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OMSB Dermatology (OED) study materials
OMSB Dermatology (OED) study resources

OMSB Dermatology (OED) practice questions

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Question 1Medical Dermatology

A 34-year-old woman has well-demarcated erythematous plaques with silvery scale on both elbows and knees. Removal of scale produces tiny bleeding points. What is the most likely diagnosis?

  1. Lichen planus
  2. Tinea corporis
  3. Plaque psoriasis Correct answer.
  4. Atopic dermatitis

Explanation

Well-demarcated plaques with silvery scale over extensor surfaces, together with pinpoint bleeding on scale removal (Auspitz sign), are classic for plaque psoriasis. Atopic dermatitis favors flexures and lacks silvery scale, while tinea has an active scaly border and lichen planus shows violaceous flat-topped papules.

Question 2Medical Dermatology

Which finding on dermoscopy most strongly supports a diagnosis of seborrheic keratosis?

  1. Pigment network with abrupt cut-off at the periphery
  2. Comedo-like openings and milia-like cysts Correct answer.
  3. Arborizing vessels over a pearly nodule
  4. Corkscrew vessels with a pink structureless background

Explanation

Seborrheic keratoses characteristically show comedo-like openings (keratin-filled crypts) and milia-like cysts, corresponding to intraepidermal horn cysts. Atypical pigment network and arborizing vessels point to melanoma and basal cell carcinoma respectively, and corkscrew vessels suggest squamous cell carcinoma.

Question 3Medical Dermatology

A patient develops tense bullae on normal-appearing skin of the trunk and has circulating autoantibodies against hemidesmosomal proteins BP180 and BP230. Which diagnosis fits this immunofluorescence pattern?

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

Explanation

Bullous pemphigoid is caused by autoantibodies to BP180 and BP230, components of the hemidesmosome, producing subepidermal tense blisters on normal or urticarial skin. Pemphigus vulgaris targets desmogleins with intraepidermal flaccid blisters, and dermatitis herpetiformis shows granular IgA at dermal papillae.

Question 4Medical Dermatology

Which organism is the causative agent of erythema chronicum migrans in Lyme disease?

  1. Leishmania major
  2. Rickettsia rickettsii
  3. Treponema pallidum
  4. Borrelia burgdorferi Correct answer.

Explanation

Erythema chronicum migrans is the early skin manifestation of Lyme borreliosis, transmitted by Ixodes ticks and caused by Borrelia burgdorferi. Treponema causes syphilis, Rickettsia causes Rocky Mountain spotted fever, and Leishmania causes cutaneous leishmaniasis.

Question 5Medical Dermatology

A 6-year-old child has honey-colored crusted lesions around the nose and mouth after scratching an insect bite. What is the most appropriate first-line topical therapy?

  1. Topical mupirocin Correct answer.
  2. Topical clotrimazole
  3. Topical hydrocortisone 1%
  4. Topical acyclovir

Explanation

The description is impetigo, most often caused by Staphylococcus aureus or group A streptococci, and limited disease responds to topical mupirocin or retapamulin. Antifungals, corticosteroids, and antivirals do not address the bacterial infection.

Question 6Medical Dermatology

A young adult presents with hypopigmented macules on the trunk that fluoresce coral-red under Wood lamp and show a spaghetti-and-meatballs appearance on potassium hydroxide microscopy. What is the diagnosis?

  1. Pityriasis alba
  2. Pityriasis versicolor Correct answer.
  3. Leprosy
  4. Vitiligo

Explanation

Pityriasis versicolor is caused by Malassezia furfur, which produces short hyphae with spores (spaghetti and meatballs) on KOH and fluoresces coral-red under Wood lamp. Vitiligo shows depigmented macules without organisms, pityriasis alba shows ill-defined scaling patches, and leprosy has anesthetic lesions with loss of sensation.

Question 7Medical Dermatology

Which feature best distinguishes malignant melanoma from a benign melanocytic nevus using the ABCDE criteria?

  1. Uniform brown color with a regular round border
  2. Diameter of 2 mm with stable appearance over years
  3. Presence of a central hair with symmetric shape
  4. Asymmetry with border irregularity and recent change Correct answer.

