Parasitic Skin Infections Practice Questions

Q: The Circle of Hebra is associated with which of the following conditions?

Scabies. **Explanation:** The **Circle of Hebra** is a classic clinical distribution pattern seen in **Scabies**, a parasitic infestation caused by the mite *Sarcoptes scabiei*. It refers to an imaginary circle connecting the most commonly affected sites of involvement in an adult. These sites include the **interdigital webs of the fingers, anterior wrists, ulnar borders of the forearms, axillary folds, nipples (in females), umbilicus, and the genitalia (in males).** Notably, the face and scalp are typically spared in adults, though they may be involved in infants. **Why the other options are incorrect:** * **Syphilis:** Primary syphilis presents with a painless chancre, while secondary syphilis is known for a generalized maculopapular rash involving the palms and soles. It does not follow the Hebra distribution. * **Leprosy:** Characterized by hypopigmented patches with sensory loss or thickened nerves. The distribution depends on the type (Tuberculoid vs. Lepromatous) but is not described by this circle. * **Lichen Planus:** Characterized by the "6 Ps" (Planar, Purple, Polygonal, Pruritic, Papules, and Plaques). It commonly affects the wrists and oral mucosa (Wickham striae) but lacks the specific "Circle of Hebra" pattern. **High-Yield Clinical Pearls for NEET-PG:** * **Pathognomonic Sign:** The **Burrow** (a short, wavy, dirty-looking line) is the diagnostic hallmark of scabies. * **Nocturnal Pruritus:** Itching is characteristically worse at night due to a Type IV hypersensitivity reaction to the mite, its eggs, and scybala (feces). * **Norwegian (Crusted) Scabies:** A highly contagious variant seen in immunocompromised patients, presenting with thick crusts and thousands of mites, but often minimal itching. * **Treatment of Choice:** Topical **Permethrin (5%)** cream is the first-line treatment (applied neck down and left overnight). Oral **Ivermectin** is an alternative, especially for institutional outbreaks or crusted scabies.

Q: In an infant with scabies, what is the preferred treatment?

1, 3, 4 (Permethrin, Benzyl benzoate, Crotamiton). ***Correct: 1, 3, 4 (Permethrin, Benzyl benzoate, Crotamiton)*** - **Permethrin 5% cream** is the **first-line treatment** for scabies in infants and children over 2 months of age due to its high efficacy (>90%) and excellent safety profile - **Benzyl benzoate (10-25% emulsion)** is a safe and effective alternative topical agent, particularly useful in resource-limited settings or when permethrin is unavailable - **Crotamiton 10% cream** is another alternative topical treatment option, though it has lower efficacy compared to permethrin - All three agents are **safe for topical use in infants** and represent appropriate treatment choices *Incorrect: 2, 4 (Ivermectin, Crotamiton)* - This option excludes **permethrin**, the first-line and most effective treatment for infant scabies - **Ivermectin is contraindicated in infants** as it is generally reserved for children over 5 years old or weighing more than 15 kg - Relying on ivermectin and crotamiton alone is not standard practice for routine infant scabies *Incorrect: 1, 2, 3 (Permethrin, Ivermectin, Benzyl benzoate)* - While this includes the first-line agent **permethrin** and the alternative **benzyl benzoate**, it incorrectly includes **ivermectin** - **Ivermectin is not recommended for routine use in infants** due to safety concerns in children under 15 kg or under 5 years of age - Ivermectin is reserved for special circumstances such as crusted scabies, treatment failures, or institutional outbreaks in older children *Incorrect: 1, 2, 4 (Permethrin, Ivermectin, Crotamiton)* - Although this includes the first-line treatment **permethrin** and alternative **crotamiton**, it inappropriately includes **ivermectin** - **Ivermectin is not standard therapy for infant scabies** and should not be routinely used in this age group - The combination with ivermectin makes this a non-preferred choice for general infant scabies management

Q: Which of the following drugs is useful for the following condition? (Recent NEET Pattern 2016-17)

