Basic Dermatology — MCQs

A 50-year-old male patient presented with characteristic skin lesions on the right shin. The skin lesion is a single indurated yellowish-brown plaque with an atrophic centre. Ectatic blood vessels are visible through the thinned skin. A biopsy was taken and histopathology examination was performed. Which of the following is the next best investigation to be done in this patient?

Q36Easy

Comedo nevus is which type of epidermal nevus?

Q37Easy

Pinch purpura are seen in which of the following conditions?

Q38Easy

Pellagra-like dermatitis occurs in which condition?

Q39Easy

Koenen's tumors are seen in which condition?

Q40Easy

Lesions of pityriasis rosea are distributed mostly on which part of the body?

Basic Dermatology Indian Medical PG Practice Questions and MCQs

Question 31: A child presents with a lesion on the buttocks that has been present for 2 years, spreading peripherally with central scarring and no symptoms. What is the most likely diagnosis?

A. Erythema annulare centrifugum (Correct Answer)
B. Erythema migrans
C. Erythema marginatum
D. Erythema gyratum

Explanation: **Explanation:** The clinical presentation of a long-standing, asymptomatic, peripherally spreading annular lesion with central clearing (or scarring) is characteristic of **Erythema Annulare Centrifugum (EAC)**. **Why Option A is Correct:** EAC is a reactive erythema that typically presents as erythematous plaques that expand centrifugally while clearing centrally. A hallmark feature of the "superficial type" is a **trailing scale** (a thin rim of scale behind the advancing edge), though chronic cases can result in post-inflammatory changes or central scarring. It is often idiopathic but can be associated with infections (tinea pedis), drugs, or malignancies. **Why Other Options are Incorrect:** * **B. Erythema Migrans:** This is the hallmark of **Lyme disease** (Borrelia burgdorferi). It expands rapidly over days to weeks (not years) and is typically associated with systemic symptoms like fever and lymphadenopathy. * **C. Erythema Marginatum:** This is a major Jones criterion for **Acute Rheumatic Fever**. The lesions are evanescent (fleeting), changing shape or disappearing within hours, unlike the 2-year duration described here. * **D. Erythema Gyratum Repens:** Characterized by a "wood-grain" appearance with rapid migration (up to 1 cm/day). It is a classic **paraneoplastic manifestation**, most commonly associated with lung cancer, and is rarely seen in children. **High-Yield Clinical Pearls for NEET-PG:** * **Trailing Scale:** Pathognomonic for the superficial variant of EAC. * **Wood-grain appearance:** Pathognomonic for Erythema Gyratum Repens. * **Target/Iris lesions:** Characteristic of Erythema Multiforme. * **Evanescent rash:** Characteristic of Erythema Marginatum and Systemic Juvenile Idiopathic Arthritis (Still's disease).

Question 32: Recurrent oral ulcers with pain and an erythematous halo around them are diagnosed as:

A. Aphthous ulcer (Correct Answer)
B. Herpes
C. Chicken pox
D. Measles

Explanation: **Explanation:** The clinical presentation of **recurrent, painful oral ulcers** characterized by a central yellowish-grey slough and a distinct **erythematous halo** is the hallmark of **Aphthous Ulcers** (Canker sores). These are non-contagious, inflammatory lesions of the oral mucosa. The pain is often disproportionate to the size of the ulcer, and they typically lack systemic symptoms like fever. **Analysis of Options:** * **Aphthous Ulcer (Correct):** These typically occur on non-keratinized mucosa (buccal/labial mucosa). The "erythematous halo" is a key diagnostic feature representing localized inflammation. * **Herpes (Incorrect):** Herpes Simplex Virus (HSV) typically presents with **grouped vesicles** on an erythematous base (often on the keratinized mucosa or vermilion border). While they can ulcerate, the primary lesion is vesicular, and they are often associated with prodromal tingling. * **Chickenpox (Incorrect):** Caused by Varicella-Zoster Virus, this presents with a generalized "dewdrop on a rose petal" rash. While oral lesions can occur, they are part of a widespread systemic exanthem. * **Measles (Incorrect):** The characteristic oral finding in measles is **Koplik spots**—small, bluish-white spots on an erythematous base found opposite the lower molars, appearing *before* the generalized maculopapular rash. **Clinical Pearls for NEET-PG:** * **Minor Aphthous:** Most common (<1 cm), heal without scarring (7–10 days). * **Major Aphthous (Sutton’s Disease):** Large (>1 cm), deep, very painful, and **heal with scarring**. * **Herpetiform Ulcers:** Multiple crops of tiny ulcers (not caused by HSV). * **Associations:** Recurrent aphthous-like ulcers are seen in **Behçet’s Disease** (associated with genital ulcers and uveitis) and **Celiac Disease**.