Explanation

The ABCDE criteria flag melanoma through Asymmetry, Border irregularity, Color variation, Diameter over 6 mm, and Evolution (change). A small, stable, symmetric, uniformly pigmented lesion with a regular border is more consistent with a benign nevus.

Question 8Medical Dermatology

Which subtype of melanoma most commonly arises on chronically sun-damaged skin of the head and neck in older adults and grows radially for a prolonged period?

  1. Acral lentiginous melanoma
  2. Lentigo maligna melanoma Correct answer.
  3. Nodular melanoma
  4. Mucosal melanoma

Explanation

Lentigo maligna melanoma develops from lentigo maligna on severely sun-damaged skin, especially the face of elderly patients, and shows a prolonged radial growth phase. Acral lentiginous melanoma occurs on palms, soles, and nail beds, nodular melanoma has early vertical growth, and mucosal melanoma arises on mucosal surfaces.

Question 9Medical Dermatology

A patient with type 1 diabetes develops intensely pruritic, grouped vesicles on the elbows, knees, and buttocks. Direct immunofluorescence shows granular IgA deposits in the dermal papillae. What is the diagnosis?

  1. Bullous pemphigoid
  2. Linear IgA bullous dermatosis
  3. Pemphigus foliaceus
  4. Dermatitis herpetiformis Correct answer.

Explanation

Dermatitis herpetiformis presents with grouped excoriated vesicles on extensor surfaces and shows granular IgA in dermal papillae; it is associated with gluten-sensitive enteropathy and other autoimmune diseases including type 1 diabetes. Linear IgA disease shows linear IgA at the basement membrane, and the pemphigus/pemphigoid group shows different patterns.

Question 10Medical Dermatology

Which of the following is the most characteristic cutaneous finding of secondary syphilis?

  1. Copper-red maculopapular rash involving palms and soles Correct answer.
  2. Annular plaques with central clearing and a collarette of scale
  3. Hypopigmented macules with anesthesia
  4. Grouped vesicles in a dermatomal distribution

Explanation

Secondary syphilis classically produces a generalized copper-red maculopapular eruption that involves the palms and soles, often with mucous patches and condylomata lata. Dermatomal vesicles indicate herpes zoster, annular scaly plaques suggest tinea, and anesthetic hypopigmented macules suggest leprosy.

Question 11Medical Dermatology

A 3-year-old child has an annular erythematous plaque on the cheek with fine scale and central clearing. Potassium hydroxide preparation shows septate branching hyphae. What is the most appropriate treatment?

  1. Topical betamethasone
  2. Topical terbinafine Correct answer.
  3. Topical mupirocin
  4. Oral acyclovir

Explanation

This is tinea faciei, confirmed by septate branching hyphae on KOH, and topical allylamines such as terbinafine are effective for limited disease. Corticosteroids can mask or worsen dermatophyte infection, and antivirals and antibacterials are irrelevant to a fungal etiology.

Question 12Medical Dermatology

A patient with psoriasis is being considered for a biologic. Which screening test is mandatory before starting treatment because of the risk of reactivation?

  1. Serum amylase
  2. Antinuclear antibody titer
  3. Serum ferritin
  4. Tuberculosis screening Correct answer.

Explanation

Biologic agents that block TNF-alpha and other immune pathways increase the risk of reactivating latent tuberculosis, so screening with an interferon-gamma release assay or tuberculin test is required before initiation. Iron studies, ANA, and amylase do not address this specific infectious risk.

Question 13Medical Dermatology

Which condition is characterized by violaceous, flat-topped polygonal papules with a fine white reticular network on the surface?

  1. Pityriasis rosea
  2. Lichen planus Correct answer.
  3. Guttate psoriasis
  4. Discoid eczema

Explanation

Lichen planus presents with the six Ps: planar, purple, polygonal, pruritic, papules, and plaques, and Wickham striae are the fine white reticular lines on the surface. Pityriasis rosea shows a herald patch and collarette scale, guttate psoriasis shows drop-like scaly papules, and discoid eczema shows coin-shaped oozing plaques.