Albendazole. ***Albendazole*** - The image displays a **serpiginous, erythematous track** on the foot, characteristic of **Cutaneous Larva Migrans (CLM)**, also known as creeping eruption. This condition is caused by hookworm larvae (e.g., *Ancylostoma braziliense*) that penetrate the skin from contaminated soil. - **Albendazole** is an anthelmintic agent that works by selectively binding to **beta-tubulin** of parasitic worms, inhibiting microtubule polymerization and impairing glucose uptake, leading to their starvation and death. It is the **first-line treatment for CLM** with high efficacy (typically 400 mg daily for 3-5 days). *Metronidazole* - This is an antiprotozoal and antibacterial agent effective against anaerobic bacteria and protozoa (*Giardia*, *Entamoeba*, *Trichomonas*) - **Not effective** against nematode larvae causing CLM - Works through reduction of the nitro group, disrupting DNA - a mechanism that doesn't affect helminth larvae *Doxycycline* - This is a tetracycline antibiotic used for bacterial infections - Has no anthelmintic activity against hookworm larvae - May be used for secondary bacterial infections complicating skin lesions, but not for treating the underlying parasitic cause *Praziquantel* - This is an anthelmintic agent primarily effective against **cestodes (tapeworms)** and **trematodes (flukes)** - Works by increasing cell membrane permeability to calcium ions - **Not effective** against nematode larvae (hookworms are nematodes) - Used for conditions like schistosomiasis, cysticercosis, and tapeworm infections

Q: An AIDS positive patient has presented with multiple crusted lesions as shown in the image below. What is the possible diagnosis?

Norwegian scabies. ***Norwegian scabies*** - This severe, crusted form of **scabies** is common in immunocompromised individuals like AIDS patients. - The image displays **widespread crusted lesions** consistent with the hyperkeratotic plaques seen in Norwegian scabies, where there are thousands of mites. *Herpes zoster* - **Herpes zoster** typically presents as a painful, vesicular rash in a **dermatomal distribution**, which progresses to crusting. - The lesions in the image are widespread and diffuse, not limited to a dermatome, and appear more crusted and hyperkeratotic than typical herpes zoster. *Bacillary angiomatosis* - **Bacillary angiomatosis** presents as reddish-purple, vascular lesions that can resemble **Kaposi sarcoma** or pyogenic granulomas. - While it can occur in AIDS patients, the lesions are primarily **angiomatous** (blood vessel proliferation) rather than crusted and hyperkeratotic as shown. *Kaposi sarcoma* - **Kaposi sarcoma** in AIDS patients typically manifests as **reddish-purple or brown macules, plaques, and nodules**, often on the skin or mucous membranes. - Although it can be widespread, the image depicts extensive **crusted, hyperkeratotic lesions** rather than the characteristic vascular lesions of Kaposi sarcoma.

Q: A patient lives in an urban slum and practices open-air defecation. He presented with continuous itching over the sole. The image shows presence of:

Cutaneous larva migrans. ***Cutaneous larva migrans*** - The image shows **serpiginous, erythematous, and highly pruritic lesions** on the sole, which are characteristic of cutaneous larva migrans. - The patient's history of living in an urban slum and engaging in **open-air defecation** indicates exposure to soil contaminated with **hookworm larvae**, which penetrate the skin and cause these migratory tracks. *Ecthyma* - Ecthyma is a **bacterial skin infection** characterized by **crusted, ulcerative lesions** that extend into the dermis. - It does not present with the characteristic **migratory, linear tracks** seen in the image. *Erysipelas* - Erysipelas is a **superficial bacterial infection** of the dermis with significant lymphatic involvement, presenting as a **sharply demarcated, erythematous, raised rash** with fever and systemic symptoms. - It does not cause the **linear, tunneling appearance** observed in the provided image. *Migratory myiasis* - Myiasis involves infection with **fly larvae** (maggots) that infest living tissue. While some forms of myiasis can be migratory, they typically present as **boil-like lesions** with a central pore, or as subcutaneous nodules, which is different from the **serpiginous tracks** of cutaneous larva migrans. - The source of infection (contaminated soil with hookworm larvae) points away from fly larvae.

