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Arab Board Dermatology Final study materials
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Arab Board Dermatology Final practice questions

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Question 1Basic science of skin and cutaneous immunology

Which epidermal cell type is the primary source of keratin and forms the stratified barrier of the skin?

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

Explanation

Keratinocytes constitute the majority of the epidermis and differentiate through spinous, granular and cornified layers to produce the keratinized barrier. The other cell types are minority populations with immune, pigmentary or sensory roles.

Question 2Basic science of skin and cutaneous immunology

The principal collagen type of the dermal extracellular matrix that provides tensile strength is:

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

Explanation

Type I collagen is the most abundant collagen in adult dermis and provides tensile strength; type III predominates in early wound repair and fetal skin. Type IV is a basement membrane component and type VII forms anchoring fibrils.

Question 3Basic science of skin and cutaneous immunology

Which layer of the epidermis is characterised by cells containing keratohyalin granules and lamellar (Odland) bodies?

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

Explanation

The stratum granulosum contains keratohyalin granules and lamellar bodies that discharge lipid into the intercellular space to form the barrier. The basal layer holds proliferative cells and the corneum is the anucleate outer layer.

Question 4Basic science of skin and cutaneous immunology

A patient with recurrent pyogenic skin infections is found to have defective neutrophil oxidative killing. Which enzyme is most directly implicated?

  1. Superoxide dismutase
  2. Catalase
  3. NADPH oxidase Correct answer.
  4. Myeloperoxidase

Explanation

NADPH oxidase generates superoxide in the respiratory burst, and its deficiency causes chronic granulomatous disease with recurrent bacterial and fungal infections. Myeloperoxidase deficiency is usually milder, and catalase and superoxide dismutase are antioxidant enzymes.

Question 5Basic science of skin and cutaneous immunology

Which cell is the principal antigen-presenting cell of the epidermis for initiating T-cell responses to cutaneous antigens?

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

Explanation

Langerhans cells are epidermal dendritic cells that capture antigen and migrate to regional lymph nodes to present it to T cells. Keratinocytes can produce cytokines but are weak professional antigen presenters.

Question 6Basic science of skin and cutaneous immunology

The desmosomal cadherin that is the target of autoantibodies in pemphigus vulgaris is:

  1. Desmoglein 1
  2. Laminin 332
  3. BP180 (BPAG2)
  4. Desmoglein 3 Correct answer.

Explanation

Pemphigus vulgaris is characterised by autoantibodies against desmoglein 3, leading to suprabasal acantholysis and mucosal-predominant blistering. Desmoglein 1 is the target in pemphigus foliaceus, while BP180 and laminin 332 are hemidesmosomal proteins.

Question 7Basic science of skin and cutaneous immunology

A 30-year-old develops tense subepidermal blisters with linear IgG and C3 along the basement membrane zone. Which structure is primarily disrupted?

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

Explanation

Tense subepidermal blisters with linear basement membrane deposition reflect disruption of hemidesmosomal adhesion between basal keratinocytes and the basement membrane, as in bullous pemphigoid. Desmosomes mediate intercellular adhesion, and tight and gap junctions serve barrier and communication functions.

Question 8Basic science of skin and cutaneous immunology

Which skin-resident T-cell population is enriched in the epidermis and provides rapid local immune surveillance?

  1. Memory T cells expressing CD8 and skin-homing receptors Correct answer.
  2. Naive CD4 T cells
  3. Regulatory B cells
  4. Natural killer T cells of the dermis only

Explanation

The epidermis contains a resident memory T-cell population, often CD8+, that persists long-term and responds rapidly to local antigen re-exposure. Naive T cells recirculate through lymphoid tissue rather than residing in skin.

Question 9Basic science of skin and cutaneous immunology

Which cytokine is central to the differentiation of naive CD4 T cells into the Th17 subset implicated in psoriasis?

  1. IL-13
  2. IL-4
  3. IL-5
  4. IL-23 Correct answer.

Explanation

IL-23 drives Th17 differentiation and maintenance, and the IL-23/Th17 axis is a key target in psoriasis therapy. IL-4 and IL-13 drive Th2 responses, and IL-5 supports eosinophil biology.

Question 10Basic science of skin and cutaneous immunology

In the skin, which immunoglobulin class is most associated with immediate-type hypersensitivity reactions such as urticaria?

