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Arab Board Dermatology Part 1 study materials
Arab Board Dermatology Part 1 study resources

Arab Board Dermatology Part 1 practice questions

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Question 1Basic and Clinical Sciences Relevant to Dermatology (anatomy, histology, immunology, microbiology, pharmacology, genetics)

Which epidermal layer contains cells that are actively dividing and attached to the basement membrane?

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

Explanation

The stratum basale is a single layer of columnar keratinocytes resting on the basement membrane; these cells are the principal proliferative compartment of the epidermis. Cells in the layers above are progressively more differentiated and no longer anchored to the basal lamina.

Question 2Basic and Clinical Sciences Relevant to Dermatology (anatomy, histology, immunology, microbiology, pharmacology, genetics)

Which cell type in the epidermis is responsible for presenting antigen to T lymphocytes?

  1. Langerhans cell Correct answer.
  2. Melanocyte
  3. Keratinocyte of the stratum corneum
  4. Merkel cell

Explanation

Langerhans cells are bone marrow-derived dendritic cells of the epidermis that capture antigen and migrate to lymph nodes to present it to T cells. They are the principal antigen-presenting cells of the skin.

Question 3Basic and Clinical Sciences Relevant to Dermatology (anatomy, histology, immunology, microbiology, pharmacology, genetics)

Which immunoglobulin class is most abundant in normal human serum?

  1. IgA
  2. IgM
  3. IgE
  4. IgG Correct answer.

Explanation

IgG accounts for roughly 75-80% of serum immunoglobulin and is also the main antibody in tissue fluid. Its long half-life and high concentration make it the dominant serum class.

Question 4Basic and Clinical Sciences Relevant to Dermatology (anatomy, histology, immunology, microbiology, pharmacology, genetics)

The dermis derives embryologically from which source?

  1. Endoderm
  2. Ectoderm
  3. Mesoderm Correct answer.
  4. Neural crest

Explanation

The dermis is of mesodermal origin and forms the connective tissue framework of the skin. The epidermis, by contrast, is ectodermal, with melanocytes and Merkel cells migrating from neural crest.

Question 5Basic and Clinical Sciences Relevant to Dermatology (anatomy, histology, immunology, microbiology, pharmacology, genetics)

Which structure is the principal barrier to water loss through the skin?

  1. Stratum corneum Correct answer.
  2. Papillary dermis
  3. Basement membrane zone
  4. Sebaceous gland

Explanation

The stratum corneum, with its cornified lipid-rich intercellular matrix, provides most of the epidermal permeability barrier. Disruption of this layer produces marked transepidermal water loss.

Question 6Basic and Clinical Sciences Relevant to Dermatology (anatomy, histology, immunology, microbiology, pharmacology, genetics)

Which organism is the causative agent of tinea versicolor?

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

Explanation

Tinea versicolor is caused by the lipophilic yeast Malassezia, which is part of normal skin flora and overgrows in warm, humid conditions. It produces hypopigmented or hyperpigmented scaly macules on the trunk.

Question 7Basic and Clinical Sciences Relevant to Dermatology (anatomy, histology, immunology, microbiology, pharmacology, genetics)

Which vitamin deficiency produces phrynoderma (toad skin) with follicular hyperkeratosis?

  1. Vitamin A Correct answer.
  2. Vitamin D
  3. Vitamin C
  4. Vitamin K

Explanation

Vitamin A is required for normal epithelial differentiation, and deficiency leads to follicular hyperkeratosis (phrynoderma), xerosis, and night blindness. The follicular plugs are characteristic of the deficiency state.

Question 8Basic and Clinical Sciences Relevant to Dermatology (anatomy, histology, immunology, microbiology, pharmacology, genetics)

Which drug class works by inhibiting calcineurin and is used topically for atopic dermatitis?

  1. Coal tar preparations
  2. Oral antihistamines
  3. Topical corticosteroids
  4. Calcineurin inhibitors Correct answer.