Question 33: A pinkish-red fluorescence of urine when examined with a Wood's lamp is seen in which condition?

A. Lead poisoning
B. Porphyria cutanea tarda (Correct Answer)
C. Erythromelalgia
D. Acrocyanosis

Explanation: **Explanation:** The correct answer is **Porphyria Cutanea Tarda (PCT)**. **1. Why Porphyria Cutanea Tarda is correct:** PCT is the most common type of porphyria, caused by a deficiency of the enzyme **uroporphyrinogen decarboxylase**. This leads to an accumulation of water-soluble **uroporphyrins** in the body. These porphyrins are excreted in the urine. When exposed to a Wood’s lamp (ultraviolet light, peak ~365 nm), these porphyrins emit a characteristic **coral-red or pinkish-red fluorescence**. Clinically, PCT presents with skin fragility, blistering, and hypertrichosis on sun-exposed areas. **2. Why other options are incorrect:** * **Lead poisoning:** While lead poisoning interferes with heme synthesis (inhibiting ALA dehydratase and ferrochelatase), it typically results in elevated **Zinc protoporphyrin** in red blood cells, not urinary uroporphyrins that fluoresce pink. * **Erythromelalgia:** This is a neurovascular condition characterized by episodes of burning pain, redness, and increased skin temperature in the extremities. It does not involve porphyrin metabolism. * **Acrocyanosis:** This is a functional peripheral vascular disorder characterized by persistent, painless bluish discoloration of the hands and feet. It is related to vasospasm, not metabolic excretion. **3. High-Yield Clinical Pearls for NEET-PG:** * **Wood’s Lamp in Porphyria:** In **Erythropoietic Protoporphyria (EPP)**, the teeth and RBCs may fluoresce, but the urine does *not* (as protoporphyrin is not water-soluble). * **Urine Color:** In PCT, the urine may also appear "tea-colored" or "port-wine colored" under natural light. * **Other Wood’s Lamp findings:** * **Tinea capitis (Microsporum):** Bright greenish fluorescence. * **Erythrasma (Corynebacterium minutissimum):** Coral-red fluorescence (due to coproporphyrin III). * **Vitiligo:** Milky-white fluorescence. * **Pseudomonas:** Yellow-green fluorescence (pyoverdin).

Question 34: A 60-year-old man presents to his physician after a routine screening test indicates hyperlipidemia. Physical examination reveals raised, irregular, yellow papules in the skin of the soft tissues below the eyes. Biopsy of these lesions would most likely show which of the following?

A. Benign nevus cells
B. Malignant nevus cells
C. Microscopic blisters
D. Multinucleated giant cells (Correct Answer)

Explanation: **Explanation:** The clinical presentation of a 60-year-old man with hyperlipidemia and yellow papules on the soft tissues below the eyes (periorbital region) is classic for **Xanthelasma palpebrarum**. Xanthelasma is a type of xanthoma characterized by the accumulation of lipids within dermal macrophages. On histopathology, these lipid-laden macrophages are known as **foam cells** (or xanthoma cells). In many xanthomatous lesions, these macrophages fuse to form **Touton multinucleated giant cells**, which feature a ring of nuclei surrounding a central non-foamy cytoplasm, with peripheral foamy cytoplasm. Therefore, **Option D** is the correct histopathological finding. **Analysis of Incorrect Options:** * **Options A & B:** Nevus cells (benign or malignant) are characteristic of melanocytic nevi or melanoma. While these can present as papules, they are typically pigmented (brown/black) rather than yellow and are not associated with hyperlipidemia. * **Option C:** Microscopic blisters (vesicles/bullae) are seen in immunobullous disorders (e.g., Pemphigus, Bullous Pemphigoid) or infections (e.g., Herpes). They do not present as solid yellow papules. **NEET-PG High-Yield Pearls:** * **Xanthelasma palpebrarum** is the most common type of xanthoma. * While often associated with **Type II and Type IV hyperlipoproteinemia**, 50% of patients with xanthelasma are normolipemic. * **Touton Giant Cells** are a hallmark of xanthomatous inflammation and are also seen in Juvenile Xanthogranuloma. * **Eruptive Xanthomas** (small yellow papules on extensors) are specifically associated with high **triglycerides**.

