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Iraqi Board Dermatology study materials
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Iraqi Board Dermatology practice questions

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Question 1Basic sciences relevant to skin (structure, function, immunology, microbiology, genetics, pathology)

Which epidermal layer contains cells that are mitotically active and attached to the basement membrane?

  1. Stratum basale Correct answer.
  2. Stratum granulosum
  3. Stratum corneum
  4. Stratum spinosum

Explanation

The stratum basale is a single layer of columnar keratinocytes resting on the basement membrane; these cells divide and renew the epidermis. Cells in higher layers have already left the cell cycle and are committed to terminal differentiation.

Question 2Basic sciences relevant to skin (structure, function, immunology, microbiology, genetics, pathology)

Which cell type in the epidermis is of neural crest origin and produces pigment transferred to keratinocytes?

  1. Melanocyte Correct answer.
  2. Langerhans cell
  3. Merkel cell
  4. Keratinocyte

Explanation

Melanocytes arise from neural crest cells and migrate into the basal epidermis, where they synthesize melanin and transfer it to keratinocytes via melanosomes. Their density is relatively constant between races; differences in pigmentation reflect melanosome number and size.

Question 3Basic sciences relevant to skin (structure, function, immunology, microbiology, genetics, pathology)

The principal collagen type of the dermal papillary layer, forming thin loosely packed fibrils, is:

  1. Type III Correct answer.
  2. Type IV
  3. Type I
  4. Type VII

Explanation

The papillary dermis is rich in type III collagen, which forms fine reticular fibers. Type I collagen dominates the deeper reticular dermis, giving it tensile strength.

Question 4Basic sciences relevant to skin (structure, function, immunology, microbiology, genetics, pathology)

A patient with recurrent staphylococcal skin abscesses is found to have a defect in neutrophil oxidative burst. Which enzyme is most directly deficient?

  1. NADPH oxidase Correct answer.
  2. Myeloperoxidase
  3. Superoxide dismutase
  4. Glucose-6-phosphatase

Explanation

Chronic granulomatous disease results from defective NADPH oxidase, so phagocytes cannot generate superoxide and are susceptible to catalase-positive organisms such as Staphylococcus aureus. The resulting infections include recurrent abscesses, lymphadenitis, and granulomas.

Question 5Basic sciences relevant to skin (structure, function, immunology, microbiology, genetics, pathology)

Which adhesion structure links keratin intermediate filaments between adjacent keratinocytes?

  1. Gap junction
  2. Hemidesmosome
  3. Focal adhesion
  4. Desmosome Correct answer.

Explanation

Desmosomes contain desmoglein and desmocollin cadherins that bind keratin filaments of neighboring cells, providing epidermal cohesion. Their disruption by autoantibodies produces intraepidermal blistering in pemphigus.

Question 6Basic sciences relevant to skin (structure, function, immunology, microbiology, genetics, pathology)

A 30-year-old develops flaccid bullae and oral erosions; direct immunofluorescence shows intercellular IgG in the epidermis. Which antigen is targeted?

  1. Type VII collagen
  2. BP180
  3. Laminin 332
  4. Desmoglein 3 Correct answer.

Explanation

Pemphigus vulgaris autoantibodies target desmoglein 3 (and sometimes desmoglein 1), producing suprabasal acantholysis with intercellular IgG on immunofluorescence. Mucosal involvement predominates because desmoglein 3 is strongly expressed in stratified squamous mucosa.

Question 7Basic sciences relevant to skin (structure, function, immunology, microbiology, genetics, pathology)

In the skin immune system, which cytokine is central to recruiting neutrophils and is a major target of biologic therapy in psoriasis?

  1. Interleukin-5
  2. Interleukin-13
  3. Interleukin-17 Correct answer.
  4. Interleukin-4

Explanation

The IL-23/Th17 axis drives psoriasis; IL-17 recruits neutrophils and induces keratinocyte proliferation and chemokine production. Biologics blocking IL-17 or its receptor are effective in plaque psoriasis.

Question 8Basic sciences relevant to skin (structure, function, immunology, microbiology, genetics, pathology)

Which organism is the most common cause of cellulitis in immunocompetent adults with intact skin?

  1. Pseudomonas aeruginosa
  2. Mycobacterium marinum
  3. Pasteurella multocida
  4. Streptococcus pyogenes Correct answer.

