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CAQ-Derm practice questions

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Question 1Dermatology

A 6-year-old child develops honey-colored crusted lesions around the nostrils and upper lip after a week of nasal discharge. Gram stain of the crust shows gram-positive cocci in clusters. Which organism is the most likely cause?

  1. Corynebacterium diphtheriae
  2. Pseudomonas aeruginosa
  3. Streptococcus pyogenes
  4. Staphylococcus aureus Correct answer.

Explanation

Nonbullous impetigo in children is most often caused by Staphylococcus aureus, which appears as gram-positive cocci in clusters; Streptococcus pyogenes is the second most common cause and typically shows chains. The honey-colored crust and perinasal distribution are classic. Corynebacterium diphtheriae produces a pseudomembrane rather than crusted impetigo, and Pseudomonas is gram-negative.

Question 2Dermatology

Which finding on potassium hydroxide microscopy is most characteristic of pityriasis versicolor?

  1. Budding yeasts with pseudohyphae and true hyphae in equal proportion
  2. Broad non-septate hyphae with right-angle branching
  3. Short hyphae with round spores producing a spaghetti-and-meatballs pattern Correct answer.
  4. Septate hyphae with arthroconidia alternating along the hair shaft

Explanation

Malassezia furfur in skin scrapings shows short hyphae admixed with clusters of round yeast cells, classically described as spaghetti and meatballs. Broad non-septate hyphae suggest mucormycosis, and arthroconidia along hair shafts suggest dermatophyte endothrix infection. This pattern is the standard diagnostic clue for pityriasis versicolor.

Question 3Dermatology

A patient with psoriasis is being considered for phototherapy. Which mechanism best explains the therapeutic effect of narrowband UVB?

  1. Direct inhibition of keratinocyte DNA polymerase
  2. Blockade of histamine release from mast cells
  3. Selective destruction of dermal Langerhans cells
  4. Induction of T-cell apoptosis and reduction of proinflammatory cytokines in skin Correct answer.

Explanation

Narrowband UVB (311–313 nm) works chiefly by inducing apoptosis of pathogenic T cells in the epidermis and dermis and by shifting cytokine profiles away from Th1/Th17 mediators. It does not act primarily through mast-cell stabilization or direct DNA polymerase inhibition. This immunomodulatory mechanism underlies its use in psoriasis, vitiligo, and atopic dermatitis.

Question 4Dermatology

Which clinical feature most strongly favors plaque psoriasis over nummular eczema?

  1. Ill-defined borders with oozing and crusting
  2. Lesions confined to flexural creases
  3. Severe pruritus that worsens at night
  4. Well-demarcated plaques with silvery scale on extensor surfaces Correct answer.

Explanation

Psoriasis classically produces sharply demarcated erythematous plaques with silvery micaceous scale, favoring extensor surfaces such as elbows and knees. Nummular eczema tends to be less well demarcated, intensely pruritic, and often oozing or crusted. Flexural involvement can occur in psoriasis but is not the discriminating feature.

Question 5Dermatology

A 24-year-old presents with grouped vesicles on an erythematous base over the left T4 dermatome, with burning pain. Which diagnosis is most likely?

  1. Herpes zoster Correct answer.
  2. Contact dermatitis
  3. Varicella
  4. Herpes simplex labialis

Explanation

Grouped vesicles on an erythematous base confined to a single dermatome with neuropathic pain is the classic presentation of herpes zoster, caused by reactivation of latent varicella-zoster virus in a dorsal root ganglion. Herpes simplex recurs at mucocutaneous sites without dermatomal restriction, and varicella is generalized. Contact dermatitis follows an exposure pattern and is not dermatomal.

Question 6Dermatology

Which histologic feature is the hallmark of lichen planus?