Question 35: A 50-year-old male patient presented with characteristic skin lesions on the right shin. The skin lesion is a single indurated yellowish-brown plaque with an atrophic centre. Ectatic blood vessels are visible through the thinned skin. A biopsy was taken and histopathology examination was performed. Which of the following is the next best investigation to be done in this patient?

A. Blood sugar levels (Correct Answer)
B. Thyroid function tests
C. Serum cortisol levels
D. Serum growth hormone levels

Explanation: ### Explanation The clinical presentation described—a single indurated, yellowish-brown plaque with an atrophic center and prominent telangiectasia (ectatic blood vessels) on the pretibial area (shin)—is the classic description of **Necrobiosis Lipoidica (NL)**. **1. Why Blood Sugar Levels is the Correct Answer:** Necrobiosis Lipoidica is a chronic granulomatous dermatitis strongly associated with **Diabetes Mellitus**. While only about 0.3% of diabetic patients develop NL, approximately **60–75% of patients with NL have or will develop diabetes**. Therefore, the immediate next step in management is to screen for underlying glucose intolerance or undiagnosed diabetes using blood sugar levels (Fasting/PP) or HbA1c. **2. Why Other Options are Incorrect:** * **Thyroid Function Tests:** These are used to investigate conditions like *Pretibial Myxedema* (Grave’s disease), which presents as waxy, "orange-peel" (peau d'orange) indurated nodules, not atrophic yellowish plaques. * **Serum Cortisol Levels:** Used to diagnose Cushing’s syndrome or Addison’s disease. While Cushing’s can cause skin thinning and striae, it does not present with localized necrobiotic plaques. * **Serum Growth Hormone:** Used for Acromegaly, which presents with skin thickening (pachydermia) and cutis verticis gyrata, rather than atrophy and telangiectasia. **3. NEET-PG High-Yield Pearls:** * **Histopathology of NL:** Shows "tiered" or "layer-cake" granulomas involving the full thickness of the dermis, consisting of necrobiotic collagen alternating with inflammatory cells. * **Key Differentiator:** Unlike Granuloma Annulare (which also shows necrobiosis), NL typically shows **plasma cells** and lacks prominent mucin. * **Clinical Fact:** The severity of NL does **not** correlate with glycemic control; however, screening is mandatory due to the high association. * **Common Site:** The pretibial area (shins) is the most common site (85% of cases).

Question 36: Comedo nevus is which type of epidermal nevus?

A. Keratinocytic
B. Verrucous
C. Inflammatory
D. Appendegeal (Correct Answer)

Explanation: **Explanation:** **Nevus Comedonicus (Comedo Nevus)** is a rare type of epidermal nevus characterized by a group of closely set, dilated follicular openings filled with dark keratinous plugs, resembling open comedones. **Why the correct answer is right:** Epidermal nevi are classified based on the predominant component of the skin they involve. **Appendegeal nevi** (also known as organoid nevi) are those that show differentiation toward skin appendages like hair follicles, sebaceous glands, or sweat glands. Since the comedo nevus represents a **developmental malformation of the pilosebaceous unit** (specifically the hair follicle), it is classified as an **appendegeal nevus**. Histologically, it shows large, dilated follicular invaginations filled with concentric layers of keratin. **Why the incorrect options are wrong:** * **Keratinocytic/Verrucous:** These terms refer to the classic "Linear Verrucous Epidermal Nevus" (IVEN), which involves only the inter-follicular epidermis (keratinocytes) without specific adnexal differentiation. * **Inflammatory:** This refers to **ILVEN** (Inflammatory Linear Verrucous Epidermal Nevus), which is characterized by pruritus and psoriasiform histological features, rather than follicular plugging. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** Usually present at birth or early childhood, appearing as a "linear track" of comedones, most commonly on the face, neck, or trunk. * **Nevus Comedonicus Syndrome:** When associated with extracutaneous findings such as cataracts, skeletal abnormalities (scoliosis), or CNS defects. * **Treatment:** Topical retinoids are used for mild cases; surgical excision or laser therapy for cosmetic concerns. * **Key Association:** It is a component of the "Epidermal Nevus Syndrome" spectrum.