Explanation

Beta-hemolytic streptococci, especially Streptococcus pyogenes, are the leading cause of nonpurulent cellulitis in immunocompetent adults. Staphylococcus aureus is the other major pathogen, particularly when purulence or abscess is present.

Question 9Basic sciences relevant to skin (structure, function, immunology, microbiology, genetics, pathology)

A dermatophyte infection is suspected in a scaly annular plaque. Which laboratory finding best confirms dermatophyte rather than Candida infection?

  1. Budding yeasts on Gram stain
  2. Spherules containing endospores
  3. Pseudohyphae on potassium hydroxide preparation
  4. Septate branching hyphae on potassium hydroxide preparation Correct answer.

Explanation

Dermatophytes produce septate, branching hyphae that may be seen on a KOH mount of skin scrapings. Candida instead shows budding yeasts and pseudohyphae, while deep dimorphic fungi may show spherules.

Question 10Basic sciences relevant to skin (structure, function, immunology, microbiology, genetics, pathology)

Which viral protein is primarily responsible for the ability of herpes simplex virus to establish latent infection in sensory ganglia?

  1. Latency-associated transcript Correct answer.
  2. DNA polymerase
  3. Thymidine kinase
  4. Glycoprotein D

Explanation

During latency in dorsal root ganglia, herpes simplex virus expresses latency-associated transcripts and few other genes, allowing immune evasion. Reactivation later produces lytic replication and recurrent vesicles.

Question 11Basic sciences relevant to skin (structure, function, immunology, microbiology, genetics, pathology)

A mutation in a gene encoding a desmosomal protein causes a disorder with woolly hair and palmoplantar keratoderma. Which gene is most likely involved?

  1. COL7A1
  2. KRT5
  3. TGM1
  4. DSP Correct answer.

Explanation

Mutations in DSP, encoding desmoplakin, cause arrhythmogenic cardiomyopathy with a cutaneous syndrome that includes woolly hair and palmoplantar keratoderma. Desmoplakin links desmosomal cadherins to keratin filaments.

Question 12Basic sciences relevant to skin (structure, function, immunology, microbiology, genetics, pathology)

Which feature best distinguishes the histopathology of lichen planus from psoriasis?

  1. Elongated rete ridges with thinning over dermal papillae
  2. Hyperkeratosis with parakeratosis
  3. Band-like lymphocytic infiltrate at the dermoepidermal junction Correct answer.
  4. Neutrophils in the stratum corneum

Explanation

Lichen planus shows a dense band-like lymphocytic infiltrate obscuring the dermoepidermal junction with basal vacuolar change and saw-tooth rete ridges. Psoriasis instead shows regular acanthosis, parakeratosis, and neutrophilic Munro microabscesses.

Question 13Basic sciences relevant to skin (structure, function, immunology, microbiology, genetics, pathology)

In the skin, which enzyme converts 7-dehydrocholesterol to previtamin D3 after ultraviolet B exposure?

  1. 25-hydroxylase
  2. Thermal isomerization, not an enzyme Correct answer.
  3. Cytochrome P450scc
  4. 1-alpha-hydroxylase

Explanation

Ultraviolet B photolyzes 7-dehydrocholesterol to previtamin D3, which then undergoes temperature-dependent isomerization to vitamin D3 without enzymatic catalysis. Subsequent hydroxylations occur in the liver and kidney.

Question 14Basic sciences relevant to skin (structure, function, immunology, microbiology, genetics, pathology)

A child has fragile skin and blisters after minor trauma; immunofluorescence is negative and electron microscopy shows cleavage within the basal keratinocyte. Which diagnosis fits?

  1. Pemphigus foliaceus
  2. Epidermolysis bullosa simplex Correct answer.
  3. Bullous pemphigoid
  4. Dermatitis herpetiformis

Explanation

Epidermolysis bullosa simplex results from keratin 5 or 14 mutations, causing basal keratinocyte cytolysis and intraepidermal blistering without immune deposits. Blisters appear at sites of friction and heal without scarring.

Question 15Basic sciences relevant to skin (structure, function, immunology, microbiology, genetics, pathology)

Which cutaneous structure is primarily responsible for the axon reflex flare seen after scratching the skin?