Question 14Medical Dermatology

A 28-year-old woman has recurrent painful oral ulcers and genital ulcers with hypopyon uveitis. Which diagnosis should be considered?

  1. Behçet disease Correct answer.
  2. Reactive arthritis
  3. Stevens-Johnson syndrome
  4. Pemphigus vulgaris

Explanation

Recurrent oral and genital ulceration with uveitis, sometimes with hypopyon, is the classic triad of Behçet disease, a systemic vasculitis. Stevens-Johnson syndrome is an acute drug-triggered mucocutaneous reaction, pemphigus vulgaris causes chronic mucosal erosions, and reactive arthritis features urethritis and conjunctivitis.

Question 15Medical Dermatology

A patient presents with palpable purpura on the lower legs after a recent upper respiratory infection. Skin biopsy shows leukocytoclastic vasculitis. Which underlying mechanism best explains this finding?

  1. Immune complex deposition in small vessel walls Correct answer.
  2. IgE-mediated mast cell degranulation
  3. Direct invasion of keratinocytes by virus
  4. Deficiency of filaggrin in the stratum corneum

Explanation

Leukocytoclastic vasculitis results from immune complex deposition in postcapillary venules, activating complement and recruiting neutrophils that cause fibrinoid necrosis and nuclear dust. IgE-mediated degranulation underlies urticaria, viral keratinocyte invasion describes herpes infections, and filaggrin deficiency relates to atopic dermatitis.

Question 16Medical Dermatology

Which nail finding is most suggestive of subungual melanoma?

  1. Transverse Beau lines
  2. Hutchinson sign with longitudinal melanonychia Correct answer.
  3. Onycholysis with green discoloration
  4. Pitting of all twenty nails

Explanation

Longitudinal melanonychia with periungual extension of pigment onto the surrounding skin, known as the Hutchinson sign, raises concern for subungual melanoma. Beau lines reflect transient nail matrix arrest, diffuse pitting suggests psoriasis, and green discoloration suggests Pseudomonas infection.

Question 17Medical Dermatology

A 60-year-old man has a pearly nodule with telangiectasia and a rolled border on the lower eyelid. What is the most likely diagnosis?

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

Explanation

A pearly papule or nodule with telangiectatic vessels and a rolled border on sun-exposed skin, particularly the eyelid, is typical of basal cell carcinoma. Squamous cell carcinoma is often hyperkeratotic or ulcerated, keratoacanthoma shows a keratin plug with rapid growth, and melanoma is pigmented and asymmetric.

Question 18Medical Dermatology

A patient with acne vulgaris has multiple inflammatory papules and pustules. Which agent acts primarily by inhibiting keratinocyte proliferation and normalizing follicular desquamation, making it suitable for maintenance therapy?

  1. Oral isotretinoin
  2. Oral doxycycline
  3. Topical benzoyl peroxide
  4. Topical tretinoin Correct answer.

Explanation

Topical retinoids such as tretinoin normalize follicular keratinization and prevent microcomedone formation, which makes them appropriate for long-term maintenance. Doxycycline and benzoyl peroxide target Propionibacterium acnes and inflammation, and isotretinoin is reserved for severe or refractory disease.

Question 19Medical Dermatology

A patient has an acute, intensely pruritic eruption with linear burrows in the web spaces of the fingers and a nocturnal itch. What is the treatment of choice for the patient and close contacts?

  1. Topical permethrin 5% Correct answer.
  2. Topical clotrimazole
  3. Oral flucloxacillin
  4. Topical hydrocortisone

Explanation

The presentation is scabies, caused by Sarcoptes scabiei, and topical permethrin 5% is first-line therapy; all close contacts must be treated simultaneously to prevent reinfestation. Antifungals, antibiotics, and corticosteroids do not eradicate the mite.

Question 20Medical Dermatology

Which adverse effect is most strongly associated with long-term systemic corticosteroid therapy in dermatology?

