Parasitic Skin Infections Practice Questions

Q: Characteristic lesion of scabies is-

Burrow. ***Burrow*** - The **burrow** is the path created by the female **scabies mite (Sarcoptes scabiei)** as it tunnels into the superficial layer of the epidermis to lay eggs. - It appears as a fine, wavy, thread-like line, often grayish or skin-colored, and is considered the **pathognomonic lesion** of scabies. *Papule* - While **papules** can be present in scabies, often as a result of an immune reaction to the mites and their products, they are not the characteristic, diagnostic lesion itself. - Papules are more general skin findings and can be associated with many different dermatological conditions. *Vesicle* - **Vesicles** (small blisters) may occasionally be seen in scabies, particularly in infants or in severe cases, but they are not the primary or most characteristic lesion. - Vesicles are more commonly associated with conditions like viral infections (e.g., herpes) or allergic contact dermatitis. *Fissure* - **Fissures** are linear cracks in the skin, often caused by extreme dryness or inflammation, and they are not a characteristic primary lesion of scabies. - While scratching from intense itching in scabies could potentially lead to secondary skin changes like excoriations or, in severe cases, fissures, they are not directly formed by the mite.

Q: A 35-year-old male presents with his wife to the dermatology clinic. The image shows characteristic lesions on the husband's skin. The lesions are intensely pruritic, especially at night, and similar lesions have started appearing on his wife's skin. What is the most appropriate initial treatment?

Permethrin. ***Permethrin*** - **Permethrin cream 5%** is the **first-line topical treatment** for scabies, effectively killing mites and their eggs. - It is applied to the entire body from the neck down, left on for 8-14 hours, and then washed off; often a second application is recommended after 7 days. - **Highly effective with minimal side effects**, making it the preferred initial treatment for uncomplicated scabies. *Ivermectin* - **Oral ivermectin** is typically reserved for **crusted (Norwegian) scabies**, cases refractory to topical treatments, or in outbreak settings where mass treatment is necessary. - It is an effective scabicide but is not the initial treatment of choice for uncomplicated scabies due to potential systemic side effects and the need for repeat dosing. *Benzyl benzoate* - **Benzyl benzoate** is an **alternative topical scabicide**, particularly useful in resource-limited settings or when permethrin is unavailable or contraindicated. - While effective, it can be more irritating to the skin compared to permethrin and requires multiple applications, making it a second-line option. *GBH (Gamma Benzene Hexachloride/Lindane)* - **Lindane 1%** is a **historical scabicide** that is now **largely discontinued** or restricted in most countries due to neurotoxicity concerns, especially in children and pregnant women. - It has been replaced by safer alternatives like permethrin and is **not recommended as initial treatment** due to its adverse effect profile and environmental persistence.

Q: Scalp and face are involved in-

Infantile scabies. ***Infantile scabies*** - In **infants** and young children, scabies can present with widespread lesions, often involving the **head, neck, face, palms, and soles**, unlike in adults. - The immune system in infants is less developed, leading to more generalized and severe manifestations. - This is the characteristic distribution pattern that distinguishes infantile scabies. *Nodular scabies* - Characterized by persistent red-brown **nodules**, typically located in the axillae, groin, and scrotum. - While a variant of scabies, it does not specifically involve the scalp and face as a primary distinguishing feature. - These nodules can persist even after treatment. *Norwegian scabies* - Also called **crusted scabies**, this severe form occurs in immunocompromised patients. - Characterized by **thick, crusted lesions** with millions of mites, highly contagious. - While it can involve extensive body areas including face in immunocompromised hosts, the typical presenting feature is thick crusts, not the predilection for scalp/face seen in infantile scabies. *Adult scabies* - In adults, scabies typically spares the **head and neck** area, affecting interdigital spaces, wrists, elbows, axillae, and groin. - Involvement of the face and scalp is rare in adults, unless they are immunocompromised. - This distribution pattern is the key differentiating feature from infantile scabies.

Q: What is the average number of mites found on the body in a person suffering from regular scabies?

10 to 15. ***10 to 15*** - In **classic scabies**, the average number of **Sarcoptes scabiei** mites present on the host's body typically ranges from 10 to 15. - This relatively low number of mites is responsible for the intense **pruritus** and characteristic rash due to the host's immune response to mite antigens and waste products. *1 to 5* - While a very small number of mites might be present in the **early stages** of infestation, an average of 1 to 5 is generally too low for a full-blown symptomatic case of **classic scabies**. - A lower mite count is more typical of **atypical presentations** or infestations in partially treated individuals. *15 - 20* - This range is slightly higher than the typical average reported for **classic scabies**, though still within a reasonable, albeit less common, variation. - A significantly higher number of mites, into the thousands or millions, is characteristic of **crusted (Norwegian) scabies**, a much more severe form of the disease. *3* - Three mites represent a very low burden for a person with **classic scabies**. - Although the total number of mites is often small, an average of three significantly underestimates the typical infestation load that causes widespread itching and rash.

