Parasitic Skin Infections Practice Questions

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.

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: 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: Scabies oral treatment of choice:

Ivermectin. ***Ivermectin*** - **Ivermectin** is the **oral treatment of choice** for scabies, especially in cases of crusted (Norwegian) scabies, immunocompromised patients, or when topical treatments fail. - It works by disrupting the **neurotransmitter system** of parasites, leading to paralysis and death of the scabies mites. *Benzyl Benzoate* - **Benzyl benzoate** is a **topical scabicide** and acaricide, used as a lotion or emulsion. - It is not available as an oral formulation and is typically reserved for cases where other topical agents are ineffective or contraindicated. *Lindane* - **Lindane** (gamma-hexachlorocyclohexane) is a topical scabicide but is **not recommended as a first-line treatment** due to potential **neurotoxicity** (seizures) especially in infants, children, and individuals with extensive skin excoriations. - It is used topically and has significant systemic absorption, making its use limited. *Permethrin* - **Permethrin** cream is considered the **first-line topical treatment** for scabies, showing high efficacy and a good safety profile. - It is not an oral medication; it is applied topically to the skin to kill mites.

Q: Drug of choice in scabies in pregnant woman is -

Permethrin. ***Permethrin*** - **Permethrin cream** (5%) is considered the **drug of choice** for scabies in pregnant women due to its high efficacy and excellent safety profile. - It has **minimal systemic absorption**, reducing potential risks to the developing fetus. *Gamma Benzene Hexachloride* - **Gamma Benzene Hexachloride (lindane)** is **not recommended** in pregnancy due to potential **neurotoxicity** and higher systemic absorption. - It can cause **seizures** and other central nervous system effects, especially in infants and young children. *Ivermectin* - **Ivermectin** is an oral medication that has **limited safety data** in pregnancy and is generally avoided unless topical treatments fail. - It is classified as **Pregnancy Category C** by the FDA, meaning animal studies have shown adverse effects on the fetus, but there are no adequate and well-controlled studies in humans. *Benzyl benzoate* - **Benzyl benzoate** is an older scabicide that can be **irritating to the skin** and is generally considered a second-line option. - While it has been used in pregnancy, **permethrin** is preferred due to its superior safety and lower irritation profile.

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.

Q: Not a feature of scabies -

Fever is a common finding. ***Fever is a common finding (Correct Answer)*** - **Fever is NOT a typical feature** of uncomplicated scabies. This makes it the correct answer to this negation question. - Scabies is a parasitic infestation causing intense itching and skin lesions, not systemic fever. - While severe scratching can lead to **secondary bacterial infections** which may cause localized fever or warmth, a generalized fever is not a direct feature of the scabies infestation itself. *Itching is more severe at night (Incorrect)* - The **itching in scabies is characteristically worse at night**, a phenomenon believed to be due to the mites' increased activity in warmer conditions under bedding or a decreased distraction from other stimuli. - This nocturnal pruritus is a **hallmark symptom** and a key diagnostic clue for scabies. *Family history is found (Incorrect)* - Scabies is **highly contagious** and spreads through direct, prolonged skin-to-skin contact, making it common for multiple family members or close contacts to be affected. - Therefore, a **family history or outbreak in a household** is a very common finding and helps in diagnosis. *Burrows are seen in Stratum Corneum (Incorrect)* - The female scabies mite burrows into the **stratum corneum** (the outermost layer of the epidermis) to lay eggs, creating characteristic linear or serpiginous lesions. - These **mite burrows** are the pathognomonic physical sign of scabies, although they can be difficult to find due to scratching and secondary skin changes.

Question 1

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 2

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

Accepted Answer

Face

Answer

Axilla

Answer

Webspace

Answer

Genitalia

Question 3

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 4

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 5

Maculae cerulea is seen in ?

Accepted Answer

Pediculosis pubis

Answer

Pediculosis hominis corporis

Answer

Scabies

Answer

Pediculosis capitis

Question 6

Scabies oral treatment of choice:

Accepted Answer

Ivermectin

Answer

Benzyl Benzoate

Answer

Lindane

Answer

Permethrin

Question 7

Drug of choice in scabies in pregnant woman is -

Accepted Answer

Permethrin

Answer

Gamma Benzene Hexachloride

Answer

Ivermectin

Answer

Benzyl benzoate

Question 8

Pathognomonic lesion of scabies is?

Accepted Answer

Burrow

Answer

Pits

Answer

Vesicle

Answer

Papules

Question 9

Incubation period of scabies is:

Accepted Answer

4 weeks

Answer

7 days

Answer

2 weeks

Answer

2-3 days

Question 10

Not a feature of scabies -

Accepted Answer

Fever is a common finding

Answer

Itching is more severe at night

Answer

Family history is found

Answer

Burrows are seen in Stratum Corneum

Parasitic Skin Infections — MCQs

Parasitic Skin Infections — MCQs

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