A 20-year-old man has painful nodules and cysts on his face and back with early pitted scars, despite 3 months of oral doxycycline with topical adapalene and benzoyl peroxide. He is started on oral isotretinoin. Which action of the drug best explains its ability to give long-term remission?

Shrinkage of sebaceous glands with less sebum

Blockade of androgen receptors in skin

Inhibition of 5-alpha-reductase in skin

Direct killing of Cutibacterium acnes

A 42-year-old man with stable plaque psoriasis for 10 years was given oral prednisolone for 'allergy' by a local practitioner for a month and stopped it abruptly a week ago. He now has fever of 39°C, malaise and sheets of pinhead-sized pustules on red, tender skin, merging into lakes of pus over his trunk and limbs. TLC is 16,000/µL with neutrophilia. What is the most likely diagnosis?

Acute generalised exanthematous pustulosis

Disseminated staphylococcal folliculitis

A 40-year-old woman with lichen planus scratched her forearm with a hairpin. Ten days later a line of identical violaceous, flat-topped papules appears exactly along the scratch. What is this phenomenon called?

Isomorphic (Koebner) phenomenon

Psoriasis, eczema, lichen planus and acne

15 NEET-PG practice questions on Psoriasis, eczema, lichen planus and acne, part of Dermatology. The first 15 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Medium
A 20-year-old man has painful nodules and cysts on his face and back with early pitted scars, despite 3 months of oral doxycycline with topical adapalene and benzoyl peroxide. He is started on oral isotretinoin. Which action of the drug best explains its ability to give long-term remission?
1. ABlockade of androgen receptors in skin
2. BInhibition of 5-alpha-reductase in skin
3. CDirect killing of Cutibacterium acnes
4. DShrinkage of sebaceous glands with less sebum
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Answer: D · Shrinkage of sebaceous glands with less sebum
Isotretinoin (13-cis-retinoic acid) acts on all the main pathogenic factors of acne, and above all it shrinks sebaceous glands and cuts sebum output markedly. Less sebum starves C. acnes indirectly and reduces follicular plugging and inflammation, which is why remissions often last after a full course. It is used for severe nodulocystic or scarring acne and acne that fails oral antibiotics; dry lips and skin are nearly universal, and liver enzymes and lipids are monitored.
- A: Androgen receptor blockers such as spironolactone or cyproterone are hormonal treatments used in women.
- B: 5-alpha-reductase inhibitors are not acne drugs, and isotretinoin does not act this way.
- C: Isotretinoin has no direct antibacterial action; C. acnes falls because sebum, its food, falls.
Question 2 · Medium
A 42-year-old man with stable plaque psoriasis for 10 years was given oral prednisolone for 'allergy' by a local practitioner for a month and stopped it abruptly a week ago. He now has fever of 39°C, malaise and sheets of pinhead-sized pustules on red, tender skin, merging into lakes of pus over his trunk and limbs. TLC is 16,000/µL with neutrophilia. What is the most likely diagnosis?
1. ASubcorneal pustular dermatosis
2. BAcute generalised exanthematous pustulosis
3. CGeneralised pustular psoriasis
4. DDisseminated staphylococcal folliculitis
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Answer: C · Generalised pustular psoriasis
Sterile pustules coalescing into lakes of pus on painful erythema, with fever and neutrophilia, in a known psoriatic after systemic steroids are withdrawn is generalised pustular psoriasis (von Zumbusch type). Steroid withdrawal is a classic trigger, along with infection, hypocalcaemia and pregnancy. It is life-threatening through fluid loss, sepsis and hypoalbuminaemia, and is treated in hospital with acitretin, methotrexate, cyclosporine or a biologic. This is why systemic steroids are not prescribed for psoriasis.
- A: Subcorneal pustular dermatosis is a chronic, relapsing flexural eruption without high fever.
- B: AGEP follows a new drug, usually an antibiotic, within days, and does not need prior psoriasis.
- D: Folliculitis gives pustules centred on hair follicles, not confluent lakes of pus.
Question 3 · Easy
A 40-year-old woman with lichen planus scratched her forearm with a hairpin. Ten days later a line of identical violaceous, flat-topped papules appears exactly along the scratch. What is this phenomenon called?
1. AWolf isotopic response
2. BPathergy phenomenon
3. CRenbök phenomenon
4. DIsomorphic (Koebner) phenomenon
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Answer: D · Isomorphic (Koebner) phenomenon
New lesions of a patient's existing skin disease arising at a site of trauma are the isomorphic or Koebner phenomenon. It is classically seen in psoriasis, lichen planus and active vitiligo, while warts and molluscum spread along scratches by direct inoculation (pseudo-Koebner). In practice it marks active disease and is a reason to advise patients to avoid scratching, friction and tight clothing.
- A: Wolf isotopic response is a new, different disease appearing at the site of a healed one, such as after herpes zoster.
- B: Pathergy is a sterile papule or pustule at a needle-prick site, typical of Behçet disease and pyoderma gangrenosum.
- C: Renbök (reverse Koebner) phenomenon is clearing of one disease, such as psoriasis, at a site affected by another.
Question 4 · Easy
A 32-year-old clerk from Pune has well-defined red plaques with silvery-white scales on both elbows and knees for 3 years. In the OPD the resident scrapes a plaque with a glass slide: the scales come off like candle wax, a moist red film appears, and then tiny bleeding points. What is this bleeding-point sign called?
1. ADarier sign
2. BNikolsky sign
3. CAsboe-Hansen sign
4. DAuspitz sign
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Answer: D · Auspitz sign
Grattage of a psoriatic plaque shows three stages: the silvery scale lifts off like candle grease, a glistening red membrane appears, and then pinpoint bleeding points emerge, the Auspitz sign. The bleeding comes from dilated, tortuous capillaries in the elongated dermal papillae, which lie close to the surface because the epidermis above the papillae is thinned. With the typical extensor distribution, it makes plaque psoriasis a clinical diagnosis in most patients.
- A: Darier sign is urtication of a lesion on rubbing, seen in mastocytosis.
- B: Nikolsky sign is shearing of the epidermis on sliding pressure, seen in pemphigus, TEN and SSSS.
- C: Asboe-Hansen sign is lateral spread of an intact bulla under pressure, seen in pemphigus.