Q: A middle-aged man came to you with itchy rash caused by the following organism. Identify the condition: (AIIMS Nov 2017)

Scabies. ***Scabies*** - The image provided shows **Sarcoptes scabiei**, the scabies mite, which is the causative organism for scabies. - Scabies is characterized by an **intensely itchy rash**, often worse at night, and typical burrows in the skin. *Pediculosis* - Pediculosis is caused by lice (e.g., **Pediculus humanus** or **Pthirus pubis**), which are distinct in appearance from the mite shown. - While also causing an itchy rash, the morphology of the causative agent in the image does not match that of a louse. *Insect bite reaction* - An insect bite reaction is a broad term for inflammatory responses to bites from various insects, but the image specifically identifies the **causative organism**. - The organism shown is a mite, which can cause an insect bite reaction, but scabies is the specific condition caused by this particular mite. *Tinea cruris* - Tinea cruris is a **fungal infection** of the groin, commonly known as jock itch. - The image displays a **mite**, not a fungus, making Tinea cruris an incorrect diagnosis.

Q: Which of the following statements about pediculosis pubis is MOST accurate?

Eggs (nits) attached to hair shafts confirm diagnosis. ***Eggs (nits) attached to hair shafts confirm diagnosis*** - The presence of **nits (eggs)** firmly attached to the hair shafts, particularly in the pubic region, is a **definitive diagnostic criterion** for pediculosis pubis. - These nits are typically oval, white or grayish, and cannot be easily removed, distinguishing them from dandruff. *It commonly infests scalp hair* - **Pediculosis pubis**, caused by *Pthirus pubis* (pubic louse or crab louse), primarily infests **coarse body hair**, most commonly in the pubic area. - **Scalp hair** is typically infested by *Pediculus humanus capitis* (head louse), which is a different species. *It requires systemic antibiotic treatment* - Pediculosis pubis is caused by an **ectoparasite** (louse), not a bacterial infection, and therefore does not require **systemic antibiotic treatment**. - Treatment involves topical insecticides like permethrin or malathion, and physical removal of lice and nits. *It is more contagious than other types of lice* - All types of lice are **highly contagious**, but pediculosis pubis is primarily transmitted through **sexual contact** or close bodily contact, making it a sexually transmitted infection (STI). - While easily spread, there is no evidence to suggest it is inherently more contagious than head lice, which spread easily through casual contact, especially among children.

Q: Which physical finding is most useful in diagnosing scabies in genital lesions?

Burrows in genital area. ***Burrows in genital area*** - The presence of **burrows** is the **pathognomonic sign of scabies**, representing the tunnels dug by the female mite. - While scabies can cause varied lesions, identifying these **serpiginous, thread-like burrows** is the most diagnostic physical finding. *Vesicular lesions on shaft of penis* - **Vesicular lesions** can be seen in various conditions like **herpes simplex virus (HSV)** infection, making them less specific for scabies. - While scabies can sometimes present with vesicles, they are not the primary diagnostic feature. *Pustules on glans penis* - **Pustules on the glans penis** are more indicative of conditions like **bacterial folliculitis** or other sexually transmitted infections (STIs), such as **gonorrhea**. - Scabies typically does not present with pustules as its primary lesion. *Excoriated nodules on scrotum* - While **scabietic nodules**, particularly on the scrotum, are a recognized manifestation of scabies, especially in chronic cases, they are often **excoriated due to intense itching**. - These nodules are a common sign but are not as specific as finding a burrow, which directly demonstrates the mite's activity.

Q: A 42-year-old man presents with multiple pruritic papules and vesicles between his fingers and on his wrists. The lesions are worse at night. His wife has similar symptoms. Microscopic examination of a skin scraping reveals mites and eggs. Which of the following is the most appropriate treatment regimen for the patient and his contacts?

Permethrin cream applied from neck down, repeat in 1 week. ***Permethrin cream applied from neck down, repeat in 1 week*** - This is the **first-line treatment** for scabies due to its high efficacy and low toxicity. Applying it from the neck down ensures coverage of all potential infestation sites, and a second application 1 week later is crucial to kill mites that hatch from eggs surviving the first treatment. - Treating **all close contacts** simultaneously, even if asymptomatic, is essential to prevent re-infestation and control transmission, as exemplified by the wife having similar symptoms. *Topical steroids for 2 weeks* - Topical steroids are used to reduce **inflammation and itching** caused by eczema or allergic reactions, but they do not kill the scabies mites or their eggs. - Using steroids alone would only provide symptomatic relief without addressing the underlying parasitic infection, leading to persistent infestation and potential **worsening of symptoms** after discontinuation. *Oral ivermectin single dose* - Oral ivermectin is an effective scabicide, particularly useful in **crusted scabies**, widespread disease, or when topical treatments are impractical or fail. - However, a **single dose** is often insufficient; current recommendations usually involve two doses 7-14 days apart for optimal eradication, and it's generally reserved for cases where topical treatments are not feasible or have failed. *Oral antihistamines only* - Oral antihistamines provide relief from **itching** by blocking histamine receptors but do not have any direct effect on **scabies mites or eggs**. - Relying solely on antihistamines would allow the **infestation to persist** and worsen, continuously causing severe pruritus and potential secondary infections.