  1. Subcorneal pustules with neutrophils
  2. Nodular dermal infiltrate of atypical lymphocytes
  3. Band-like lymphocytic infiltrate at the dermoepidermal junction with saw-tooth rete ridges Correct answer.
  4. Perivascular eosinophils with dermal edema

Explanation

Lichen planus shows a dense band-like (lichenoid) lymphocytic infiltrate hugging the dermoepidermal junction, with basal vacuolar degeneration and saw-tooth rete ridges. Subcorneal neutrophilic pustules suggest pustular psoriasis or impetigo, while eosinophil-rich perivascular infiltrates suggest drug eruption or urticaria. Recognizing the lichenoid pattern is essential for diagnosis.

Question 7Dermatology

Which topical agent is a first-line treatment for mild-to-moderate acne vulgaris because of both comedolytic and anti-inflammatory effects?

  1. Clindamycin lotion
  2. Hydrocortisone 1% cream
  3. Benzoyl peroxide 5% gel
  4. Tretinoin Correct answer.

Explanation

Topical retinoids such as tretinoin are first-line for acne because they normalize follicular keratinization (comedolysis) and have anti-inflammatory activity. Benzoyl peroxide and topical antibiotics target Cutibacterium acnes but lack the comedolytic effect, and topical corticosteroids can worsen acne. Retinoids address the primary microcomedone.

Question 8Dermatology

Which feature best distinguishes a superficial spreading melanoma from a benign melanocytic nevus on dermoscopy?

  1. Comma-shaped vessels at the periphery
  2. Symmetric pigmentation with a single uniform color
  3. Irregular pigment network with abrupt cutoff and multiple colors Correct answer.
  4. Central scar with white lines

Explanation

Melanoma on dermoscopy typically shows asymmetry, an irregular or atypical pigment network, abrupt cutoff of pigment at the periphery, and multiple colors. Benign nevi are symmetric with a regular network and one or two colors. Comma vessels and central scars are features of other lesions such as dermatofibroma or Spitz nevus patterns.

Question 9Dermatology

A 30-year-old presents with intensely pruritic vesicles on the sides of the fingers and wrists, worsening after handling detergents. Examination shows excoriations and lichenification. Which diagnosis is most likely?

  1. Palmoplantar psoriasis
  2. Tinea manuum
  3. Dyshidrotic eczema Correct answer.
  4. Scabies

Explanation

Dyshidrotic eczema (pompholyx) produces deep-seated, intensely pruritic vesicles on the palms, soles, and lateral fingers, often triggered by irritants, sweat, or stress. Scabies favors web spaces with burrows and nocturnal itch, and tinea manuum is usually unilateral with a scaly advancing edge. Psoriasis is less vesicular and more hyperkeratotic.

Question 10Dermatology

A patient on lithium develops multiple inflamed follicular papules and pustules on the trunk. Which mechanism best explains this drug eruption?

  1. Follicular epithelial proliferation and altered keratinization Correct answer.
  2. Direct toxic necrosis of eccrine glands
  3. Immune complex deposition in dermal vessels
  4. IgE-mediated mast cell degranulation

Explanation

Lithium is a well-recognized acneiform trigger; it promotes follicular epithelial proliferation and altered keratinization, leading to follicular plugging and pustule formation. This is not an IgE-mediated reaction or immune complex vasculitis. Recognizing drug-induced acneiform eruptions guides withdrawal of the offending agent.

Question 11Dermatology

A 55-year-old with type 2 diabetes develops a painless ulcer on the sole with a callused rim and loss of protective sensation. Which factor is most important in pathogenesis?

  1. Venous hypertension
  2. Arterial insufficiency alone
  3. Autoimmune small-vessel vasculitis
  4. Peripheral neuropathy with repetitive pressure Correct answer.

Explanation

Diabetic neuropathic ulcers arise from loss of protective sensation combined with repetitive mechanical pressure over bony prominences, producing callus and underlying tissue breakdown. Venous hypertension causes stasis ulcers near the malleoli, and pure arterial insufficiency produces painful, punched-out distal ulcers. Vasculitis causes palpable purpura and necrosis, not callused plantar ulcers.