Explanation

Topical calcineurin inhibitors such as tacrolimus and pimecrolimus block T-cell activation by inhibiting calcineurin, reducing inflammation without steroid-related atrophy. They are used as steroid-sparing agents in atopic dermatitis.

Question 9Basic and Clinical Sciences Relevant to Dermatology (anatomy, histology, immunology, microbiology, pharmacology, genetics)

In which skin layer are Meissner corpuscles located?

  1. Stratum basale
  2. Subcutaneous fat
  3. Reticular dermis
  4. Dermal papilla Correct answer.

Explanation

Meissner corpuscles are encapsulated mechanoreceptors located in the dermal papillae just beneath the epidermis, where they detect light touch. Pacinian corpuscles, by contrast, lie deeper in the reticular dermis and hypodermis.

Question 10Basic and Clinical Sciences Relevant to Dermatology (anatomy, histology, immunology, microbiology, pharmacology, genetics)

A patient has a defect in desmoglein 1 and desmoglein 3 causing intraepidermal blistering. Which structure is primarily disrupted?

  1. Gap junctions
  2. Tight junctions
  3. Desmosomes Correct answer.
  4. Hemidesmosomes

Explanation

Desmogleins are cadherin components of desmosomes, which mediate keratinocyte-to-keratinocyte adhesion. Loss of desmoglein function produces acantholysis and intraepidermal blisters, as in pemphigus.

Question 11Basic and Clinical Sciences Relevant to Dermatology (anatomy, histology, immunology, microbiology, pharmacology, genetics)

Which complement component deficiency predisposes to recurrent Neisserial infections?

  1. C3
  2. C1 inhibitor
  3. C2
  4. C5-C9 (membrane attack complex) Correct answer.

Explanation

Terminal complement components C5 through C9 assemble the membrane attack complex, which is essential for killing Neisseria species. Deficiency of these components markedly increases susceptibility to disseminated gonococcal and meningococcal disease.

Question 12Basic and Clinical Sciences Relevant to Dermatology (anatomy, histology, immunology, microbiology, pharmacology, genetics)

Which type of hypersensitivity reaction underlies allergic contact dermatitis?

  1. Type IV cell-mediated Correct answer.
  2. Type II antibody-mediated
  3. Type I immediate
  4. Type III immune complex

Explanation

Allergic contact dermatitis is a delayed-type (Type IV) hypersensitivity reaction mediated by hapten-specific T lymphocytes. Sensitization and elicitation occur over days, producing a spongiotic eczematous response.

Question 13Basic and Clinical Sciences Relevant to Dermatology (anatomy, histology, immunology, microbiology, pharmacology, genetics)

Which property makes a topical corticosteroid more potent?

  1. Larger molecular size
  2. Lower concentration in the vehicle
  3. Increased water solubility
  4. Increased lipophilicity and receptor affinity Correct answer.

Explanation

Potency of topical corticosteroids is determined largely by lipophilicity, which enhances penetration through the stratum corneum, and by binding affinity for the glucocorticoid receptor. Structural modifications such as halogenation increase both.

Question 14Basic and Clinical Sciences Relevant to Dermatology (anatomy, histology, immunology, microbiology, pharmacology, genetics)

Which feature distinguishes eccrine from apocrine sweat glands?

  1. Eccrine glands are confined to the axillae
  2. Eccrine glands enlarge at puberty
  3. Eccrine glands secrete into hair follicles
  4. Eccrine glands open directly onto the skin surface Correct answer.

Explanation

Eccrine glands are widespread and their coiled ducts open directly onto the epidermal surface through a sweat pore. Apocrine glands are limited to axillae, areolae, and anogenital regions and empty into hair follicles.

Question 15Basic and Clinical Sciences Relevant to Dermatology (anatomy, histology, immunology, microbiology, pharmacology, genetics)

A child has hypohidrotic ectodermal dysplasia. Which embryonic interaction is most directly disrupted?

