Basic Dermatology Practice Questions

Q: All of the following conditions are a differential diagnosis for Koebner Phenomenon, EXCEPT:

Pyoderma gangrenosum. ### Explanation The key to answering this question lies in distinguishing between the **Koebner Phenomenon** and **Pathergy**. **1. Why Pyoderma Gangrenosum (PG) is the correct answer:** Pyoderma gangrenosum is characterized by **Pathergy**, not the Koebner phenomenon. While both involve skin lesions developing at sites of trauma, they are pathophysiologically distinct. Pathergy refers to an exaggerated inflammatory response (often pustular or ulcerative) to minor trauma (e.g., a needle prick). In contrast, the Koebner phenomenon involves the appearance of new lesions of a *pre-existing* skin disease on previously healthy skin following trauma. **2. Why the other options are incorrect:** * **Lichen planus (A):** This is one of the "classic" examples of the Koebner phenomenon. Linear lichenoid papules often appear along scratch marks. * **Vitiligo (B):** Depigmented patches frequently develop at sites of friction or injury (e.g., elbows, waistline), representing a positive Koebner response. * **Leukocytoclastic vasculitis (D):** This is a recognized cause of the "Pseudo-Koebner" or true Koebner response, where palpable purpura develops in areas of pressure or trauma. **3. NEET-PG High-Yield Pearls:** * **True Koebner Phenomenon (Isomorphic response):** Psoriasis (most common), Lichen Planus, Vitiligo, Pityriasis Rubra Pilaris (PRP). * **Pseudo-Koebner Phenomenon:** Seen in infectious conditions where trauma inoculates the virus into the skin (e.g., **Molluscum contagiosum, Verruca plana**). * **Pathergy Positive Conditions:** Pyoderma Gangrenosum, **Behçet’s Disease**, and Sweet Syndrome. * **Reverse Koebner:** Disappearance of a lesion following trauma to the area.

Q: All of the following are seen in Neurofibromatosis, except?

Shagreen patch. **Explanation:** The correct answer is **C. Shagreen patch**. This is because Shagreen patches are a pathognomonic feature of **Tuberous Sclerosis (Epiloia)**, not Neurofibromatosis. A Shagreen patch is a connective tissue nevus, typically appearing as a leathery, "orange-peel" textured plaque on the lower back. **Analysis of Options:** * **A. Lisch nodules:** These are melanocytic hamartomas of the iris. They are the most common ocular finding in **Neurofibromatosis Type 1 (NF1)** and are present in over 90% of adult patients. * **B. Axillary freckling (Crowe’s sign):** This refers to multiple small hyperpigmented macules in the axillary or inguinal folds. It is a highly specific diagnostic criterion for NF1. * **D. Cafe-au-lait spots:** These are "coffee-with-milk" colored macules. For a diagnosis of NF1, there must be $\geq$ 6 spots measuring $>5$ mm (pre-pubertal) or $>15$ mm (post-pubertal). **High-Yield Clinical Pearls for NEET-PG:** * **NF1 (von Recklinghausen disease)** is caused by a mutation in the *NF1* gene on **Chromosome 17** (encodes Neurofibromin). * **Tuberous Sclerosis Complex (TSC)** is associated with the "Vogt’s Triad": Adenoma sebaceum (angiofibromas), Mental retardation, and Epilepsy. * **Differentiating Skin Signs:** * **NF1:** Cafe-au-lait spots, Lisch nodules, Neurofibromas, Optic gliomas. * **TSC:** Ash-leaf spots (earliest sign), Shagreen patch, Adenoma sebaceum, Periungual fibromas (Koenen tumors).

Q: What is the term for a discrete, pus-filled, raised lesion?

