NEET PG dermatology questions

In psoriasis, the rete ridges are elongated and the suprapapillary epidermis is markedly thinned, while the dermal papillae are edematous and contain dilated, tortuous capillaries that come to lie very close to the surface. Scraping off the scale removes this thin covering and ruptures the superficial capillaries, producing pinpoint bleeding, the Auspitz sign. This sign helps clinically distinguish psoriasis from other papulosquamous disorders. It is not seen in conditions with a thick, intact suprapapillary epidermis.

• B. A lymphocytic band at the junction does not by itself explain pinpoint bleeding on scale removal.
• C. A thick suprapapillary epidermis would protect the capillaries and prevent bleeding on scraping.
• D. This describes a subepidermal blistering mechanism, not the pinpoint bleeding of the Auspitz sign.

The Koebner (isomorphic response) phenomenon refers to the development of new lesions of a pre-existing skin disease at the site of trauma, such as scratches, scars, sunburn, or surgical incisions. It is classically described in psoriasis but also occurs in lichen planus, vitiligo, and lichen nitidus. The traumatized skin undergoes the same pathological changes as the primary dermatosis within one to two weeks of injury. Recognizing this phenomenon is important for counseling patients to avoid unnecessary skin trauma.

• A. Nikolsky sign refers to epidermal shearing seen in pemphigus and toxic epidermal necrolysis, not trauma-induced new lesions.
• C. Darier sign is urtication on stroking a lesion, seen in mastocytosis/urticaria pigmentosa.
• D. Dermographism is a wheal response of normal-appearing skin to firm stroking, not the reproduction of an existing disease's lesions.

The oil drop sign (also called salmon patch) is a yellowish-brown, translucent discoloration seen under the nail plate in psoriasis, caused by glycoprotein deposition and parakeratosis within the nail bed, mimicking a drop of oil. Along with nail pitting, it is one of the most characteristic nail findings in psoriasis and helps support the diagnosis when combined with typical skin plaques. Other psoriatic nail changes include onycholysis, subungual hyperkeratosis, and splinter hemorrhages. These nail findings are also more common in patients who go on to develop psoriatic arthritis.

• A. Terry nails show whitening of most of the nail plate with a narrow distal pink band, classically associated with cirrhosis.
• B. Beau lines are transverse grooves from temporary disruption of nail matrix growth, typically due to systemic illness, not psoriasis-specific.
• C. Mees lines are transverse white bands seen in arsenic poisoning, not a feature of psoriasis.

Munro microabscesses are collections of neutrophils within the stratum corneum, a classic histological feature of psoriasis, resulting from neutrophil migration from dilated dermal papillary capillaries through the thinned epidermis. When these neutrophilic collections occur within the stratum spinosum instead, they are called spongiform pustules of Kogoj. Together with parakeratosis, regular acanthosis, and loss of the granular layer, these findings confirm the diagnosis of psoriasis on biopsy. This is distinct from neutrophilic or lymphocytic collections seen in other dermatoses.

• A. Pautrier microabscesses are collections of atypical lymphocytes in the epidermis, seen in mycosis fungoides, not psoriasis.
• B. Civatte bodies are apoptotic keratinocytes seen at the dermo-epidermal junction in lichen planus.
• C. Caseating granulomas are seen in tuberculosis and other granulomatous diseases, not psoriasis.

Folic acid supplementation, typically given on days other than the methotrexate dosing day, reduces methotrexate-induced gastrointestinal side effects and myelosuppression without significantly reducing its efficacy in psoriasis. Methotrexate works as a folate antagonist by inhibiting dihydrofolate reductase, so replacing folate helps mitigate toxicity related to this mechanism while sparing the antiproliferative effect on keratinocytes. Regular monitoring of complete blood count and liver function is also required during therapy because of the risks of bone marrow suppression and hepatotoxicity. Methotrexate remains a standard systemic option for moderate to severe psoriasis as per Indian and international guidelines.

• A. Iron supplementation does not address methotrexate's antifolate-mediated toxicity.
• B. Vitamin B12 is not used to reduce methotrexate toxicity; this is not standard practice.
• D. Pyridoxine is used to prevent isoniazid-induced neuropathy, unrelated to methotrexate toxicity.

Pityriasis rosea classically begins with a single larger herald patch, followed one to two weeks later by multiple smaller oval, salmon-colored, scaly lesions distributed along skin cleavage lines on the trunk, producing the characteristic 'Christmas tree' pattern on the back. It is thought to be associated with reactivation of human herpesvirus 6 or 7 and is usually self-limiting, resolving within six to eight weeks without scarring. Mild prodromal symptoms such as malaise or headache may precede the rash. Recognizing the herald patch and the collarette of scale at the lesion margins helps distinguish it from other papulosquamous conditions.

• B. Tinea corporis presents as annular, pruritic plaques with an active, scaly advancing border, not oval lesions aligned with skin tension lines.
• C. Guttate psoriasis presents as multiple small drop-like papules, usually following streptococcal pharyngitis, without a preceding herald patch.
• D. Secondary syphilis presents with a widespread papulosquamous rash including palms and soles, not a herald patch followed by a Christmas tree pattern.

Lichen planus shows a dense, band-like (lichenoid) lymphocytic infiltrate hugging the dermo-epidermal junction, causing a characteristic saw-tooth appearance of the rete ridges, along with hyperkeratosis, wedge-shaped hypergranulosis, and degeneration of basal keratinocytes seen as Civatte bodies. The fine white lacy network visible on the papules clinically corresponds to Wickham striae, caused by irregular hypergranulosis and thickening of the granular layer. These violaceous, pruritic, polygonal papules affecting flexor wrists are a classic presentation. Together, the clinical and histological pictures are diagnostic of lichen planus.

