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Dermatology Board practice questions

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Question 1Medical dermatology

A 34-year-old man has well-demarcated erythematous plaques with silvery scale on both elbows and knees. Which histologic finding is most characteristic of this condition?

  1. Parakeratosis with neutrophils in the stratum corneum Correct answer.
  2. Interface dermatitis with basal vacuolization
  3. Subepidermal blister formation with eosinophils
  4. Dermal granulomas with multinucleated giant cells

Explanation

Psoriasis shows parakeratosis, acanthosis, and Munro microabscesses, which are collections of neutrophils in the stratum corneum. Subepidermal blistering suggests bullous pemphigoid, while interface dermatitis suggests lichen planus or lupus erythematosus. Granulomas point toward sarcoidosis or a granulomatous infection.

Question 2Medical dermatology

A 45-year-old woman has painful oral erosions and flaccid bullae on the trunk that rupture easily. Which autoantibody is most closely associated with this disorder?

  1. Anti-BP180
  2. Anti-transglutaminase
  3. Anti-laminin 332
  4. Anti-desmoglein 3 Correct answer.

Explanation

Pemphigus vulgaris targets desmoglein 3 and often desmoglein 1, producing intraepidermal acantholysis and flaccid bullae. Anti-BP180 is associated with bullous pemphigoid, and anti-transglutaminase with dermatitis herpetiformis. Anti-laminin 332 occurs in mucous membrane pemphigoid.

Question 3Medical dermatology

A 30-year-old man has intensely pruritic grouped vesicles on the elbows and buttocks. He also reports bloating and diarrhea. Which test is most appropriate to confirm the diagnosis?

  1. Perilesional direct immunofluorescence Correct answer.
  2. Patch testing with a standard series
  3. Serum tryptase level
  4. Skin scraping for fungus

Explanation

Dermatitis herpetiformis shows granular IgA deposits in the dermal papillae on direct immunofluorescence of perilesional skin and is associated with celiac disease. Serum tryptase is used for mastocytosis, and fungal scraping for tinea. Patch testing evaluates contact dermatitis.

Question 4Medical dermatology

A 6-year-old boy has a scaly patch on the scalp with broken hairs and mild erythema. Which organism is the most common cause of this condition in the United States?

  1. Trichophyton tonsurans Correct answer.
  2. Microsporum canis
  3. Malassezia furfur
  4. Candida albicans

Explanation

Trichophyton tonsurans is the most common cause of tinea capitis in the United States and produces broken hairs and scaling. Microsporum canis causes a minority of cases, while Candida and Malassezia do not cause typical tinea capitis.

Question 5Medical dermatology

A 22-year-old woman develops a single 3-cm oval salmon-colored patch on the back, followed 1 week later by many smaller oval patches in a Christmas-tree distribution. Which finding is most characteristic of the smaller lesions?

  1. Honey-colored crust
  2. Collarette of scale at the periphery Correct answer.
  3. Central umbilication
  4. Violaceous color with Wickham striae

Explanation

Pityriasis rosea typically begins with a herald patch followed by oval patches with a peripheral collarette of scale along the cleavage lines. Central umbilication suggests molluscum contagiosum, and honey-colored crust suggests impetigo. Violaceous papules with Wickham striae indicate lichen planus.

Question 6Medical dermatology

A 25-year-old man develops target lesions on the palms and oral erosions 10 days after a cold sore. Which trigger is most commonly associated with erythema multiforme?

  1. Penicillin administration
  2. Beta-hemolytic streptococcal pharyngitis
  3. Mycoplasma pneumoniae infection
  4. Herpes simplex virus infection Correct answer.

Explanation

Herpes simplex virus is the most common trigger of erythema multiforme, especially recurrent cases. Streptococcal infection is linked to guttate psoriasis, and Mycoplasma can cause atypical pneumonia with a minor exanthem. Penicillin is more often associated with urticarial or morbilliform drug eruptions.