  1. Irreversible hair loss
  2. Acute renal failure
  3. Osteoporosis and adrenal suppression Correct answer.
  4. Permanent depigmentation

Explanation

Prolonged systemic glucocorticoid use causes osteoporosis, adrenal suppression, hyperglycemia, hypertension, and cataracts. It does not cause irreversible alopecia or permanent depigmentation, and acute renal failure is not a typical direct consequence.

Question 21Medical Dermatology

A patient develops a widespread blistering eruption with mucosal erosions and epidermal detachment covering 20% of body surface area two weeks after starting carbamazepine. Which diagnosis is most likely?

  1. Bullous pemphigoid
  2. Stevens-Johnson syndrome/toxic epidermal necrolysis Correct answer.
  3. Erythema multiforme minor
  4. Staphylococcal scalded skin syndrome

Explanation

A drug-triggered eruption with mucosal erosions and epidermal detachment is Stevens-Johnson syndrome when detachment is under 10% and toxic epidermal necrolysis when over 30%, with overlap in between. Erythema multiforme minor lacks widespread detachment, staphylococcal scalded skin syndrome occurs in children with a superficial split, and pemphigoid is autoimmune with tense blisters.

Question 22Medical Dermatology

A patient with chronic urticaria has wheals lasting less than 24 hours that leave no residual pigmentation. Which feature would instead suggest urticarial vasculitis?

  1. Individual lesions persisting beyond 24 hours with residual bruising Correct answer.
  2. Association with cold exposure
  3. Wheals that resolve within one hour
  4. Dermatographism at the site of scratching

Explanation

Urticarial vasculitis lesions typically last more than 24 hours, may be painful or burning, and resolve with residual purpura or pigmentation because of vessel damage. Ordinary chronic urticaria wheals resolve within 24 hours without residual marks, and dermatographism and cold-induced wheals are forms of physical urticaria.

Question 23Medical Dermatology

Which cutaneous finding is most characteristic of dermatomyositis?

  1. Hypopigmented anesthetic patches
  2. Auspitz sign on extensor plaques
  3. Nikolsky sign with flaccid bullae
  4. Heliotrope rash with Gottron papules Correct answer.

Explanation

Dermatomyositis produces a violaceous periorbital heliotrope rash and Gottron papules over the knuckles, along with proximal muscle weakness. Anesthetic hypopigmented patches suggest leprosy, the Auspitz sign indicates psoriasis, and a positive Nikolsky sign occurs in pemphigus and toxic epidermal necrolysis.

Question 24Medical Dermatology

A patient with long-standing discoid lupus erythematosus develops a new, non-healing ulcerated nodule within a chronic scar on the scalp. What is the most likely diagnosis?

  1. Dermatofibroma
  2. Squamous cell carcinoma arising in a scar Correct answer.
  3. Melanoma
  4. Basal cell carcinoma

Explanation

Chronic scarring and inflammation, as in discoid lupus, predispose to squamous cell carcinoma, which may present as an ulcerated nodule in a scar (Marjolin ulcer). Basal cell carcinoma is less typical in this setting, and melanoma and dermatofibroma do not characteristically arise in chronic scars.

Question 25Medical Dermatology

Which of the following is the most appropriate first-line treatment for mild-to-moderate atopic dermatitis in an adult?

  1. Topical terbinafine
  2. Topical corticosteroid with emollient Correct answer.
  3. Systemic corticosteroids
  4. Oral cyclosporine

Explanation

Mild-to-moderate atopic dermatitis is managed with liberal emollients and topical corticosteroids, which reduce inflammation and restore the skin barrier. Cyclosporine and systemic corticosteroids are reserved for severe or refractory disease, and terbinafine is an antifungal with no role here.

Question 26Medical Dermatology

A 24-year-old man presents with multiple dome-shaped, skin-colored to pearly papules with central umbilication on the trunk. He is otherwise healthy and HIV-negative. Which causative agent is most likely responsible?

  1. Herpes simplex virus type 2
  2. Varicella-zoster virus
  3. Human papillomavirus type 16
  4. Molluscum contagiosum virus Correct answer.

