site of involvement. **2. Why Options B and C are Incorrect:** * **Option B (Face):** The face and scalp are characteristically **spared** in adult scabies. This is because adults have a higher density of sebaceous glands; the sebum is thought to be inhibitory to the mites. Facial involvement is a hallmark of **infantile scabies** or **crusted (Norwegian) scabies**. * **Option C (Anterior Abdomen):** While the periumbilical area is involved, "anterior abdomen" is too broad and less specific than the involvement of the palms/soles or the web spaces. **Clinical Pearls for NEET-PG:** * **Infantile Scabies:** Unlike adults, infants show involvement of the **face, scalp, palms, and soles** with common secondary vesicopustules. * **Pathognomonic Sign:** The **Burrow** (a S-shaped track) is the clinical hallmark, most commonly found on the finger webs and wrists. * **Nocturnal Pruritus:** Itching is worst at night due to a Type IV hypersensitivity reaction to the mite, its eggs, and scybala (feces). * **Treatment of Choice:** Topical **Permethrin (5%)** is the gold standard. Oral Ivermectin (200 µg/kg) is an alternative or adjunct for crusted scabies.

Question 2: An 8-month-old child presented with itchy, exudative lesions on the face, palms, and soles. The siblings also have similar complaints. Which of the following is the treatment of choice?

A. Systemic ampicillin
B. Topical permethrin (Correct Answer)
C. Systemic prednisolone
D. Topical betamethasone

Explanation: ### Explanation **Diagnosis: Infantile Scabies** The clinical presentation of itchy, exudative lesions involving the **palms and soles**, combined with a **positive family history** (siblings affected), is pathognomonic for Scabies. In infants, unlike adults, the lesions frequently involve the face, scalp, palms, and soles and often present as vesicles or pustules due to secondary eczematization. **1. Why Topical Permethrin is Correct:** * **Permethrin (5% cream)** is the **drug of choice** for scabies in infants older than 2 months. * **Mechanism:** It acts by disrupting the sodium channel currents in the neurons of the *Sarcoptes scabiei* mite, leading to paralysis and death. * **Application:** It should be applied from head to toe in infants (including the face and scalp, avoiding eyes/mouth) and washed off after 8–12 hours. **2. Why Other Options are Incorrect:** * **Systemic Ampicillin:** While lesions may appear "exudative" due to secondary bacterial infection (impetiginization), the primary pathology is parasitic. Antibiotics alone will not cure the underlying infestation. * **Systemic Prednisolone & Topical Betamethasone:** These are corticosteroids. Using steroids in scabies is contraindicated as they mask the symptoms ("Scabies Incognito") and can worsen the infestation by suppressing the local immune response against the mites. **3. NEET-PG High-Yield Pearls:** * **Drug of Choice in Pregnancy/Lactation:** Permethrin 5%. * **Ivermectin:** Oral ivermectin (200 µg/kg) is an alternative but is generally **avoided in children weighing <15 kg** or pregnant women. * **Nodular Scabies:** Characterized by reddish-brown itchy nodules in the axilla and genitalia; treated with intralesional steroids. * **Crusted (Norwegian) Scabies:** Seen in immunocompromised patients; characterized by thousands of mites and minimal itching. Requires combination therapy (Oral Ivermectin + Topical Permethrin). * **Key Management Rule:** Always treat all close contacts simultaneously, even if asymptomatic, to prevent re-infestation.

Question 3: An infant presents with papulovesicular lesions on the palms, soles, face, and trunk. What is the most likely diagnosis?

A. Scabies (Correct Answer)
B. Atopic dermatitis
C. Urticaria
D. Seborrheic dermatitis

Explanation: ### Explanation **Correct Answer: A. Scabies** The clinical presentation of papulovesicular lesions involving the **palms, soles, and face** in an infant is classic for **Infantile Scabies**. While scabies in adults typically spares the head and neck (due to the distribution of sebaceous glands), infants are an exception. In this age group, the infestation is often generalized, frequently involving the face, scalp, palms, and soles. The lesions are often inflammatory, presenting as vesicles, pustules, or nodules rather than the classic burrows seen in adults. **Why other options are incorrect:** * **Atopic Dermatitis:** While common in infants, it typically presents as erythematous, itchy, scaly patches on the cheeks and extensor surfaces. It rarely involves the palms and soles. * **Urticaria:** Presents as transient, evanescent wheals (hives) that migrate. It does not present as persistent papulovesicular lesions. * **Seborrheic Dermatitis:** Characterized by "cradle cap" (greasy yellow scales) on the scalp and involvement of skin folds (intertriginous areas). It is generally non-pruritic and does not affect the palms and soles. **High-Yield Clinical Pearls for NEET-PG:** * **Pathogen:** *Sarcoptes scabiei var. hominis*. * **Hallmark Sign:** The **Burrow** (S-shaped track), most commonly found in finger webs and wrist creases. * **Infantile Scabies Key Difference:** Involvement of the **face, scalp, palms, and soles** is a high-yield diagnostic pointer. * **Treatment of Choice:** Topical **Permethrin (5%)** cream. For infants under 2 months, **Precipitated Sulfur (6-10%)** is often preferred due to safety profiles. * **Nodular Scabies:** Persistent itchy nodules in the axilla or genitalia, representing a hypersensitivity reaction.