• A. Suprabasal acantholysis describes pemphigus vulgaris, an autoimmune blistering disease, not lichen planus.
• C. A granulomatous infiltrate suggests conditions like sarcoidosis or granuloma annulare, not lichen planus.
• D. This describes the histology of psoriasis, including Munro microabscesses, not lichen planus.

The clinical picture of flaccid bullae, oral mucosal erosions, and a positive Nikolsky sign (shearing of apparently normal skin with lateral pressure) is classic for pemphigus vulgaris. The underlying pathology is acantholysis due to loss of desmosomal adhesion between keratinocytes, which occurs just above the basal layer, producing a suprabasal intraepidermal split. This leaves a single row of basal keratinocytes attached to the basement membrane, described histologically as a "row of tombstones." The positive Nikolsky sign reflects this fragile intraepidermal plane of separation.

• A. A subcorneal split is characteristic of pemphigus foliaceus, a more superficial variant with crusted lesions and minimal mucosal involvement.
• B. A subepidermal split at the dermo-epidermal junction is seen in bullous pemphigoid, which presents with tense bullae and a negative Nikolsky sign.
• D. Intradermal splitting does not occur in pemphigus; the pathology is entirely intraepidermal.

Pemphigus vulgaris is caused by circulating IgG autoantibodies directed against desmoglein 3, a desmosomal cadherin responsible for keratinocyte adhesion in the deeper epidermis and mucosa (with desmoglein 1 also involved in mucocutaneous disease). ELISA for anti-desmoglein 3 (and desmoglein 1) antibodies is the most specific and sensitive test to confirm the diagnosis and correlates well with disease activity, making it useful for monitoring treatment response. Direct immunofluorescence confirms the intercellular IgG deposition pattern but does not identify the specific antigen. ELISA has largely replaced indirect immunofluorescence titers for quantitative monitoring in clinical practice.

• A. Routine histopathology shows suprabasal acantholysis but cannot identify the specific target antigen.
• C. Anti-BP180 antibodies are the target in bullous pemphigoid, a subepidermal blistering disease, not pemphigus vulgaris.
• D. Salt-split skin immunofluorescence is used to differentiate subepidermal bullous diseases like bullous pemphigoid and epidermolysis bullosa acquisita, not pemphigus.

Bullous pemphigoid typically occurs in elderly patients and presents with tense, intact subepidermal bullae because the full thickness of the epidermis remains attached to the blister roof. The Nikolsky sign is negative, and mucosal involvement, if present at all, is mild and late, unlike pemphigus vulgaris where oral erosions are often the presenting feature. This is because bullous pemphigoid results from a subepidermal split due to antibodies against hemidesmosomal proteins, giving stronger blister roofs compared to the intraepidermal acantholytic split in pemphigus vulgaris. These clinical clues allow bedside differentiation before immunopathology confirms the diagnosis.

• B. Early and predominant oral mucosal involvement is typical of pemphigus vulgaris, not bullous pemphigoid.
• C. A positive Nikolsky sign is seen in pemphigus, not bullous pemphigoid, which has a negative Nikolsky sign.
• D. Flaccid bullae that rupture easily are characteristic of pemphigus vulgaris due to the fragile intraepidermal split, not bullous pemphigoid.

Bullous pemphigoid is an autoimmune subepidermal blistering disease caused by IgG autoantibodies directed against BP180 (type XVII collagen) and BP230, components of the hemidesmosome that anchors basal keratinocytes to the underlying basement membrane. Antibody binding activates complement and recruits inflammatory cells, leading to dermo-epidermal separation and formation of a subepidermal, tense bulla. Direct immunofluorescence classically shows linear IgG and C3 deposition along the basement membrane zone, distinguishing it from the intercellular pattern of pemphigus. This mechanism explains why the blister roof contains the full thickness of epidermis, producing a tense, durable bulla.

• A. This describes the mechanism of lichen planus, not bullous pemphigoid.
• C. This describes dermatitis herpetiformis, which involves IgA deposition in dermal papillae with neutrophilic infiltration.
• D. This describes the mechanism of pemphigus vulgaris, which targets desmoglein 3 and produces an intraepidermal split.

Dermatitis herpetiformis is an intensely pruritic papulovesicular eruption that characteristically affects the extensor surfaces (elbows, knees, buttocks, scalp) and is strongly associated with gluten-sensitive enteropathy (celiac disease), even when gastrointestinal symptoms are mild or absent. Direct immunofluorescence of perilesional skin shows granular IgA deposits localized to the dermal papillae, which is diagnostic. The IgA antibodies are directed against epidermal transglutaminase and cross-react with gluten-derived peptides, linking the skin disease to the small bowel pathology. A gluten-free diet improves both the enteropathy and the skin lesions.

• A. Linear IgG deposition along the basement membrane is seen in bullous pemphigoid, not dermatitis herpetiformis, and malignancy association is not its hallmark feature.
• B. Intercellular IgG in a fishnet pattern is seen in pemphigus, and thymoma is associated with paraneoplastic pemphigus, not dermatitis herpetiformis.
• C. Linear IgA deposition along the basement membrane describes linear IgA bullous dermatosis, a distinct entity from dermatitis herpetiformis, which shows a granular papillary pattern.

Dapsone is the drug of choice for dermatitis herpetiformis and produces dramatic relief of pruritus and new blister formation within 24 to 48 hours, acting primarily by inhibiting neutrophil chemotaxis and function rather than by any direct effect on the IgA-mediated process. While a strict lifelong gluten-free diet is the definitive long-term management that addresses the underlying immune trigger and allows eventual tapering of dapsone, its benefit takes months to manifest, so dapsone bridges this gap. Patients on dapsone need screening for G6PD deficiency before starting therapy, as it can precipitate hemolysis, and regular monitoring for methemoglobinemia and hemolytic anemia during treatment.

