Parasitic Skin Infections Practice Questions

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: Lepromin test is strongly positive in:

Tuberculoid (TT). ***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.

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.

Q: 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?

5-15. ***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.

Q: 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?

Cutaneous Leishmaniasis. ***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**.

Q: Slit smear negative leprosy is:

All of the options. ***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**.

Q: Maculae cerulea is seen in ?

Pediculosis pubis. ***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.

Q: Pathognomonic lesion of scabies is?

Burrow. ***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.

Q: Incubation period of scabies is:

4 weeks. ***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.

Question 1

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 2

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 3

Lepromin test is strongly positive in:

Accepted Answer

Tuberculoid (TT)

Answer

Lepromatous (LL)

Answer

Borderline lepromatous (BL)

Answer

Borderline borderline (BB)

Question 4

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

Accepted Answer

Face

Answer

Axilla

Answer

Webspace

Answer

Genitalia

Question 5

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?

Accepted Answer

5-15

Answer

20-25

Answer

30-50

Answer

25-30

Question 6

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?

Accepted Answer

Cutaneous Leishmaniasis

Answer

Chronic Fungal infections

Answer

Cutaneous tuberculosis

Answer

Leprosy

Question 7

Slit smear negative leprosy is:

Accepted Answer

All of the options

Answer

Neuritic type

Answer

Tuberculoid type

Answer

Indeterminate type

Question 8

Maculae cerulea is seen in ?

Accepted Answer

Pediculosis pubis

Answer

Pediculosis hominis corporis

Answer

Scabies

Answer

Pediculosis capitis

Question 9

Pathognomonic lesion of scabies is?

Accepted Answer

Burrow

Answer

Pits

Answer

Vesicle

Answer

Papules

Question 10

Incubation period of scabies is:

Accepted Answer

4 weeks

Answer

7 days

Answer

2 weeks

Answer

2-3 days

Parasitic Skin Infections — MCQs

Parasitic Skin Infections — MCQs

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