Parasitic Skin Infections — MCQs
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Which physical finding is most useful in diagnosing scabies in genital lesions?
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?
Lepromin test is strongly positive in:
Scabies in children differs from that in adults in that it affects
A girl who is staying in a hostel presented with severe itching all over her body for two days. The intense itching worsens at night and after a hot shower. Burrows are seen between the fingers. Approximately how many live mites are there in an adult with scabies?
A 42-year-old Bengali male presents with painless nodules over the face. The face is erythematous, and the surface of some of the large nodules is discolored. He gives a history of an insect bite in the past while he went to the jungle for work. What is the most likely diagnosis?
Slit smear negative leprosy is:
Maculae cerulea is seen in ?
Pathognomonic lesion of scabies is?
Incubation period of scabies is:
Parasitic Skin Infections Indian Medical PG Practice Questions and MCQs
Question 41: Which physical finding is most useful in diagnosing scabies in genital lesions?
- A. Vesicular lesions on shaft of penis
- B. Burrows in genital area (Correct Answer)
- C. Pustules on glans penis
- D. Excoriated nodules on scrotum
Explanation: ***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.
Question 42: 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?
- A. Topical steroids for 2 weeks
- B. Oral ivermectin single dose
- C. Oral antihistamines only
- D. Permethrin cream applied from neck down, repeat in 1 week (Correct Answer)
Explanation: ***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.
Question 43: Lepromin test is strongly positive in:
- A. Lepromatous (LL)
- B. Borderline lepromatous (BL)
- C. Borderline borderline (BB)
- D. Tuberculoid (TT) (Correct Answer)
Explanation: ***Tuberculoid (TT)*** - The lepromin test measures the host's **cell-mediated immune response** to *Mycobacterium leprae* antigens. - A strong positive reaction indicates a robust immune response and is characteristic of the **tuberculoid pole** of leprosy. *Lepromatous (LL)* - Patients with lepromatous leprosy have a **weak or absent cell-mediated immune response** to *M. leprae* antigens. - This results in a **negative or very weak lepromin test** due to anergy. *Borderline lepromatous (BL)* - This form lies on the spectrum between lepromatous and tuberculoid leprosy, but still leans towards a **poor cell-mediated response**. - The lepromin test is typically **negative or mildly positive**, reflecting anergy and numerous bacilli. *Borderline borderline (BB)* - The borderline forms represent an unstable middle ground, but BB often shows a **weak or negative lepromin test**. - As the disease moves towards the lepromatous pole, the CMI response weakens, making the test less reactive.
Question 44: Scabies in children differs from that in adults in that it affects
- A. Axilla
- B. Webspace
- C. Genitalia
- D. Face (Correct Answer)
Explanation: ***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 45: A girl who is staying in a hostel presented with severe itching all over her body for two days. The intense itching worsens at night and after a hot shower. Burrows are seen between the fingers. Approximately how many live mites are there in an adult with scabies?
- A. 20-25
- B. 5-15 (Correct Answer)
- C. 30-50
- D. 25-30
Explanation: ***Approximately 5-15*** - In an adult with typical scabies, the **mite burden is usually low**, with an average of 5-15 live mites. - The intense itching is primarily due to a **hypersensitivity reaction** to the mites and their products, rather than the sheer number of mites. - This is the **characteristic range for classic, uncomplicated scabies** in immunocompetent individuals. *20-25* - This number is generally **higher than the typical mite count** found in classic scabies infestations. - A burden this high might be seen in cases approaching **crusted scabies**, or in prolonged untreated cases. *25-30* - This number is significantly higher than the average mite count for typical scabies. - Such a high burden is characteristic of **crusted (Norwegian) scabies**, a severe form often seen in immunocompromised individuals with widespread crusted lesions. *30-50* - This represents a very high mite burden far exceeding typical scabies. - Such numbers are seen in **crusted (Norwegian) scabies**, which can harbor hundreds to thousands of mites and occurs primarily in immunocompromised patients, elderly, or those with neurological conditions preventing scratching.
Question 46: A 42-year-old Bengali male presents with painless nodules over the face. The face is erythematous, and the surface of some of the large nodules is discolored. He gives a history of an insect bite in the past while he went to the jungle for work. What is the most likely diagnosis?
- A. Chronic Fungal infections
- B. Cutaneous Leishmaniasis (Correct Answer)
- C. Cutaneous tuberculosis
- D. Leprosy
Explanation: ***Cutaneous Leishmaniasis*** - The presentation of **painless erythematous nodules** on the face, especially in a person with a history of **insect bites** and exposure to a **jungle environment** (where sandflies, vectors of Leishmania, are common), strongly suggests cutaneous leishmaniasis. - The discoloration of the surface of large nodules is also consistent with the typical appearance of **chronic cutaneous leishmaniasis lesions**. *Chronic Fungal infections* - While chronic fungal infections can cause skin nodules, they typically present with features like **scaling, itching, or satellite lesions**, which are not described here. - The specific history of **insect bites** and geographical context points away from common fungal etiologies. *Cutaneous tuberculosis* - Cutaneous tuberculosis can manifest as nodules (**lupus vulgaris** or **scrofuloderma**), but these are often associated with other signs of tuberculosis, such as **pulmonary involvement** or **lymph nodal enlargement**, and typically have a slower progression. - The history of **insect bite** is not a primary risk factor for cutaneous tuberculosis. *Leprosy* - Leprosy, particularly **lepromatous leprosy**, can cause extensive facial nodules, but these are often associated with **nerve involvement** leading to sensory loss, and the lesions tend to be diffusely infiltrative rather than discrete, discolored nodules. - The rapid onset or history of a single insect bite is less characteristic of leprosy, which has a very **long incubation period**.