• A. Doxycycline has no established role in the treatment of dermatitis herpetiformis.
• B. Azathioprine is not a first-line agent for dermatitis herpetiformis; it is occasionally used in resistant cases.
• C. Systemic corticosteroids are not preferred for dermatitis herpetiformis due to limited efficacy and long-term side effects compared to dapsone.

Systemic corticosteroids, typically oral prednisolone at a dose of 1 to 2 mg/kg/day, remain the first-line treatment for inducing remission in moderate to severe pemphigus vulgaris, rapidly suppressing autoantibody-mediated acantholysis and halting new blister formation. Steroid-sparing adjuvants such as azathioprine, mycophenolate mofetil, or rituximab are commonly added to allow steroid tapering and reduce long-term corticosteroid toxicity, with rituximab increasingly used as a first-line steroid-sparing agent in current guidelines. Topical therapy alone is inadequate given the extensive body surface area involved and the risk of fluid loss, infection, and sepsis from widespread erosions. Early, adequate systemic immunosuppression is critical since pemphigus vulgaris was almost universally fatal before corticosteroids became available.

• A. Dapsone is not first-line for pemphigus vulgaris; it has a role mainly in dermatitis herpetiformis and as an adjuvant in some pemphigus cases.
• C. Topical corticosteroids alone are insufficient for extensive disease involving 30% of body surface area and oral mucosa; systemic therapy is required.
• D. Intravenous immunoglobulin is used as an adjunct in refractory or severe cases, not as sole initial therapy in place of corticosteroids.

The Hanifin-Rajka criteria require an obligatory major feature of pruritus, combined with typical morphology (flexural lichenification in adults, facial/extensor involvement in infants) and a chronic or chronically relapsing course, plus a threshold number of minor features. Without pruritus and the characteristic flexural distribution, the diagnosis cannot be made regardless of other supportive findings. Raised IgE, eosinophilia, and family history of atopy are only minor or supportive criteria, not obligatory ones. This child's flexural eczema, itching, and chronicity fulfill the essential major criterion.

• B. Family history of atopy is a minor criterion, not an essential one.
• C. Eosinophilia is a minor supportive finding, not required for diagnosis.
• D. Raised IgE is a supportive minor criterion, not the obligatory feature.

The atopic triad classically refers to the co-occurrence of atopic dermatitis, allergic rhinitis, and bronchial asthma in the same individual or family, reflecting a shared underlying predisposition to IgE-mediated hypersensitivity. Many children with atopic dermatitis go on to develop allergic rhinitis and asthma later in childhood, a phenomenon termed the 'atopic march.' This progression is driven by Th2-skewed immune responses and barrier dysfunction. Recognizing this triad helps anticipate and screen for respiratory allergic disease in children with eczema.

• A. Though associated with atopy, this combination is not the classically described triad.
• C. These are allergic conditions but not part of the classic atopic triad.
• D. These can occur in atopic individuals but do not constitute the classic triad.

Patch test readings are graded using the International Contact Dermatitis Research Group scale. A strong positive (2+) reaction shows erythema, infiltration, and discrete papules confined to the test site, as described here, indicating a true allergic contact sensitization to nickel. A weak positive (1+) shows only faint erythema with slight infiltration, without papules. Irritant reactions typically show glazed erythema or a burning sensation that fades quickly and does not show infiltration or papules, while a doubtful reaction shows only macular erythema.

• A. A doubtful reaction shows faint macular erythema only, without infiltration or papules.
• B. A weak positive lacks papules and shows only mild erythema with faint infiltration.
• D. Irritant reactions are usually sharply marginated, fade quickly, and lack true infiltration or papules.

Toxic epidermal necrolysis (TEN) is defined by epidermal detachment involving more than 30% of total body surface area, as seen in this patient with 42% involvement. Stevens-Johnson syndrome involves less than 10% body surface area detachment, while 10-30% detachment is classified as SJS-TEN overlap. This classification is based on the extent of skin detachment and is clinically important because mortality and management intensity, including the threshold for burns-unit-level care, rise sharply with increasing body surface area involvement.

• A. Overlap SJS-TEN involves 10-30% detachment, less than this patient's 42%.
• C. Erythema multiforme major involves mucosal lesions with target lesions but minimal, not extensive, skin detachment.
• D. SJS involves less than 10% body surface area detachment, far less than seen here.

Carbamazepine is one of the most common and well-established causes of Stevens-Johnson syndrome and toxic epidermal necrolysis, particularly in patients carrying the HLA-B*1502 allele, which is prevalent in South and Southeast Asian populations. It is frequently used for trigeminal neuralgia and seizure disorders, and reactions typically occur within 1-3 weeks of starting therapy. Other classic offenders include allopurinol, sulfonamides, lamotrigine, and NSAIDs of the oxicam group. Screening for HLA-B*1502 before starting carbamazepine is recommended in high-risk populations.

• A. Gabapentin is rarely implicated in SJS/TEN compared to carbamazepine.
• B. Baclofen is not a recognized major cause of SJS/TEN.
• D. Amitriptyline is not a classic causative agent for SJS/TEN.

SCORTEN includes seven independent prognostic variables: age above 40 years, heart rate above 120/min, presence of malignancy, body surface area of epidermal detachment above 10%, serum urea above 10 mmol/L, serum bicarbonate below 20 mmol/L, and serum glucose above 14 mmol/L. Each parameter present scores one point, and the total score correlates with predicted mortality. C-reactive protein is a general inflammatory marker but is not part of the validated SCORTEN criteria. This score is calculated within the first 24 hours of admission for accurate prognostication.

• A. Serum bicarbonate below 20 mmol/L is a validated SCORTEN parameter.
• B. Serum glucose above 14 mmol/L is a validated SCORTEN parameter.
• C. Body surface area detachment above 10% is a validated SCORTEN parameter.