Pustule. ### Explanation **Correct Option: A. Pustule** A **pustule** is defined as a small, circumscribed, elevated lesion of the skin that contains purulent exudate (pus). Pus is a cloudy inflammatory fluid composed of white blood cells (primarily neutrophils), cellular debris, and sometimes necrotic tissue. Pustules can be follicular (centered around a hair follicle, as seen in folliculitis) or non-follicular (as seen in pustular psoriasis). **Incorrect Options:** * **B. Scale:** This is a **secondary lesion** representing the visible exfoliation or shedding of the outermost layer of the skin (stratum corneum). It is dry and flaky, not fluid-filled. * **C. Wheal:** A transient, edematous, elevated papule or plaque caused by dermal edema. It is the hallmark of **urticaria** and typically disappears within 24 hours without leaving a trace. * **D. Plaque:** A solid, raised, flat-topped lesion that is greater than **1 cm** in diameter. It is often formed by the coalescence of multiple papules (e.g., in Psoriasis). **NEET-PG High-Yield Pearls:** * **Vesicle vs. Pustule:** Both are fluid-filled elevations, but a vesicle contains clear serum, whereas a pustule contains pus. * **Sterile Pustules:** Not all pustules indicate infection. High-yield examples of sterile pustules include **Pustular Psoriasis** and **Subcorneal Pustular Dermatosis (Sneddon-Wilkinson disease)**. * **Munro’s Microabscess:** A classic histopathological finding in Psoriasis where neutrophils collect within the parakeratotic stratum corneum, essentially forming microscopic pustules.

Q: Casal's necklace is caused by:

Pellagra. **Explanation:** **Casal’s necklace** is a pathognomonic clinical sign of **Pellagra**, which results from a deficiency of **Niacin (Vitamin B3)** or its precursor, the amino acid Tryptophan. The underlying mechanism involves the failure of NAD/NADP-dependent cellular repair. In Pellagra, the skin becomes exquisitely sensitive to ultraviolet radiation. Casal’s necklace presents as a well-demarcated, hyperpigmented, scaly erythematous eruption encircling the lower neck and upper manubrium, corresponding to the area exposed to sunlight (photosensitivity). **Analysis of Options:** * **Lichen Planus:** Characterized by the "6 Ps" (Planar, Purple, Polygonal, Pruritic, Papules, and Plaques) and Wickham striae. It is an inflammatory condition, not a nutritional deficiency. * **Pernicious Anemia:** Caused by Vitamin B12 deficiency due to lack of intrinsic factor. While it causes glossitis and hyperpigmentation (especially of knuckles), it does not present with Casal’s necklace. * **Systemic Lupus Erythematosus (SLE):** While SLE features photosensitivity, its classic manifestation is the **Malar (butterfly) rash**. It does not produce the specific circumferential hyperpigmentation seen in Pellagra. **High-Yield Clinical Pearls for NEET-PG:** * **The 4 Ds of Pellagra:** Dermatitis, Diarrhea, Dementia, and Death (if untreated). * **Dietary Link:** Classically associated with **maize (corn)** or **jowar (sorghum)** based diets. Maize contains niacin in a bound form (niacytin), and sorghum contains high levels of **Leucine**, which interferes with tryptophan metabolism. * **Hartnup Disease:** An autosomal recessive disorder of tryptophan transport that can present with pellagra-like skin lesions. * **Carcinoid Syndrome:** Can lead to Pellagra because tumor cells divert tryptophan to produce excessive Serotonin, leaving insufficient amounts for Niacin synthesis.

Q: A 24-year-old male presents with a skin condition. What is the provisional diagnosis for this condition?

Erythema multiforme. ***Erythema multiforme*** - Characterized by **target/iris lesions** with a central dusky area surrounded by a pale ring and outer erythematous border, which is the classic presentation. - Commonly affects **young adults** and is often triggered by **HSV infections** or certain medications like **sulfonamides**. *Psoriasis* - Presents with **well-demarcated silvery-scaled plaques** typically on extensor surfaces like knees and elbows. - Lesions show **Koebner phenomenon** and **Auspitz sign** when scales are removed, not target-like morphology. *Lichen planus* - Characterized by **purple, polygonal, pruritic papules** with **Wickham's striae** on the surface. - Commonly affects **flexor surfaces** and mucous membranes, showing a different morphology than target lesions. *Lichen striatus* - Presents as a **linear band** of small, flesh-colored to pink papules following **Blaschko's lines**. - Typically occurs in **children** and shows a distinctive linear pattern, not circular target lesions.

Q: Crocodile skin or sauroderma is seen in which of the following conditions?