Question 7Medical dermatology

An infant has greasy yellow scales on the scalp and eyebrows, and an adult has flaking along the nasolabial folds. Which organism is most strongly implicated in this condition?

  1. Staphylococcus aureus
  2. Trichophyton rubrum
  3. Malassezia species Correct answer.
  4. Corynebacterium minutissimum

Explanation

Seborrheic dermatitis is associated with Malassezia yeasts, and antifungal shampoos often help. Staphylococcus aureus causes impetigo, and Corynebacterium minutissimum causes erythrasma. Trichophyton rubrum causes tinea corporis or pedis.

Question 8Medical dermatology

A 68-year-old fair-skinned man has a rough, gritty 5-mm erythematous papule on the bald scalp. Which diagnosis is most likely?

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

Explanation

Actinic keratosis is a rough, scaly lesion on sun-damaged skin and is considered premalignant. Seborrheic keratosis is waxy and stuck-on, while basal cell carcinoma is pearly with telangiectasia. Melanoma is typically pigmented, asymmetric, and irregular.

Question 9Medical dermatology

An 80-year-old man has tense pruritic bullae on the trunk and extremities, and direct immunofluorescence shows linear IgG and C3 along the basement membrane zone. Which antigen is most likely targeted?

  1. BP180 (type XVII collagen) Correct answer.
  2. Desmoglein 1
  3. Type VII collagen
  4. Desmoglein 3

Explanation

Bullous pemphigoid targets BP180 and BP230, components of the hemidesmosome, producing subepidermal tense bullae with linear IgG and C3. Desmoglein 1 and 3 are pemphigus antigens, and type VII collagen is the target in epidermolysis bullosa acquisita.

Question 10Medical dermatology

A 50-year-old woman has pruritic, purple, polygonal papules on the wrists and white lacy streaks on the buccal mucosa. Which diagnosis is most likely?

  1. Pityriasis rosea
  2. Lichen planus Correct answer.
  3. Psoriasis
  4. Lupus erythematosus

Explanation

Lichen planus classically presents with the six Ps, including pruritic purple polygonal planar papules, and Wickham striae on mucosal surfaces. Psoriasis has silvery scale, and lupus has photodistributed lesions with systemic features. Pityriasis rosea shows oval patches with collarette scale.

Question 11Medical dermatology

A 60-year-old woman develops fever, painful mucosal erosions, and a dusky maculopapular rash with epidermal detachment after starting allopurinol. Which factor best predicts mortality in this condition?

  1. Serum eosinophil count
  2. Body surface area detached Correct answer.
  3. Presence of oral erosions
  4. Duration of antibiotic therapy

Explanation

In Stevens-Johnson syndrome and toxic epidermal necrolysis, mortality correlates with the extent of epidermal detachment, which is part of the SCORTEN score. Mucosal involvement is characteristic but not the main prognostic factor. Eosinophilia suggests DRESS rather than SJS/TEN.

Question 12Medical dermatology

A 55-year-old man has slowly progressive scaly patches and plaques on the trunk, and biopsy shows a dense dermal infiltrate of atypical lymphocytes with epidermotropism. Which immunophenotype is most typical?

  1. CD8+ T cells
  2. CD4+ T cells Correct answer.
  3. CD30+ large cells
  4. CD20+ B cells

Explanation

Mycosis fungoides is a CD4+ cutaneous T-cell lymphoma with epidermotropism and Pautrier microabscesses. CD8+ disorders are less common, and CD20 marks B-cell lymphomas. CD30 is characteristic of lymphomatoid papulosis and anaplastic large cell lymphoma.

Question 13Medical dermatology

A 28-year-old woman has well-circumscribed, smooth patches of hair loss on the scalp without scarring. At the edges, short broken hairs taper toward the scalp. Which diagnosis is most likely?