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

Explanation

IgE binds mast cell Fc receptors and triggers degranulation on antigen cross-linking, producing immediate wheal-and-flare reactions. IgG and IgM mediate complement-dependent and cytotoxic reactions, and IgA predominates in mucosal secretions.

Question 11Basic science of skin and cutaneous immunology

Which adhesion molecule on T cells mediates rolling along dermal endothelial cells during skin homing?

  1. Integrin alpha-4 beta-7
  2. ICAM-1
  3. L-selectin Correct answer.
  4. PECAM-1

Explanation

Selectins, including L-selectin on leukocytes, mediate the weak rolling interaction with endothelial ligands before firm integrin-dependent adhesion. ICAM-1 and PECAM-1 participate in firm adhesion and transmigration rather than rolling.

Question 12Basic science of skin and cutaneous immunology

The cutaneous lymphocyte antigen (CLA) on T cells functions by binding which endothelial ligand to promote entry into skin?

  1. E-selectin Correct answer.
  2. MAdCAM-1
  3. P-selectin glycoprotein ligand-1
  4. VCAM-1

Explanation

CLA is a carbohydrate epitope that binds E-selectin on dermal venules, directing skin-homing T cells into the skin. MAdCAM-1 supports gut homing, and VCAM-1 binds integrin alpha-4 beta-1.

Question 13Basic science of skin and cutaneous immunology

Which antimicrobial peptide is produced by keratinocytes and contributes to innate cutaneous defence?

  1. Complement C3b
  2. Fibrinogen
  3. Immunoglobulin G
  4. Beta-defensin Correct answer.

Explanation

Beta-defensins are cationic antimicrobial peptides secreted by keratinocytes and other epithelial cells that disrupt microbial membranes. IgG, C3b and fibrinogen are plasma proteins with immune or clotting roles rather than epithelial antimicrobial peptides.

Question 14Basic science of skin and cutaneous immunology

Melanin synthesis in melanocytes requires which copper-dependent enzyme for the conversion of tyrosine to dopaquinone?

  1. Phenylalanine hydroxylase
  2. Tyrosinase Correct answer.
  3. Catalase
  4. Dopamine beta-hydroxylase

Explanation

Tyrosinase is the rate-limiting copper-dependent enzyme that hydroxylates tyrosine to DOPA and oxidises it to dopaquinone in melanogenesis. The other enzymes act in unrelated metabolic pathways.

Question 15Basic science of skin and cutaneous immunology

Which epidermal growth factor receptor ligand is important for keratinocyte proliferation and is targeted by drugs causing acneiform eruptions?

  1. TGF-beta
  2. VEGF
  3. EGF Correct answer.
  4. IL-10

Explanation

EGFR signalling drives keratinocyte proliferation and survival, and EGFR inhibitors commonly produce acneiform follicular eruptions. VEGF acts on vasculature, TGF-beta is largely growth-inhibitory in epithelium, and IL-10 is immunosuppressive.

Question 16Basic science of skin and cutaneous immunology

A defect in the gene encoding filaggrin most strongly predisposes to which condition?

  1. Atopic dermatitis Correct answer.
  2. Pemphigus vulgaris
  3. Psoriasis
  4. Vitiligo

Explanation

Loss-of-function filaggrin mutations impair epidermal barrier formation and are a major risk factor for atopic dermatitis and ichthyosis vulgaris. The other conditions have different genetic or autoimmune bases.

Question 17Basic science of skin and cutaneous immunology

Which feature best distinguishes the lamina lucida from the lamina densa in the cutaneous basement membrane zone?

  1. The lamina lucida is electron-lucent and contains anchoring filaments Correct answer.
  2. The lamina densa lies between the basal keratinocyte membrane and the lamina lucida
  3. The lamina lucida contains type IV collagen as its main component
  4. The lamina densa is electron-lucent and contains laminin 332

Explanation

On electron microscopy the lamina lucida is the pale zone beneath the basal cell containing anchoring filaments such as laminin 332, while the lamina densa is the electron-dense layer rich in type IV collagen. This distinction underpins the level of split in blistering diseases.

Question 18Basic science of skin and cutaneous immunology

Which complement component deficiency is classically associated with recurrent Neisserial infections and also predisposes to cutaneous vasculitis?

  1. C5 Correct answer.
  2. C2
  3. C3
  4. C1 inhibitor

Explanation

Terminal complement components such as C5 to C9 are required for membrane attack complex formation, and their deficiency predisposes to recurrent Neisserial infection. C1 inhibitor deficiency causes hereditary angioedema, and C2 deficiency is linked more to immune-complex disease.