Question 4: A 6-month-old infant presented with multiple erythematous papules and exudative lesions on the face, scalp, trunk, and a few vesicles on palms and soles for 2 weeks. The infant's mother has a history of itchy lesions. What is the most likely diagnosis?

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

Explanation: ### Explanation **Correct Answer: A. Scabies** The clinical presentation is classic for **Infantile Scabies**. Unlike adults, where scabies typically spares the head and neck, infants frequently present with involvement of the **face, scalp, palms, and soles**. The presence of **vesicles** on the palms and soles is a high-yield diagnostic clue in this age group. Furthermore, the history of itchy lesions in the mother (a close contact) strongly points toward a contagious parasitic infestation. **Why other options are incorrect:** * **Infantile Eczema (Atopic Dermatitis):** While it involves the face and trunk with exudative lesions, it typically **spares the diaper area** and rarely presents with discrete vesicles on the palms and soles. There is usually a family history of atopy rather than a history of acute contagious itching. * **Infantile Seborrheic Dermatitis:** This presents with greasy, yellow 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 superficial bacterial infection characterized by honey-colored crusts. While it can complicate scabies (secondary infection), it would not explain the widespread distribution and the mother’s symptoms. **NEET-PG High-Yield Pearls:** * **Pathognomonic sign:** The **Burrow** (S-shaped track), though often difficult to find in infants due to secondary eczematization or infection. * **Nodular Scabies:** Common in infants; occurs on the axillae and groin as a hypersensitivity reaction. * **Treatment of Choice:** **Permethrin 5% cream** (applied from head to toe in infants). * **Alternative:** Oral Ivermectin (only for children >15 kg or >5 years old). * **Key Rule:** Always treat all close household contacts simultaneously to prevent re-infestation.

Question 5: A 10-year-old girl presents with multiple excoriations on her hands that have appeared over the past week. She reports itching and scratching her hands. Physical examination reveals multiple 0.2- to 0.6-cm linear streaks in the interdigital regions. The condition resolved with topical lindane lotion. Which of the following organisms is most likely responsible for these findings?

A. Ixodes scapularis
B. Poxvirus
C. Staphylococcus aureus
D. Sarcoptes scabiei (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Sarcoptes scabiei** The clinical presentation is classic for **Scabies**, caused by the mite *Sarcoptes scabiei* var. *hominis*. The pathognomonic sign described—**linear streaks** (0.2 to 0.6 cm)—represents **burrows** created by the female mite as she tunnels through the stratum corneum to lay eggs. * **Key Diagnostic Features:** Intense nocturnal pruritus (a Type IV hypersensitivity reaction to mite feces/saliva) and predilection for "sites of election" such as the **interdigital webs**, flexor wrists, axillae, and genitalia. * **Treatment:** While the question mentions Lindane (an organochlorine), the current first-line treatment is **Topical Permethrin (5%)**. --- ### Why the other options are incorrect: * **A. Ixodes scapularis:** This is the deer tick, the vector for Lyme disease. It typically presents with *Erythema Chronicum Migrans* (a "bull’s-eye" rash), not interdigital burrows. * **B. Poxvirus:** Specifically, Molluscum Contagiosum is caused by a poxvirus. It presents as firm, umbilicated, pearly papules, not linear burrows or excoriations. * **C. Staphylococcus aureus:** This is a common cause of secondary bacterial infections (impetiginization) in scabies patients, but it does not cause the primary linear lesions described. --- ### High-Yield NEET-PG Pearls: 1. **Burrow Identification:** The "Ink test" (applying fountain pen ink to the lesion) can help visualize the burrow. 2. **Nodular Scabies:** A variant seen in children, often involving the scrotum or axillae; these are hypersensitivity nodes that persist after the mites are eradicated. 3. **Crusted (Norwegian) Scabies:** Seen in immunocompromised or elderly patients; characterized by thousands of mites and thick crusts, but often **minimal itching**. 4. **Treatment Protocol:** Treat the **entire family/close contacts** simultaneously to prevent re-infestation. Permethrin should be applied from the neck down and left for 8–12 hours.