Question 5 · Medium
A 16-year-old boy has many open and closed comedones on his forehead, nose and chin with a few small papules; there are no pustules, nodules or scars. He has used a 'fairness' cream and an over-the-counter steroid cream without benefit. What is the best initial treatment?
1. ATopical adapalene at night
2. BOral isotretinoin for 6 months
3. CTopical clindamycin alone
4. DOral doxycycline for 3 months
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Answer: A · Topical adapalene at night
Comedonal acne arises mainly from follicular hyperkeratinisation, and topical retinoids such as adapalene or tretinoin normalise keratinisation and clear microcomedones, the precursor of every acne lesion; benzoyl peroxide may be added. Steroid creams, widely misused in India, worsen acne and cause steroid-induced acneiform eruptions, so they must be stopped. Retinoids cause dryness and irritation in the first weeks, so they are applied thinly at night with sunscreen by day.
- B: Isotretinoin is reserved for severe nodulocystic or scarring acne, or acne that fails adequate therapy.
- C: Topical antibiotics used alone breed resistant Cutibacterium acnes and do little for comedones.
- D: Oral antibiotics are for moderate to severe inflammatory acne, not purely comedonal acne.
Question 6 · Hard
A 29-year-old long-distance truck driver comes to a district hospital OPD with a red, greasy, scaly rash on the scalp, eyebrows, nasolabial folds and front of the chest that has spread rapidly over 2 months and has responded poorly to ketoconazole cream. He has lost 6 kg and has oral thrush and generalised lymphadenopathy. What is the most appropriate next step?
1. AKOH mount of skin scrapings
2. BSerum zinc level estimation
3. CHIV test after counselling and consent
4. DSkin biopsy from a chest lesion
Answer and explanation in LearnFree account
Question 7 · Medium
A 54-year-old man whose plaque psoriasis was well controlled for years has had a severe flare over 2 months. He sees three different doctors, and his current prescriptions are: 1. Lithium carbonate for bipolar disorder 2. Metoprolol for hypertension 3. Hydroxychloroquine for joint pains 4. Metformin for diabetes. Which of these drugs could have worsened his psoriasis?
1. A1, 2 and 3 only
2. B1 and 4 only
3. C2, 3 and 4 only
4. D1 and 2 only
Answer and explanation in LearnFree account
Question 8 · Medium
A 50-year-old woman from Delhi has had painful erosions on both buccal mucosae for 6 months, bordered by white lacy streaks, and a few violaceous papules on her wrists. She received several blood transfusions after a postpartum haemorrhage 20 years ago. Screening for which infection is most appropriate?
1. AEpstein-Barr virus
2. BHerpes simplex virus
3. CHepatitis C virus
4. DHuman papillomavirus
Answer and explanation in LearnFree account
Question 9 · Medium
A 28-year-old woman has plaque psoriasis covering about 25% of her body surface that has not improved with topical steroids and calcipotriol. She and her husband are trying to conceive this year. Which treatment is the most suitable next step?
1. AOral methotrexate weekly
2. BNarrowband UVB phototherapy
3. COral prednisolone tapering course
4. DOral acitretin daily
Answer and explanation in LearnFree account
Question 10 · Hard
A 30-year-old woman has had itchy eczema under the buckle of her wristwatch, on her earlobes and around her navel for a year. Patch tests are applied on her back and read after removal at 48 hours and again at 96 hours. Nickel sulphate: 48 h, 1+ (erythema and papules); 96 h, 2+ (erythema, papules and vesicles spreading beyond the patch). Fragrance mix: 48 h, sharply limited glazed erythema; 96 h, negative. Petrolatum control: negative at both readings. How should the results be interpreted?
1. AAllergy to fragrance; irritant reaction to nickel
2. BAllergy to nickel; irritant reaction to fragrance
3. CAllergy to both nickel and fragrance
4. DIrritant reaction to both nickel and fragrance
Answer and explanation in LearnFree account
Question 11 · Hard
A 38-year-old schoolteacher has itchy, violaceous, flat-topped polygonal papules on both wrists and ankles for 4 months, and one great toenail is thinned, with a wing of skin growing forward into the nail plate. The resident lists four statements about her disease: 1. The fine white lines on the papules are due to focal parakeratosis. 2. New lesions may arise along scratch marks. 3. The nail change can lead to permanent nail loss. 4. The skin lesions usually heal leaving depigmented scars. Which statements are correct?
1. A1 and 4 only
2. B1, 2 and 3 only
3. C2 and 3 only
4. D2, 3 and 4 only
Answer and explanation in LearnFree account
Question 12 · Medium
An 8-month-old girl is brought to a paediatric OPD in Kochi with an intensely itchy, oozing, crusted rash on both cheeks and the outer aspects of her arms and legs for 3 months. The napkin area is spared. She rubs her face against the bedsheet all night, and her father has asthma. What is the most likely diagnosis?
1. AInfantile psoriasis
2. BInfantile seborrhoeic dermatitis
3. CInfantile scabies
4. DAtopic dermatitis
Answer and explanation in LearnFree account
Question 13 · Medium
A 6-year-old boy with known atopic eczema develops fever and painful, clustered, punched-out erosions with a few umbilicated vesicles over the eczematous skin of his face and neck over 2 days. His mother had a cold sore last week. What is the next best step?
1. AStart systemic acyclovir
2. BIncrease topical steroid potency
3. CWet wrap therapy with emollients
4. DOral cloxacillin alone
Answer and explanation in LearnFree account
Question 14 · Medium
A 13-year-old girl is brought to the dermatology OPD with a sudden crop of many small, scaly, drop-like red papules on her trunk and upper limbs. Two weeks earlier she had a sore throat with fever. There is no herald patch, and the palms and soles are spared. What is the most likely diagnosis?
1. APityriasis rosea
2. BGuttate psoriasis
3. CSecondary syphilis
4. DPityriasis versicolor
Answer and explanation in LearnFree account
Question 15 · Easy
A 45-year-old man has itchy, shiny, violaceous, flat-topped polygonal papules on the flexor wrists and shins, with a lacy white network on the buccal mucosa. A punch biopsy is taken from a wrist papule. Which histological finding is most characteristic?
1. ASuprabasal acantholysis with a row of basal cells
2. BSpongiosis with intraepidermal vesicles
3. CNeutrophil microabscesses in a parakeratotic stratum corneum
4. DBand-like lymphocytic infiltrate at the dermo-epidermal junction
Answer and explanation in LearnFree account