Acute urticaria results from degranulation of dermal mast cells, typically triggered by cross-linking of IgE bound to high-affinity FcεRI receptors following allergen exposure, as with the shellfish in this case. This releases histamine and other mediators such as leukotrienes and prostaglandins, causing vasodilation and increased vascular permeability, producing the characteristic transient, blanching, pruritic wheals. The short-lived nature of individual lesions, each resolving within 24 hours, reflects rapid mediator clearance and differentiates urticaria from vasculitic or immune-complex-mediated skin lesions. Antihistamines are therefore first-line treatment, as they block the histamine receptor-mediated effects.

• A. Immune complex deposition characterizes urticarial vasculitis, which presents with lesions lasting over 24 hours and residual pigmentation.
• C. Complement-mediated basal cell lysis is not the mechanism of urticaria.
• D. Cytotoxic T-cell-mediated keratinocyte apoptosis is seen in conditions like erythema multiforme, not urticaria.

Kerion is a severe inflammatory form of tinea capitis caused by a hypersensitivity reaction to zoophilic or geophilic dermatophytes (e.g., Trichophyton verrucosum, Microsporum canis), producing a boggy, pus-filled, tender swelling that can scar and cause permanent alopecia if untreated. It differs from the non-inflammatory grey patch and black dot patterns caused by anthropophilic species, which present with scaling and broken hairs without significant inflammation. Treatment requires systemic antifungals (griseofulvin or terbinafine) along with oral corticosteroids/antibiotics for secondary infection. Early recognition prevents scarring alopecia.

• A. Grey patch pattern shows dull grey scaly patches with hairs broken above the surface, not an inflamed suppurative mass.
• C. Black dot pattern shows hairs broken at the scalp surface without the boggy pustular swelling described.
• D. Favus presents with yellowish cup-shaped crusts (scutula) and a mousy odor, not pustular boggy swelling.

Post-herpetic neuralgia (PHN) is defined as pain persisting for more than 90 days after the onset of the acute herpes zoster rash, resulting from neuronal damage and central sensitization caused by varicella-zoster virus reactivation in the dorsal root ganglion. Risk increases with age, with PHN affecting up to 50% of patients over 60 years. Management includes gabapentin, pregabalin, tricyclic antidepressants, or topical lidocaine; early antiviral therapy (within 72 hours of rash onset) reduces the risk. Advanced age is the single most important risk factor for developing PHN.

• A. Disseminated zoster involves lesions spreading beyond the primary and adjacent dermatomes, typically in immunocompromised patients, which is not described here.
• B. Ramsay Hunt syndrome involves facial palsy with vesicles in the ear canal due to geniculate ganglion involvement, not a thoracic dermatome with persistent pain.
• C. Herpes zoster ophthalmicus refers to involvement of the ophthalmic division of the trigeminal nerve, not the thoracic dermatome described.

Molluscum contagiosum virus, a member of the Poxviridae family, causes discrete, flesh-colored, dome-shaped papules with a characteristic central umbilication, most common in children and spread by direct skin contact or fomites. Histopathology shows intracytoplasmic inclusion bodies called Henderson-Paterson bodies within infected keratinocytes. The condition is usually self-limited in immunocompetent children, resolving over months to a couple of years, though extensive or persistent lesions may warrant curettage, cryotherapy, or topical agents. Widespread lesions in adults should raise suspicion for HIV infection.

• A. Human papillomavirus causes verrucae (warts) with a rough, papillomatous surface, not smooth umbilicated papules.
• C. Varicella-zoster virus causes vesicular chickenpox lesions or dermatomal zoster, not umbilicated papules.
• D. Herpes simplex virus causes grouped painful vesicles that ulcerate, not chronic umbilicated papules.

Scabies is caused by the mite Sarcoptes scabiei var. hominis, which burrows into the stratum corneum, producing intensely pruritic papules and characteristic linear burrows at classic sites including finger web spaces, wrist flexors, axillae, areola, and genitalia. Nocturnal itching and similar symptoms in close contacts or family members are classic clues, since transmission occurs through prolonged skin-to-skin contact. Diagnosis can be confirmed by dermoscopy showing the delta-wing sign or by microscopic identification of mites, eggs, or fecal pellets from skin scrapings. The genital site involvement and household clustering strongly support scabies over other ectoparasitic infestations.

• B. Demodex folliculorum is associated with facial rosacea-like eruptions, not pruritic burrows at classic scabies sites.
• C. Pediculus humanus causes pediculosis, affecting hairy areas like the scalp or body, not finger webs and genitalia with burrows.
• D. Cimex lectularius (bedbug) causes grouped bite papules, typically without burrows and without the classic web space and genital predilection.

The treatment of choice for scabies is permethrin 5% cream applied to the entire body from the neck down (including web spaces, under nails, and genitalia) and left on for 8-14 hours before washing off, as even asymptomatic close contacts and household members should be treated simultaneously because of the incubation period before symptoms appear. This simultaneous treatment of all contacts prevents reinfestation and interrupts transmission. Bedding and clothing should be washed in hot water or kept away from body contact for at least 72 hours. A second application after 1 week is often recommended to kill newly hatched mites.

• A. Treating only affected areas misses mites in other body regions, and withholding treatment from asymptomatic contacts risks continued transmission within the household.
• C. Ivermectin is an acceptable alternative in certain situations (e.g., crusted scabies, outbreaks) but treating the patient alone without covering asymptomatic contacts fails to prevent reinfestation.
• D. Benzyl benzoate is an alternative scabicide but applying it only to the patient without treating contacts, and using it alone without covering the whole body, is suboptimal management.

Pediculosis capitis (head lice infestation) is treated first-line with permethrin 1% lotion or cream rinse, applied to clean, towel-dried hair and scalp and rinsed off after 10 minutes, with a repeat application after 7-9 days to kill any newly hatched nits. Nit combing with a fine-toothed comb helps mechanically remove eggs attached to hair shafts. Topical permethrin has a favorable safety profile and low toxicity, making it suitable for children, as described in this case. Oral ivermectin is reserved as an alternative for resistant cases or when topical treatment is impractical.