Explanation

Umbilicated pearly papules with a central keratinous plug are the classic morphology of molluscum contagiosum, caused by a poxvirus. The lesions are typically multiple, asymptomatic, and self-limiting in immunocompetent adults. HPV causes verrucous or flat warty lesions without umbilication.

Question 27Medical Dermatology

A 34-year-old woman has well-demarcated erythematous plaques with silvery scale on the extensor elbows and knees. Which histologic finding is most characteristic?

  1. Necrotic keratinocytes with a sparse superficial infiltrate
  2. Subepidermal blister with linear IgG at the basement membrane
  3. Parakeratosis with neutrophils in the stratum corneum and regular acanthosis Correct answer.
  4. Band-like lymphocytic infiltrate obscuring the dermoepidermal junction

Explanation

Psoriasis shows parakeratosis, Munro microabscesses of neutrophils in the stratum corneum, regular acanthosis with clubbed rete ridges, and dilated capillaries in the papillary dermis. The other options describe pemphigoid, lichen planus, and erythema multiforme respectively.

Question 28Medical Dermatology

A 45-year-old man has a chronic, pruritic, scaly annular plaque on the glans penis with an active advancing border. Which diagnostic test most directly confirms the diagnosis?

  1. Wood lamp examination
  2. Potassium hydroxide microscopy of scale Correct answer.
  3. Tzanck smear
  4. Serum IgE level

Explanation

Tinea of the genital skin is confirmed by demonstrating septate branching hyphae on KOH microscopy of scraped scale. Wood lamp is unhelpful because dermatophytes do not fluoresce. Tzanck smear and IgE levels address unrelated conditions.

Question 29Medical Dermatology

A 58-year-old woman has a chronic, intensely pruritic, lichenified plaque on the nape of the neck with exaggerated skin markings. Which term best describes this secondary skin change?

  1. Sclerosis
  2. Atrophy
  3. Induration
  4. Lichenification Correct answer.

Explanation

Lichenification refers to thickening of the epidermis with accentuated skin markings caused by chronic rubbing or scratching. It is typical of chronic eczema and lichen simplex chronicus. Induration, sclerosis, and atrophy describe different dermal or epidermal changes.

Question 30Medical Dermatology

A 30-year-old woman has a fixed, dusky violaceous annular plaque on the shin that recurs at the same site after healing. She takes a nonsteroidal anti-inflammatory drug intermittently. What is the most likely diagnosis?

  1. Erythema nodosum
  2. Erythema annulare centrifugum
  3. Pityriasis rosea
  4. Fixed drug eruption Correct answer.

Explanation

A fixed drug eruption recurs at the identical site with each exposure to the culprit drug, typically leaving residual hyperpigmentation. NSAIDs are common triggers. Erythema nodosum produces tender nodules on the shins without site fixation.

Question 31Medical Dermatology

A 26-year-old woman has multiple flesh-colored, dome-shaped papules with a central dell on the lower abdomen. She is otherwise well. What is the most appropriate management for immunocompetent adults with limited lesions?

  1. Oral fluconazole for four weeks
  2. Systemic acyclovir for two weeks
  3. Reassurance and observation, with destructive therapy if desired Correct answer.
  4. Topical corticosteroid under occlusion

Explanation

Molluscum contagiosum in immunocompetent adults is self-limiting, so observation is appropriate; cryotherapy or curettage can be offered for cosmetic reasons. Antivirals, antifungals, and steroids are not indicated. Lesions in adults may also be sexually transmitted and warrant counseling.

Question 32Medical Dermatology

A 40-year-old man has a well-circumscribed, tender, erythematous nodule on the dorsal wrist that drains purulent material. What is the most likely diagnosis?

  1. Cellulitis
  2. Hidradenitis suppurativa
  3. Erysipelas
  4. Cutaneous abscess Correct answer.

Explanation

A fluctuant, tender, purulent nodule indicates a localized collection of pus, an abscess, which requires incision and drainage. Cellulitis and erysipelas are diffuse spreading infections without a localized pus collection. Hidradenitis affects intertriginous areas.