Question 37: Pinch purpura are seen in which of the following conditions?

A. Secondary amyloidosis
B. Primary systemic amyloidosis (Correct Answer)
C. Pseudoxanthoma elasticum
D. Toxic shock syndrome

Explanation: **Explanation:** **Primary Systemic Amyloidosis (AL Amyloidosis)** is the correct answer. The hallmark of this condition is the deposition of amyloid fibrils (immunoglobulin light chains) within the walls of dermal blood vessels. This makes the vessels extremely fragile. Minor trauma, such as pinching the skin or even coughing (Valsalva maneuver), leads to vessel rupture and the formation of ecchymoses. This classic clinical sign is known as **Pinch Purpura** or "Post-proctoscopic purpura" (when it occurs around the eyes after a procedure). **Analysis of Options:** * **Secondary Amyloidosis (AA):** Unlike the primary form, secondary amyloidosis (associated with chronic inflammation like TB or RA) rarely involves the skin. Cutaneous manifestations like pinch purpura are characteristically absent. * **Pseudoxanthoma Elasticum:** This is a genetic disorder of connective tissue (fragmentation of elastic fibers). While it causes "plucked chicken skin" appearance and angioid streaks in the retina, it does not typically present with pinch purpura. * **Toxic Shock Syndrome:** This is a toxin-mediated systemic illness presenting with high fever, hypotension, and a diffuse macular erythroderma (sunburn-like rash) followed by desquamation, not purpuric lesions caused by vessel fragility. **High-Yield Clinical Pearls for NEET-PG:** * **Macroglossia:** The most common oral finding in primary systemic amyloidosis. * **Raccoon Eyes:** Periorbital ecchymosis (a form of pinch purpura) is a highly specific sign for AL amyloidosis. * **Diagnosis:** Skin biopsy shows **Apple-green birefringence** under polarized light when stained with **Congo Red**. * **Shoulder Pad Sign:** Swelling of the shoulder joints due to amyloid deposition in the periarticular structures.

Question 38: Pellagra-like dermatitis occurs in which condition?

A. Dermatomyositis
B. Carcinoid syndrome (Correct Answer)
C. Systemic Lupus Erythematosus (SLE)
D. Lymphoma

Explanation: **Explanation:** Pellagra is caused by a deficiency of **Niacin (Vitamin B3)** or its precursor, the amino acid **Tryptophan**. Under normal physiological conditions, approximately 1% of dietary tryptophan is converted into niacin. In **Carcinoid Syndrome**, enterochromaffin cell tumors (usually in the small intestine) divert up to 60% of the body’s tryptophan to synthesize massive amounts of **Serotonin (5-HT)**. This "tryptophan steal" results in a profound secondary deficiency of niacin, leading to the classic clinical triad of Pellagra: Dermatitis (photosensitive Casal’s necklace), Diarrhea, and Dementia. **Analysis of Incorrect Options:** * **Dermatomyositis:** Presents with photosensitive rashes like the Heliotrope rash and Gottron’s papules, but these are autoimmune inflammatory processes, not nutritional deficiencies. * **Systemic Lupus Erythematosus (SLE):** Characterized by a malar (butterfly) rash and photosensitivity. While it may mimic the distribution of pellagra, the pathophysiology involves immune complex deposition (Type III hypersensitivity). * **Lymphoma:** While some cutaneous lymphomas (like Mycosis Fungoides) cause erythroderma, they do not present with the specific niacin-deficiency pattern seen in pellagra. **NEET-PG High-Yield Pearls:** * **The 4 D’s of Pellagra:** Dermatitis, Diarrhea, Dementia, and Death. * **Hartnup Disease:** An autosomal recessive disorder of neutral amino acid transport that also causes pellagra-like symptoms due to impaired tryptophan absorption. * **Drug-induced Pellagra:** Isoniazid (INH) is a common culprit as it inhibits the enzyme pyridoxine phosphokinase; Vitamin B6 is a necessary cofactor for converting tryptophan to niacin. * **Dietary Cause:** Diets primarily consisting of **Maize** (corn) or **Jowar** (sorghum) are pellagragenic because niacin is in a bound form (niacytin) and they are low in tryptophan.