Q: All of the following are true regarding Norwegian scabies except

Children commonly affected. ***Children commonly affected*** - **Norwegian scabies** (also known as **crusted scabies**) primarily affects individuals with **immunocompromise**, **neurological impairment**, or the **elderly**. - While scabies can affect children, the crusted form is **uncommon** in healthy children. *Large number of parasites present* - This statement is true; **crusted scabies** is characterized by an **exceedingly high mite burden**, sometimes numbering in the millions. - The large number of mites leads to the characteristic **crusting and hyperkeratosis**. *Psoriasiform plaques common* - This statement is true; the extensive **hyperkeratosis** and **crusting** in Norwegian scabies often manifest as **thick, scaly plaques** that can resemble **psoriasis**. - These lesions are typically found on the **extremities**, **trunk**, and often involve the **nails** and **scalp**. *Itching is mild or absent* - This statement is true; despite the massive mite load, patients with crusted scabies often experience **surprisingly little or no pruritus**. - This reduced or absent itching is thought to be due to an impaired immune response that also prevents the typical inflammatory reaction to the mites.

Q: Which is TRUE about scabies?

Treatment includes treating contacts. ***Treatment includes treating contacts*** - **Scabies** is highly contagious and spreads easily through close physical contact, so treating all close contacts, even if asymptomatic, is crucial to prevent re-infestation and control outbreaks. - This approach helps break the cycle of transmission and effectively eradicates the **mite infestation** from a household or community setting. *Burrows commonly affect face* - **Scabies burrows** are typically found in skin folds and warm areas, such as between fingers, wrists, armpits, and groin, but rarely affect the face in adults. - In infants and young children, however, **facial involvement** can occur due to their underdeveloped immune systems. *Ivermectin is contraindicated* - **Ivermectin** is an effective oral treatment for scabies, particularly in cases of resistant or crusted scabies. - It is **not contraindicated** in most patients, though it should be used with caution in pregnant or breastfeeding women and young children. *Single application is sufficient* - A single application of topical treatments like **permethrin cream** is often insufficient to eradicate all mites and eggs, necessitating a second application 7 to 14 days later. - This two-dose regimen ensures that any newly hatched mites from eggs that survived the initial treatment are also eliminated, preventing treatment failure.

Q: A 5-year-old child presents with burrows on the hands and wrists, particularly between the fingers. What is the first-line treatment to eradicate the causative organism?

Topical permethrin. **Topical permethrin** - **Permethrin cream (5%)** is the **first-line treatment** for **scabies** in children aged 2 months and older, applied to all skin surfaces from the neck down. - It works as a **neurotoxin** to the **Sarcoptes scabiei mite**, effectively killing both the mites and their eggs. *Oral ivermectin* - **Oral ivermectin** is used for **crusted scabies**, in immunocompromised patients, or when topical treatments fail or are not tolerated. - It is generally **not recommended as first-line** for uncomplicated scabies due to potential side effects and limited data in young children. *Topical corticosteroids* - **Topical corticosteroids** are used to reduce the **inflammation** and **itching** associated with scabies, but they do **not kill the mites** or treat the underlying infestation. - Their primary role is symptomatic relief, usually prescribed **after or in conjunction with** a miticide. *Oral antihistamines* - **Oral antihistamines** are used to alleviate severe **pruritus (itching)** caused by scabies by blocking histamine release. - Similar to corticosteroids, they provide **symptomatic relief** but do not eradicate the *Sarcoptes scabiei* mites.

Q: Which drug is used as a single oral dose agent for the treatment of scabies?

Ivermectin. ***Ivermectin*** - **Ivermectin** is the only **oral agent** that can be given as a **single dose** for scabies treatment. - Its mechanism involves targeting **gamma-aminobutyric acid (GABA)**-gated chloride channels in the parasite, causing paralysis and death. *Permethrin* - **Permethrin** is a topical cream and not an oral agent; it is applied to the skin, typically for 8-14 hours. - It works by disrupting the **sodium channels** in the parasite's nervous system, leading to paralysis and death. *Retinoids* - **Retinoids** are primarily used for conditions like **acne** and **psoriasis**, and they are not effective against parasitic infections like scabies. - They function by modulating **gene expression** and influencing cell growth and differentiation. *Co-trimoxazole* - **Co-trimoxazole** is an **antibiotic** used to treat bacterial infections and has no efficacy against the scabies mite. - It is a combination of **sulfamethoxazole** and **trimethoprim**, both of which inhibit bacterial folic acid synthesis.

Q: Patient presents with pruritus of the interdigital spaces of the left hand as shown in the image. Identify the condition.