  1. Neural tube closure
  2. Dermal blood vessel angiogenesis
  3. Melanoblast migration from the neural crest
  4. Epithelial-mesenchymal signaling for appendage formation Correct answer.

Explanation

Ectodermal dysplasias result from defective reciprocal signaling between ectoderm and underlying mesenchyme during appendage development, leading to absent or reduced sweat glands, hair, and teeth. The EDAR/NF-kB pathway is classically involved.

Question 16Basic and Clinical Sciences Relevant to Dermatology (anatomy, histology, immunology, microbiology, pharmacology, genetics)

Which bacterial toxin produces the desquamation seen in staphylococcal scalded skin syndrome?

  1. Toxic shock syndrome toxin-1
  2. Panton-Valentine leukocidin
  3. Exotoxin A
  4. Exfoliative toxin Correct answer.

Explanation

Staphylococcal scalded skin syndrome is caused by exfoliative toxins that cleave desmoglein 1 in the superficial epidermis, producing a split at the granular layer. This results in widespread tender erythema and sheet-like desquamation.

Question 17Basic and Clinical Sciences Relevant to Dermatology (anatomy, histology, immunology, microbiology, pharmacology, genetics)

Which genetic inheritance pattern is characteristic of neurofibromatosis type 1?

  1. Autosomal recessive
  2. Mitochondrial
  3. X-linked dominant
  4. Autosomal dominant Correct answer.

Explanation

Neurofibromatosis type 1 is an autosomal dominant disorder caused by loss-of-function mutations in the NF1 tumor suppressor gene. About half of cases arise from new mutations, and penetrance is high.

Question 18Basic and Clinical Sciences Relevant to Dermatology (anatomy, histology, immunology, microbiology, pharmacology, genetics)

Which of the following best explains why the same topical drug can have different potency when applied to the palm versus the forearm?

  1. Differences in sebum composition only
  2. Differences in dermal blood flow only
  3. Regional differences in stratum corneum thickness and percutaneous absorption Correct answer.
  4. Differences in skin temperature only

Explanation

Percutaneous absorption varies markedly by body site because of differences in stratum corneum thickness, follicular density, and hydration. Palmar skin is thick and relatively resistant, which reduces penetration compared with the thin forearm skin.

Question 19Basic and Clinical Sciences Relevant to Dermatology (anatomy, histology, immunology, microbiology, pharmacology, genetics)

Which type of collagen predominates in the dermal extracellular matrix?

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

Explanation

Type I collagen is the most abundant collagen in the dermis and provides tensile strength to the connective tissue. Type III is present in smaller amounts, especially in fetal skin and around vessels.

Question 20Basic and Clinical Sciences Relevant to Dermatology (anatomy, histology, immunology, microbiology, pharmacology, genetics)

A patient with chronic mucocutaneous candidiasis is found to have a defect in Th17-mediated immunity. Which cytokine axis is most directly implicated?

  1. IL-17/IL-23 Correct answer.
  2. IL-5/eosinophil pathway
  3. IL-4/IL-13
  4. Interferon-gamma/Th1

Explanation

Th17 cells produce IL-17, which drives neutrophil recruitment and antimicrobial peptide production at mucosal and cutaneous surfaces; IL-23 sustains Th17 responses. Defects in this axis underlie susceptibility to mucocutaneous Candida infection.

Question 21Basic and Clinical Sciences Relevant to Dermatology (anatomy, histology, immunology, microbiology, pharmacology, genetics)

Why does the skin of the scrotum appear darker than the adjacent thigh even in the absence of sun exposure?

  1. Increased number of keratinocyte layers
  2. Reduced sebaceous gland activity
  3. Greater dermal vascularity
  4. Higher melanocyte density relative to body surface area in genital skin Correct answer.

Explanation

Genital skin, including the scrotum, has a higher density of melanocytes per unit area than many other body regions, contributing to darker pigmentation independent of UV exposure. Regional variation in melanocyte density is a recognized feature of human skin.