• A. Lindane carries risk of neurotoxicity, especially in children, and is no longer recommended as first-line therapy due to safety concerns.
• C. Selenium sulfide shampoo is used for seborrheic dermatitis and tinea versicolor, not as a pediculicide.
• D. Oral ivermectin is an alternative for resistant or extensive infestations, not the routine first-line choice over topical permethrin.

Cutaneous larva migrans is most commonly caused by the larvae of Ancylostoma braziliense (dog/cat hookworm), which penetrate intact skin on contact with soil or sand contaminated with animal feces, typically affecting the feet of people walking barefoot on beaches. Since humans are an accidental dead-end host, the larvae lack the collagenase needed to penetrate the dermis and migrate only within the epidermis, producing the characteristic itchy, serpiginous, slowly advancing track. The condition is self-limited but treatment with oral albendazole or ivermectin shortens the course and relieves symptoms. Topical thiabendazole is an alternative option.

• A. Dracunculus medinensis causes Guinea worm disease with a blistering lesion and emerging worm, not a serpiginous migrating track.
• C. Strongyloides stercoralis causes larva currens, a rapidly migrating urticarial track typically on the buttocks/trunk, moving much faster (cm/hour) than the slow track described.
• D. Necator americanus is a human hookworm whose larvae can penetrate skin but typically migrate to the lungs and intestine rather than cause prolonged cutaneous tracks.

Vitiligo results from autoimmune destruction of melanocytes, chiefly by CD8+ cytotoxic T cells directed against melanocyte antigens, leading to complete loss of pigment-producing cells in affected skin. This explains the chalky-white, well-demarcated macules that fluoresce brilliant blue-white under Wood's lamp due to the total absence of melanin. Associated circulating antimelanocyte antibodies and a higher prevalence of other autoimmune diseases support the autoimmune basis. Unlike inflammatory or infective hypopigmentation, vitiligo lesions are macular, non-scaly and non-tender.

• A. Vitiligo is acquired, not due to a congenital absence of melanocyte precursors.
• B. This describes pityriasis versicolor, which shows golden-yellow fluorescence and scaling, not the clinical picture here.
• D. This describes a mechanism closer to some forms of hypopigmentation like piebaldism variants, not vitiligo's melanocyte loss.

Vitiligo is frequently associated with autoimmune thyroid disease, most commonly Hashimoto thyroiditis, reflecting a shared predisposition to organ-specific autoimmunity. The patient's symptoms of fatigue, weight gain and a diffuse firm goiter are classic for hypothyroidism due to Hashimoto thyroiditis. Although Graves disease, Addison disease and pernicious anemia can also occur in patients with vitiligo, Hashimoto thyroiditis is the most frequent association seen in clinical practice and epidemiological studies. Screening for thyroid dysfunction is recommended in patients with vitiligo.

• B. Graves disease is associated with vitiligo but is less common than Hashimoto thyroiditis and would present with hyperthyroid features, not fatigue and weight gain.
• C. Addison disease is associated with vitiligo but is a less frequent association than autoimmune thyroiditis.
• D. Pernicious anemia can coexist with vitiligo but is a less common association than thyroid autoimmunity.

Oculocutaneous albinism type 1 results from mutations in the tyrosinase gene, which encodes the enzyme converting tyrosine to DOPA, the rate-limiting step in melanin synthesis. The condition follows an autosomal recessive pattern, consistent with unaffected carrier parents and an affected maternal uncle, who would represent another homozygous individual in the extended family rather than a maternally linked transmission. Affected individuals have generalized hypopigmentation of skin, hair and eyes along with ocular manifestations such as nystagmus, photophobia and reduced visual acuity due to foveal hypoplasia. Management includes sun protection and correction of visual defects.

• B. Mitochondrial inheritance follows exclusive maternal transmission to all offspring, which does not fit tyrosinase-related albinism.
• C. X-linked recessive inheritance would not explain an affected maternal uncle unless transmitted through carrier mothers, but tyrosinase is encoded on an autosome.
• D. Autosomal dominant inheritance would typically show an affected parent, which is not the case here.

This patient has diffuse cutaneous systemic sclerosis, indicated by skin thickening extending proximal to the metacarpophalangeal joints, Raynaud phenomenon and interstitial lung disease evidenced by restrictive pattern with reduced diffusion capacity. Anti-topoisomerase I (anti-Scl-70) antibody is strongly associated with diffuse cutaneous systemic sclerosis and carries a higher risk of pulmonary fibrosis. In contrast, anticentromere antibody is associated with limited cutaneous systemic sclerosis (CREST syndrome), which typically spares proximal skin and has a lower risk of early lung fibrosis. The combination of diffuse skin involvement and lung disease in this patient points specifically toward anti-Scl-70 positivity.

• A. Anticentromere antibody is characteristic of limited cutaneous systemic sclerosis with distal skin involvement, not the diffuse proximal skin thickening and early lung fibrosis seen here.
• C. Anti-Jo-1 antibody is associated with antisynthetase syndrome in dermatomyositis/polymyositis, not systemic sclerosis.
• D. Anti-double-stranded DNA antibody is specific for systemic lupus erythematosus, not systemic sclerosis.

This patient's heliotrope rash and Gottron papules with proximal myopathy are classic for dermatomyositis. Dermatomyositis in adults, particularly those over 40 years, has a well-recognized association with occult malignancy, most commonly ovarian, lung, pancreatic, gastric and colorectal cancers, and lymphoma. Therefore, age-appropriate malignancy screening is essential in all adults newly diagnosed with dermatomyositis, especially around the time of diagnosis and for the following few years. Early detection of an underlying malignancy can significantly change management and prognosis.