  1. Tinea capitis
  2. Lichen planopilaris
  3. Alopecia areata Correct answer.
  4. Androgenetic alopecia

Explanation

Alopecia areata causes nonscarring, well-circumscribed patches with exclamation-mark hairs at the margins. Androgenetic alopecia produces patterned diffuse thinning, and lichen planopilaris causes scarring. Tinea capitis usually shows scale and inflammation.

Question 14Medical dermatology

A 35-year-old woman has sharply demarcated depigmented macules on the hands and around the mouth. Which treatment is most appropriate first-line for limited disease?

  1. Oral prednisone
  2. Methotrexate
  3. Excimer laser
  4. Topical steroid Correct answer.

Explanation

Limited vitiligo is first treated with topical corticosteroids or topical calcineurin inhibitors. Oral corticosteroids are reserved for rapidly progressive disease, and methotrexate is not standard therapy. Excimer laser is generally considered second-line.

Question 15Medical dermatology

A 40-year-old woman has recurrent flushing, facial erythema, and visible telangiectasias without papules or pustules. Which feature best describes this rosacea subtype?

  1. Papules and pustules with central erythema
  2. Thickening of the nasal skin with fibrosis
  3. Ocular irritation and blepharitis
  4. Flushing and telangiectasias Correct answer.

Explanation

The erythematotelangiectatic subtype of rosacea is characterized by flushing, persistent central facial erythema, and telangiectasias. Papules and pustules define papulopustular rosacea, and nasal thickening defines phymatous rosacea. Ocular symptoms indicate ocular rosacea.

Question 16Medical dermatology

A 30-year-old woman has recurrent painful nodules in the axillae and groin, with sinus tracts and double-ended comedones. Which diagnosis is most likely?

  1. Hidradenitis suppurativa Correct answer.
  2. Crohn disease
  3. Dissecting cellulitis of the scalp
  4. Folliculitis decalvans

Explanation

Hidradenitis suppurativa causes recurrent nodules, abscesses, sinus tracts, and double-ended comedones in intertriginous areas. Folliculitis decalvans and dissecting cellulitis affect the scalp. Crohn disease can cause perianal fistulas but not typical axillary double-ended comedones.

Question 17Medical dermatology

A 50-year-old woman has fever, neutrophilia, and tender erythematous plaques on the arms. Biopsy shows a dense neutrophilic infiltrate without vasculitis. Which diagnosis is most likely?

  1. Sweet syndrome Correct answer.
  2. Cellulitis
  3. Erythema multiforme
  4. Leukocytoclastic vasculitis

Explanation

Sweet syndrome is a neutrophilic dermatosis characterized by fever, neutrophilia, and tender erythematous plaques with a dense neutrophilic infiltrate but no vasculitis. Leukocytoclastic vasculitis shows fibrinoid necrosis of vessel walls. Erythema multiforme has target lesions, and cellulitis is an infection.

Question 18Medical dermatology

A 30-year-old woman has tender red nodules on the anterior shins after starting an oral contraceptive. Which histologic pattern is expected?

  1. Septal panniculitis Correct answer.
  2. Lobular panniculitis
  3. Leukocytoclastic vasculitis
  4. Interface dermatitis

Explanation

Erythema nodosum is a septal panniculitis and is associated with oral contraceptives, streptococcal infection, sarcoidosis, and inflammatory bowel disease. Lobular panniculitis suggests pancreatic disease or alpha-1 antitrypsin deficiency. Leukocytoclastic vasculitis and interface dermatitis have different histologic patterns.

Question 19Medical dermatology

A 40-year-old woman has an indurated plaque on the thigh with a violaceous border and central sclerosis. Which diagnosis is most likely?

  1. Lichen sclerosus
  2. Morphea Correct answer.
  3. Systemic sclerosis
  4. Eosinophilic fasciitis

Explanation

Morphea is localized scleroderma and presents with indurated plaques and a lilac or violaceous border. Systemic sclerosis involves Raynaud phenomenon and acral skin thickening. Eosinophilic fasciitis affects the fascia, and lichen sclerosus produces white atrophic plaques.