Question 33Medical Dermatology

A 52-year-old woman has a chronic, pruritic, scaly plaque on the scalp with associated hair loss in the affected area. Which feature most favors tinea capitis over seborrheic dermatitis?

  1. Symmetrical involvement of the eyebrows
  2. Response to topical ketoconazole shampoo
  3. Greasy yellow scale along the hairline
  4. Broken hairs and a positive potassium hydroxide preparation Correct answer.

Explanation

Tinea capitis typically shows broken or lusterless hairs and is confirmed by KOH microscopy or culture. Seborrheic dermatitis produces greasy scale in seborrheic areas and does not typically cause true hair breakage. Both can respond partially to azole shampoos, so response alone is not discriminative.

Question 34Medical Dermatology

A 62-year-old man with type 2 diabetes develops a rapidly enlarging, exquisitely painful, erythematous plaque on the leg with a violaceous undermined border and crepitus. What is the most urgent next step?

  1. Wet-to-dry dressings and review in one week
  2. Oral flucloxacillin as an outpatient
  3. Topical corticosteroid under occlusion
  4. Immediate surgical debridement and broad-spectrum intravenous antibiotics Correct answer.

Explanation

Crepitus, violaceous undermined borders, and pain out of proportion suggest necrotizing fasciitis, a surgical emergency requiring prompt debridement and broad-spectrum IV antibiotics. Delay increases mortality. Outpatient therapy and topical steroids would be dangerous.

Question 35Medical Dermatology

A 27-year-old woman has multiple tense bullae on normal-appearing skin of the trunk and limbs, and direct immunofluorescence shows linear IgG and C3 along the basement membrane zone. Which antigen is most likely targeted?

  1. BP180 and BP230 hemidesmosomal proteins Correct answer.
  2. Transglutaminase 3
  3. Desmoglein 1 and desmoglein 3
  4. Type VII collagen

Explanation

Bullous pemphigoid is characterized by subepidermal blisters with linear IgG and C3 at the basement membrane, targeting the hemidesmosomal proteins BP180 and BP230. Desmogleins are targeted in pemphigus vulgaris and foliaceus. Type VII collagen is the target in epidermolysis bullosa acquisita.

Question 36Medical Dermatology

A 22-year-old woman has flaccid bullae, erosions of the oral mucosa, and a positive Nikolsky sign. Direct immunofluorescence shows intercellular IgG deposition in the epidermis. Which diagnosis is most likely?

  1. Bullous pemphigoid
  2. Dermatitis herpetiformis
  3. Pemphigus vulgaris Correct answer.
  4. Linear IgA bullous dermatosis

Explanation

Pemphigus vulgaris produces intraepidermal acantholytic blisters with intercellular IgG on direct immunofluorescence, and mucosal involvement is common. Bullous pemphigoid shows subepidermal blisters with linear fluorescence. Dermatitis herpetiformis shows granular IgA in dermal papillae.

Question 37Medical Dermatology

A 48-year-old woman with chronic kidney disease develops intensely pruritic, excoriated papules and nodules on the forearms and trunk with a markedly elevated serum IgE and peripheral eosinophilia. Which diagnosis best fits?

  1. Acquired perforating dermatosis Correct answer.
  2. Neurotic excoriations
  3. Prurigo nodularis
  4. Lichen simplex chronicus

Explanation

Acquired perforating dermatosis occurs in chronic kidney disease and diabetes, presenting with pruritic keratotic papules and transepidermal elimination of dermal material. Prurigo nodularis and lichen simplex chronicus are related to scratching but lack the perforating histology.

Question 38Medical Dermatology

A 35-year-old woman has a painful, erythematous nodule on the anterior shin with a central crust and a history of minor trauma at the site. She is afebrile. What is the most likely diagnosis?

  1. Ecthyma Correct answer.
  2. Erysipeloid
  3. Erythema induratum
  4. Pyoderma gangrenosum

Explanation

Ecthyma is a deeper form of impetigo that begins after minor trauma and produces a punched-out ulcer with an adherent crust, usually on the legs. Erysipeloid follows animal exposure, and pyoderma gangrenosum produces a rapidly enlarging ulcer with a violaceous border.

