Parasitic Skin Infections Practice Questions

Q: Which of the following drugs is most efficacious against Pediculosis humanus as well as Sarcoptes Scabiei?

Permethrin. **Explanation:** **1. Why Permethrin is the Correct Answer:** Permethrin (5% for Scabies, 1% for Pediculosis) is currently the **gold standard** and first-line treatment for both conditions. It is a synthetic pyrethroid that acts by disrupting the sodium channel currents in the neuronal membranes of parasites, leading to delayed repolarization, paralysis, and death. Its high efficacy (cure rates >95%), low systemic absorption, and excellent safety profile in infants (above 2 months) and pregnant women make it the drug of choice. **2. Analysis of Incorrect Options:** * **B. Hexachlorocyclohexane (Lindane):** Once widely used, it is now a second-line agent due to concerns regarding **neurotoxicity** (seizures), especially in children and underweight individuals. It is less efficacious than Permethrin due to emerging resistance. * **C. Monobenzone:** This is a **depigmenting agent** used in conditions like Vitiligo universalis to remove remaining normal skin pigment. It has no antiparasitic properties. * **D. Crotamiton:** While it has anti-scabietic and anti-pruritic properties, its efficacy is significantly lower than Permethrin, often requiring multiple applications over several days. **3. High-Yield Clinical Pearls for NEET-PG:** * **Application Rule:** For Scabies, Permethrin 5% cream should be applied from the **neck down to the toes** and left for 8–12 hours. In infants, the face and scalp must also be included. * **Ivermectin:** The oral drug of choice for **Crusted (Norwegian) Scabies** (used in combination with topical Permethrin) and for institutional outbreaks. * **Nits:** In Pediculosis, nits (eggs) within 1 cm of the scalp indicate active infection. * **Post-scabietic Pruritus:** Itching may persist for 2–4 weeks even after successful treatment due to a hypersensitivity reaction to dead mites; this does not necessarily indicate treatment failure.

Q: Which drug is used orally for treating scabies?

Ivermectin. **Explanation:** **Ivermectin** is the correct answer as it is the only drug among the options approved for the **systemic (oral) treatment** of scabies. It works by binding to glutamate-gated chloride channels in the nerve and muscle cells of the invertebrate, leading to paralysis and death of the *Sarcoptes scabiei* mite. The standard dosage is **200 μg/kg** as a single dose, repeated after 1–2 weeks to kill nymphs that have hatched from surviving eggs. **Analysis of Incorrect Options:** * **Permethrin (5%):** While it is the **gold standard/first-line treatment** for scabies, it is administered **topically** (as a cream), not orally. * **Levamisole:** This is an anthelmintic used for roundworm infections and sometimes as an immunomodulator, but it has no role in treating scabies. * **Chloroquine:** This is an antimalarial and DMARD; it is ineffective against ectoparasites like mites. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC):** Topical **5% Permethrin** is the overall DOC for classical scabies. * **Crusted (Norwegian) Scabies:** Characterized by thousands of mites in immunocompromised patients; treatment requires a **combination** of oral Ivermectin and topical Permethrin. * **Contraindications:** Oral Ivermectin should be avoided in children weighing **<15 kg**, pregnant women, and lactating mothers (due to the blood-brain barrier concerns). * **Nodular Scabies:** Represents a hypersensitivity reaction; treated with intralesional or potent topical steroids, not just scabicides.

Q: A 32-year-old female is suffering from scabies due to Sarcoptes scabiei. Which of the following drugs is prescribed for her?