Ichthyosis vulgaris. **Explanation:** **Ichthyosis vulgaris** is the correct answer. The term "Ichthyosis" is derived from the Greek word *ichthys*, meaning fish. It is an autosomal dominant disorder caused by a mutation in the **filaggrin (FLG) gene**, which leads to defective keratinization and impaired skin barrier function. Clinically, it presents as diffuse, fine, polygonal scales that resemble **crocodile skin** or **fish scales** (sauroderma). These scales are most prominent on the extensors of the lower limbs, while the flexures (axilla, cubital fossa) are characteristically spared. **Analysis of Incorrect Options:** * **Toxic Epidermal Necrolysis (TEN):** This is a severe drug reaction characterized by widespread erythema and full-thickness epidermal detachment (sheeting off of skin), not scaling. It presents with a positive Nikolsky sign. * **Psoriasis:** Characterized by well-demarcated erythematous plaques with **silvery-white scales**. Key features include the Auspitz sign and Koebner phenomenon. * **Darier’s Disease:** An autosomal dominant acantholytic disorder presenting with greasy, brown, malodorous **keratotic papules** in seborrheic areas, rather than diffuse fish-like scaling. **Clinical Pearls for NEET-PG:** * **Hyperlinear palms:** A classic association with Ichthyosis vulgaris and Atopic Dermatitis. * **Sparing of flexures:** A key diagnostic feature distinguishing Ichthyosis vulgaris from X-linked recessive ichthyosis (which involves flexures and presents with "dirty" brown scales). * **Filaggrin mutation:** Also the most significant genetic risk factor for **Atopic Dermatitis**. * **Treatment:** Emollients and keratolytics (e.g., urea, lactic acid, or salicylic acid).

Q: What is the most characteristic feature of lichen planus?

Wickham's striae.. **Explanation:** Lichen Planus (LP) is a chronic inflammatory condition affecting the skin, mucous membranes, hair, and nails. **Why Wickham’s Striae is the correct answer:** Wickham’s striae are fine, whitish, lace-like lines visible on the surface of the papules or oral lesions. They are considered the **most characteristic clinical hallmark** of LP. Pathologically, they correspond to focal areas of **wedge-shaped hypergranulosis** (thickening of the granular layer) above the peaks of the saw-toothed rete ridges. **Analysis of Incorrect Options:** * **Option A:** While nail involvement occurs in 10% of cases, the most characteristic nail finding is **Pterygium formation** (fusing of the proximal nail fold to the nail bed). Thinning of the plate is common but non-specific. * **Option B:** LP of the scalp (Lichen Planopilaris) typically causes **scarring (cicatricial) alopecia**, not non-scarring. It presents with follicular plugging and permanent hair loss. * **Option C:** While LP classically presents as "Purple/Violaceous" lesions, this is a descriptive feature shared by other lichenoid eruptions. Wickham’s striae are more pathognomonic for the diagnosis. **NEET-PG High-Yield Pearls:** * **The 6 P’s of LP:** Planar (flat-topped), Purple, Polygonal, Pruritic, Papules, and Plaques. * **Koebner Phenomenon:** New lesions appearing at sites of trauma (also seen in Psoriasis and Vitiligo). * **Histopathology:** "Saw-tooth" appearance of rete ridges, Civatte bodies (apoptotic keratinocytes), and a band-like lymphocytic infiltrate at the dermo-epidermal junction. * **Max-Joseph Spaces:** Small areas of separation between the epidermis and dermis due to basal cell degeneration.

Q: Which of the following histological findings is characteristically associated with dermatitis?

Spongiosis. ### Explanation **Spongiosis** is the hallmark histological feature of **acute and subacute dermatitis** (eczema). It refers to **intercellular edema** within the epidermis. As fluid accumulates between keratinocytes, it pushes them apart, making the desmosomes (intercellular bridges) more prominent, giving the tissue a "sponge-like" appearance. If the fluid accumulation is severe, it leads to the formation of intraepidermal vesicles. **Analysis of Incorrect Options:** * **B. Orthokeratosis:** This refers to the normal cornified layer (stratum corneum) without retained nuclei. While seen in many conditions, it is not a diagnostic feature of dermatitis; in fact, dermatitis often shows *parakeratosis* (retention of nuclei in the stratum corneum). * **C. Hypergranulosis:** This is the thickening of the stratum granulosum. It is a classic feature of **Lichen Planus**, not dermatitis. In most eczematous conditions, the granular layer is actually thinned or absent. * **D. Acanthosis:** This refers to the thickening of the stratum spinosum. While acanthosis is seen in **chronic dermatitis** (like Lichen Simplex Chronicus), it is a non-specific reactive change seen in many inflammatory skin diseases (e.g., Psoriasis). Spongiosis remains the more specific "defining" feature of the dermatitic process. **High-Yield NEET-PG Pearls:** * **Acantholysis:** Loss of intercellular connections (desmosomes) resulting in "tombstoning"—characteristic of **Pemphigus Vulgaris**. * **Munro’s Microabscess:** Neutrophils in the stratum corneum, seen in **Psoriasis**. * **Civatte/Colloid Bodies:** Degenerating keratinocytes in the basal layer, seen in **Lichen Planus**. * **Papillary Microabscess:** Neutrophils at the tips of dermal papillae, seen in **Dermatitis Herpetiformis**.