Q: Scabies in children differs from that in adults in that it affects

Face. ***Face*** - In infants and young children, **scabies** can present with atypical lesions involving the **face**, scalp, palms, and soles. - This is because the mite infestation can be more widespread due to their delicate skin and immature immune response. *Axilla* - The **axilla** is a common site for **scabies** in both adults and children due to skin folds providing a favorable environment for mites. - Involvement in this area does not specifically differentiate childhood scabies from adult scabies. *Webspace* - The **finger and toe web spaces** are classic sites for **scabies** burrow formation in both adults and children. - This is considered a typical presentation across all age groups and not a distinguishing feature for children. *Genitalia* - **Genital involvement**, particularly nodular lesions, can occur in both adult and pediatric **scabies**. - While it can be a source of significant discomfort, it is not an exclusive or differentiating feature of scabies in children compared to adults.

Question 1

The Circle of Hebra is associated with which of the following conditions?

Accepted Answer

Scabies

Answer

Syphilis

Answer

Leprosy

Answer

Lichen planus

Question 2

In an infant with scabies, what is the preferred treatment?

Accepted Answer

1, 3, 4 (Permethrin, Benzyl benzoate, Crotamiton)

Answer

1, 2, 4 (Permethrin, Ivermectin, Crotamiton)

Answer

1, 2, 3 (Permethrin, Ivermectin, Benzyl benzoate)

Answer

2, 4 (Ivermectin, Crotamiton)

Question 3

Which of the following drugs is useful for the following condition? (Recent NEET Pattern 2016-17)

Accepted Answer

Albendazole

Answer

Metronidazole

Answer

Doxycycline

Answer

Praziquantel

Question 4

An AIDS positive patient has presented with multiple crusted lesions as shown in the image below. What is the possible diagnosis?

Accepted Answer

Norwegian scabies

Answer

Herpes zoster

Answer

Bacillary angiomatosis

Answer

Kaposi sarcoma

Question 5

A patient lives in an urban slum and practices open-air defecation. He presented with continuous itching over the sole. The image shows presence of:

Accepted Answer

Cutaneous larva migrans

Answer

Ecthyma

Answer

Erysipelas

Answer

Migratory myiasis

Question 6

A middle-aged man came to you with itchy rash caused by the following organism. Identify the condition: (AIIMS Nov 2017)

Accepted Answer

Scabies

Answer

Insect bite reaction

Answer

Pediculosis

Answer

Tinea cruris

Question 7

Which of the following statements about pediculosis pubis is MOST accurate?

Accepted Answer

Eggs (nits) attached to hair shafts confirm diagnosis

Answer

It commonly infests scalp hair

Answer

It requires systemic antibiotic treatment

Answer

It is more contagious than other types of lice

Question 8

Which physical finding is most useful in diagnosing scabies in genital lesions?

Accepted Answer

Burrows in genital area

Answer

Vesicular lesions on shaft of penis

Answer

Pustules on glans penis

Answer

Excoriated nodules on scrotum

Question 9

A 42-year-old man presents with multiple pruritic papules and vesicles between his fingers and on his wrists. The lesions are worse at night. His wife has similar symptoms. Microscopic examination of a skin scraping reveals mites and eggs. Which of the following is the most appropriate treatment regimen for the patient and his contacts?

Accepted Answer

Permethrin cream applied from neck down, repeat in 1 week

Answer

Topical steroids for 2 weeks

Answer

Oral ivermectin single dose

Answer

Oral antihistamines only

Question 10

Scabies in children differs from that in adults in that it affects

Accepted Answer

Face

Answer

Axilla

Answer

Webspace

Answer

Genitalia

Parasitic Skin Infections — MCQs

Parasitic Skin Infections — MCQs

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