Ivermectin 200 mcg/kg body weight. **Explanation:** **Sarcoptes scabiei** is an ectoparasite that causes scabies by burrowing into the stratum corneum. While topical 5% Permethrin is the first-line treatment, oral **Ivermectin** is the systemic drug of choice, particularly for institutional outbreaks, crusted (Norwegian) scabies, or patients who cannot tolerate topical therapy. * **Correct Option (C):** The standard therapeutic dose of Ivermectin for scabies is **200 mcg/kg body weight** as a single oral dose. A second dose is usually repeated after 7–14 days to kill newly hatched nymphs, as the drug is not ovicidal. * **Incorrect Options (A & B):** **Diethylcarbamazine (DEC)** is the drug of choice for lymphatic filariasis (caused by *W. bancrofti* or *B. malayi*) and Tropical Pulmonary Eosinophilia (TPE). It is ineffective against the *Sarcoptes* mite. * **Incorrect Option (D):** The dosage **100 mg/kg** is incorrect and potentially toxic. Ivermectin is measured in **micrograms (mcg)**, not milligrams (mg), per kilogram of body weight. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism of Action:** Ivermectin acts by binding to glutamate-gated chloride channels, leading to hyperpolarization and paralysis of the parasite. * **Contraindication:** Ivermectin should be avoided in children weighing <15 kg and pregnant/lactating women (due to potential disruption of the blood-brain barrier). * **Crusted Scabies:** In severe, crusted (Norwegian) scabies, a combination of oral Ivermectin and topical Permethrin is required. * **Classical Site:** The most common site for scabies burrows is the **interdigital webs** of the hands.

Q: A 27-year-old male presents with a 3-year history of itchy, excoriated papules on the forehead and exposed parts of the arms and legs. The condition is most severe during the rainy season and completely improves in winter. What is the most likely diagnosis?

Insect bite hypersensitivity. ### Explanation **Correct Option: D. Insect bite hypersensitivity** **Why it is correct:** Insect bite hypersensitivity (also known as **Papular Urticaria**) is a common allergic reaction to the bites of insects like mosquitoes, fleas, or bedbugs. The clinical presentation is classic for this condition: 1. **Morphology:** It presents as chronic or recurrent crops of intensely itchy, excoriated papules. 2. **Distribution:** Lesions are typically found on **exposed areas** (forehead, arms, and legs), where insects have easy access to the skin. 3. **Seasonality:** In tropical climates like India, insect activity peaks during the **rainy (monsoon) season** due to increased breeding and humidity, while it significantly subsides during the cold winter months. **Why other options are incorrect:** * **A. Scabies:** Characterized by nocturnal itching and involvement of finger webs, wrists, and genitals. It does not typically spare the trunk or show such marked seasonal variation related to the monsoon. * **B. Urticaria:** Presents as transient, evanescent wheals that resolve within 24 hours without leaving scars or excoriated papules. * **C. Atopic dermatitis:** While it causes itchy papules, it usually involves flexures (antecubital/popliteal fossae) and typically **worsens in winter** due to xerosis (dry skin), contradicting the seasonal pattern described. **Clinical Pearls for NEET-PG:** * **Histopathology:** Shows a superficial and deep wedge-shaped perivascular infiltrate with numerous **eosinophils**. * **Delayed Hypersensitivity:** It is primarily a Type I and Type IV hypersensitivity reaction to insect salivary antigens. * **Desensitization:** Over time, older children and adults may develop "immunological tolerance," leading to the spontaneous resolution of the condition. * **Management:** Primarily involves symptomatic relief (topical steroids/antihistamines) and prevention (insect nets/repellents).

Q: A 20-year-old male from Jaipur presents with an erythematous lesion on his cheek with central crusting. What is the likely diagnosis?