  1. Sympathetic vasoconstrictor fibers
  2. Sensory C-fiber release of substance P and CGRP Correct answer.
  3. Sebaceous gland secretion
  4. Eccrine sweat duct reabsorption

Explanation

Antidromic conduction in sensory C fibers releases neuropeptides such as substance P and calcitonin gene-related peptide, producing vasodilation and the flare component of the triple response. This neurogenic inflammation also contributes to itch and urticaria.

Question 16Basic sciences relevant to skin (structure, function, immunology, microbiology, genetics, pathology)

Which skin barrier component is most directly reduced in atopic dermatitis and contributes to increased transepidermal water loss?

  1. Type IV collagen
  2. Desmoglein 1
  3. Factor XIIIa
  4. Filaggrin Correct answer.

Explanation

Loss-of-function filaggrin mutations impair profilaggrin processing into natural moisturizing factors, weakening the cornified envelope and increasing water loss. This barrier defect permits allergen penetration and promotes inflammation in atopic dermatitis.

Question 17Basic sciences relevant to skin (structure, function, immunology, microbiology, genetics, pathology)

An infant presents with generalized erythema and large flaccid bullae; histology shows subcorneal acantholysis and direct immunofluorescence shows intercellular IgG. Which target antigen is most likely?

  1. Desmoglein 1 Correct answer.
  2. Desmoglein 3
  3. BP230
  4. Collagen XVII

Explanation

Pemphigus foliaceus and its infantile form target desmoglein 1, which predominates in superficial epidermis, producing subcorneal blisters. Mucous membranes are spared because desmoglein 3 compensates there.

Question 18Basic sciences relevant to skin (structure, function, immunology, microbiology, genetics, pathology)

Which feature is characteristic of the normal cutaneous microbiome of the axilla compared with the forearm?

  1. Predominance of Mycobacterium species
  2. Sterility due to apocrine secretion
  3. Predominance of dermatophyte fungi
  4. Predominance of Corynebacterium and Staphylococcus species Correct answer.

Explanation

Occluded, moist, lipid-rich sites such as the axilla favor lipophilic Corynebacterium and Staphylococcus species, which contribute to odor. The forearm is drier and has a different, more diverse bacterial community.

Question 19Basic sciences relevant to skin (structure, function, immunology, microbiology, genetics, pathology)

Which process explains the pale halo around a resolving ecchymosis as hemoglobin is degraded?

  1. Conversion of biliverdin to bilirubin Correct answer.
  2. Hemosiderin deposition followed by macrophage clearance
  3. Fibrin polymerization in the dermis
  4. Increased melanin transfer from melanocytes

Explanation

Macrophages degrade extravasated hemoglobin into biliverdin (green) and then bilirubin (yellow), producing the color changes of a resolving bruise. Hemosiderin may persist longer and appears golden-brown.

Question 20Basic sciences relevant to skin (structure, function, immunology, microbiology, genetics, pathology)

Which structure is responsible for anchoring the eccrine sweat gland coil to surrounding dermal tissue and preventing its displacement?

  1. Dense connective tissue sheath with elastic fibers Correct answer.
  2. Basement membrane of the epidermis
  3. Adipose capsule only
  4. Arrector pili muscle

Explanation

The eccrine secretory coil is surrounded by a connective tissue sheath containing elastic and collagen fibers that anchor it within the dermis or subcutis. This sheath also supports the gland during mechanical stress.

Question 21Diagnostic dermatology: history, morphology, dermatoscopy, and dermatopathology

A 24-year-old man presents with recurrent itchy vesicles on the sides of his fingers and toes, worsening in summer. He has a personal history of asthma and allergic rhinitis. Which single historical feature most strongly supports a diagnosis of dyshidrotic eczema over tinea manuum?

  1. Unilateral involvement of one hand only
  2. History of recent travel to a humid climate
  3. Positive family history of diabetes mellitus
  4. Presence of atopic background with seasonal recurrence Correct answer.

Explanation

Dyshidrotic eczema is strongly associated with an atopic diathesis and typically recurs seasonally, especially in warm weather. A personal or family history of atopy is a key historical clue that helps separate it from dermatophyte infection, which is more often unilateral and asymmetric.

Question 22Diagnostic dermatology: history, morphology, dermatoscopy, and dermatopathology

On dermatoscopy, a pigmented lesion shows a network of pigmented lines that is prominent in the center and fades toward the periphery. This finding is most consistent with which diagnosis?