Question 20Medical dermatology

A 45-year-old man develops fever, a diffuse morbilliform rash, facial edema, and eosinophilia 4 weeks after starting carbamazepine. Which diagnosis is most likely?

  1. Sweet syndrome
  2. Stevens-Johnson syndrome
  3. Urticarial vasculitis
  4. DRESS syndrome Correct answer.

Explanation

DRESS syndrome is a drug hypersensitivity reaction with fever, rash, facial edema, eosinophilia, and internal organ involvement, often starting weeks after an anticonvulsant. SJS features mucosal erosions and epidermal detachment. Urticarial vasculitis and Sweet syndrome have different clinical and histologic findings.

Question 21Medical dermatology

A 65-year-old man has tense bullae in an annular arrangement on the trunk. Direct immunofluorescence shows linear IgA deposition along the basement membrane zone. Which diagnosis is most likely?

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

Explanation

Linear IgA disease shows linear IgA at the basement membrane zone and often produces annular tense bullae. Dermatitis herpetiformis shows granular IgA in the dermal papillae. Bullous pemphigoid shows linear IgG and C3, and pemphigus vulgaris shows intercellular IgG.

Question 22Medical dermatology

A 55-year-old man has severe stomatitis, polymorphic skin lesions, and a newly diagnosed retroperitoneal mass. Which autoantibody is most characteristic of this paraneoplastic disorder?

  1. Anti-desmoglein 1
  2. Anti-type VII collagen
  3. Anti-BP230
  4. Anti-envoplakin Correct answer.

Explanation

Paraneoplastic pemphigus targets plakin family proteins such as envoplakin and periplakin and is associated with Castleman disease, lymphoma, and other neoplasms. Anti-desmoglein 1 is seen in pemphigus foliaceus, and anti-BP230 in bullous pemphigoid. Anti-type VII collagen occurs in epidermolysis bullosa acquisita.

Question 23Medical dermatology

A 60-year-old woman with end-stage renal disease has painful violaceous plaques on the thighs that progress to necrotic ulcers. Which diagnosis is most likely?

  1. Pyoderma gangrenosum
  2. Calciphylaxis Correct answer.
  3. Warfarin necrosis
  4. Cholesterol embolization

Explanation

Calciphylaxis occurs in end-stage renal disease and causes painful violaceous plaques that ulcerate because of vascular calcification. Pyoderma gangrenosum is associated with inflammatory bowel disease and pathergy. Warfarin necrosis and cholesterol embolization have different clinical settings and distributions.

Question 24Medical dermatology

A 60-year-old woman has severe vulvar pruritus and white, crinkled, atrophic plaques with loss of labial architecture. Which complication is most important to monitor for?

  1. Bartholin cyst
  2. Herpes simplex
  3. Squamous carcinoma Correct answer.
  4. Melanoma of the vulva

Explanation

Lichen sclerosus carries a modest but important risk of vulvar squamous cell carcinoma, so long-term follow-up and biopsy of suspicious areas are recommended. Vulvar melanoma, Bartholin cysts, and herpes simplex are not the main neoplastic complications of lichen sclerosus.

Question 25Medical dermatology

A 40-year-old woman with ulcerative colitis has a painful expanding ulcer on the leg with a violaceous undermined border. Which treatment is most appropriate initially?

  1. Surgical debridement
  2. Systemic steroids Correct answer.
  3. Topical antibiotics
  4. Anticoagulation

Explanation

Pyoderma gangrenosum is a neutrophilic dermatosis treated initially with systemic corticosteroids or immunosuppressants. Surgery can worsen the condition through pathergy, and antibiotics do not address the underlying inflammatory process. Anticoagulation is not indicated.

Question 26Medical dermatology

A 22-year-old student has intense itching that worsens at night, with excoriations and thin gray ridges in the finger web spaces. His roommate has similar itching. Which finding best supports the diagnosis?