Psoriasis, eczema, lichen planus and acne

A 20-year-old man has painful nodules and cysts on his face and back with early pitted scars, despite 3 months of oral doxycycline with topical adapalene and benzoyl peroxide. He is started on oral isotretinoin. Which action of the drug best explains its ability to give long-term remission?

A 40-year-old woman with lichen planus scratched her forearm with a hairpin. Ten days later a line of identical violaceous, flat-topped papules appears exactly along the scratch. What is this phenomenon called?

A 16-year-old boy has many open and closed comedones on his forehead, nose and chin with a few small papules; there are no pustules, nodules or scars. He has used a 'fairness' cream and an over-the-counter steroid cream without benefit. What is the best initial treatment?

A 28-year-old woman has plaque psoriasis covering about 25% of her body surface that has not improved with topical steroids and calcipotriol. She and her husband are trying to conceive this year. Which treatment is the most suitable next step?

A 6-year-old boy with known atopic eczema develops fever and painful, clustered, punched-out erosions with a few umbilicated vesicles over the eczematous skin of his face and neck over 2 days. His mother had a cold sore last week. What is the next best step?

A 13-year-old girl is brought to the dermatology OPD with a sudden crop of many small, scaly, drop-like red papules on her trunk and upper limbs. Two weeks earlier she had a sore throat with fever. There is no herald patch, and the palms and soles are spared. What is the most likely diagnosis?

A 45-year-old man has itchy, shiny, violaceous, flat-topped polygonal papules on the flexor wrists and shins, with a lacy white network on the buccal mucosa. A punch biopsy is taken from a wrist papule. Which histological finding is most characteristic?