Cutaneous Leishmaniasis. ### **Explanation** **Correct Answer: D. Cutaneous Leishmaniasis** **Medical Concept:** The diagnosis is based on the classic clinical presentation and geographical context. Jaipur (Rajasthan) is a known endemic belt for **Cutaneous Leishmaniasis (CL)** in India, caused primarily by *Leishmania tropica*. The typical lesion starts as a papule that evolves into a "volcano-like" ulcer or an erythematous plaque with **central crusting** (often called the "Oriental Sore"). The presence of a chronic, painless, crusted lesion on exposed areas like the cheek in a young patient from an endemic zone is highly suggestive of CL. **Why other options are incorrect:** * **A. Systemic Lupus Erythematosus (SLE):** While SLE presents with a malar rash, it is typically a transient or persistent photosensitive erythema (butterfly distribution) without central crusting or ulceration. * **B. Lupus Vulgaris:** This is a form of cutaneous tuberculosis. It typically presents as "apple-jelly" nodules on diascopy and progresses slowly with peripheral expansion and central scarring, rather than acute crusting. * **C. Chilblain:** These are localized inflammatory lesions (perniosis) resulting from exposure to cold. They usually occur on acral areas (fingers/toes) and are unlikely to present as a solitary crusted cheek lesion in the climate of Jaipur. **NEET-PG High-Yield Pearls:** * **Vector:** Sandfly (*Phlebotomus papatasi*). * **Diagnosis:** Skin smear (Giemsa stain) shows **LD bodies** (Amastigote form) within macrophages. * **Leishmanin (Montenegro) Test:** Positive in Cutaneous Leishmaniasis but **negative** in Visceral Leishmaniasis (Kala-azar). * **Treatment of Choice:** Sodium Stibogluconate (Pentavalent antimonials) or Miltefosine. * **Key Sign:** "Volcano sign" (ulcer with raised dusky red borders).

Q: What is true about scabies?

All family members should be treated together.. **Explanation:** Scabies is a contagious infestation caused by the mite *Sarcoptes scabiei* var. *hominis*. The hallmark of management is treating the "household unit" rather than just the symptomatic individual. **Why Option C is correct:** Scabies has an **incubation period of 3–6 weeks**. During this time, an infested person can be asymptomatic but still transmit the mites to others through close skin-to-skin contact. To prevent a "ping-pong" reinfection cycle within a household, all close contacts and family members must be treated simultaneously, regardless of whether they are itching. **Analysis of Incorrect Options:** * **Option A:** In adults, scabies typically spares the face, scalp, palms, and soles (the "Circle of Hebra"). However, in **infants** and the elderly, these areas are frequently involved. * **Option B:** Scabies is a parasitic infestation, not bacterial. The primary treatment involves **topical scabicides** (e.g., 5% Permethrin) or **oral Ivermectin**. Antibiotics are only indicated if there is a secondary bacterial infection (impetiginization) due to scratching. * **Option D:** Itching in scabies is a Type IV hypersensitivity reaction to the mite, its eggs, and scybala (feces). It characteristically **worsens at night** (nocturnal pruritus) due to increased mite activity and warmth under bedclothes. **High-Yield Clinical Pearls for NEET-PG:** * **Pathognomonic sign:** The **Burrow** (a linear or S-shaped track), most commonly found in finger webs and wrist flexures. * **Drug of Choice:** Topical **Permethrin 5%** (applied neck down, left for 8–12 hours). * **Crusted (Norwegian) Scabies:** Seen in immunocompromised patients; characterized by thousands of mites and minimal itching. It is highly contagious. * **Nodular Scabies:** Persistent itchy nodules (often on genitalia) that remain even after the mites are eradicated; treated with intralesional steroids.

Q: Regarding cutaneous amoebiasis, which statement is NOT true?

The infection reaches the skin through the bloodstream.. **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.

Q: A 10-year-old school girl has recurrent episodes of boils on the scalp. The boils subside with antibiotic therapy but recur after some time. What is the most likely cause of these recurrences?