Question 47: Slit smear negative leprosy is:
- A. Neuritic type
- B. Tuberculoid type
- C. Indeterminate type
- D. All of the options (Correct Answer)
Explanation: ***All of the options*** - All mentioned types of leprosy—**neuritic**, **tuberculoid**, and **indeterminate**—are characterized by being **slit smear negative**. - This indicates a **paucibacillary** form of the disease with a low bacterial load, making direct detection of bacilli difficult. *Neuritic type* - This type primarily affects **nerves** with minimal or no skin lesions, making it difficult to find bacilli in skin smears. - Due to the low bacterial load, it is typically **slit smear negative**. *Tuberculoid type* - Characterized by **strong cell-mediated immunity**, which effectively contains the infection and results in a low bacillary index. - The few, well-defined skin lesions usually yield **negative slit smears** due to the scarcity of *Mycobacterium leprae*. *Indeterminate type* - This is an early stage of leprosy, often presenting with a single or few poorly defined skin lesions. - The bacterial load is very low, making it almost always **slit smear negative**.
Question 48: Maculae cerulea is seen in ?
- A. Pediculosis hominis corporis
- B. Scabies
- C. Pediculosis capitis
- D. Pediculosis pubis (Correct Answer)
Explanation: ***Pediculosis pubis*** - **Maculae ceruleae** (blue spots) are **pathognomonic** for pubic louse (*Pthirus pubis*) infestation. - These characteristic **bluish-gray macules** are typically found on the trunk, thighs, and lower abdomen. - They result from the **anticoagulant in louse saliva** converting hemoglobin to biliverdin at feeding sites, causing localized hemorrhage and pigment deposition. - This is a **classic diagnostic feature** of pediculosis pubis. *Pediculosis hominis corporis* - Body louse infestation causes **pruritus** and **excoriations**, typically along clothing lines (waistband, collar). - **Maculae ceruleae** are not a feature of body louse infestation. *Pediculosis capitis* - Head lice infestation presents with **scalp pruritus**, **nits on hair shafts**, and excoriations. - **Maculae ceruleae** do not occur with head lice. *Scabies* - Caused by *Sarcoptes scabiei* mite burrowing in the stratum corneum. - Presents with **burrows**, **papules**, **vesicles**, and intense **nocturnal pruritus**. - **Maculae ceruleae** are NOT associated with scabies infestation.
Question 49: Pathognomonic lesion of scabies is?
- A. Burrow (Correct Answer)
- B. Pits
- C. Vesicle
- D. Papules
Explanation: ***Burrow*** - A **burrow** is a short, wavy, thread-like lesion, typically a few millimeters long, caused by the female **Sarcoptes scabiei mite** tunneling into the stratum corneum of the skin. - It is considered the **pathognomonic lesion** of scabies, meaning its presence is highly characteristic and diagnostic of the infestation. *Pits* - **Pits** are depressions in the skin or nails, often associated with conditions like **psoriasis** or certain fungal infections, but not scabies. - They are not formed by parasitic tunneling and lack the linear, raised appearance characteristic of a scabies burrow. *Vesicle* - A **vesicle** is a small, fluid-filled blister, which can be present in some forms of scabies, particularly in infants or crusted scabies. - While vesicles can be associated with scabies, they are a secondary finding and not the unique primary lesion (burrow) that is pathognomonic. *Papules* - **Papules** are small, raised bumps that can be seen in scabies due to an inflammatory response to the mites, their feces, and eggs. - While common, papules are a non-specific finding and can occur in many other skin conditions, making them not pathognomonic for scabies.
Question 50: Incubation period of scabies is:
- A. 7 days
- B. 4 weeks (Correct Answer)
- C. 2 weeks
- D. 2-3 days
Explanation: ***4 weeks*** - The incubation period for **primary scabies infection** typically ranges from **2 to 6 weeks**, with an average of **3-4 weeks**. - **4 weeks** is the most commonly cited typical incubation period in standard dermatology references. - During this period, the patient is often **asymptomatic** as the body has not yet developed an allergic reaction to the mites, their eggs, and their feces. - Once sensitization occurs, the characteristic **pruritus** (especially nocturnal) and skin lesions appear. *2 weeks* - While 2 weeks falls within the acceptable range (2-6 weeks), it represents the **shorter end** of the spectrum for primary infection. - This duration is less commonly seen and does not represent the **typical or average** incubation period. - Most patients develop symptoms closer to **3-4 weeks** after initial infestation. *7 days* - This period is **too short** for symptoms of **primary scabies** to manifest in an immunologically naive individual. - It takes approximately 2-6 weeks for the immune system to develop a hypersensitivity response to mite antigens. - A shorter incubation period **(1-4 days)** is characteristic of **re-infestation** in previously sensitized individuals. *2-3 days* - This very short timeframe is characteristic of **re-infestation** in individuals who have been previously exposed to scabies. - In re-infestation, the immune system is already primed, leading to rapid onset of symptoms (**1-4 days**). - This is **not applicable** to primary scabies infection, where the initial immunological sensitization takes several weeks.
Practice by Chapter
Scabies
Practice Questions
Pediculosis
Practice Questions
Cutaneous Larva Migrans
Practice Questions
Leishmaniasis
Practice Questions
Onchocerciasis
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Myiasis
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Tungiasis
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Cutaneous Amebiasis
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Cutaneous Manifestations of Malaria
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Ectoparasitic Infestations
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Diagnosis of Parasitic Infestations
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Antiparasitic Therapy
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