Question 39Medical Dermatology

A 55-year-old man has a chronic, well-demarcated, hyperkeratotic plaque on the sole that is painful on walking. He has no history of psoriasis elsewhere. Which diagnosis should be considered first?

  1. Palmoplantar pustulosis
  2. Lichen planus
  3. Tinea pedis
  4. Plantar psoriasis Correct answer.

Explanation

Plantar psoriasis can present with hyperkeratotic plaques on the soles even without lesions elsewhere, and it is often painful and fissured. Tinea pedis is scaly and pruritic, typically in toe webs. Palmoplantar pustulosis shows sterile pustules rather than hyperkeratotic plaques.

Question 40Medical Dermatology

A 68-year-old man has a large, superficial, erythematous scaly patch on the sun-exposed shoulder that has slowly enlarged over years. Biopsy shows atypical keratinocytes confined above the basement membrane. What is the diagnosis?

  1. Actinic keratosis Correct answer.
  2. Basal cell carcinoma
  3. Invasive squamous cell carcinoma
  4. Squamous cell carcinoma in situ

Explanation

Actinic keratosis is a premalignant lesion of atypical keratinocytes confined to the epidermis on sun-damaged skin, presenting as a rough scaly macule or patch. Full-thickness epidermal atypia would indicate squamous cell carcinoma in situ. Invasive carcinoma breaches the basement membrane.

Question 41Medical Dermatology

A 42-year-old woman has multiple tense bullae on the trunk with a subepidermal blister and linear IgA deposition along the basement membrane zone. Which diagnosis is most likely?

  1. Epidermolysis bullosa acquisita
  2. Pemphigus foliaceus
  3. Linear IgA bullous dermatosis Correct answer.
  4. Bullous pemphigoid

Explanation

Linear IgA bullous dermatosis shows linear IgA at the basement membrane zone and often presents with tense blisters, sometimes in an annular arrangement. Bullous pemphigoid shows linear IgG and C3. Pemphigus foliaceus shows intercellular IgG.

Question 42Medical Dermatology

A 50-year-old woman has a chronic, pruritic, erythematous plaque on the cheek with fine scale and a slightly raised border. She has no history of atopy. Which feature most strongly favors tinea faciei over discoid lupus erythematosus?

  1. Follicular plugging with adherent scale
  2. Photosensitivity and positive antinuclear antibodies
  3. Negative immunofluorescence and hyphae on potassium hydroxide microscopy Correct answer.
  4. Scarring alopecia at the site

Explanation

Tinea faciei is diagnosed by demonstrating hyphae on KOH and by negative immunofluorescence. Discoid lupus shows follicular plugging, scarring, and sometimes positive ANA with photosensitivity. Response to topical steroids is not discriminative because steroids can partially suppress both.

Question 43Medical Dermatology

A 33-year-old man has grouped vesicles on an erythematous base on the buttock and a history of similar episodes. He is HIV-negative. What is the most appropriate treatment for the acute episode?

  1. Oral fluconazole for two weeks
  2. Topical acyclovir alone
  3. Oral valacyclovir for seven days Correct answer.
  4. Intralesional corticosteroid

Explanation

Acute genital herpes is treated with systemic nucleoside analogues such as valacyclovir or acyclovir for five to ten days. Topical agents are ineffective. Antifungals do not treat herpesviruses, and intralesional steroids may worsen infection.

Question 44Medical Dermatology

A 60-year-old woman has a violaceous, indurated plaque on the thigh that has slowly enlarged over months without ulceration. She has no systemic symptoms. Which diagnosis is most likely?

  1. Cellulitis
  2. Cutaneous lymphoma Correct answer.
  3. Erythema nodosum
  4. Morphea

Explanation

Cutaneous T-cell lymphoma can present as violaceous, indurated plaques that enlarge slowly and may be mistaken for inflammatory dermatoses. Morphea produces sclerotic plaques with a lilac border rather than violaceous infiltrated plaques. Cellulitis is acute and tender.