• A. Nerve conduction studies are relevant for peripheral nerve disorders, not for the primary association being tested in dermatomyositis.
• B. Echocardiography for valvular disease is not the standard evaluation for dermatomyositis; cardiac involvement in dermatomyositis is more related to myocarditis, not valvulopathy.
• C. HIV-associated myopathy is a differential consideration but is not the most important next step given the classic cutaneous findings and the known malignancy association of dermatomyositis.

This patient has discoid lupus erythematosus (DLE), characterized by chronic scarring plaques with follicular plugging and atrophy, typically without systemic involvement and often with negative or low-titer ANA. A recognized long-term complication of chronic DLE lesions, particularly longstanding scarred plaques, is the development of squamous cell carcinoma within the scar tissue, similar to malignant change in other chronic scarring dermatoses. Only a minority (roughly 5-10%) of localized DLE patients progress to systemic lupus erythematosus, so this is not the majority outcome. Regular follow-up of chronic discoid lesions is recommended to detect early malignant change.

• A. Cutaneous T-cell lymphoma is not a recognized complication of discoid lupus erythematosus.
• B. Basal cell carcinoma is not the characteristic malignancy associated with chronic DLE scars; squamous cell carcinoma is.
• D. Only a small minority of patients with purely discoid lesions progress to SLE; it is not the majority.

This patient's lesion, a pearly papule with central ulceration, rolled borders and telangiectasia on a chronically sun-exposed site like the nose, is classic for nodular basal cell carcinoma, which is the most common histological and clinical subtype of basal cell carcinoma overall. Basal cell carcinoma arises from basal keratinocytes of the epidermis and typically occurs on sun-exposed areas of the head and neck in older, fair-skinned individuals with chronic ultraviolet exposure. Superficial and morpheaform subtypes are less common and have different presentations: superficial BCC appears as a scaly erythematous patch, often on the trunk, while morpheaform BCC presents as a scar-like, indurated plaque with ill-defined borders. Nodular BCC is locally invasive but rarely metastasizes, and treatment is usually surgical excision or Mohs micrographic surgery depending on site and size.

• A. Superficial basal cell carcinoma presents as a scaly, erythematous patch usually on the trunk, not a pearly nodule on the face as described.
• B. Pigmented basal cell carcinoma is a variant of nodular BCC with increased melanin pigmentation, but it is less common than the classic non-pigmented nodular form.
• C. Morpheaform basal cell carcinoma presents as a scar-like indurated plaque with ill-defined borders, not the pearly rolled-border nodule described here.

Basal cell carcinoma characteristically shows nests or islands of basaloid cells budding off from the epidermis, with the peripheral row of cells aligned perpendicular to the surrounding stroma in an orderly, fence-like pattern called peripheral palisading, often with retraction artifact between the tumor nest and stroma. This is the single most reliable histological clue to basal cell carcinoma and distinguishes it from squamous cell carcinoma, which shows keratin pearls and more haphazard, pleomorphic cells. The tumor arises from the basal layer of the epidermis or hair follicle, explaining the basaloid cytology. Recognizing this pattern on biopsy is essential since BCC rarely metastasizes but is locally destructive, particularly in the H-zone of the face.

• A. Pseudoepitheliomatous hyperplasia is a reactive epidermal proliferation mimicking SCC, seen in chronic inflammatory conditions, not a feature of BCC nests.
• B. Keratin pearls are concentric layers of keratinization seen in well-differentiated squamous cell carcinoma, not BCC.
• C. Pagetoid spread refers to single atypical melanocytes scattered through the epidermis, a feature of melanoma in situ, not BCC.

Marjolin ulcer refers to squamous cell carcinoma arising in a chronic scar, burn wound, sinus tract, or long-standing venous ulcer, typically after a latent period of decades. The proposed mechanism is repeated cycles of tissue breakdown, chronic inflammation, and attempted re-epithelialization in a poorly vascularized, scarred bed, which promotes accumulation of genetic mutations in keratinocytes and impairs immune surveillance locally. This differs from typical sun-induced SCC, which is UV-mediated. Any ulcer that fails to heal or shows sudden changes such as everted edges, increased discharge, or friable tissue in a chronic scar should raise suspicion for malignant transformation and prompt biopsy.

• A. UVB-induced pyrimidine dimers explain sun-exposure-related SCC on exposed skin, not malignancy arising within a covered chronic scar.
• C. HPV is implicated in genital and periungual SCC, not typically in Marjolin ulcer arising from burn scars.
• D. Topical antibiotics are not a recognized cause of immunosuppression or viral oncogenesis in this setting.

Breslow thickness, measured in millimeters from the top of the granular layer of the epidermis to the deepest point of tumor invasion, is the single most important prognostic factor in cutaneous melanoma and forms the basis of the T-staging in the AJCC system. Greater depth correlates directly with risk of metastasis and mortality, with thresholds at 1 mm, 2 mm, and 4 mm guiding staging and management decisions including sentinel node biopsy. ABCDE criteria (Asymmetry, Border irregularity, Color variation, Diameter >6 mm, Evolution) are useful for clinical screening and raising suspicion, but they do not predict survival once melanoma is diagnosed. Clark level, based on anatomical layer of invasion, has been largely replaced by Breslow depth due to its superior reproducibility and prognostic value.

• A. Diameter is part of the ABCDE clinical screening criteria but does not independently predict survival once melanoma is confirmed.
• B. Color variegation raises clinical suspicion of melanoma but has no established independent prognostic value after diagnosis.
• D. Clark level has been superseded by Breslow depth as the standard prognostic measure due to poor interobserver reproducibility.

Sentinel lymph node biopsy is indicated in clinically node-negative melanoma patients with a Breslow thickness of at least 0.8 mm, or in thinner melanomas if adverse features such as ulceration or high mitotic rate are present, since these patients carry a significant risk of occult regional nodal micrometastasis. It allows accurate staging without the morbidity of a complete lymphadenectomy and guides decisions on adjuvant systemic therapy. Elective complete lymph node dissection without first performing sentinel node biopsy is not recommended in a clinically node-negative patient, as it causes unnecessary morbidity such as lymphedema when most patients do not have nodal disease. Observation alone would miss the opportunity to stage and risk-stratify this intermediate-thickness melanoma.

