NEET-PG 2013 Dermatology MCQs — Questions 31–34 (Page 4 of 4)

Q: What is the most common trigger associated with erythema multiforme?

Herpes simplex. ***Herpes simplex*** - **Herpes simplex virus (HSV)** is the most common precipitating factor for **erythema multiforme**, accounting for **50-60% of identifiable cases**, particularly the recurrent form. - The rash typically appears **10-14 days after an HSV outbreak**, suggesting an immune-mediated reaction. - **HSV-1** is more commonly implicated than HSV-2. *Mycoplasma pneumoniae* - **Mycoplasma pneumoniae** is the **second most common infectious trigger** for erythema multiforme, especially in children and young adults. - EM associated with Mycoplasma typically occurs during or after respiratory infection. - However, it is still less common than HSV as a trigger. *TB* - **Tuberculosis (TB)** is not typically associated with erythema multiforme. - While other infections can trigger erythema multiforme, TB is rarely implicated. *Drugs* - **Drug reactions** are a recognized cause of erythema multiforme, but they are less common than HSV infection as a trigger. - Certain medications like **sulfonamides, anticonvulsants, NSAIDs, and penicillins** are among the drugs that can induce erythema multiforme.

Q: A man with pain during defecation, no gastrointestinal symptoms, and ulcers extending into the anal canal. Diagnosis?

Genital herpes. Herpes simplex virus (HSV) infection of the anal canal is characterized by lesions that present as painful ulcers [1]. Direct extension into the anal canal is common in individuals with receptive anal intercourse or autoinoculation, often causing symptoms such as anal or rectal pain [1]. CMV proctitis typically causes more diffuse inflammation, often with bloody stools, diarrhea, and abdominal pain, which are not described in this case. While CMV can cause ulcers, they are usually shallow and often associated with immunocompromised states. Gonococcal proctitis often presents with purulent anal discharge, rectal pain, itching, and tenesmus, but typically without deep ulcerations. HIV infection can cause various anorectal complications, including aphthous ulcers, but isolated anal ulcers and defecation pain would prompt investigation into sexually transmitted infections like herpes as a more direct cause.

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: Wood's lamp has a wavelength of –

360 nm. ***360 nm*** - A **Wood's lamp** emits **long-wave ultraviolet (UV-A) light**, which is typically in the range of 320 to 450 nm. - The precise wavelength of **360 nm** is the most common and effective for dermatological diagnostic applications, allowing visualization of specific fluorescence patterns. *320 nm* - While 320 nm falls within the UV-A spectrum, it is at the lower end and less characteristic of the peak emission wavelength used in Wood's lamps for diagnostic purposes. - Using this lower wavelength might result in less pronounced or absent fluorescence for some conditions. *300 nm* - A wavelength of 300 nm is in the **UV-B spectrum** which is primarily used for therapeutic purposes like **phototherapy for psoriasis**, not for diagnostic fluorescence with a Wood's lamp. - UV-B light has different biological effects and is too short to elicit the characteristic fluorescence observed with a Wood's lamp. *250 nm* - This wavelength falls into the **UV-C spectrum**, which is **germicidal** and harmful to human tissue. - UV-C light is not used in Wood's lamps for diagnostic purposes due to its damaging properties and inability to produce the desired fluorescence.

Q31

What is the most common trigger associated with erythema multiforme?

Q32

A man with pain during defecation, no gastrointestinal symptoms, and ulcers extending into the anal canal. Diagnosis?

Q33

Scalp and face are involved in-

Q34

Wood's lamp has a wavelength of –

NEET-PG 2013 — Dermatology