Question 19Basic science of skin and cutaneous immunology

Which sensory receptor cell in the epidermis is associated with slowly adapting mechanoreceptors and Merkel discs?

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

Explanation

Merkel cells form synapse-like contacts with sensory nerve endings to transduce sustained mechanical stimuli. The other epidermal cells subserve immune, pigmentary or structural functions.

Question 20Basic science of skin and cutaneous immunology

In cutaneous wound healing, which cell type is the principal source of the collagen that reconstitutes the dermal defect during granulation tissue formation?

  1. Keratinocyte
  2. Endothelial cell
  3. Fibroblast Correct answer.
  4. Mast cell

Explanation

Fibroblasts migrate into the wound, proliferate and synthesise collagen and matrix to form granulation tissue and the subsequent scar. Keratinocytes re-epithelialise, endothelial cells form new vessels and mast cells modulate inflammation.

Question 21Papulosquamous and eczematous disorders

A 28-year-old man has well-demarcated erythematous plaques with silvery-white scale on both elbows and knees, and his nails show pitting. Which diagnosis is most likely?

  1. Atopic dermatitis
  2. Lichen planus
  3. Pityriasis rosea
  4. Plaque psoriasis Correct answer.

Explanation

Well-demarcated plaques with silvery scale over extensor surfaces plus nail pitting are the classic presentation of chronic plaque psoriasis. Atopic dermatitis favors flexures, lichen planus is violaceous and flexural, and pityriasis rosea follows a herald-patch distribution on the trunk.

Question 22Papulosquamous and eczematous disorders

Which clinical feature most strongly supports a diagnosis of atopic dermatitis in a child?

  1. Chronic pruritus with flexural lichenification Correct answer.
  2. Grouped vesicles on an erythematous base
  3. Hypopigmented macules with fine branny scale
  4. Sharply demarcated annular plaques with central clearing

Explanation

Atopic dermatitis is defined by chronic pruritus and a flexural distribution with lichenification in older children. Annular plaques with central clearing suggest tinea, hypopigmented scaly macules suggest pityriasis alba or tinea versicolor, and grouped vesicles suggest herpes or contact dermatitis.

Question 23Papulosquamous and eczematous disorders

A patient has pruritic, violaceous, flat-topped papules on the flexor wrists with fine white lines on the surface. Which finding is most characteristic of this condition?

  1. Herald patch
  2. Koebner phenomenon with silvery scale
  3. Auspitz sign
  4. Wickham striae Correct answer.

Explanation

Wickham striae are fine white reticular lines on the surface of lichen planus lesions. Auspitz sign and silvery scale belong to psoriasis, and a herald patch belongs to pityriasis rosea.

Question 24Papulosquamous and eczematous disorders

A 35-year-old woman has a single oval salmon-colored patch on the trunk followed 1 week later by smaller similar lesions along the ribs in a christmas-tree pattern. What is the most likely diagnosis?

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

Explanation

A herald patch followed by smaller lesions distributed along skin cleavage lines in a christmas-tree pattern is classic for pityriasis rosea. Guttate psoriasis follows streptococcal infection with drop-like plaques, secondary syphilis involves palms and soles, and tinea corporis is annular with central clearing.

Question 25Papulosquamous and eczematous disorders

Which histologic finding is most characteristic of psoriasis?

  1. Subepidermal blister with linear IgA deposition
  2. Spongiosis with eosinophils in the epidermis
  3. Regular acanthosis with parakeratosis and Munro microabscesses Correct answer.
  4. Interface dermatitis with saw-tooth rete ridges

Explanation

Psoriasis shows regular acanthosis, parakeratosis, loss of the granular layer, and neutrophilic Munro microabscesses in the stratum corneum. Spongiosis with eosinophils suggests eczema, saw-tooth rete ridges suggest lichen planus, and subepidermal blistering suggests bullous disease.

Question 26Papulosquamous and eczematous disorders

A 6-year-old boy has intensely pruritic, ill-defined erythematous patches on the cheeks and extensor arms, with a personal history of asthma. What is the most appropriate first-line topical treatment?

  1. Topical antibiotic ointment
  2. Topical calcineurin inhibitor as monotherapy
  3. Topical antifungal cream
  4. Medium-potency topical corticosteroid Correct answer.

Explanation

Atopic dermatitis flares are treated first with topical corticosteroids of appropriate potency for the site and age. Calcineurin inhibitors are useful for sensitive sites or steroid-sparing but are not first-line for an active flare, and antifungals or antibiotics do not treat eczema.