  1. Dermatofibroma
  2. Pigmented actinic keratosis
  3. Melanoma Correct answer.
  4. Seborrheic keratosis

Explanation

A pigmented network that is irregular and fades or terminates abruptly at the periphery is a classic dermatoscopic feature of melanoma. Benign melanocytic nevi usually show a regular, symmetric network that thins gradually toward the edge.

Question 23Diagnostic dermatology: history, morphology, dermatoscopy, and dermatopathology

A skin biopsy shows a subepidermal blister with a dense band of neutrophils along the dermoepidermal junction and linear deposition of IgA at the basement membrane zone on direct immunofluorescence. What is the most likely diagnosis?

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

Explanation

Linear IgA bullous dermatosis is defined by linear IgA deposition along the basement membrane zone on direct immunofluorescence. Histology typically shows subepidermal blistering with neutrophils aligned at the dermoepidermal junction, matching this description.

Question 24Diagnostic dermatology: history, morphology, dermatoscopy, and dermatopathology

A patient describes a rash that appears only on skin exposed to sunlight and spares covered areas. Which historical detail is most useful in confirming a photosensitive eruption?

  1. Lesions confined to sun-exposed sites with sparing of covered skin Correct answer.
  2. Family history of psoriasis
  3. Presence of pruritus worse at night
  4. Recent use of a new soap

Explanation

A photodistributed pattern, in which lesions are confined to sun-exposed areas and spare covered skin, is the key historical clue for a photosensitive eruption. This distribution helps distinguish photodermatoses from contact dermatitis and other generalized rashes.

Question 25Diagnostic dermatology: history, morphology, dermatoscopy, and dermatopathology

A lesion on the trunk shows multiple milia-like cysts, comedo-like openings, and a cerebriform surface on dermatoscopy. Which diagnosis is most likely?

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

Explanation

Milia-like cysts and comedo-like openings, together with a cerebriform or brain-like surface, are hallmark dermatoscopic features of seborrheic keratosis. These findings reflect keratin-filled cysts and follicular plugging within the lesion.

Question 26Diagnostic dermatology: history, morphology, dermatoscopy, and dermatopathology

A patient has erythematous scaly plaques on the elbows and knees with silvery scale. Which histologic finding most supports psoriasis?

  1. Granulomatous inflammation with Langhans giant cells
  2. Interface dermatitis with basal vacuolization
  3. Regular acanthosis with parakeratosis and Munro microabscesses Correct answer.
  4. Subepidermal blister with eosinophils

Explanation

Psoriasis shows regular acanthosis, parakeratosis, and collections of neutrophils in the stratum corneum known as Munro microabscesses. These features correspond to the thickened, rapidly turning over epidermis with retained nuclei.

Question 27Diagnostic dermatology: history, morphology, dermatoscopy, and dermatopathology

A 45-year-old woman has a firm, dimpled plaque on the shin that pinches inward when squeezed. Which dermatoscopic finding best supports dermatofibroma?

  1. Multiple milia-like cysts
  2. Central white patch with delicate peripheral pigment network Correct answer.
  3. Homogeneous blue pigmentation with no network
  4. Arborizing telangiectasia with blue-gray ovoid nests

Explanation

Dermatofibroma classically shows a central white patch surrounded by a delicate peripheral pigment network on dermatoscopy. The white central area corresponds to dermal fibrosis, which also explains the dimple sign on lateral compression.

Question 28Diagnostic dermatology: history, morphology, dermatoscopy, and dermatopathology

A patient reports intensely itchy burrows in the finger webs and wrists, worse at night, with similar symptoms in family members. Which historical feature is most specific for scabies?

  1. Pruritic burrows in web spaces with affected household contacts Correct answer.
  2. Association with asthma
  3. Lesions confined to sun-exposed skin
  4. Seasonal worsening in winter

Explanation

Scabies classically causes nocturnal pruritus with burrows in the finger webs and wrists, and it spreads readily among household contacts. The combination of typical burrows and affected close contacts is highly specific.

Question 29Diagnostic dermatology: history, morphology, dermatoscopy, and dermatopathology

Histology of a skin lesion shows atypical melanocytes with pagetoid spread confined to the epidermis, without dermal invasion. What is the most appropriate diagnosis?