Question 22Basic and Clinical Sciences Relevant to Dermatology (anatomy, histology, immunology, microbiology, pharmacology, genetics)

Which mechanism best explains the efficacy of dapsone in dermatitis herpetiformis?

  1. Inhibition of T-cell calcineurin signaling
  2. Direct lysis of IgA deposits
  3. Inhibition of neutrophil chemotaxis and myeloperoxidase Correct answer.
  4. Blockade of histamine H1 receptors

Explanation

Dapsone suppresses neutrophil function, including chemotaxis and myeloperoxidase activity, and reduces the neutrophilic inflammation that produces the lesions of dermatitis herpetiformis. It does not remove the underlying IgA deposits.

Question 23Basic and Clinical Sciences Relevant to Dermatology (anatomy, histology, immunology, microbiology, pharmacology, genetics)

Which feature best distinguishes the role of the papillary versus reticular dermis?

  1. Papillary dermis is finer and more cellular, reticular dermis is denser and thicker Correct answer.
  2. Papillary dermis is ectodermal, reticular dermis is endodermal
  3. Papillary dermis is avascular, reticular dermis is vascular
  4. Papillary dermis contains no collagen, reticular dermis is collagen-rich

Explanation

The papillary dermis is the superficial layer with finer collagen bundles, more cells, and a rich capillary network; the reticular dermis is deeper with thicker, denser collagen bundles and fewer cells. This structural difference affects disease patterns and healing.

Question 24Basic and Clinical Sciences Relevant to Dermatology (anatomy, histology, immunology, microbiology, pharmacology, genetics)

Which factor most influences the choice of vehicle for a topical agent on an oozing, weeping lesion?

  1. Use of a thick cream with high oil content
  2. Use of an occlusive ointment
  3. Use of a transdermal patch
  4. Use of a drying vehicle such as a lotion or gel Correct answer.

Explanation

Acute weeping lesions are best treated with drying, non-occlusive vehicles such as lotions, gels, or wet dressings. Occlusive ointments trap moisture and can worsen maceration on exudative skin.

Question 25Basic and Clinical Sciences Relevant to Dermatology (anatomy, histology, immunology, microbiology, pharmacology, genetics)

Which characteristic is typical of eccrine sweat in contrast to apocrine sweat?

  1. Clear, odorless, and rich in electrolytes Correct answer.
  2. Milky and rich in lipids
  3. Odorless only after bacterial action
  4. Produced mainly in the axillae

Explanation

Eccrine sweat is a clear, dilute electrolyte solution that is essentially odorless when fresh; odor develops after bacterial metabolism. Apocrine secretion is thicker, lipid-rich, and confined to specific regions.

Question 26Basic and Clinical Sciences Relevant to Dermatology (anatomy, histology, immunology, microbiology, pharmacology, genetics)

Which cell type in the epidermis is responsible for presenting antigen to T lymphocytes and is derived from the bone marrow rather than from keratinocyte lineage?

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

Explanation

Langerhans cells are bone-marrow-derived dendritic cells that reside in the suprabasal epidermis, express CD1a, and migrate to regional lymph nodes to present antigen to T cells. Keratinocytes, melanocytes, and Merkel cells arise from other lineages and are not the principal antigen-presenting population.

Question 27Basic and Clinical Sciences Relevant to Dermatology (anatomy, histology, immunology, microbiology, pharmacology, genetics)

A topical drug is applied to two sites: the forearm and the scrotal skin. Assuming identical formulation and dose, which property of scrotal skin best explains the markedly greater percutaneous absorption at that site?

  1. Higher density of hair follicles with sebaceous glands
  2. Thicker stratum corneum with more desmosomal cohesion
  3. More abundant subcutaneous fat acting as a drug reservoir
  4. Greater skin surface temperature and a thinner, more hydrated stratum corneum Correct answer.

Explanation

Regional variation in percutaneous absorption is driven largely by stratum corneum thickness, hydration, and temperature; scrotal skin has a thin, well-hydrated barrier and higher temperature, so absorption is several-fold greater than on the forearm. Barrier thickness, not follicle density or fat stores, is the dominant determinant of regional absorption differences.