• B. Elective complete axillary dissection without sentinel node sampling is not recommended for a clinically node-negative patient and causes unnecessary morbidity.
• C. Adjuvant radiotherapy to a clinically negative, unstaged axilla is not indicated at this stage.
• D. Observation alone fails to stage occult nodal disease in a melanoma already beyond the thickness threshold for sentinel node biopsy.

Actinic keratosis is a premalignant lesion caused by cumulative ultraviolet-induced keratinocyte dysplasia, presenting classically as rough, gritty, scaly erythematous papules on chronically sun-exposed sites such as the face, scalp, and dorsal hands in fair-skinned or outdoor workers. Although the risk of any individual lesion progressing to invasive squamous cell carcinoma per year is low, the cumulative lifetime risk is significant, and actinic keratosis is considered a marker of field cancerization. Management includes cryotherapy, topical 5-fluorouracil, or imiquimod, with biopsy reserved for lesions that become indurated, tender, or rapidly enlarging, suggesting transformation. It is not a melanocytic lesion and is not linked to basal cell carcinoma, which arises de novo rather than through a recognized premalignant precursor.

• B. Actinic keratosis arises from epidermal keratinocytes due to UV damage, not from melanocytes.
• C. Actinic keratosis is a precursor of squamous cell carcinoma, not basal cell carcinoma, and progression is not near-universal.
• D. Actinic keratosis does carry malignant potential and is not purely a benign reactive process.

Fixed drug eruption is characterized by recurrence of a well-demarcated erythematous to violaceous plaque or bulla at exactly the same cutaneous or mucosal site each time the offending drug is re-administered, with the genitalia, lips, and acral sites being commonly affected. Cotrimoxazole (trimethoprim-sulfamethoxazole) is among the most frequently implicated drugs, followed by NSAIDs and tetracyclines, through an immunological mechanism involving drug-specific CD8+ resident memory T cells retained at the previously affected site. Repeated exposure triggers localized immune reactivation at the same location rather than a generalized eruption, and the lesion typically heals with postinflammatory hyperpigmentation. Identifying the culprit drug and lifelong avoidance is essential since re-exposure causes recurrence, and cross-reactivity with related sulfonamide-containing drugs should be anticipated.

• A. Paracetamol can rarely cause fixed drug eruption but is a far less common cause compared to cotrimoxazole.
• B. Chlorpheniramine, an antihistamine, is rarely implicated in fixed drug eruption.
• D. Amoxicillin typically causes a morbilliform or urticarial generalized rash rather than a localized recurrent fixed eruption.

Prolonged use of topical corticosteroids, especially high-potency agents on thin-skinned areas like the face, inhibits fibroblast proliferation and collagen and glycosaminoglycan synthesis in the dermis, leading to epidermal and dermal atrophy, which clinically manifests as skin thinning, telangiectasia, striae, purpura, and easy bruising. This risk is higher with occlusion, prolonged duration, and use on intertriginous or facial skin, which is why potent steroids should generally be avoided on the face and used for the shortest effective duration. Other recognized adverse effects of chronic topical steroid use include steroid-induced acne, perioral dermatitis, hypopigmentation, and tachyphylaxis. Patient education against unsupervised prolonged use, particularly of fairness or anti-pigmentation creams that are often adulterated with potent steroids, is important in preventing this complication.

• A. Topical corticosteroids cause functional hypopigmentation through reduced melanocyte activity, not direct toxic melanocyte destruction, and this does not explain skin thinning or striae.
• B. Topical corticosteroids suppress rather than increase sebaceous activity, though they can paradoxically cause steroid acne through a different mechanism unrelated to atrophy.
• C. The skin changes described are due to direct dermal atrophy, not a hypersensitivity vasculitis reaction.

Isotretinoin is a potent teratogen that causes craniofacial, cardiac, thymic, and central nervous system malformations even with short exposure during pregnancy, so pregnancy must be excluded before starting and reliably prevented throughout treatment and for one month after stopping. Regulatory pregnancy prevention programs mandate two forms of contraception, monthly pregnancy tests, and strict counseling in women of reproductive age. The other listed effects (hepatotoxicity, hypertriglyceridemia, mucocutaneous dryness) occur with isotretinoin but are managed by routine monitoring, not by mandatory contraception.

• B. Dryness of skin and lips is a common minor side effect, not an indication for contraception.
• C. Liver enzyme elevation is monitored with blood tests but does not require contraception counseling.
• D. Lipid abnormalities are monitored periodically but are not the reason for contraception mandates.

Dapsone and its hydroxylamine metabolite generate oxidative stress on red blood cells, and patients with G6PD deficiency have reduced capacity to regenerate reduced glutathione, making them highly susceptible to dose-related hemolysis. Screening for G6PD deficiency is recommended before starting dapsone, especially in populations with high prevalence. Dapsone also commonly causes dose-dependent methemoglobinemia even in G6PD-normal patients, but severe hemolysis with reticulocytosis strongly points to underlying G6PD deficiency. The other hemolytic conditions are not specifically precipitated by dapsone oxidative stress.

• B. Paroxysmal nocturnal hemoglobinuria causes complement-mediated hemolysis unrelated to dapsone's oxidative mechanism.
• C. Hereditary spherocytosis causes chronic hemolysis from a membrane defect, not an oxidant-drug trigger like dapsone.
• D. Autoimmune hemolytic anemia involves antibody-mediated destruction, not oxidative damage from dapsone metabolites.