  1. Gram-positive cocci on Gram stain
  2. Scabies mite on mineral oil mount Correct answer.
  3. Multinucleated giant cells on Tzanck smear
  4. Fungal hyphae on hair mount

Explanation

Scabies classically causes nocturnal pruritus with burrows in the finger webs and a history of similar symptoms in close contacts. Mineral oil microscopy can demonstrate the mite, eggs, or fecal pellets and confirms the diagnosis. Topical permethrin is first-line therapy, and close contacts should be treated simultaneously.

Question 27Medical dermatology

A 6-year-old child has several erosions with golden-yellow crusts around the nose and mouth. He is otherwise well. Which organism is the most common cause?

  1. Streptococcus pyogenes
  2. Staphylococcus aureus Correct answer.
  3. Candida albicans
  4. Pseudomonas aeruginosa

Explanation

Nonbullous impetigo classically shows honey-colored crusts and is most often caused by Staphylococcus aureus, with Streptococcus pyogenes as a less common cause. The diagnosis is usually clinical. Topical mupirocin or oral antibiotics may be used depending on extent.

Question 28Medical dermatology

A 24-year-old man has a 3-cm oval salmon-colored patch with a collarette of scale on the back, followed 10 days later by many smaller oval lesions along the ribs. Which diagnosis is most likely?

  1. Pityriasis rosea Correct answer.
  2. Tinea corporis
  3. Guttate psoriasis
  4. Secondary syphilis

Explanation

Pityriasis rosea typically begins with a herald patch, followed by smaller oval lesions with collarette scale in a Christmas-tree distribution along the ribs. It is self-limited and often resolves within weeks. Secondary syphilis can mimic it, so serologic testing is reasonable when the presentation is atypical.

Question 29Medical dermatology

A 17-year-old girl has inflammatory papules and comedones on the cheeks and no nodules or scarring. She is not pregnant. Which initial treatment is most appropriate?

  1. Benzoyl peroxide plus a topical retinoid Correct answer.
  2. Oral isotretinoin at a low cumulative dose
  3. Oral erythromycin plus topical steroid
  4. Topical corticosteroid alone

Explanation

Mild to moderate inflammatory acne is initially treated with a topical retinoid plus benzoyl peroxide, which targets comedones and inflammation. Oral isotretinoin is reserved for severe, scarring, or refractory disease. Topical steroids can worsen acne and are not appropriate monotherapy.

Question 30Medical dermatology

A 19-year-old woman develops dozens of small teardrop-shaped scaly plaques on the trunk and proximal limbs 2 weeks after a sore throat. Which test is most likely to support the suspected diagnosis?

  1. Antistreptolysin O titer Correct answer.
  2. Serum tryptase after symptom resolution
  3. HIV RNA PCR with CD4 count
  4. Patch testing to standard allergens

Explanation

Guttate psoriasis often follows a streptococcal pharyngitis by 1 to 3 weeks, and an antistreptolysin O titer can support recent infection. Throat culture may be negative by the time the eruption appears. The eruption usually responds to topical therapy and phototherapy.

Question 31Medical dermatology

A 3-year-old child has chronic pruritic flexural eczema and a history of asthma. Which feature is most characteristic of the skin barrier defect in atopic dermatitis?

  1. Reduced filaggrin expression Correct answer.
  2. Deficiency of desmoglein 1
  3. Absence of Langerhans cells
  4. Loss of type VII collagen

Explanation

Atopic dermatitis is associated with impaired barrier function, often from loss-of-function filaggrin mutations that reduce natural moisturizing factors and allow allergen penetration. This predisposes to Staphylococcus aureus colonization and recurrent inflammation. Emollients and anti-inflammatory therapy are mainstays of management.

Question 32Medical dermatology

A 7-year-old boy has a scaly patch of hair loss on the scalp with broken hairs and enlarged cervical nodes. KOH of plucked hairs shows spores. Which treatment is indicated?

