Family Practice Exam Dermatology 5 ā Questions and Answers
Question 1: A 32-year-old develops target-shaped lesions with concentric rings on the palms and trunk after starting trimethoprim-sulfamethoxazole. Oral and conjunctival erosions are present. What is the diagnosis?
- Stevens-Johnson syndrome (Correct answer)
- Erythema multiforme minor
- Toxic epidermal necrolysis
- Drug reaction with eosinophilia and systemic symptoms (DRESS)
Correct answer: Stevens-Johnson syndrome
Stevens-Johnson syndrome involves mucous membrane erosions and skin detachment affecting less than 10% of body surface area, often triggered by sulfonamides.
Question 2: A 7-year-old child presents with diffuse erythema and superficial skin peeling in sheets after a localized staphylococcal infection. The Nikolsky sign is positive. What is the mechanism?
- Exfoliative toxin A/B cleaving desmoglein-1 (Correct answer)
- Direct bacterial invasion of the epidermis
- Type IV hypersensitivity to staphylococcal antigen
- Immune complex deposition at the dermoepidermal junction
Correct answer: Exfoliative toxin A/B cleaving desmoglein-1
Staphylococcal scalded skin syndrome is caused by exfoliative toxins A and B produced by S. aureus that cleave desmoglein-1 in the superficial epidermis.
Question 3: A 55-year-old farmer presents with a verrucous, slowly enlarging plaque on the dorsum of the hand that developed at a minor trauma site. Biopsy reveals pseudoepitheliomatous hyperplasia and suppurative granulomas with dark-walled fungal cells. What is the diagnosis?
- Chromoblastomycosis (Correct answer)
- Sporotrichosis
- Blastomycosis
- Cutaneous leishmaniasis
Correct answer: Chromoblastomycosis
Chromoblastomycosis presents as verrucous plaques with Medlar (sclerotic) bodies (dark-walled cells) on biopsy, typically in agricultural workers after traumatic inoculation.
Question 4: A 60-year-old presents with yellow, thickened, crumbling toenails with subungual debris. KOH of nail scrapings shows hyphae. What is the most appropriate treatment?
- Oral terbinafine for 12 weeks (Correct answer)
- Topical clotrimazole cream
- Oral fluconazole single dose
- Surgical nail avulsion alone
Correct answer: Oral terbinafine for 12 weeks
Onychomycosis requires systemic antifungals; oral terbinafine for 12 weeks (toenails) achieves the highest cure rates due to poor nail penetration of topical agents.
Question 5: A 28-year-old presents with annular plaques with raised indurated borders on the extremities and face, central atrophy, and telangiectasia. ANA is positive. What skin finding is most specific for discoid lupus erythematosus?
- Follicular plugging within the plaques (Correct answer)
- Butterfly-shaped malar erythema
- Photosensitive widespread urticaria
- Livedo reticularis
Correct answer: Follicular plugging within the plaques
Follicular plugging (dilated, keratin-filled follicles) within discoid lupus plaques is a histological and clinical hallmark that distinguishes DLE from other lupus subtypes.
Question 6: A 50-year-old presents with pruritic, flat-topped, violaceous polygonal papules on the wrists and ankles with white lacy lines on the buccal mucosa. What is the pathophysiology?
- T-cellāmediated autoimmune attack on basal keratinocytes (Correct answer)
- IgE-mediated mast cell degranulation
- IgG autoantibodies against desmoglein
- Neutrophil-mediated subepidermal blistering
Correct answer: T-cellāmediated autoimmune attack on basal keratinocytes
Lichen planus is a T-cellāmediated autoimmune disorder where cytotoxic CD8+ T cells attack basal keratinocytes, producing the characteristic band-like lymphocytic infiltrate.
Question 7: A 35-year-old presents with erythematous, well-demarcated plaques with fine scaling confined to the hairline, nasolabial folds, eyebrows, and external ears. Which organism plays a pathogenic role?
- Malassezia furfur (Correct answer)
- Candida albicans
- Staphylococcus epidermidis
- Demodex folliculorum
Correct answer: Malassezia furfur
Seborrheic dermatitis is associated with an abnormal immune response to Malassezia yeast species colonizing sebaceous-rich skin areas.
Family Practice Exam Dermatology 5
A 32-year-old develops target-shaped lesions with concentric rings on the palms and trunk after starting trimethoprim-sulfamethoxazole.
Oral and conjunctival erosions are present.
What is the diagnosis?