Dermatology MCQ 4 Questions With Answers And Detailed Explanations USMLE PLAB DHA MOH

Dermatology MCQ 4 Questions With Answers And Detailed Explanations For USMLE PLAB DHA MOH 

A 56-year-old man on treatment for hypertension, epilepsy and gastro-esophageal reflux disease presented with an urticarial skin eruption. A drug reaction is suspected since he has recently started a new drug. Which of the following medications is most likely to be responsible?

A. Atorvastatin

B. Omeprazole

C. Aspirin ✅

D. Paracetamol

E. Sodium valproate

Question Explanation:

Urticaria is one of the most common dermatologic problems seen by primary care physicians and often a source of frustration for patient and physician alike. Pinpointing the cause nay be challenging-or impossible- because of the many and varied triggers.

Patients with aspirin sensitivity can present with either mucosal reactions (the aspirin triad of nasal polyposis, sinusitis and asthma) or cutaneous reactions (urticaria or anaphylaxis).

A 12-year-old male has acne vulgaris. Topical erythromycin was used for 2 weeks, several months ago, with no response. What treatment would you prescribe now?

A. Accutane immediately

B. Topical tretinoin

C. Topical benzoyl peroxide

D. Topical antibiotic other than erythromycin

E. Oral antibiotic and topical tretinoin ✅

Question Explanation:

Mild inflammatory acne should be treated with topical benzoyl peroxide and/or topical antibiotics (e.g., erythromycin, clindamycin) or topical tretinoin. Moderate acne responds best to oral systemic therapy with antibiotics. Antibiotics effective for acne include tetracycline, minocycline, erythromycin, and doxycycline. For severe acne, oral isotretinoin (accutane) is the best treatemnt for patients in whom antibiotics are unsuccessful and for those with severe inflammatory acne.

Which of the following suggest a diagnosis of molluscum contagiosum rather than chickenpox?

A. Lesions disappearing within a month

B. Positive contact history

C. Absence of erythema surrounding lesions ✅

D. Presence of macules and papules

E. Presence of pruritis

Question Explanation:

Molluscum contagiosum is caused by a deoxyribonucleic acid (DNA) pox virus. The lesions are small, skin- colored papules with central umbilication. There is little surrounding inflammation and they may be spread following scratching to other sites.

Chickenpox lesions in the early stages may be mistaken for molluscum. However, the presence of associated macules and later vesicles and pustules help to differentiate them. These lesions also affect the mucous membranes, and usually disappear within a few weeks, while molluscum can persist for up to a year.

A 60-year-old patient of South Asian origin presents with a widespread blistering rash. Which of the following features would be consistent with a diagnosis of Pemphigus?

A. Flaccid blistering and oral involvement ✅

B. Acanthosis

C. Blisters arising within the subepidermal area

D. Salmon Pink color

E. Violet lesions

Question Explanation:

Pemphigus is associated with loss of intercellular cohesion in the lower part of the epidermis, leading to acantholysis (separation of keratinocytes). Pemphigus is classically associated with flaccid blistering, and often with immunoglobulin IgG antibodies. Treatment may be successful with azathioprine. Pemphigoid is associated with subepidermal bullae.

Which statement regarding tinea capitis is correct?

A. It is transmitted sexually

B. It is effectively treated with topical nystatin ointment

C. It is most commonly caused by the fungus Trichophyton tonsurans ✅

D. It often results in permanent alopecia

E. Its presence should suggest immunological deficiency.

Question Explanation:

Tinea capitis is a dermatophyte infection of the scalp most often caused by Trichophyton tonsurans, and occasionally by Microsporum canis. It is commonest in areas of socio-economic deprivation. M. canis is a zoophilic species acquired from cats and dogs.

There is initially a small papule at the base of the hair follicle which spreads peripherally forming a scaly circular plaque (ringworm) within which there are brittle, broken infected hairs (exclamation mark hairs). Confluent patches of alopecia develop and there may be pruritic. Sometimes a severe inflammatory response produces an elevated boggy granulomatous mass (kerion), studded with sterile pustules.

There may be fever and regional lymphadenopathy, and occasionally permanent scarring and alopecia may result. The crusted patches fluoresce dull green under Wood's light. Microscopic examination of a potassium hydroxide (KOH) preparation shows tiny spores and the fungi may be grown in Sabouraud medium with antibiotics. Oral griseofulvin for two to three months is required, or ketoconazole for resistant cases.

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