In erythroderma, massive cutaneous vasodilation across the involved skin shunts a large volume of blood to the periphery, increasing cardiac output to maintain perfusion and eventually precipitating high-output cardiac failure, especially in elderly patients or those with pre-existing cardiac reserve limitations. This presents with tachycardia, edema, and a displaced apex beat from ventricular dilation rather than primary myocardial inflammation. Other systemic complications of erythroderma include hypothermia from heat loss, fluid and electrolyte imbalance, and increased susceptibility to infection. Myocarditis, pulmonary embolism, and constrictive pericarditis are not characteristic complications of erythroderma.

• A. Erythroderma does not directly cause myocardial inflammation; the cardiac strain is from increased output, not myocarditis.
• C. Pulmonary embolism is not a typical or direct complication of erythroderma.
• D. Constrictive pericarditis is not associated with erythroderma.

Alopecia areata presents as sudden, well-circumscribed, non-scarring patches of hair loss, classically showing exclamation mark hairs at the margin, which are short hairs that are thicker distally and taper to a narrow, pigmented shaft proximally due to abrupt follicular miniaturization. This reflects an autoimmune attack on anagen hair follicles with sparing of the follicular stem cells, allowing eventual regrowth. Trichotillomania shows irregular patches with hairs of varying lengths from mechanical pulling but lacks the characteristic tapering exclamation mark hairs. Tinea capitis and discoid lupus erythematosus typically show scaling, erythema, or scarring, which are absent here.

• A. Discoid lupus erythematosus causes scarring alopecia with erythema and follicular plugging, unlike this smooth non-scarring patch.
• B. Tinea capitis typically shows scaling, broken hair stubs, and sometimes pustules, not smooth non-scarring patches.
• D. Trichotillomania produces irregular, broken hairs of varying lengths from pulling, not tapered exclamation mark hairs.

Pyoderma gangrenosum is a neutrophilic dermatosis characterized by rapidly progressive, painful ulcers with violaceous, undermined borders, and it is most frequently associated with inflammatory bowel disease, particularly ulcerative colitis, as well as rheumatoid arthritis and hematologic malignancies. The pathergy phenomenon, where minor trauma triggers new lesions, is a supportive clinical feature. Diagnosis is clinical and by exclusion of infection, vasculitis, and malignancy, since biopsy findings are nonspecific. While other systemic diseases have cutaneous associations, pyoderma gangrenosum is not classically linked to viral hepatitis, lupus, or primary biliary cholangitis.

• A. Systemic lupus erythematosus has characteristic skin findings like malar rash, not classically pyoderma gangrenosum.
• C. Viral hepatitis is associated with other cutaneous findings like polyarteritis nodosa, not pyoderma gangrenosum.
• D. Primary biliary cholangitis is associated with pruritus and xanthomas, not pyoderma gangrenosum.

Neurofibromatosis type 1 is diagnosed using clinical criteria that include six or more café-au-lait macules greater than 5 mm in prepubertal or greater than 15 mm in postpubertal individuals, along with axillary or inguinal freckling (Crowe sign), neurofibromas, optic glioma, Lisch nodules, a distinctive osseous lesion, and a first-degree relative with NF1. The presence of multiple café-au-lait macules with axillary freckling in a child with an affected parent strongly supports this diagnosis. Ash leaf macules and shagreen patches are characteristic of tuberous sclerosis, not neurofibromatosis. Port-wine stains relate to Sturge-Weber syndrome, and periungual fibromas are also a tuberous sclerosis finding.

• A. Ash leaf macules and shagreen patches are characteristic of tuberous sclerosis, not neurofibromatosis type 1.
• C. Port-wine stains and venous malformations suggest Sturge-Weber syndrome or other vascular malformation syndromes.
• D. Vitiligo and periungual fibromas are not features of neurofibromatosis type 1; periungual fibromas suggest tuberous sclerosis.

Tuberous sclerosis complex presents with characteristic cutaneous markers including hypopigmented, lance-shaped (ash leaf) macules, which are often the earliest visible sign, and adenoma sebaceum, which are angiofibromas appearing as reddish-brown papules in a butterfly distribution over the nose and cheeks, typically becoming apparent in childhood. Other associated findings include shagreen patches, periungual (Koenen) fibromas, and subependymal giant cell astrocytomas, correlating with the seizures and developmental delay seen in this child. Café-au-lait macules with axillary freckling are features of neurofibromatosis type 1, not tuberous sclerosis. Malar erythema with photosensitivity suggests systemic lupus erythematosus, a different disease entity altogether.

• B. Café-au-lait macules and axillary freckling are diagnostic features of neurofibromatosis type 1, not tuberous sclerosis.
• C. Malar erythema with photosensitivity is characteristic of systemic lupus erythematosus, unrelated to tuberous sclerosis.
• D. Periungual telangiectasia is not a classic finding of tuberous sclerosis; periungual fibromas are.

Xeroderma pigmentosum is an autosomal recessive disorder caused by mutations in genes encoding proteins of the nucleotide excision repair (NER) pathway, most commonly the XPA to XPG genes. NER normally removes bulky DNA lesions such as UV-induced pyrimidine dimers by excising a stretch of nucleotides around the damage and resynthesizing the strand. Failure of this repair allows UV-induced mutations to accumulate, leading to extreme photosensitivity, pigmentary changes, and a markedly increased risk of basal cell carcinoma, squamous cell carcinoma, and melanoma at a young age. Consanguinity, as in this case, increases the likelihood of such autosomal recessive conditions.

• A. Non-homologous end joining repairs double-strand breaks and is not involved in correcting UV-induced pyrimidine dimers.
• B. Base excision repair corrects small, non-helix-distorting base lesions such as those from oxidation or deamination, not UV-induced bulky dimers.
• C. Mismatch repair corrects errors introduced during DNA replication, such as base mispairs and small insertion-deletion loops, and its defect causes Lynch syndrome, not xeroderma pigmentosum.