Question 27Papulosquamous and eczematous disorders

Which statement about the Auspitz sign is correct?

  1. It is a white line appearing after scratching in dermographism
  2. It is the Koebner response in lichen planus
  3. It is pinpoint bleeding after removal of scale in psoriasis Correct answer.
  4. It is the honey-colored crust of impetigo

Explanation

Auspitz sign refers to pinpoint bleeding when psoriatic scale is removed, reflecting elongated dermal papillae close to the surface. It is not the white dermographism line, honey-colored crust, or Koebner phenomenon.

Question 28Papulosquamous and eczematous disorders

A patient with widespread plaque psoriasis involving 20% body surface area has failed topical therapy. Which systemic agent requires screening for latent tuberculosis before initiation?

  1. Oral methotrexate
  2. Biologic TNF-alpha inhibitor Correct answer.
  3. Topical coal tar
  4. Narrowband UVB phototherapy

Explanation

TNF-alpha inhibitors carry a risk of reactivating latent tuberculosis, so screening is mandatory before starting. Methotrexate requires hepatic and hematologic monitoring, phototherapy requires skin cancer surveillance, and coal tar is topical with no TB screening requirement.

Question 29Papulosquamous and eczematous disorders

Which condition is most strongly associated with the Koebner phenomenon?

  1. Seborrheic dermatitis
  2. Pityriasis rosea
  3. Tinea corporis
  4. Lichen planus Correct answer.

Explanation

The Koebner phenomenon, appearance of lesions at sites of trauma, is classically seen in lichen planus and psoriasis. Pityriasis rosea, tinea corporis, and seborrheic dermatitis do not show this response.

Question 30Papulosquamous and eczematous disorders

A 40-year-old man has greasy yellowish scales on the scalp, eyebrows, and nasolabial folds. Which diagnosis is most likely?

  1. Discoid eczema
  2. Psoriasis vulgaris
  3. Seborrheic dermatitis Correct answer.
  4. Lichen simplex chronicus

Explanation

Greasy yellowish scale in sebaceous-rich areas such as the scalp, eyebrows, and nasolabial folds is typical of seborrheic dermatitis. Psoriasis has thicker silvery scale, lichen simplex chronicus is a localized lichenified plaque from scratching, and discoid eczema is coin-shaped on the limbs.

Question 31Papulosquamous and eczematous disorders

A 50-year-old woman has a chronic, intensely pruritic, lichenified plaque on the posterior neck. She reports years of rubbing the area. What is the most likely diagnosis?

  1. Psoriasis
  2. Lichen simplex chronicus Correct answer.
  3. Lichen planus
  4. Tinea corporis

Explanation

A single lichenified plaque in an accessible area produced by chronic rubbing is lichen simplex chronicus. Lichen planus is violaceous and papular, psoriasis has silvery scale, and tinea corporis is annular with active borders.

Question 32Papulosquamous and eczematous disorders

Which feature best distinguishes guttate psoriasis from pityriasis rosea?

  1. Presence of a herald patch
  2. Distribution along skin cleavage lines
  3. Self-limited course over 6 to 8 weeks
  4. Preceding streptococcal throat infection with drop-like plaques Correct answer.

Explanation

Guttate psoriasis follows a streptococcal infection and presents as small drop-like plaques, often with silvery scale. A herald patch, cleavage-line distribution, and a self-limited course are features of pityriasis rosea.

Question 33Papulosquamous and eczematous disorders

Which topical agent is most appropriate for a patient with psoriasis who wants to avoid corticosteroids and phototherapy?

  1. Calcipotriol Correct answer.
  2. Mupirocin
  3. Clotrimazole
  4. Hydrocortisone 1%

Explanation

Calcipotriol is a vitamin D analogue that is effective for plaque psoriasis and is steroid-sparing. Hydrocortisone is a low-potency steroid, clotrimazole is an antifungal, and mupirocin is an antibiotic.

Question 34Papulosquamous and eczematous disorders

A patient with atopic dermatitis develops rapidly spreading punched-out erosions with grouped vesicles and a positive Tzanck smear. What is the most likely complication?

  1. Eczema herpeticum Correct answer.
  2. Allergic contact dermatitis
  3. Secondary impetiginization
  4. Kaposi varicelliform eruption due to smallpox

Explanation

Eczema herpeticum is a disseminated herpes simplex infection complicating atopic dermatitis, producing punched-out erosions and vesicles with a positive Tzanck smear. Impetigo shows honey-colored crusts, contact dermatitis is localized to exposure, and smallpox is not the relevant pathogen.