  1. Topical clobetasol solution
  2. Oral griseofulvin Correct answer.
  3. Topical ketoconazole shampoo
  4. Topical terbinafine cream

Explanation

Tinea capitis involves the hair follicle and requires systemic antifungal therapy; griseofulvin or terbinafine is used depending on the organism. Topical agents do not penetrate the hair shaft adequately. Oral therapy should continue for several weeks until clinical and mycologic resolution.

Question 33Medical dermatology

A 58-year-old man has a 7-mm asymmetric pigmented lesion on the back with irregular borders and color variation. Excisional biopsy shows melanoma. Which feature is the strongest predictor of survival?

  1. Lesion diameter
  2. Presence of itching
  3. Patient age
  4. Breslow thickness Correct answer.

Explanation

Breslow thickness, the depth of invasion in millimeters, is the single most important prognostic factor for cutaneous melanoma. Ulceration and mitotic rate add prognostic information. Tumor diameter and symptoms are less reliable predictors of outcome.

Question 34Medical dermatology

A 70-year-old woman has a pearly papule with rolled borders and fine telangiectasias on the nasal ala. Which diagnosis is most likely?

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

Explanation

Basal cell carcinoma classically presents as a pearly papule with rolled edges and telangiectasias, especially on sun-exposed areas such as the nose. It is locally destructive but rarely metastasizes. Surgical excision or Mohs micrographic surgery is often used for facial lesions.

Question 35Medical dermatology

A 32-year-old woman has itchy, vesicular, well-demarcated dermatitis on the earlobes and wrists that began after wearing new jewelry. Which test is most appropriate to confirm the cause?

  1. Skin prick test
  2. Patch test Correct answer.
  3. Direct immunofluorescence
  4. Serum IgE to nickel

Explanation

Allergic contact dermatitis is a delayed type IV hypersensitivity reaction, and patch testing is the standard method for identifying the responsible allergen. Nickel is a common cause of earlobe and wrist dermatitis from jewelry. Avoidance of the allergen is the key treatment.

Question 36Medical dermatology

A 29-year-old woman has hives and angioedema for 8 weeks, each lesion resolving within 24 hours, with no systemic symptoms. Which initial treatment is recommended?

  1. Topical doxepin four times daily
  2. Oral cyclosporine with drug monitoring
  3. Oral prednisone at 1 mg/kg daily
  4. Daily second-generation antihistamine Correct answer.

Explanation

Chronic spontaneous urticaria is first treated with a daily second-generation H1 antihistamine, which can be uptitrated if symptoms persist. Systemic steroids are reserved for short courses in severe exacerbations. Cyclosporine and omalizumab are later options for refractory disease.

Question 37Medical dermatology

A 66-year-old man has grouped vesicles on an erythematous base in a unilateral thoracic dermatome, with pain. He presents 2 days after onset. Which treatment is most appropriate?

  1. Oral valacyclovir Correct answer.
  2. Topical acyclovir cream
  3. Topical capsaicin
  4. Oral prednisone alone

Explanation

Herpes zoster is treated with systemic antiviral therapy, ideally within 72 hours of rash onset, to shorten the eruption and reduce complications. Valacyclovir is commonly used because of convenient dosing. Prednisone alone is not antiviral and topical agents are insufficient for acute zoster.

Question 38Medical dermatology

A 45-year-old woman has painful oral erosions and flaccid blisters on the trunk that rupture easily, leaving denuded areas. Biopsy shows intraepidermal acantholysis, and direct immunofluorescence shows intercellular IgG deposition. Which autoantigen is most specific?

  1. Desmoglein 3 Correct answer.
  2. Desmoglein 1
  3. Type VII collagen
  4. BP180

Explanation

Pemphigus vulgaris is caused by IgG autoantibodies against desmoglein 3, and often desmoglein 1 as disease generalizes. The result is intraepidermal acantholysis with intercellular IgG on direct immunofluorescence. Mucosal involvement is common with anti-desmoglein 3 antibodies.