Sarcoptes scabiei. ***Sarcoptes scabiei*** - The image shows **papules and excoriations** in the **interdigital spaces**, a classic presentation of **scabies**. Patients typically experience **intense pruritus**, especially at night. - The presence of **burrows**, which are linear or serpiginous tracks, further supports this diagnosis, as these are created by the female mite tunneling into the epidermis. *Dermatitis herpetiformis* - This condition is characterized by **intensely pruritic, symmetrically grouped vesicles and bullae** on extensor surfaces, such as elbows, knees, and buttocks, not primarily interdigital spaces. - It is strongly associated with **celiac disease** and typically responds to a gluten-free diet and dapsone. *Xerotic dermatitis* - **Xerotic dermatitis**, also known as **eczema craquelé** or **winter itch**, is characterized by **dry, fissured skin** that resembles cracked porcelain, often exacerbated by dry weather. - While it causes pruritus, it does not typically present with the papules and burrows seen in scabies, nor is it confined to interdigital spaces in this manner. *Erythema multiforme* - **Erythema multiforme** is an acute, self-limiting inflammatory skin condition characterized by **target lesions** (concentric rings of erythema and edema) and often involves mucous membranes. - It is often triggered by infections (e.g., herpes simplex virus) or drugs and does not primarily present with pruritic papules in interdigital areas.

Q: Treatment of choice for scabies in an infant < 6 months is?

Permethrin. ***Permethrin*** - **Permethrin 5% cream** is the **first-line treatment** for scabies in infants and children, including those **aged 2 months and older**. - It is highly effective (95-97% cure rate), safe, and well-tolerated with minimal systemic absorption. - For infants **< 2 months**, permethrin can be used off-label with caution, though some guidelines prefer sulfur ointment in this very young age group. - Applied from neck down (including scalp in infants), left for 8-14 hours, then washed off; single application is usually sufficient. - **Recommended by CDC, AAP, and IAP** as the preferred scabicide for infants and children. *Sulfur ointment* - **5-10% sulfur ointment** is a safe and effective alternative, especially for infants **< 2 months** where permethrin data is limited. - It is the oldest scabicide with an excellent safety profile and no systemic toxicity. - Disadvantages include unpleasant odor, skin irritation, staining of clothes, and need for application on 3 consecutive nights. - Often considered when permethrin is unavailable or contraindicated. *Crotamiton* - **Crotamiton 10% cream/lotion** has limited efficacy (50-70% cure rate) compared to permethrin. - It is considered a **second or third-line agent** due to variable effectiveness. - Requires application for 2-5 consecutive days, which affects compliance. - Not recommended as first-line treatment in current guidelines. *Ivermectin* - **Oral ivermectin** is contraindicated in infants < 15 kg or < 5 years of age due to lack of safety data. - It does not cross the blood-brain barrier well in very young children, raising theoretical safety concerns. - Reserved for crusted scabies or treatment failures in older children and adults.

Question 1

Characteristic lesion of scabies is-

Accepted Answer

Burrow

Answer

Papule

Answer

Vesicle

Answer

Fissure

Question 2

A 35-year-old male presents with his wife to the dermatology clinic. The image shows characteristic lesions on the husband's skin. The lesions are intensely pruritic, especially at night, and similar lesions have started appearing on his wife's skin. What is the most appropriate initial treatment?

Accepted Answer

Permethrin

Answer

Ivermectin

Answer

Benzyl benzoate

Answer

GBH

Question 3

Scalp and face are involved in-

Accepted Answer

Infantile scabies

Answer

Nodular scabies

Answer

Norwegian scabies

Answer

Adult scabies

Question 4

What is the average number of mites found on the body in a person suffering from regular scabies?

Accepted Answer

10 to 15

Answer

1 to 5

Answer

15 - 20

Answer

3

Question 5

All of the following are true regarding Norwegian scabies except

Accepted Answer

Children commonly affected

Answer

Large number of parasites present

Answer

Psoriasiform plaques common

Answer

Itching is mild or absent

Question 6

Which is TRUE about scabies?

Accepted Answer

Treatment includes treating contacts

Answer

Burrows commonly affect face

Answer

Ivermectin is contraindicated

Answer

Single application is sufficient

Question 7

A 5-year-old child presents with burrows on the hands and wrists, particularly between the fingers. What is the first-line treatment to eradicate the causative organism?

Accepted Answer

Topical permethrin

Answer

Oral ivermectin

Answer

Topical corticosteroids

Answer

Oral antihistamines

Question 8

Which drug is used as a single oral dose agent for the treatment of scabies?

Accepted Answer

Ivermectin

Answer

Permethrin

Answer

Retinoids

Answer

Co-trimoxazole

Question 9

Patient presents with pruritus of the interdigital spaces of the left hand as shown in the image. Identify the condition.

Accepted Answer

Sarcoptes scabiei

Answer

Dermatitis herpetiformis

Answer

Xerotic dermatitis

Answer

Erythema multiforme

Question 10

Treatment of choice for scabies in an infant < 6 months is?

Accepted Answer

Permethrin

Answer

Crotamiton

Answer

Sulfur ointment

Answer

Ivermectin

Parasitic Skin Infections — MCQs

Parasitic Skin Infections — MCQs

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