Question 12Dermatology

A patient with known psoriasis develops sudden generalized erythema with shedding of sheets of scale and systemic symptoms after stopping systemic corticosteroids. Which complication is most likely?

  1. Guttate psoriasis
  2. Erythrodermic psoriasis Correct answer.
  3. Pustular psoriasis of the palms
  4. Psoriatic arthritis

Explanation

Abrupt withdrawal of systemic corticosteroids can trigger erythrodermic psoriasis, characterized by generalized erythema and desquamation involving nearly the entire body surface, with risk of hypothermia, fluid loss, and infection. Guttate psoriasis follows streptococcal infection, and palmoplantar pustulosis is localized. This is a dermatologic emergency requiring inpatient management.

Question 13Dermatology

A 40-year-old presents with tense bullae on normal-appearing skin and oral erosions; direct immunofluorescence shows linear IgG and C3 along the basement membrane zone. Which diagnosis is most likely?

  1. Epidermolysis bullosa acquisita
  2. Pemphigus vulgaris
  3. Dermatitis herpetiformis
  4. Bullous pemphigoid Correct answer.

Explanation

Bullous pemphigoid produces tense subepidermal bullae on normal or urticarial skin with linear IgG and C3 deposition along the basement membrane zone. Pemphigus vulgaris shows intercellular (net-like) IgG in the epidermis with flaccid bullae. Dermatitis herpetiformis shows granular IgA in dermal papillae, and epidermolysis bullosa acquisita also shows linear IgG but is distinguished by clinical and salt-split skin studies.

Question 14Dermatology

A 3-week-old infant has a bright red, rapidly growing vascular plaque on the cheek that has ulcerated. Which treatment is most appropriate?

  1. Topical corticosteroid
  2. Pulsed dye laser as first-line
  3. Observation alone
  4. Oral propranolol Correct answer.

Explanation

Infantile hemangiomas that are complicated (ulceration, functional impairment, or rapid growth) are treated first-line with oral propranolol, which induces vasoconstriction and accelerates involution. Topical steroids have limited efficacy for large lesions, and pulsed dye laser is reserved for residual or ulcerated superficial lesions after medical therapy. Observation alone is inappropriate when complications are present.

Question 15Dermatology

A patient with a history of anaphylaxis to penicillin requires treatment for severe acne. Which agent should be avoided because of cross-reactivity risk?

  1. Amoxicillin Correct answer.
  2. Benzoyl peroxide
  3. Doxycycline
  4. Isotretinoin

Explanation

Amoxicillin is an aminopenicillin and shares the beta-lactam ring, so it carries cross-reactivity risk in penicillin-allergic patients. Doxycycline, isotretinoin, and benzoyl peroxide are structurally unrelated and safe alternatives. Recognizing cross-reactivity is essential for safe prescribing.

Question 16Dermatology

Which feature is most characteristic of atopic dermatitis in an adult?

  1. Annular scaly plaques with central clearing
  2. Well-demarcated silvery plaques on the elbows
  3. Grouped vesicles in a dermatomal distribution
  4. Flexural lichenified plaques with a personal or family history of atopy Correct answer.

Explanation

Adult atopic dermatitis typically presents with flexural lichenified plaques and a personal or family history of atopy, asthma, or allergic rhinitis. Silvery extensor plaques indicate psoriasis, annular scaly plaques with central clearing suggest tinea, and dermatomal vesicles indicate herpes zoster. Recognizing the flexural distribution is key.

Question 17Dermatology

A patient with chronic urticaria has lesions that resolve within 24 hours without residual marks. Which feature would suggest urticarial vasculitis instead?

  1. Individual lesions that persist beyond 24 hours and leave purpura Correct answer.
  2. Dermographism
  3. Angioedema of the lips
  4. Wheals triggered by cold exposure

Explanation

Urticarial vasculitis lesions last more than 24 hours, may be painful or burning, and often leave residual purpura or hyperpigmentation because of leukocytoclastic vasculitis. Ordinary chronic urticaria resolves within 24 hours and leaves no marks. Dermographism, angioedema, and cold-induced wheals are features of other urticarial syndromes.