Q: Which of the following statements about Langerhans cells is true?

They play an immunological role in the skin.. ### Explanation **Correct Answer: D. They play an immunological role in the skin.** Langerhans cells (LCs) are specialized **dendritic cells** derived from the bone marrow. They are the primary **antigen-presenting cells (APCs)** of the skin. Their main function is to capture antigens entering the epidermis, process them, and migrate to regional lymph nodes to present them to T-lymphocytes, thereby initiating a cutaneous immune response (Type IV hypersensitivity). **Why the other options are incorrect:** * **Option A:** Langerhans cells are primarily located in the **stratum spinosum** of the **epidermis**, not the dermis. While they can migrate through the dermis to reach lymphatics, their resident home is the epidermis. * **Option B:** **Merkel cells** function as sensory mechanoreceptors (light touch). * **Option C:** **Krause end bulbs** are the specialized nerve endings traditionally associated with cold thermoreception. **High-Yield Clinical Pearls for NEET-PG:** * **Origin:** Bone marrow (Mesodermal). * **Microscopy:** On Electron Microscopy, they show characteristic rod or tennis-racket shaped granules called **Birbeck Granules**. * **Markers:** They are positive for **S-100**, **CD1a**, and **Langerin (CD207)**. Langerin is the most specific marker and is involved in the formation of Birbeck granules. * **Clinical Correlation:** **Langerhans Cell Histiocytosis (LCH)** is a proliferative disorder of these cells, often presenting with seborrheic dermatitis-like rashes in infants and "punched-out" bone lesions.

Question 1

All of the following conditions are a differential diagnosis for Koebner Phenomenon, EXCEPT:

Accepted Answer

Pyoderma gangrenosum

Answer

Lichen planus

Answer

Vitiligo

Answer

Leukocytoclastic vasculitis

Question 2

All of the following are seen in Neurofibromatosis, except?

Accepted Answer

Shagreen patch

Answer

Lisch nodules

Answer

Axillary freckling

Answer

Cafe-au-lait spots

Question 3

What is the term for a discrete, pus-filled, raised lesion?

Accepted Answer

Pustule

Answer

Scale

Answer

Wheal

Answer

Plaque

Question 4

An 85-year-old male cigar smoker with no notable medical history presented with black discoloration and hairy appearance of the tongue, which had lasted several years. He denied using bismuth-containing compounds. What is the cause of this lesion on the tongue?

Accepted Answer

Lingua villosa nigra

Answer

Aspergillosis

Answer

Adrenal insufficiency

Answer

Pellagra

Question 5

Casal's necklace is caused by:

Accepted Answer

Pellagra

Answer

Lichen planus

Answer

Pernicious anemia

Answer

Systemic lupus erythematosus

Question 6

A 24-year-old male presents with a skin condition. What is the provisional diagnosis for this condition?

Accepted Answer

Erythema multiforme

Answer

Psoriasis

Answer

Lichen planus

Answer

Lichen striatus

Question 7

Crocodile skin or sauroderma is seen in which of the following conditions?

Accepted Answer

Ichthyosis vulgaris

Answer

Toxic epidermal necrolysis

Answer

Psoriasis

Answer

Darier's disease

Question 8

What is the most characteristic feature of lichen planus?

Accepted Answer

Wickham's striae.

Answer

Thinning of the nail plate is most common.

Answer

Non-scarring alopecia.

Answer

Violaceous lesions on skin and mucous membranes.

Question 9

Which of the following histological findings is characteristically associated with dermatitis?

Accepted Answer

Spongiosis

Answer

Orthokeratosis

Answer

Hypergranulosis

Answer

Acanthosis

Question 10

Which of the following statements about Langerhans cells is true?

Accepted Answer

They play an immunological role in the skin.

Answer

They are commonly found in the dermis.

Answer

They function as sensory mechanoreceptors.

Answer

They function as receptors for cold.

Basic Dermatology — MCQs

Basic Dermatology — MCQs

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