  1. Compound nevus
  2. Lentigo simplex
  3. Invasive melanoma
  4. Melanoma in situ Correct answer.

Explanation

Melanoma in situ is defined by atypical melanocytes with pagetoid spread that remain confined to the epidermis, without invasion into the dermis. Once atypical melanocytes extend into the dermis, the lesion is classified as invasive melanoma.

Question 30Diagnostic dermatology: history, morphology, dermatoscopy, and dermatopathology

A lesion on the face shows a pink, translucent papule with fine branching vessels. On dermatoscopy, which vascular pattern is most characteristic of basal cell carcinoma?

  1. Dotted vessels in a patch
  2. Hairpin vessels in a cluster
  3. Comma-shaped vessels
  4. Arborizing telangiectasia Correct answer.

Explanation

Arborizing telangiectasia, appearing as branching tree-like vessels, is a hallmark dermatoscopic feature of basal cell carcinoma. It reflects the prominent superficial vasculature within the tumor.

Question 31Diagnostic dermatology: history, morphology, dermatoscopy, and dermatopathology

A patient has a chronic, intensely pruritic eruption with lichenified plaques in the flexures. Which historical factor most supports atopic dermatitis as the cause?

  1. History of recurrent herpes labialis
  2. Occupational exposure to nickel
  3. Personal or family history of atopy with childhood onset Correct answer.
  4. Recent antibiotic use

Explanation

Atopic dermatitis is strongly associated with a personal or family history of atopy and often begins in childhood, with flexural lichenified plaques. This historical pattern helps distinguish it from contact dermatitis and other eczemas.

Question 32Diagnostic dermatology: history, morphology, dermatoscopy, and dermatopathology

A biopsy of a violaceous, pruritic, polygonal papule shows a band-like lymphocytic infiltrate obscuring the dermoepidermal junction with saw-tooth rete ridges. What is the most likely diagnosis?

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

Explanation

Lichen planus shows a band-like lymphocytic infiltrate at the dermoepidermal junction with saw-tooth rete ridges and basal layer damage. These features correspond to the classic violaceous, polygonal, pruritic papules.

Question 33Diagnostic dermatology: history, morphology, dermatoscopy, and dermatopathology

A patient has a pigmented lesion on the sole. Which dermatoscopic feature should raise the greatest concern for acral melanoma?

  1. Lattice-like pattern
  2. Regular fibrillar pattern
  3. Parallel ridge pattern Correct answer.
  4. Parallel furrow pattern

Explanation

On acral skin, a parallel ridge pattern, in which pigment follows the ridges, is highly suggestive of acral melanoma. Benign acral nevi typically show parallel furrow or lattice-like patterns.

Question 34Diagnostic dermatology: history, morphology, dermatoscopy, and dermatopathology

A patient presents with grouped vesicles on an erythematous base along a dermatome. Which historical feature best supports herpes zoster over herpes simplex?

  1. Recurrence at the same site multiple times per year
  2. Bilateral symmetric involvement
  3. Association with asthma
  4. Unilateral dermatomal distribution with pain preceding the rash Correct answer.

Explanation

Herpes zoster classically produces unilateral, dermatomal grouped vesicles with pain that often precedes the rash. Herpes simplex tends to recur at the same mucocutaneous site rather than following a dermatome.

Question 35Diagnostic dermatology: history, morphology, dermatoscopy, and dermatopathology

A skin biopsy shows epidermal spongiosis with a perivascular lymphocytic infiltrate and no interface change. This pattern is most consistent with which condition?

  1. Acute eczematous dermatitis Correct answer.
  2. Lichen planus
  3. Dermatofibroma
  4. Pemphigus vulgaris

Explanation

Spongiosis with a perivascular lymphocytic infiltrate is the hallmark histologic pattern of acute eczematous dermatitis. It reflects intercellular edema within the epidermis.

Question 36Diagnostic dermatology: history, morphology, dermatoscopy, and dermatopathology

A patient has a slowly enlarging pearly nodule with a rolled edge and central ulceration on the nose. Which dermatoscopic feature most supports nodular basal cell carcinoma?

  1. Blue-gray ovoid nests with arborizing vessels Correct answer.
  2. Comedo-like openings
  3. Central white patch
  4. Parallel furrow pattern

Explanation

Blue-gray ovoid nests combined with arborizing vessels are classic dermatoscopic features of nodular basal cell carcinoma. The ovoid nests represent pigmented tumor islands within the dermis.