Question 18Dermatology

Which topical agent is the treatment of choice for localized vitiligo on the face in an adult?

  1. Ketoconazole 2% cream
  2. Tacrolimus 0.1% ointment Correct answer.
  3. Clobetasol propionate 0.05% cream applied continuously
  4. Tretinoin 0.05% cream

Explanation

Topical calcineurin inhibitors such as tacrolimus are preferred for facial vitiligo because they avoid the atrophy and telangiectasia risks of potent steroids on thin skin. Continuous use of clobetasol on the face risks skin atrophy and should be intermittent at most. Tretinoin and ketoconazole have no role in repigmentation.

Question 19Dermatology

A patient presents with a pearly papule on the nasal ala with telangiectasia and a rolled border. Which diagnosis is most likely?

  1. Basal cell carcinoma Correct answer.
  2. Melanoma
  3. Squamous cell carcinoma
  4. Seborrheic keratosis

Explanation

A pearly papule with telangiectasia and a rolled border on a sun-exposed area such as the nose is the classic description of nodular basal cell carcinoma. Squamous cell carcinoma is typically hyperkeratotic and ulcerated, melanoma is pigmented and asymmetric, and seborrheic keratosis has a stuck-on appearance. Prompt biopsy is warranted.

Question 20Dermatology

A patient on a TNF-alpha inhibitor develops a new scaly plaque on the trunk; KOH prep shows septate hyphae. Which factor most contributed to this infection?

  1. Enhanced barrier function
  2. Impaired cell-mediated immunity from biologic therapy Correct answer.
  3. Increased sebum production
  4. Antibiotic-induced gram-negative overgrowth

Explanation

TNF-alpha inhibitors impair cell-mediated immunity and granuloma formation, increasing susceptibility to dermatophyte and other fungal infections. Sebum production and barrier function are unrelated, and antibiotic-induced overgrowth would favor bacteria. Recognizing this risk guides surveillance and prompt treatment.

Question 21Dermatology

A 60-year-old with chronic sun exposure presents with a rough, sandpaper-like patch on the dorsal hand; biopsy shows atypical keratinocytes confined to the epidermis. Which diagnosis is correct?

  1. Actinic keratosis Correct answer.
  2. Lentigo maligna
  3. Basal cell carcinoma
  4. Squamous cell carcinoma in situ

Explanation

Actinic keratosis presents as a rough, gritty macule or patch on sun-damaged skin and histologically shows atypical keratinocytes confined to the lower epidermis. Full-thickness epidermal atypia would indicate squamous cell carcinoma in situ (Bowen disease). Basal cell carcinoma involves the dermis, and lentigo maligna shows atypical melanocytes.

Question 22Dermatology

A patient with a history of melanoma in situ on the back reports a new pigmented lesion with a blue-white veil and irregular streaks on dermoscopy. Which step is most appropriate?

  1. Reassurance and follow-up in one year
  2. Excisional biopsy with narrow margins Correct answer.
  3. Cryotherapy of the lesion
  4. Topical imiquimod

Explanation

Dermoscopic features such as a blue-white veil and irregular streaks raise concern for melanoma, so excisional biopsy with narrow margins is the appropriate next step to allow histologic diagnosis and Breslow thickness measurement. Reassurance, topical imiquimod, and cryotherapy are inappropriate for suspected melanoma. Prompt excision avoids misdiagnosis.

Question 23Dermatology

A patient with psoriasis is being considered for methotrexate. Which baseline test is most important before initiation?