Question 39: Koenen's tumors are seen in which condition?

A. Neurofibromatosis
B. Tuberous sclerosis (Correct Answer)
C. Sturge-Weber syndrome
D. Tuberculosis

Explanation: **Explanation:** **Koenen’s tumors** (also known as periungual or subungual fibromas) are a pathognomonic cutaneous feature of **Tuberous Sclerosis Complex (TSC)**. These are smooth, flesh-colored, or reddish papules/nodules that arise from the nail fold or under the nail plate. They typically appear during puberty and are one of the major diagnostic criteria for TSC. **Analysis of Options:** * **Tuberous Sclerosis (Correct):** TSC is an autosomal dominant neurocutaneous syndrome caused by mutations in *TSC1* (hamartin) or *TSC2* (tuberin) genes. Koenen's tumors are fibrous hamartomas characteristic of this condition. * **Neurofibromatosis (Incorrect):** While also a neurocutaneous syndrome, its hallmark features include Café-au-lait spots, Lisch nodules, and neurofibromas (plexiform or cutaneous), but not periungual fibromas. * **Sturge-Weber Syndrome (Incorrect):** This is characterized by a Port-wine stain (Nevus Flammeus) in the V1/V2 distribution of the trigeminal nerve, glaucoma, and leptomeningeal angiomas. * **Tuberculosis (Incorrect):** Though the names sound similar, Koenen’s tumor is a genetic hamartoma and has no association with *Mycobacterium tuberculosis* infection. **High-Yield Clinical Pearls for NEET-PG:** * **Vogt’s Triad of TSC:** Adenoma sebaceum (facial angiofibromas), Mental retardation, and Seizures. * **Earliest sign of TSC:** Ash-leaf spots (hypopigmented macules), best seen under **Wood’s lamp**. * **Shagreen patch:** A connective tissue nevus (leathery plaque) usually found on the lumbosacral area. * **Confetti lesions:** Multiple tiny hypopigmented macules on the limbs. * **Gingival fibromas** and **dental pitting** are also common oral findings.

Question 40: Lesions of pityriasis rosea are distributed mostly on which part of the body?

A. Face
B. Trunk (Correct Answer)
C. Scalp
D. Palms and soles

Explanation: ### Explanation **Pityriasis Rosea (PR)** is a common, self-limiting inflammatory skin disorder characterized by a specific clinical progression and distribution. **Why the Trunk is Correct:** The hallmark of Pityriasis Rosea is its distribution in the **"Christmas Tree" (or fir tree) pattern**. The lesions are primarily located on the **trunk** and proximal limbs. They follow the lines of cleavage (Langer’s lines), creating a symmetrical, V-shaped distribution on the upper back and a horizontal distribution on the lower back. The eruption typically begins with a single, large **"Herald Patch"** (usually on the trunk), followed days later by smaller, oval, erythematous scaly plaques with a characteristic **collarette of scale**. **Analysis of Incorrect Options:** * **A. Face:** PR is known for "sparing" the face in its classic form. Involvement of the face is rare and usually only seen in the "inverse" variant or in pediatric cases. * **C. Scalp:** Similar to the face, the scalp is typically spared. Scalp involvement is more characteristic of Psoriasis or Seborrheic Dermatitis. * **D. Palms and Soles:** These areas are characteristically spared in PR. This is a crucial diagnostic differentiator from **Secondary Syphilis**, which presents with similar scaly lesions but *includes* the palms and soles. **High-Yield Clinical Pearls for NEET-PG:** * **Etiology:** Associated with **HHV-6 and HHV-7** reactivation. * **Herald Patch:** The initial lesion; larger (2–6 cm), salmon-colored, and heralds the generalized eruption. * **Collarette Scale:** The scale is attached at the periphery and free toward the center. * **Hanging Curtain Sign:** When the skin is stretched across the long axis of the lesion, the scales fold like a curtain. * **Differential Diagnosis:** Always rule out Secondary Syphilis (perform VDRL/RPR if palms/soles are involved).

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