Question 37Diagnostic dermatology: history, morphology, dermatoscopy, and dermatopathology

A patient reports a burning sensation and blistering on sun-exposed skin after taking a new medication. Which historical detail is most useful in identifying a drug-induced photosensitivity reaction?

  1. Presence of burrows in web spaces
  2. Seasonal worsening in winter
  3. Family history of melanoma
  4. Temporal relationship between drug initiation and eruption in sun-exposed sites Correct answer.

Explanation

A temporal relationship between starting a culprit drug and the onset of an eruption confined to sun-exposed sites strongly supports drug-induced photosensitivity. This helps distinguish it from idiopathic photodermatoses and contact dermatitis.

Question 38Diagnostic dermatology: history, morphology, dermatoscopy, and dermatopathology

A biopsy shows intraepidermal acantholysis with a tombstone row of basal keratinocytes and IgG deposition on the keratinocyte cell surfaces. What is the most likely diagnosis?

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

Explanation

Pemphigus vulgaris shows suprabasal acantholysis with a tombstone row of basal cells and intercellular IgG deposition on direct immunofluorescence. This pattern reflects autoantibodies against desmogleins.

Question 39Diagnostic dermatology: history, morphology, dermatoscopy, and dermatopathology

A patient has hypopigmented macules with reduced but not absent melanin on Wood lamp examination, and sensation is intact. Which diagnosis is most likely?

  1. Post-inflammatory hypopigmentation
  2. Vitiligo
  3. Pityriasis versicolor Correct answer.
  4. Leprosy

Explanation

Pityriasis versicolor shows hypopigmented macules with reduced melanin and intact sensation, and it may fluoresce on Wood lamp examination. Leprosy causes anesthetic patches, while vitiligo shows complete depigmentation.

Question 40Diagnostic dermatology: history, morphology, dermatoscopy, and dermatopathology

A lesion shows a homogeneous blue color without any pigment network on dermatoscopy. Which diagnosis should be considered?

  1. Blue nevus Correct answer.
  2. Dermatofibroma
  3. Clear cell acanthoma
  4. Seborrheic keratosis

Explanation

A homogeneous blue color without a pigment network is characteristic of a blue nevus, reflecting dermal pigment. This pattern can also occur in nodular melanoma, so clinical correlation is essential.

Question 41Inflammatory and papulosquamous dermatoses (eczema, psoriasis, lichenoid and interface dermatoses)

A 34-year-old woman has pruritic, ill-defined erythematous plaques with scaling on both antecubital fossae and the neck. She has a personal history of asthma and allergic rhinitis. Which diagnosis is most likely?

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

Explanation

Atopic dermatitis classically affects flexural sites such as the antecubital and popliteal fossae and is strongly associated with a personal or family history of atopy, including asthma and allergic rhinitis. The intense pruritus and ill-defined lichenified plaques fit this pattern well.

Question 42Inflammatory and papulosquamous dermatoses (eczema, psoriasis, lichenoid and interface dermatoses)

Which clinical feature is most characteristic of lichen planus?

  1. Honey-coloured crusted lesions around the mouth and nose
  2. Annular plaques with trailing scale and central clearing
  3. Violaceous, flat-topped, polygonal papules with Wickham striae Correct answer.
  4. Salmon-pink plaques with a collarette of scale

Explanation

Lichen planus is described by the six Ps: planar (flat-topped), purple (violaceous), polygonal, pruritic, papules and plaques. Fine white lacy lines on the surface, known as Wickham striae, are the classic dermoscopic and clinical clue.

Question 43Inflammatory and papulosquamous dermatoses (eczema, psoriasis, lichenoid and interface dermatoses)

A 28-year-old man has well-demarcated erythematous plaques with silvery scale over both elbows and knees. Which histologic finding best supports psoriasis?

  1. Interface dermatitis with basal vacuolar change
  2. Subepidermal blister with linear IgA deposition
  3. Spongiosis with intraepidermal eosinophils
  4. Regular acanthosis with thinned suprapapillary plates and parakeratosis Correct answer.

Explanation

Psoriasis shows regular elongation of rete ridges with thinning of the suprapapillary plates, confluent parakeratosis, loss of the granular layer and dilated capillaries in the dermal papillae. Munro microabscesses of neutrophils in the stratum corneum are also typical.