  1. Echocardiogram
  2. Bone marrow biopsy
  3. Liver function tests and hepatitis serologies Correct answer.
  4. Serum cortisol

Explanation

Methotrexate can cause hepatotoxicity and bone marrow suppression, so baseline liver function tests, hepatitis B and C serologies, and complete blood counts are essential before starting therapy. Echocardiography and cortisol measurement are unrelated. Recognizing these monitoring requirements prevents serious toxicity.

Question 24Dermatology

A patient develops a morbilliform eruption two weeks after starting allopurinol, with fever, facial edema, and eosinophilia. Which diagnosis is most likely?

  1. Stevens-Johnson syndrome
  2. Acute generalized exanthematous pustulosis
  3. Drug reaction with eosinophilia and systemic symptoms (DRESS) Correct answer.
  4. Erythema multiforme

Explanation

DRESS presents with a morbilliform eruption, fever, facial edema, eosinophilia, and internal organ involvement, typically 2–8 weeks after starting a drug such as allopurinol. Stevens-Johnson syndrome shows mucosal erosions and epidermal detachment, AGEP shows pustules, and erythema multiforme shows target lesions. Recognizing DRESS is critical because of its high mortality.

Question 25Dermatology

A patient with known pemphigus vulgaris develops new flaccid bullae despite prednisone. Which additional therapy is best supported by evidence for inducing remission?

  1. Rituximab Correct answer.
  2. Dapsone
  3. Topical tacrolimus
  4. Hydroxychloroquine

Explanation

Rituximab, an anti-CD20 monoclonal antibody, is supported by randomized evidence as a first-line adjuvant to corticosteroids in moderate-to-severe pemphigus vulgaris and can induce sustained remission. Dapsone and hydroxychloroquine have limited evidence, and topical tacrolimus is not adequate for widespread disease. Early biologic therapy improves outcomes.

Question 26Dermatology

A 28-year-old presents with grouped tense vesicles on an erythematous base along the left T8 dermatome, accompanied by burning pain. Which diagnosis is most likely?

  1. Dermatitis herpetiformis
  2. Pemphigus vulgaris
  3. Herpes zoster Correct answer.
  4. Bullous pemphigoid

Explanation

Herpes zoster produces a unilateral, dermatomal band of grouped vesicles on an erythematous base with pain, reflecting reactivation of latent varicella-zoster virus in a dorsal root ganglion. The dermatomal distribution and prodromal pain are the key discriminators.

Question 27Dermatology

Which organism is the causative agent of erythrasma, a brown, scaly intertriginous patch that fluoresces coral-red under Wood lamp?

  1. Staphylococcus aureus
  2. Corynebacterium minutissimum Correct answer.
  3. Candida albicans
  4. Trichophyton rubrum

Explanation

Erythrasma is caused by Corynebacterium minutissimum, a Gram-positive bacterium that colonizes intertriginous skin and produces porphyrins giving the characteristic coral-red fluorescence. It is treated with topical or oral erythromycin.

Question 28Dermatology

A 6-year-old has multiple 2-3 mm dome-shaped flesh-colored papules with central umbilication on the trunk. Which diagnosis is most likely?

  1. Varicella
  2. Verruca vulgaris
  3. Pityriasis rosea
  4. Molluscum contagiosum Correct answer.

Explanation

Molluscum contagiosum is a poxvirus infection producing discrete dome-shaped papules with a central umbilication, common in children. The lesions are typically asymptomatic and spread by autoinoculation.

Question 29Dermatology

Which condition is characterized by a violaceous, pruritic, annular plaque on the trunk with fine white scale and a collarette of scale at the advancing edge?

  1. Pityriasis rosea
  2. Lichen planus
  3. Tinea corporis Correct answer.
  4. Psoriasis vulgaris

Explanation

Tinea corporis produces annular plaques with central clearing and a scaly advancing border, and KOH microscopy reveals septate hyphae. The collarette scale at the active edge is a helpful clue.

Question 30Dermatology

A fair-skinned 70-year-old has a pearly papule with rolled borders and telangiectasia on the lower eyelid. Which histologic finding confirms the diagnosis?