Question 35Papulosquamous and eczematous disorders

A 60-year-old man has well-demarcated erythematous plaques in the axillae and groin with minimal scale. Which form of psoriasis is most likely?

  1. Erythrodermic psoriasis
  2. Pustular psoriasis
  3. Guttate psoriasis
  4. Inverse psoriasis Correct answer.

Explanation

Inverse psoriasis affects intertriginous areas and lacks the typical silvery scale because of moisture. Guttate psoriasis is drop-like, pustular psoriasis shows pustules, and erythrodermic psoriasis involves nearly the entire body surface.

Question 36Papulosquamous and eczematous disorders

Which nail finding is most characteristic of psoriasis?

  1. Pincer-shaped lateral nail plates
  2. Subungual hyperkeratosis with yellow streaks
  3. Transverse ridging after illness
  4. Oil-drop discoloration with onycholysis Correct answer.

Explanation

Oil-drop (salmon) patches with onycholysis are classic nail signs of psoriasis. Transverse ridging relates to illness or trauma, yellow streaks suggest onychomycosis, and pincer nails are a morphologic variant unrelated to psoriasis.

Question 37Papulosquamous and eczematous disorders

Which statement about the natural history of pityriasis rosea is correct?

  1. It usually resolves spontaneously within 6 to 8 weeks Correct answer.
  2. It progresses to chronic plaques in most patients
  3. It requires systemic antibiotics for cure
  4. It is highly contagious through casual contact

Explanation

Pityriasis rosea is typically self-limited and resolves in 6 to 8 weeks, though it may recur. It does not progress to chronic plaques, is not treated with antibiotics, and is not highly contagious.

Question 38Papulosquamous and eczematous disorders

A 30-year-old woman has pruritic violaceous papules on the oral mucosa and flexor wrists. Which associated condition should be screened for?

  1. Hepatitis C infection Correct answer.
  2. Iron deficiency anemia
  3. Hypothyroidism
  4. Latent tuberculosis

Explanation

Lichen planus, particularly with mucosal involvement, is associated with hepatitis C infection, and screening is often recommended. Latent TB screening relates to TNF inhibitors, iron deficiency to koilonychia or glossitis, and hypothyroidism is not a classic association.

Question 39Papulosquamous and eczematous disorders

Which feature is most consistent with a diagnosis of chronic hand eczema rather than hand psoriasis?

  1. Pitting of the fingernails
  2. Family history of psoriasis
  3. Ill-defined borders with vesiculation and fissuring Correct answer.
  4. Sharply demarcated plaques with silvery scale

Explanation

Chronic hand eczema shows ill-defined borders, vesiculation, and fissuring, often with a history of atopy. Sharply demarcated plaques with silvery scale, nail pitting, and a family history of psoriasis favor hand psoriasis.

Question 40Papulosquamous and eczematous disorders

A patient with psoriasis is started on methotrexate. Which monitoring is most important?

  1. Thyroid function tests
  2. Serum calcium and phosphate
  3. Liver function tests and complete blood count Correct answer.
  4. Serum amylase and lipase

Explanation

Methotrexate can cause hepatic toxicity and bone marrow suppression, so liver function tests and complete blood counts are monitored regularly. Calcium, thyroid, and pancreatic enzymes are not the relevant parameters.

Question 41Cutaneous infections and infestations

A 7-year-old child presents with multiple honey-coloured crusted lesions around the nose and mouth. Gram stain of the exudate shows gram-positive cocci in clusters. Which organism is the most likely cause?

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

Explanation

Non-bullous impetigo is most often caused by Staphylococcus aureus, either alone or with Streptococcus pyogenes, and the classic lesion is a honey-coloured crust. Gram-positive cocci in clusters support a staphylococcal cause. Streptococci would appear in chains.

Question 42Cutaneous infections and infestations

A 4-year-old has flaccid bullae with clear fluid and a collarette of scale on the trunk. Gram stain of bulla fluid shows gram-positive cocci. Which mechanism best explains the blister formation?