Question 6: Vagabond disease is transmitted by which of the following?

A. Mite
B. Louse (Correct Answer)
C. Tick
D. Black Fly

Explanation: **Explanation:** **Vagabond disease** (also known as Parasitophobia or Vagabond's Melanoderma) is a skin condition caused by a chronic infestation of **Body Lice (*Pediculus humanus corporis*)**. 1. **Why Louse is correct:** The disease typically occurs in individuals with poor hygiene, such as the homeless or "vagabonds." Chronic scratching due to persistent body lice infestation leads to post-inflammatory hyperpigmentation and thickening (lichenification) of the skin. The skin becomes dark, dry, and scaly, resembling a "melanoderma." Unlike head lice, body lice live in the seams of clothing and only move to the skin to feed. 2. **Why other options are incorrect:** * **Mite:** *Sarcoptes scabiei* causes Scabies, characterized by nocturnal itching and burrows in web spaces, but it does not cause the generalized melanoderma seen in Vagabond disease. * **Tick:** Ticks are vectors for systemic diseases like Rocky Mountain Spotted Fever or Lyme disease, but they do not cause chronic infestation-related skin pigmentation. * **Black Fly:** These are vectors for Onchocerciasis (River Blindness) and do not cause Vagabond disease. **High-Yield Clinical Pearls for NEET-PG:** * **Vector Potential:** Body lice are significant because they transmit **Epidemic Typhus** (*Rickettsia prowazekii*), **Trench Fever** (*Bartonella quintana*), and **Epidemic Relapsing Fever** (*Borrelia recurrentis*). * **Diagnosis:** Look for lice or nits in the **seams of the patient's clothing**, rather than on the body itself. * **Treatment:** The primary treatment is laundering clothing in hot water (>60°C) and improving personal hygiene; topical pediculicides (e.g., Permethrin) are secondary.

Question 7: Prurigo of Hebra is most probably caused by which of the following?

A. Autoimmune etiology
B. Allergy to insect bites (Correct Answer)
C. Caused by papova virus
D. Focal infection

Explanation: **Explanation:** **Prurigo of Hebra** (also known as Prurigo Ferox) is a chronic, severely pruritic skin disorder primarily seen in children and young adults. **1. Why Option B is Correct:** The underlying medical concept is a **hypersensitivity reaction (Type I and Type IV)** to antigens introduced by **insect bites** (most commonly mosquitoes, fleas, or bedbugs). It is considered a severe, chronic variant of papular urticaria. The condition is characterized by extremely itchy, firm, dome-shaped papules, often with a central crust or "pitting," predominantly affecting the extensor surfaces of the limbs. **2. Why Other Options are Incorrect:** * **Option A (Autoimmune):** While some pruritic conditions like Pemphigoid are autoimmune, Prurigo of Hebra is strictly an inflammatory response to external parasitic stimuli. * **Option C (Papova virus):** Papovaviruses (like HPV) cause warts. There is no viral etiology associated with Prurigo of Hebra. * **Option D (Focal infection):** While secondary bacterial infection (impetiginization) is a common complication due to intense scratching, a focal internal infection is not the primary cause of the disease. **3. NEET-PG High-Yield Pearls:** * **Clinical Presentation:** Look for the "Hard Papules of Hebra" on the legs, associated with **post-inflammatory hyperpigmentation** and **lymphadenopathy** (Prurigo buboes). * **Epidemiology:** More common in lower socioeconomic groups and tropical climates where insect exposure is high. * **Management:** Focuses on insect bite prevention (nets/repellents), topical steroids, and antihistamines. In refractory cases, phototherapy (PUVA) may be used. * **Differential Diagnosis:** Must be distinguished from Atopic Dermatitis; however, Hebra's lacks the typical flexural involvement.

Question 8: Scabies can be effectively treated systemically by:

A. Psoralens
B. Ivermectin (Correct Answer)
C. Permethrin
D. Cotrimoxazole

Explanation: ### Explanation **Correct Answer: B. Ivermectin** **Why Ivermectin is correct:** Ivermectin is the only **systemic (oral)** treatment option listed for Scabies. It is an anthelmintic agent that works by binding to glutamate-gated chloride channels in the invertebrate nerve and muscle cells, leading to paralysis and death of the *Sarcoptes scabiei* mite. * **Dosage:** 200 μg/kg body weight as a single oral dose, repeated after 1–2 weeks (to kill mites that hatched from eggs after the first dose). * **Indications:** It is particularly useful for institutional outbreaks, bedridden patients, and is the drug of choice for **Crusted (Norwegian) Scabies** (used in combination with topical agents). **Why other options are incorrect:** * **A. Psoralens:** These are photosensitizing agents used in PUVA therapy for conditions like Psoriasis and Vitiligo; they have no role in treating parasitic infections. * **C. Permethrin (5%):** While Permethrin is the **overall drug of choice** for scabies, it is a **topical** cream, not a systemic treatment. * **D. Cotrimoxazole:** This is an antibiotic used for bacterial infections or *Pneumocystis jirovecii*. While it has been studied for head lice, it is not a standard treatment for scabies. **High-Yield Clinical Pearls for NEET-PG:** 1. **Drug of Choice (Topical):** 5% Permethrin (apply neck down, leave for 8–12 hours). 2. **Drug of Choice (Systemic/Crusted Scabies):** Oral Ivermectin. 3. **Nodular Scabies:** Treated with intralesional or potent topical steroids (it is a hypersensitivity reaction, not active infestation). 4. **Contraindication:** Oral Ivermectin is generally avoided in children weighing <15 kg and pregnant/lactating women. 5. **The "Seven Year Itch":** Itching is typically worse at night (nocturnal exacerbation).

Question 9: A 7-month-old infant presents with itchy erythematous papules and vesicles on the palms and soles. Examination reveals serpentine, thread-like lesions and eczematous, crusted lesions on the face and trunk. The mother reports similar lesions in other family members. What is the most probable diagnosis?

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

Explanation: **Explanation:** The clinical presentation is classic for **Infantile Scabies**, caused by the mite *Sarcoptes scabiei*. Unlike adults, where lesions are typically restricted to the "Circle of Hebra," infants frequently show involvement of the **palms, soles, face, and scalp**. The presence of **serpentine, thread-like lesions (burrows)** is pathognomonic. The history of similar symptoms in family members strongly suggests a contagious parasitic infestation rather than an endogenous dermatitis. **Why other options are incorrect:** * **Atopic Dermatitis:** While it causes itchy eczematous lesions on the face and trunk, it typically spares the diaper area and does not present with burrows or a strong family history of acute contagion. * **Papular Urticaria:** This is a hypersensitivity reaction to insect bites. It presents as recurrent, grouped erythematous papules (often with a central punctum), but it does not feature burrows or widespread palm/sole involvement. * **Seborrheic Dermatitis:** This presents as "cradle cap" (greasy yellow scales) on the scalp and flexures. It is generally non-pruritic and does not involve the palms and soles with vesicles. **High-Yield Clinical Pearls for NEET-PG:** * **Pathognomonic sign:** The Burrow (linear track representing the female mite's tunnel). * **Nodular Scabies:** Often seen in children on the axillae and genitalia; represents a hypersensitivity reaction. * **Drug of Choice:** **Permethrin 5% cream** (applied neck-down in adults; head-to-toe in infants). * **Alternative:** Oral Ivermectin (200 µg/kg), but it is generally avoided in children weighing <15 kg. * **Treatment Rule:** Always treat all close contacts simultaneously to prevent re-infection.

Question 10: Where is nodular scabies typically found?

A. Web space of fingers
B. Axilla
C. Abdomen
D. Scrotum (Correct Answer)

Explanation: **Explanation:** **Nodular scabies** is a clinical variant of scabies characterized by persistent, intensely pruritic, reddish-brown nodules. These nodules represent a **hypersensitivity reaction** to the mite, its eggs, or scybala (feces), rather than an active infestation in those specific lesions. **Why Scrotum is the Correct Answer:** The most characteristic and high-yield site for nodular scabies is the **scrotum and penis** in males. Other common sites include the groin and the axillary folds. These nodules are unique because they often persist for weeks or months even after the mites have been successfully eradicated by scabicides (post-scabietic nodules). **Analysis of Incorrect Options:** * **A. Web space of fingers:** This is the most common site for **classic scabies** and the typical location to find "burrows." While common in general scabies, it is not the classic site for the *nodular* variant. * **B. Axilla:** While nodular scabies can occur in the axillary folds, the **scrotum** is considered the most pathognomonic and frequently tested site for this specific presentation. * **C. Abdomen:** The periumbilical area is a common site for the "Circle of Hebra" in classic scabies, but it is less common for the persistent nodular form compared to the genitalia. **Clinical Pearls for NEET-PG:** * **Circle of Hebra:** Refers to the distribution of scabies (axilla, elbow, wrist, finger webs, and genitals). * **Treatment:** Nodular scabies does not respond to repeat scabicides alone. It requires **intralesional or topical corticosteroids** or coal tar to suppress the hypersensitivity reaction. * **Infants:** In infants, scabies can involve the face, scalp, palms, and soles (areas usually spared in adults). * **Norwegian (Crusted) Scabies:** Seen in immunocompromised patients; characterized by thousands of mites and minimal itching.

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