  1. Basaloid islands with peripheral palisading and clefting Correct answer.
  2. Mucin deposition in the dermis
  3. Atypical keratinocytes with parakeratosis
  4. Nests of melanocytes at the dermoepidermal junction

Explanation

Basal cell carcinoma shows nests of basaloid cells with peripheral palisading and retraction clefts between tumor islands and the surrounding stroma. These features are diagnostic and correlate with the pearly, telangiectatic clinical appearance.

Question 31Dermatology

Which topical agent is considered first-line therapy for mild localized plaque psoriasis on the trunk and limbs?

  1. Topical tretinoin
  2. Medium-potency topical corticosteroid Correct answer.
  3. Topical clotrimazole
  4. Oral terbinafine

Explanation

Medium-potency topical corticosteroids are first-line for limited plaque psoriasis because they reduce inflammation and scale. Emollients, coal tar, and vitamin D analogues are adjuncts, but corticosteroids remain the initial mainstay for localized disease.

Question 32Dermatology

A patient with a history of anaphylaxis to sulfonamide antibiotics requires treatment for a moderately severe acne flare. Which agent should be avoided?

  1. Benzoyl peroxide
  2. Trimethoprim-sulfamethoxazole Correct answer.
  3. Isotretinoin
  4. Doxycycline

Explanation

Trimethoprim-sulfamethoxazole contains a sulfonamide moiety and must be avoided in a patient with documented sulfonamide anaphylaxis. Doxycycline, isotretinoin, and benzoyl peroxide are appropriate alternatives without cross-reactivity.

Question 33Dermatology

A 4-year-old has an intensely pruritic eruption in the finger webs and wrists with small burrows. Which organism is responsible?

  1. Sarcoptes scabiei Correct answer.
  2. Pediculus humanus capitis
  3. Dermatobia hominis
  4. Demodex folliculorum

Explanation

Scabies is caused by the mite Sarcoptes scabiei, which burrows into the stratum corneum and causes intense pruritus, especially in web spaces and wrists. The classic presentation includes burrows and nocturnal worsening.

Question 34Dermatology

A 45-year-old with type 2 diabetes has a painless, punched-out ulcer on the plantar surface with a surrounding callus and reduced sensation. Which diagnosis is most likely?

  1. Arterial insufficiency ulcer
  2. Venous stasis ulcer
  3. Pyoderma gangrenosum
  4. Neuropathic diabetic foot ulcer Correct answer.

Explanation

Neuropathic ulcers in diabetes occur at pressure points such as the plantar surface, are painless, and have a callused rim due to repeated mechanical trauma on insensate skin. The loss of protective sensation is the key clinical clue.

Question 35Dermatology

A 32-year-old woman has well-demarcated erythematous plaques with silvery scale on the elbows and knees. Which histologic finding is most characteristic?

  1. Regular acanthosis with parakeratosis and Munro microabscesses Correct answer.
  2. Dermal mucin with perivascular lymphocytes
  3. Interface dermatitis with saw-tooth rete ridges
  4. Subepidermal blister with eosinophils

Explanation

Psoriasis shows regular acanthosis, thinning of the suprapapillary plates, parakeratosis, and neutrophils forming Munro microabscesses in the stratum corneum. These features correlate with the well-demarcated scaly plaques on extensor surfaces.

Question 36Dermatology

A 25-year-old has recurrent grouped vesicles on the lips preceded by tingling. Which pathogen is most likely?

  1. Herpes simplex virus type 1 Correct answer.
  2. Varicella-zoster virus
  3. Coxsackievirus A16
  4. Human papillomavirus

Explanation

Herpes labialis is most commonly caused by herpes simplex virus type 1, presenting as recurrent grouped vesicles with a prodrome of tingling or burning. Reactivation is triggered by stress, sun exposure, or illness.

Question 37Dermatology

A 50-year-old has a chronic pruritic eruption on the wrists with violaceous, flat-topped polygonal papules and white lacy lines on the surface. What are these lines called?