  1. Epidermolytic toxin acting at the zona granulosa Correct answer.
  2. Direct invasion of the basal layer with acantholysis
  3. Type IV hypersensitivity to bacterial antigen
  4. IgA-mediated complement activation in dermal vessels

Explanation

Bullous impetigo is caused by epidermolytic (exfoliative) toxins that cleave desmoglein-1 in the superficial epidermis, producing a subcorneal split and flaccid bullae. This is a toxin-mediated rather than immune-mediated process.

Question 43Cutaneous infections and infestations

A 12-year-old presents with a well-demarcated annular plaque on the cheek with central clearing and a raised scaly edge. KOH mount shows septate hyphae. What is the most appropriate first-line treatment?

  1. Topical terbinafine Correct answer.
  2. Topical hydrocortisone
  3. Oral itraconazole
  4. Oral griseofulvin

Explanation

Tinea faciei is a superficial dermatophyte infection, and limited disease responds to topical antifungal agents such as terbinafine. Oral therapy is reserved for extensive, hair-bearing, or recalcitrant disease.

Question 44Cutaneous infections and infestations

An 8-year-old has patchy alopecia with broken hairs and black dots on the scalp. Wood's lamp shows no fluorescence. Which organism is the most likely cause?

  1. Microsporum audouinii
  2. Trichophyton rubrum
  3. Microsporum canis
  4. Trichophyton tonsurans Correct answer.

Explanation

Trichophyton tonsurans causes endothrix infection with broken hairs and black dots and does not fluoresce under Wood's lamp. Microsporum species classically produce green fluorescence, but T. tonsurans is now the commonest cause of tinea capitis in many regions.

Question 45Cutaneous infections and infestations

A patient has extensive tinea corporis with multiple annular plaques. Which oral agent is a first-line systemic antifungal for dermatophyte infection?

  1. Amphotericin B
  2. Terbinafine Correct answer.
  3. Nystatin
  4. Fluconazole

Explanation

Terbinafine is a first-line oral agent for dermatophyte infections because it is fungicidal against dermatophytes and achieves good skin and nail levels. Itraconazole is an alternative.

Question 46Cutaneous infections and infestations

A patient has hypopigmented scaly macules on the upper trunk with a positive KOH showing short hyphae and spores in a 'spaghetti and meatballs' pattern. What is the most appropriate treatment for extensive disease?

  1. Topical clotrimazole
  2. Oral flucloxacillin
  3. Oral itraconazole Correct answer.
  4. Topical acyclovir

Explanation

Pityriasis versicolor is caused by Malassezia, and extensive or recurrent disease is treated with oral azoles such as itraconazole or fluconazole. Topical agents are used for limited disease.

Question 47Cutaneous infections and infestations

A 30-year-old presents with an itchy, scaly annular plaque on the sole. KOH shows hyphae. Which feature best distinguishes tinea pedis from contact dermatitis?

  1. Bilateral symmetrical involvement
  2. Response to topical corticosteroids
  3. Presence of vesicles on the instep
  4. Presence of fungal hyphae on KOH microscopy Correct answer.

Explanation

Demonstration of septate branching hyphae on KOH is the definitive feature that separates dermatophyte infection from eczematous processes. Clinical features alone can overlap, so mycological confirmation is important.

Question 48Cutaneous infections and infestations

A patient has a chronic scaly eruption of the groin with an active border. Which topical agent is appropriate first-line therapy for tinea cruris?

  1. Topical permethrin
  2. Topical terbinafine Correct answer.
  3. Topical betamethasone
  4. Topical mupirocin

Explanation

Topical allylamines such as terbinafine are effective first-line treatment for localized tinea cruris. Corticosteroids alone would worsen the infection.

Question 49Cutaneous infections and infestations

A 60-year-old diabetic presents with multiple grouped vesicles on an erythematous base in a dermatomal distribution. Which pathogen is responsible?

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

Explanation

Herpes zoster results from reactivation of latent varicella-zoster virus in a dorsal root ganglion, producing dermatomal grouped vesicles. Antiviral therapy is most effective when started within 72 hours of rash onset.

Question 50Cutaneous infections and infestations

A pregnant woman at 30 weeks has a primary genital HSV infection. What is the most important reason for suppressive antiviral therapy near term?

  1. To prevent post-herpetic neuralgia
  2. To reduce the risk of neonatal herpes transmission Correct answer.
  3. To prevent cervical carcinoma
  4. To eradicate latent virus from the sacral ganglion

Explanation

Suppressive acyclovir from 36 weeks reduces recurrences at delivery and thereby lowers the risk of neonatal herpes, which carries high mortality and morbidity. Antivirals do not eradicate latent virus.