Question 44Inflammatory and papulosquamous dermatoses (eczema, psoriasis, lichenoid and interface dermatoses)

A 45-year-old woman develops a pruritic rash on the wrists and ankles three weeks after starting hydrochlorothiazide. Examination shows violaceous flat-topped papules and lacy white lines on the surface. What is the most likely diagnosis?

  1. Pityriasis rosea
  2. Erythema multiforme
  3. Nummular eczema
  4. Lichenoid drug eruption Correct answer.

Explanation

Lichenoid drug eruptions mimic lichen planus clinically and histologically and classically appear weeks to months after starting a culprit drug such as thiazides, antimalarials or gold. They tend to be more widespread and often show more eczematous or parakeratotic changes on histology.

Question 45Inflammatory and papulosquamous dermatoses (eczema, psoriasis, lichenoid and interface dermatoses)

Which statement best describes the Auspitz sign in psoriasis?

  1. Greasy yellow scale on the scalp and eyebrows
  2. A ring of scale at the advancing edge of a lesion
  3. Pinpoint bleeding after removal of scale from a plaque Correct answer.
  4. Yellowish discolouration of the nail bed with onycholysis

Explanation

The Auspitz sign refers to pinpoint bleeding when scale is gently removed from a psoriatic plaque, reflecting the elongated dermal papillae and their dilated superficial capillaries. It is helpful but not specific, as it can also occur in other conditions with thinned suprapapillary epidermis.

Question 46Inflammatory and papulosquamous dermatoses (eczema, psoriasis, lichenoid and interface dermatoses)

A 60-year-old man presents with tense blisters and erosions on sun-exposed skin, and direct immunofluorescence shows linear IgG and C3 along the basement membrane zone. Which diagnosis fits best?

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

Explanation

Bullous pemphigoid is a subepidermal autoimmune blistering disease with linear deposition of IgG and C3 along the basement membrane zone on direct immunofluorescence. It typically affects older adults with tense blisters on an urticarial base in flexural and sun-exposed areas.

Question 47Inflammatory and papulosquamous dermatoses (eczema, psoriasis, lichenoid and interface dermatoses)

Which topical agent is the first-line anti-inflammatory treatment for chronic plaque psoriasis of limited extent?

  1. Potent topical corticosteroid Correct answer.
  2. Topical mupirocin
  3. Topical acyclovir
  4. Topical terbinafine

Explanation

Potent topical corticosteroids are a first-line treatment for limited chronic plaque psoriasis because they reduce inflammation and scale. Vitamin D analogues such as calcipotriol are also first-line and are often combined with steroids to reduce steroid-related atrophy.

Question 48Inflammatory and papulosquamous dermatoses (eczema, psoriasis, lichenoid and interface dermatoses)

A 22-year-old woman has an oval scaly patch on the trunk, followed two weeks later by multiple smaller oval lesions arranged along the lines of cleavage on the back. What is the most likely diagnosis?

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

Explanation

Pityriasis rosea classically begins with a single herald patch followed by a secondary eruption of smaller oval lesions with a collarette of scale distributed along the lines of cleavage, producing a Christmas-tree pattern on the back. It is self-limiting and often resolves over weeks.

Question 49Inflammatory and papulosquamous dermatoses (eczema, psoriasis, lichenoid and interface dermatoses)

Which finding on skin biopsy is most characteristic of lichen planus?

  1. Neutrophilic folliculitis with perifollicular abscess
  2. Nodular dermal infiltrate of foamy histiocytes
  3. Band-like lymphocytic infiltrate with basal layer vacuolar degeneration and saw-tooth rete ridges Correct answer.
  4. Epidermal hyperplasia with prominent spongiosis and eosinophils

Explanation

Lichen planus shows a lichenoid interface dermatitis: a dense band-like lymphocytic infiltrate hugging the dermoepidermal junction with vacuolar degeneration of the basal layer. Saw-tooth rete ridges, hyperkeratosis and Civatte bodies are accompanying features.

Question 50Inflammatory and papulosquamous dermatoses (eczema, psoriasis, lichenoid and interface dermatoses)

A 30-year-old man with psoriasis has sudden eruption of numerous small scaly papules two weeks after a sore throat. What is the most likely diagnosis?

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

Explanation

Guttate psoriasis typically erupts suddenly with many small drop-like papules and plaques, usually following a streptococcal upper respiratory infection, particularly in younger patients. Throat swab and antistreptolysin O titres may be positive.