Question 28Basic and Clinical Sciences Relevant to Dermatology (anatomy, histology, immunology, microbiology, pharmacology, genetics)

Which mechanism best accounts for the antifungal action of terbinafine against dermatophytes?

  1. Binding to fungal microtubules and blocking mitotic spindle formation
  2. Complexing with fungal cell membrane sterols to increase permeability
  3. Inhibition of lanosterol 14-alpha-demethylase
  4. Inhibition of squalene epoxidase in the ergosterol synthesis pathway Correct answer.

Explanation

Terbinafine is an allylamine that inhibits squalene epoxidase, an early step in the ergosterol pathway; the resulting squalene accumulation is directly toxic to dermatophytes, making the drug fungicidal against them. Azoles act at a later step (14-alpha-demethylase) and are generally fungistatic against dermatophytes.

Question 29Basic and Clinical Sciences Relevant to Dermatology (anatomy, histology, immunology, microbiology, pharmacology, genetics)

In a patient with a homozygous loss-of-function mutation in the gene encoding filaggrin, which downstream consequence most directly explains the impaired epidermal barrier?

  1. Reduced breakdown of profilaggrin into natural moisturizing factors and impaired keratin filament aggregation Correct answer.
  2. Defective assembly of desmosomal cadherins at cell-cell junctions
  3. Failure of hemidesmosomal integrin anchoring to the basement membrane
  4. Loss of melanin transfer from melanocytes to keratinocytes

Explanation

Profilaggrin is cleaved into filaggrin monomers that aggregate keratin filaments and into free amino acids that form natural moisturizing factors; loss of this protein therefore weakens both structural integrity and stratum corneum hydration. The resulting barrier defect predisposes to atopic dermatitis and allows enhanced allergen and irritant penetration.

Question 30Basic and Clinical Sciences Relevant to Dermatology (anatomy, histology, immunology, microbiology, pharmacology, genetics)

Which feature distinguishes the cutaneous blood supply of the dermis as it relates to thermoregulation?

  1. Dermal capillaries are innervated directly by parasympathetic fibers that cause vasodilation
  2. Dermal arterioles constrict in response to cold via alpha-adrenergic sympathetic fibers Correct answer.
  3. Cutaneous vessels lack sympathetic innervation and respond only to circulating catecholamines
  4. Arteriovenous anastomoses in the papillary dermis dilate in response to cold to conserve heat

Explanation

Cutaneous resistance vessels are innervated by sympathetic adrenergic fibers; cold triggers alpha-adrenergic vasoconstriction, shunting blood away from the skin to conserve heat. Arteriovenous anastomoses are concentrated in acral skin and dilate in response to warmth, not cold.

Question 31Dermatopathology and Diagnostic Techniques (dermoscopy, patch testing, laboratory and molecular diagnostics)

On dermoscopy of a pigmented skin lesion, which structure is the histological correlate of a pigment network?

  1. Melanin within the stratum corneum
  2. Melanin along the rete ridges Correct answer.
  3. Hemoglobin within the papillary dermis
  4. Collagen bundles in the reticular dermis

Explanation

The pigment network reflects melanin pigment located in basal keratinocytes and melanocytes along the elongated rete ridges; the lines correspond to the rete and the holes to the dermal papillae. Loss or distortion of this network is a key clue to malignancy.

Question 32Dermatopathology and Diagnostic Techniques (dermoscopy, patch testing, laboratory and molecular diagnostics)

Which dermoscopic feature is most characteristic of a seborrheic keratosis?

  1. Blue-white veil over a structureless area
  2. Atypical network with pseudopods
  3. Leaf-like pigment at the periphery
  4. Comedo-like openings and milia-like cysts Correct answer.

Explanation

Comedo-like openings (keratin-filled invaginations) and milia-like cysts (intraepidermal keratin cysts) are classic dermoscopic hallmarks of seborrheic keratosis, often with fissures and ridges. These features reflect the acanthotic, keratin-trapping architecture of the lesion.