Question 45Medical Dermatology

A 38-year-old woman has a history of recurrent aphthous ulcers, genital ulcers, and a positive pathergy test. She develops a painful nodule at a venipuncture site. Which phenomenon explains this finding?

  1. Koebner phenomenon
  2. Pathergy Correct answer.
  3. Darier sign
  4. Nikolsky sign

Explanation

Pathergy is the development of a papulopustular lesion at a site of minor trauma or needle puncture and is characteristic of Behçet disease. Koebner phenomenon refers to the appearance of lesions at trauma sites in psoriasis or lichen planus. Nikolsky and Darier signs are elicited differently.

Question 46Medical Dermatology

A 70-year-old man has a pearly nodule with a central ulcer and rolled border on the nasal ala. Biopsy shows basaloid islands with peripheral palisading and clefting. What is the most likely diagnosis?

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

Explanation

Basal cell carcinoma shows peripheral palisading of basaloid cells with retraction clefting from the stroma, and typically presents as a pearly nodule with telangiectasia. Squamous cell carcinoma shows keratin pearls and intercellular bridges. Keratoacanthoma is a dome-shaped nodule with a keratin plug.

Question 47Medical Dermatology

A 45-year-old woman with systemic lupus erythematosus has a widespread photosensitive eruption with erythema and fine scale on the extensor surfaces. Which histologic finding most supports a lupus-specific skin lesion?

  1. Interface dermatitis with mucin deposition and perivascular lymphocytic infiltrate Correct answer.
  2. Neutrophilic folliculitis with eosinophils
  3. Epidermal acantholysis with intercellular IgG
  4. Subepidermal blister with eosinophils

Explanation

Cutaneous lupus shows interface dermatitis with vacuolar change at the dermoepidermal junction, dermal mucin, and a perivascular lymphocytic infiltrate. Subepidermal blisters with eosinophils suggest bullous pemphigoid. Neutrophilic folliculitis is seen in other conditions.

Question 48Medical Dermatology

A 55-year-old man with chronic venous insufficiency has a brownish discoloration of the lower legs with induration and a shallow ulcer above the medial malleolus. What is the primary underlying mechanism?

  1. Lymphatic obstruction with protein-rich edema
  2. Venous hypertension with hemosiderin deposition Correct answer.
  3. Small-vessel vasculitis with fibrinoid necrosis
  4. Arterial insufficiency with tissue ischemia

Explanation

Venous stasis dermatitis results from chronic venous hypertension, leading to red cell extravasation, hemosiderin deposition, and fibrosis. Ulcers typically occur near the medial malleolus. Arterial ulcers are painful and punched out, and vasculitic ulcers have an undermined border.

Question 49Medical Dermatology

A 30-year-old woman develops a widespread eruption with targetoid lesions, mucosal erosions, and epidermal detachment involving 15% of the body surface after starting carbamazepine. Which management step is most critical?

  1. Immediate withdrawal of the culprit drug and supportive burn-style care Correct answer.
  2. Topical corticosteroid under occlusion
  3. Oral antihistamines and observation
  4. Oral acyclovir for ten days

Explanation

This is a severe cutaneous adverse reaction such as Stevens-Johnson syndrome or toxic epidermal necrolysis, and the single most important step is prompt withdrawal of the culprit drug with supportive care. Steroids and antihistamines are adjunctive at best. Antivirals do not treat drug reactions.

Question 50Medical Dermatology

A 40-year-old man has multiple hyperpigmented, velvety plaques in the axillae and neck with acanthosis nigricans on biopsy. He is obese and has no other symptoms. Which underlying condition should be excluded?

  1. Hyperthyroidism
  2. Hemochromatosis
  3. Addison disease
  4. Insulin resistance and diabetes mellitus Correct answer.

Explanation

Acanthosis nigricans is strongly associated with insulin resistance and obesity, and its presence should prompt screening for diabetes. When it appears abruptly in a non-obese adult, an internal malignancy should be excluded. Thyroid disease, adrenal insufficiency, and hemochromatosis do not typically cause acanthosis nigricans.