Pediculosis capitis. **Explanation:** The clinical presentation of recurrent boils (furunculosis) on the scalp of a school-going girl, which respond to antibiotics but recur shortly after, is a classic sign of an underlying **predisposing factor** rather than a primary infectious failure [1]. **Why Pediculosis Capitis is the correct answer:** Pediculosis capitis (head lice) is the most common cause of recurrent scalp pyoderma in school-aged children. The lice cause intense pruritus; subsequent scratching leads to **micro-abrasions and skin breaches**. These breaches serve as a portal of entry for commensal bacteria like *Staphylococcus aureus*, leading to secondary bacterial infections (boils/impetigo) [1]. While antibiotics clear the current infection, they do not eliminate the lice. The persistent itching and scratching cycle leads to inevitable recurrence. **Analysis of Incorrect Options:** * **Primary Immunodeficiency:** While these can cause recurrent infections, they typically present with systemic involvements (pneumonia, abscesses in deep organs, or failure to thrive) rather than localized scalp boils alone. * **Juvenile Diabetes Mellitus:** Poor glycemic control predisposes to skin infections, but it is a less common cause in this specific age group compared to the high prevalence of head lice in schools. It would usually present with systemic symptoms like polyuria or weight loss. * **HPV Infection:** Human Papillomavirus causes warts (verrucae), not acute inflammatory boils or furuncles. **NEET-PG Clinical Pearls:** * In any case of **recurrent pyoderma** in children, always look for an underlying itchy dermatosis (Lice, Scabies, or Atopic Dermatitis) [1]. * **Occipital lymphadenopathy** is a common physical finding associated with secondary infection in pediculosis capitis. * The drug of choice for Pediculosis capitis is **Topical Permethrin (1%)**; alternatively, Ivermectin can be used.

Question 1

A caretaker in a nursing home presents with pruritus of her trunk and extremities. On physical examination, she has several erythematous papules in her finger webs, axillae, umbilicus, and groin areas. Her scalp is clear. Which of the following is the best treatment for this woman?

Accepted Answer

Permethrin cream

Answer

Clindamycin solution

Answer

Oral erythromycin

Answer

Topical steroids

Question 2

Which of the following drugs is most efficacious against Pediculosis humanus as well as Sarcoptes Scabiei?

Accepted Answer

Permethrin

Answer

Hexachlorocyclohexane

Answer

Monobenzone

Answer

Crotomiton

Question 3

Which drug is used orally for treating scabies?

Accepted Answer

Ivermectin

Answer

Levamisole

Answer

Permethrin

Answer

Chloroquine

Question 4

A 32-year-old female is suffering from scabies due to Sarcoptes scabiei. Which of the following drugs is prescribed for her?

Accepted Answer

Ivermectin 200 mcg/kg body weight

Answer

Diethylcarbamazine (DEC) 6 mg/kg body weight for 12 days

Answer

Diethylcarbamazine (DEC) 9 mg/kg body weight for 12 days

Answer

Ivermectin 100 mg/kg body weight

Question 5

A 27-year-old male presents with a 3-year history of itchy, excoriated papules on the forehead and exposed parts of the arms and legs. The condition is most severe during the rainy season and completely improves in winter. What is the most likely diagnosis?

Accepted Answer

Insect bite hypersensitivity

Answer

Scabies

Answer

Urticaria

Answer

Atopic dermatitis

Question 6

A 20-year-old male from Jaipur presents with an erythematous lesion on his cheek with central crusting. What is the likely diagnosis?

Accepted Answer

Cutaneous Leishmaniasis

Answer

Systemic Lupus Erythematosus (SLE)

Answer

Lupus Vulgaris

Answer

Chilblain

Question 7

An 8-year-old boy presents with an itchy rash affecting his entire body. All members of his family are also affected. What is the drug of choice for this condition?

Accepted Answer

Topical permethrin

Answer

Ivermectin

Answer

Prednisolone

Answer

Antibiotics

Question 8

What is true about scabies?

Accepted Answer

All family members should be treated together.

Answer

It affects the palms and soles in adults.

Answer

Oral antibiotics are needed in every patient.

Answer

Itching is more pronounced in the morning.

Question 9

Regarding cutaneous amoebiasis, which statement is NOT true?

Accepted Answer

The infection reaches the skin through the bloodstream.

Answer

It is a spreading necrotizing inflammation of the skin and cutaneous tissue.

Answer

Rapid improvement with anti-amoebic treatment occurs.

Answer

It can occur in the perianal region.

Question 10

A 10-year-old school girl has recurrent episodes of boils on the scalp. The boils subside with antibiotic therapy but recur after some time. What is the most likely cause of these recurrences?

Accepted Answer

Pediculosis capitis

Answer

Primary immunodeficiency syndrome

Answer

Juvenile diabetes mellitus

Answer

HPV infection

Parasitic Skin Infections — MCQs

Parasitic Skin Infections — MCQs

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