Question 33Dermatopathology and Diagnostic Techniques (dermoscopy, patch testing, laboratory and molecular diagnostics)

In dermoscopy, arborizing (branching) telangiectasias are a hallmark of which tumor?

  1. Clear cell acanthoma
  2. Basal cell carcinoma Correct answer.
  3. Angiokeratoma
  4. Dermatofibroma

Explanation

Arborizing telangiectasias are sharply focused, branching vessels that reflect the tumor's rich vascular supply and are a classic criterion for basal cell carcinoma. They are usually accompanied by other BCC clues such as ulceration, blue-gray ovoid nests, and shiny structures.

Question 34Dermatopathology and Diagnostic Techniques (dermoscopy, patch testing, laboratory and molecular diagnostics)

During patch testing, when is the standard delayed (late) reading typically performed?

  1. Day 2
  2. Within 30 minutes
  3. At 12 hours
  4. Day 4 to Day 7 Correct answer.

Explanation

Patch test reactions are read initially around day 2 and then again at a delayed reading between days 4 and 7, since allergic contact dermatitis is a delayed-type hypersensitivity that may peak late. A single early reading can miss late positive reactions.

Question 35Dermatopathology and Diagnostic Techniques (dermoscopy, patch testing, laboratory and molecular diagnostics)

A patch test shows erythema, infiltration, and discrete papules at the test site. According to the standard grading scale, this reaction is best classified as:

  1. Strong positive (2+)
  2. Irritant reaction
  3. Weak positive (1+) Correct answer.
  4. Negative

Explanation

A weak positive (1+) reaction is defined by erythema, infiltration, and possibly discrete papules. Stronger grades add vesiculation (2+) or coalescing vesicles and bullae (3+), while irritant reactions have different morphology such as sharply demarcated erythema without infiltration.

Question 36Dermatopathology and Diagnostic Techniques (dermoscopy, patch testing, laboratory and molecular diagnostics)

Which laboratory test is most appropriate to confirm immediate-type sensitization to a suspected allergen such as latex?

  1. Direct immunofluorescence
  2. Patch testing
  3. Specific serum IgE immunoassay Correct answer.
  4. Serum complement C3 level

Explanation

Immediate (type I) hypersensitivity is mediated by allergen-specific IgE, which can be detected by serum immunoassay or skin prick testing. Patch testing detects delayed (type IV) hypersensitivity and is not used for immediate reactions.

Question 37Dermatopathology and Diagnostic Techniques (dermoscopy, patch testing, laboratory and molecular diagnostics)

Direct immunofluorescence of perilesional skin in pemphigus vulgaris characteristically shows which pattern?

  1. Linear IgG and C3 along the basement membrane zone
  2. Granular IgA in the dermal papillae
  3. Intercellular IgG deposition in the epidermis Correct answer.
  4. Fibrinogen deposition around dermal vessels

Explanation

Pemphigus vulgaris is caused by autoantibodies against desmogleins, so direct immunofluorescence shows intercellular (chicken-wire) IgG and often C3 throughout the epidermis. Linear basement membrane deposition instead indicates a pemphigoid-type subepidermal disease.

Question 38Dermatopathology and Diagnostic Techniques (dermoscopy, patch testing, laboratory and molecular diagnostics)

Granular deposits of IgA at the tips of dermal papillae on direct immunofluorescence are diagnostic of which condition?

  1. Bullous pemphigoid
  2. Linear IgA bullous dermatosis
  3. Lupus erythematosus
  4. Dermatitis herpetiformis Correct answer.

Explanation

Dermatitis herpetiformis shows granular IgA deposits concentrated at the papillary tips on direct immunofluorescence, reflecting its association with gluten-sensitive enteropathy. This pattern is distinct from the linear IgA deposition of linear IgA bullous dermatosis.