  1. Koebner lines
  2. Auspitz sign
  3. Wickham striae Correct answer.
  4. Dennie-Morgan folds

Explanation

Wickham striae are fine white lacy lines on the surface of lichen planus papules, representing hypergranulosis. They are a classic clinical clue to the diagnosis along with the violaceous, polygonal morphology.

Question 38Dermatology

A 60-year-old with a history of rosacea develops persistent erythema and telangiectasia on the cheeks. Which topical treatment is most appropriate for the erythematotelangiectatic subtype?

  1. Topical terbinafine
  2. Topical brimonidine Correct answer.
  3. Topical mupirocin
  4. Topical clobetasol

Explanation

Topical brimonidine is an alpha-adrenergic agonist that reduces facial erythema in rosacea by constricting cutaneous vessels. It is specifically indicated for the erythematotelangiectatic subtype, while metronidazole or ivermectin target papulopustular disease.

Question 39Dermatology

A 19-year-old presents with multiple inflamed nodules and draining sinus tracts in the axillae and groin. Which diagnosis is most likely?

  1. Folliculitis decalvans
  2. Hidradenitis suppurativa Correct answer.
  3. Epidermoid cyst
  4. Carbuncle

Explanation

Hidradenitis suppurativa is a chronic follicular occlusion disorder producing painful nodules, abscesses, sinus tracts, and scarring in intertriginous areas such as the axillae and groin. The recurrent nature and sinus tract formation are characteristic.

Question 40Dermatology

A patient on a TNF-alpha inhibitor develops a new scaly annular plaque on the trunk, and KOH preparation shows septate hyphae. Which factor best explains this presentation?

  1. Photosensitivity induced by the drug
  2. Direct fungal superinfection of the injection site
  3. Allergic contact dermatitis to the drug
  4. Impaired cell-mediated immunity from the biologic Correct answer.

Explanation

TNF-alpha inhibitors impair cell-mediated immunity, increasing susceptibility to fungal infections such as dermatophytosis that may present atypically. KOH-confirmed septate hyphae support a dermatophyte rather than an eczematous or allergic process.

Question 41Dermatology

A 65-year-old with chronic sun exposure has a rough, sandpaper-like patch on the dorsal hand, and biopsy shows atypia confined to the lower epidermis. Which diagnosis is most likely?

  1. Seborrheic keratosis
  2. Actinic keratosis Correct answer.
  3. Squamous cell carcinoma in situ
  4. Lentigo maligna

Explanation

Actinic keratosis presents as a rough, gritty patch on sun-exposed skin with atypical keratinocytes confined to the lower epidermis. It is a precursor lesion to squamous cell carcinoma and is treated with cryotherapy or topical field therapy.

Question 42Dermatology

A 12-year-old has multiple hypopigmented, slightly scaly patches on the trunk with a fine furfuraceous scale. Which diagnosis is most likely?

  1. Pityriasis versicolor Correct answer.
  2. Vitiligo
  3. Pityriasis alba
  4. Tinea nigra

Explanation

Pityriasis versicolor is caused by Malassezia furfur and produces hypopigmented or hyperpigmented scaly macules on the trunk, often with a fine branny scale. KOH shows short hyphae and spores in a spaghetti-and-meatballs pattern.

Question 43Dermatology

A patient with known pemphigus vulgaris develops new flaccid bullae despite prednisone. Which additional therapy is best supported?

  1. Hydroxychloroquine
  2. Rituximab Correct answer.
  3. Topical clotrimazole
  4. Oral terbinafine

Explanation

Rituximab, an anti-CD20 monoclonal antibody, is an effective adjunct in pemphigus vulgaris and is used to reduce pathogenic autoantibodies and steroid requirements in refractory disease. It is supported by randomized trial evidence.

Question 44Dermatology

A 35-year-old has recurrent, painful oral ulcers and genital ulcers with hypopyon uveitis. Which diagnosis is most likely?