Question 39Medical dermatology

A 40-year-old man with untreated HIV has violaceous macules and plaques on the trunk and oral palate. Biopsy shows spindle cells and slit-like vascular spaces. Which agent is causally associated?

  1. Cytomegalovirus
  2. Human herpesvirus 8 Correct answer.
  3. Human papillomavirus type 16
  4. Epstein-Barr virus

Explanation

Kaposi sarcoma is caused by human herpesvirus 8, also called Kaposi sarcoma-associated herpesvirus. It commonly presents as violaceous macules, plaques, or nodules in HIV-infected individuals. Biopsy shows spindle cells with slit-like vascular spaces and extravasated red cells.

Question 40Medical dermatology

A 52-year-old woman has violet periorbital erythema, erythematous papules over the knuckles, and proximal muscle weakness. Which antibody is most strongly associated with this presentation?

  1. Anti-topoisomerase I
  2. Anti-Mi-2 Correct answer.
  3. Anti-centromere
  4. Anti-U1 RNP

Explanation

Anti-Mi-2 antibodies are strongly associated with classic dermatomyositis, including heliotrope rash, Gottron papules, and proximal muscle weakness. Patients with anti-Mi-2 often have a favorable response to therapy. Anti-TIF1-gamma is more associated with malignancy-associated dermatomyositis.

Question 41Dermatopathology

A shave biopsy from a pearly papule on the nasal ala shows dermal nests of basaloid cells with peripheral palisading, retraction clefts separating the nests from a mucinous stroma, and scattered apoptotic cells. Which diagnosis is most likely?

  1. Seborrheic keratosis
  2. Melanoma in situ
  3. Squamous cell carcinoma in situ
  4. Nodular basal cell carcinoma Correct answer.

Explanation

Peripheral palisading of basaloid cells together with retraction clefts between tumor nests and a fibromyxoid stroma is the classic pattern of nodular basal cell carcinoma. Squamous carcinoma in situ remains confined to the epidermis, and melanoma in situ consists of intraepidermal atypical melanocytes; neither forms palisaded basaloid islands in the dermis.

Question 42Dermatopathology

A plaque biopsy shows uniform acanthosis with elongated bulbous rete ridges, thinning of the suprapapillary plates, confluent parakeratosis containing neutrophils, and dilated capillaries in the dermal papillae. What is the most likely diagnosis?

  1. Lichen planus
  2. Psoriasis vulgaris Correct answer.
  3. Atopic dermatitis
  4. Pemphigus foliaceus

Explanation

Regular psoriasiform acanthosis with thin suprapapillary plates, confluent parakeratosis, neutrophils within the stratum corneum, and dilated papillary vessels is the standard constellation of psoriasis. The other choices produce interface change, spongiosis, or acantholysis rather than this combination.

Question 43Dermatopathology

An 78-year-old presents with tense bullae on urticarial skin. Biopsy shows a subepidermal blister containing numerous eosinophils, with the basal keratinocytes still attached to the blister floor. Which diagnosis fits best?

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

Explanation

A subepidermal split with a preserved basal layer and an eosinophil-rich blister cavity in an elderly patient with tense bullae is typical of bullous pemphigoid, caused by autoantibodies against the hemidesmosomal antigens BP180 and BP230.

Question 44Dermatopathology

A pigmented, stuck-on plaque on the back shows a sharply demarcated epidermal proliferation of uniform basaloid cells with numerous keratin-filled horn cysts and pseudohorn cysts. What is the diagnosis?

  1. Seborrheic keratosis Correct answer.
  2. Actinic keratosis
  3. Pigmented basal cell carcinoma
  4. Melanoma

Explanation

A sharply demarcated, stuck-on epidermal proliferation of bland basaloid cells containing horn pseudocysts defines seborrheic keratosis. Absence of atypia, stromal retraction, and invasiveness separates it from basal cell carcinoma and melanoma.