Question 39Dermatopathology and Diagnostic Techniques (dermoscopy, patch testing, laboratory and molecular diagnostics)

A skin biopsy for suspected cutaneous lymphoma should ideally be processed and interpreted with which approach?

  1. Electron microscopy alone
  2. Polarized light examination
  3. Only routine hematoxylin-eosin staining
  4. Immunophenotyping plus molecular clonality studies Correct answer.

Explanation

Diagnosis of cutaneous lymphoma requires correlation of histology with immunophenotyping (immunohistochemistry or flow cytometry) and often molecular assessment of T-cell or B-cell clonality. Routine histology alone is frequently insufficient because reactive infiltrates can mimic lymphoma.

Question 40Dermatopathology and Diagnostic Techniques (dermoscopy, patch testing, laboratory and molecular diagnostics)

Which molecular technique is most commonly used to assess T-cell receptor gene rearrangement in suspected mycosis fungoides?

  1. Polymerase chain reaction amplification of TCR gene rearrangements Correct answer.
  2. Karyotyping
  3. Serum protein electrophoresis
  4. Fluorescence in situ hybridization for BCR-ABL

Explanation

PCR-based clonality testing amplifies rearranged T-cell receptor genes to detect a monoclonal population, supporting a diagnosis of mycosis fungoides when correlated with clinical and histologic findings. A monoclonal result must be interpreted cautiously because benign clones can occur.

Question 41Dermatopathology and Diagnostic Techniques (dermoscopy, patch testing, laboratory and molecular diagnostics)

Which finding on a potassium hydroxide preparation supports a diagnosis of pityriasis versicolor?

  1. Broad non-septate hyphae with right-angle branching
  2. Septate branching hyphae with arthroconidia in a 'spaghetti and meatballs' pattern Correct answer.
  3. Acantholytic cells with multinucleation
  4. Budding yeasts with pseudohyphae in pseudomembranes

Explanation

Malassezia in skin scrapings appears as short hyphae with round spores, described as 'spaghetti and meatballs.' This reflects the dimorphic yeast-to-hyphal transition seen in pityriasis versicolor.

Question 42Dermatopathology and Diagnostic Techniques (dermoscopy, patch testing, laboratory and molecular diagnostics)

A Tzanck smear from the base of a vesicle shows multinucleated giant keratinocytes with margination of chromatin. This finding most supports infection by which agent?

  1. Candida albicans
  2. Herpes simplex virus Correct answer.
  3. Staphylococcus aureus
  4. Varicella-zoster virus

Explanation

Multinucleated giant cells with chromatin margination and molding are cytopathic effects of herpesviruses; Tzanck smear cannot reliably distinguish herpes simplex from varicella-zoster, so both are compatible. The finding reflects viral-induced keratinocyte fusion.

Question 43Dermatopathology and Diagnostic Techniques (dermoscopy, patch testing, laboratory and molecular diagnostics)

Wood's lamp examination of a hypopigmented macule shows accentuation of depigmentation with bright blue-white fluorescence. This finding is most consistent with which disorder?

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

Explanation

In vitiligo the loss of melanin allows dermal collagen to fluoresce brightly under Wood's lamp, making depigmented areas stand out sharply. Disorders with partial melanin loss show less accentuation.

Question 44Dermatopathology and Diagnostic Techniques (dermoscopy, patch testing, laboratory and molecular diagnostics)

Which histologic feature best distinguishes a lichenoid tissue reaction from a spongiotic dermatitis?

  1. Parakeratosis with neutrophils in the stratum corneum
  2. Dermal mucin deposition
  3. Intraepidermal vesiculation with eosinophils
  4. Band-like lymphocytic infiltrate obscuring the dermoepidermal junction Correct answer.

Explanation

Lichenoid reactions are defined by a band-like lymphocytic infiltrate hugging the dermoepidermal junction with basal cell damage and apoptotic keratinocytes. Spongiotic dermatitis instead shows intercellular edema within the epidermis.