  1. Reiter syndrome
  2. Behçet disease Correct answer.
  3. Herpes simplex infection
  4. Aphthous stomatitis

Explanation

Behçet disease is a systemic vasculitis characterized by recurrent oral and genital ulcers plus ocular involvement such as uveitis with hypopyon. The triad of mucocutaneous and ocular findings is classic.

Question 45Dermatology

A 55-year-old with melanoma in situ on the back reports a new pigmented lesion with a blue-white veil and irregular streaks on dermoscopy. Which feature most strongly suggests invasive melanoma?

  1. Fissures and ridges
  2. Blue-white veil with atypical network and irregular streaks Correct answer.
  3. Milia-like cysts
  4. Comedo-like openings

Explanation

A blue-white veil combined with an atypical network and irregular streaks on dermoscopy raises concern for melanoma and suggests deeper dermal invasion. Comedo openings and milia-like cysts are benign features of seborrheic keratosis.

Question 46Dermatology

A 40-year-old develops a morbilliform eruption two weeks after starting allopurinol, with fever, facial edema, and eosinophilia. Which diagnosis is most likely?

  1. Erythema multiforme
  2. Drug reaction with eosinophilia and systemic symptoms Correct answer.
  3. Stevens-Johnson syndrome
  4. Acute generalized exanthematous pustulosis

Explanation

DRESS syndrome presents with a morbilliform eruption, fever, facial edema, eosinophilia, and internal organ involvement, typically two to six weeks after starting a drug such as allopurinol. The facial edema and eosinophilia are key discriminators.

Question 47Dermatology

A patient with known psoriasis develops sudden generalized erythema with shedding of sheets of scale and systemic symptoms. Which electrolyte disturbance is most concerning in this condition?

  1. Hypercalcemia and hypermagnesemia
  2. Hyperkalemia and hyperphosphatemia
  3. Hypernatremia and hypocalcemia Correct answer.
  4. Hyperchloremia and hyperalbuminemia

Explanation

Erythrodermic psoriasis causes massive transepidermal water loss and protein loss, leading to dehydration, hypernatremia, and hypocalcemia. These disturbances require careful fluid and electrolyte monitoring.

Question 48Dermatology

A 70-year-old with chronic kidney disease develops intensely pruritic, excoriated papules and nodules on the extensor forearms. Which underlying mechanism is most likely?

  1. Autoantibodies against desmoglein 3
  2. Uremic pruritus from retained solutes and neuropathy Correct answer.
  3. IgE-mediated mast cell degranulation
  4. Deposition of amyloid in the dermis

Explanation

Uremic pruritus in chronic kidney disease results from retained solutes, altered calcium-phosphate metabolism, and uremic neuropathy, producing excoriated papules and nodules. It is not primarily an IgE-mediated or autoimmune blistering process.

Question 49Dermatology

A 30-year-old woman has a malar erythematous rash, photosensitivity, and oral ulcers, and biopsy shows interface dermatitis with mucin. Which autoantibody is most specific for this condition?

  1. Anti-double-stranded DNA Correct answer.
  2. Anti-transglutaminase
  3. Anti-desmoglein 1
  4. Anti-BP180

Explanation

The clinical and histologic picture is systemic lupus erythematosus, for which anti-double-stranded DNA is highly specific and correlates with disease activity and nephritis. Anti-Smith is also specific but less commonly tested.

Question 50Dermatology

A 28-year-old presents with an annular, scaly plaque on the trunk. A KOH preparation of skin scrapings shows short septate hyphae and spores. Which organism is the most likely cause?

  1. Sporothrix schenckii
  2. Trichophyton rubrum Correct answer.
  3. Malassezia furfur
  4. Candida albicans

Explanation

Dermatophyte infections of glabrous skin are most commonly caused by Trichophyton species, with T. rubrum the leading agent worldwide. KOH shows branching septate hyphae, and culture confirms the species.