Question 45Dermatopathology

A biopsy of a rough erythematous macule on the balding scalp of an older man shows atypical keratinocytes confined to the lower third of the epidermis, overlying parakeratosis, and basophilic degeneration of dermal collagen. What is the diagnosis?

  1. Actinic keratosis Correct answer.
  2. Bowen disease
  3. Lichen simplex chronicus
  4. Squamous cell carcinoma

Explanation

Partial-thickness epidermal atypia with parakeratosis and solar elastosis in sun-damaged skin defines actinic keratosis. When the atypia involves the full thickness of the epidermis the lesion is instead classified as Bowen disease, that is, squamous cell carcinoma in situ.

Question 46Dermatopathology

A potassium hydroxide preparation is negative, but a periodic acid-Schiff stain of an annular scaly plaque reveals septate, branching hyphae confined to the stratum corneum. Which organism category is most consistent?

  1. Malassezia furfur
  2. Dermatophyte Correct answer.
  3. Candida species
  4. Corynebacterium minutissimum

Explanation

Septate, branching hyphae within the stratum corneum are the morphologic signature of a dermatophyte. Candida typically shows pseudohyphae with spores, Corynebacterium minutissimum is a bacterium seen as short rods, and Malassezia appears as short hyphae with round yeast cells in a spaghetti-and-meatballs pattern.

Question 47Dermatopathology

An ulcerated nodule on the lip of a 70-year-old man shows invasive nests of atypical squamous cells extending into the dermis with central whorls of keratinized cells. Which diagnosis is most likely?

  1. Squamous cell carcinoma Correct answer.
  2. Verruca vulgaris
  3. Nodular basal cell carcinoma
  4. Amelanotic melanoma

Explanation

Invasive atypical squamous cells with central keratin pearls and intercellular bridges identify squamous cell carcinoma. Keratin pearl formation reflects the keratinizing differentiation of the tumor and is absent in basal cell carcinoma and melanoma.

Question 48Dermatopathology

A pruritic violaceous flat-topped papule on the wrist shows hyperkeratosis, wedge-shaped hypergranulosis, sawtooth rete ridges, basal vacuolar change, and a band-like lymphocytic infiltrate obscuring the dermoepidermal junction. What is the diagnosis?

  1. Psoriasis vulgaris
  2. Lichen planus Correct answer.
  3. Subacute cutaneous lupus erythematosus
  4. Pityriasis rosea

Explanation

Wedge-shaped hypergranulosis, sawtooth rete ridges, and a band-like interface lymphocytic infiltrate with basal damage are the classic features of lichen planus. Colloid (Civatte) bodies and melanin incontinence in the upper dermis often accompany these findings.

Question 49Dermatopathology

A biopsy of an oral erosion shows separation of the epithelium immediately above the basal layer, with basal keratinocytes still attached to the basement membrane in a tombstone row. Which diagnosis does this pattern indicate?

  1. Pemphigus foliaceus
  2. Bullous pemphigoid
  3. Pemphigus vulgaris Correct answer.
  4. Lichen planus

Explanation

Suprabasal acantholysis that spares the basal layer creates the tombstone row characteristic of pemphigus vulgaris, in which IgG autoantibodies target desmoglein 3. Direct immunofluorescence shows intercellular IgG coating keratinocytes in a net-like pattern.

Question 50Dermatopathology

A patient with gluten-sensitive enteropathy develops grouped vesicles on the elbows. Biopsy shows neutrophils clustered at the tips of dermal papillae with early subepidermal vesicle formation. Which diagnosis is most likely?

  1. Dermatitis herpetiformis Correct answer.
  2. Bullous pemphigoid
  3. Linear IgA bullous dermatosis
  4. Erythema multiforme

Explanation

Neutrophilic microabscesses localizing to the dermal papillary tips are the hallmark of dermatitis herpetiformis, which shows granular IgA deposits along the basement membrane zone on direct immunofluorescence and is associated with celiac disease.