Question 45Dermatopathology and Diagnostic Techniques (dermoscopy, patch testing, laboratory and molecular diagnostics)

A punch biopsy is planned for a suspected panniculitis. Which technique best preserves architecture for interpretation?

  1. Fine-needle aspiration
  2. Superficial shave biopsy
  3. Deep incisional or excisional biopsy including subcutaneous fat Correct answer.
  4. Curettage

Explanation

Panniculitis requires evaluation of the full thickness of subcutaneous fat, so a deep biopsy that includes adequate fat is needed to assess the lobular versus septal pattern and vessel involvement. Superficial sampling often yields nondiagnostic tissue.

Question 46Dermatopathology and Diagnostic Techniques (dermoscopy, patch testing, laboratory and molecular diagnostics)

In the histologic assessment of a melanocytic lesion, which feature most strongly suggests malignancy?

  1. Symmetric well-circumscribed architecture
  2. Uniform melanocytes with maturation in the dermis
  3. Nests of melanocytes confined to the dermoepidermal junction
  4. Pagetoid spread of atypical melanocytes into the upper epidermis Correct answer.

Explanation

Pagetoid scatter of atypical melanocytes into the upper epidermis is a major criterion for melanoma, reflecting disordered intraepidermal migration. Benign nevi typically show ordered nests and maturation with depth.

Question 47Dermatopathology and Diagnostic Techniques (dermoscopy, patch testing, laboratory and molecular diagnostics)

A patient with recurrent angioedema and no urticaria has a low C4 with a normal C1 inhibitor level. Which additional test is most useful to evaluate for hereditary angioedema with normal C1 inhibitor?

  1. Serum tryptase
  2. C1 inhibitor functional assay and genetic testing Correct answer.
  3. Erythrocyte sedimentation rate
  4. Skin prick test panel

Explanation

Hereditary angioedema with normal C1 inhibitor requires assessment of C1 inhibitor function and, where available, genetic testing for factor XII or other mutations. Functional assays and genetics help separate this entity from acquired and classic hereditary forms.

Question 48Dermatopathology and Diagnostic Techniques (dermoscopy, patch testing, laboratory and molecular diagnostics)

In dermoscopy of an amelanotic or hypopigmented lesion, which vascular pattern is most suggestive of amelanotic melanoma?

  1. Hairpin vessels surrounded by a white halo
  2. Comma vessels in a regular distribution
  3. Dotted vessels arranged uniformly in a patch
  4. Milky-red areas with irregular linear-irregular vessels Correct answer.

Explanation

Amelanotic melanoma often shows milky-red or pink structureless areas with irregular linear or polymorphous vessels. Uniform, monomorphic vessel patterns are more typical of benign lesions.

Question 49Dermatopathology and Diagnostic Techniques (dermoscopy, patch testing, laboratory and molecular diagnostics)

Which laboratory abnormality is most consistent with a diagnosis of dermatitis herpetiformis?

  1. Anti-transglutaminase IgA antibodies Correct answer.
  2. Elevated serum angiotensin-converting enzyme
  3. Positive antinuclear antibody
  4. Elevated serum IgE

Explanation

Dermatitis herpetiformis is associated with gluten-sensitive enteropathy, and most patients have circulating IgA antibodies against tissue transglutaminase or epidermal transglutaminase. Serology supports the diagnosis alongside direct immunofluorescence.

Question 50Dermatopathology and Diagnostic Techniques (dermoscopy, patch testing, laboratory and molecular diagnostics)

A skin biopsy is submitted for direct immunofluorescence. Which handling practice best preserves the immunoreactants?

  1. Storage at room temperature for 48 hours
  2. Boiling to remove background staining
  3. Immediate freezing or transport in Michel's medium Correct answer.
  4. Fixation in formalin before transport

Explanation

Direct immunofluorescence requires preservation of tissue-bound immunoglobulins and complement, best achieved by snap-freezing or placing the specimen in Michel's transport medium. Formalin fixation can denature antigens and reduce staining.