Basic Dermatology Practice Questions

Q: Which pigment, when yellow, brown, or black, shows fluorescence under UV light?

Tetracycline. **Explanation:** **Tetracycline (Option A)** is the correct answer. Tetracyclines are known to cross the placental barrier and have a high affinity for calcifying tissues. When ingested during the period of tooth development (mineralization), the drug forms a stable **tetracycline-calcium orthophosphate complex**. This leads to permanent intrinsic staining of the teeth, which can range from yellow and brown to gray or black. A hallmark diagnostic feature of tetracycline staining is its ability to exhibit **bright yellow fluorescence** when viewed under **Wood’s lamp (UV light)**. **Why other options are incorrect:** * **Internal Resorption (Option B):** This is a pathological process where the dentin is destroyed by odontoclasts. It typically presents as a "Pink Spot" (Mummery's spot) due to the vascular pulp showing through the thinned enamel. It does not exhibit fluorescence. * **Fluorosis (Option C):** Caused by excessive fluoride intake during tooth development, it results in hypomineralization. It presents as white flecks or brown pitting (mottled enamel) but does not fluoresce under UV light. **Clinical Pearls for NEET-PG:** * **Wood’s Lamp in Dermatology:** * **Erythrasma:** Coral red fluorescence (due to Porphyrins). * **Tinea Versicolor:** Golden yellow/Copper-orange fluorescence. * **Tinea Capitis (Microsporum):** Bright greenish fluorescence. * **Pseudomonas:** Blue-green fluorescence (due to Pyoverdin). * **Porphyria Cutanea Tarda:** Urine shows pink-red fluorescence. * **Contraindication:** Tetracyclines are contraindicated in pregnant women and children under 8 years of age due to their effects on bone growth and permanent tooth discoloration.

Q: Which one of the following is not a lichenoid reaction?

Pemphigus. **Explanation:** The term **Lichenoid Reaction** refers to a specific histopathological pattern characterized by **interface dermatitis**. The hallmark of this reaction is a dense, band-like infiltrate of lymphocytes at the dermo-epidermal junction, leading to "liquefaction degeneration" (vacuolar degeneration) of the basal layer of the epidermis. **Why Pemphigus is the correct answer:** Pemphigus (such as Pemphigus Vulgaris) is an **autoimmune bullous disorder** caused by antibodies against desmogleins (cell-to-cell adhesion molecules). Its primary pathology is **acantholysis** (loss of intercellular connections) leading to intraepidermal blisters. It does not involve an interface lymphocytic reaction or basal layer degeneration; therefore, it is not a lichenoid reaction. **Analysis of Incorrect Options:** * **Lichenoid Contact Reaction:** This is a localized T-cell mediated delayed hypersensitivity reaction (Type IV) occurring at the site of contact with certain substances (e.g., dental amalgam), mimicking lichen planus histologically. * **Lichenoid Drug Eruption:** Many drugs (e.g., Beta-blockers, NSAIDs, Antimalarials) can trigger a "lichen planus-like" eruption. Histology shows the classic band-like infiltrate, often with eosinophils. * **Lichenoid Graft vs. Host Disease (GVHD):** Chronic GVHD frequently presents with lichenoid papules and plaques. The pathology shows a classic interface dermatitis as the donor T-cells attack the host's basal keratinocytes. **High-Yield Clinical Pearls for NEET-PG:** * **Civatte Bodies (Colloid Bodies):** These are apoptotic keratinocytes found in the lower epidermis/upper dermis in lichenoid reactions. * **Max Joseph Spaces:** Small areas of separation between the epidermis and dermis due to extensive basal cell degeneration in Lichen Planus. * **Wickham Striae:** The clinical white reticular lines seen in Lichen Planus, caused by focal orthokeratosis and wedge-shaped hypergranulosis.

Q: Regarding Erythema multiforme, all are true except?

Absence of vesicles. **Explanation:** **Erythema Multiforme (EM)** is an acute, self-limiting Type IV hypersensitivity reaction. The correct answer is **A** because the statement "Absence of vesicles" is false. In EM, the characteristic "target" or "iris" lesion often features a central zone that can become **vesicular, bullous, or necrotic**. Therefore, vesicles are a common clinical finding in the center of the lesions. **Analysis of Options:** * **Option B (Target lesions):** This is the hallmark of EM. A classic target lesion consists of three concentric zones: a dusky/vesicular center, a pale edematous ring, and an erythematous outer halo. * **Option C (Face and neck involvement):** EM typically has a symmetrical acral distribution, frequently involving the face, neck, and distal extremities (palms and soles). * **Option D (Sign of internal malignancy):** While most cases are triggered by infections (HSV being the most common), EM can occasionally occur as a paraneoplastic phenomenon associated with underlying internal malignancies (e.g., carcinomas or lymphomas). **High-Yield Clinical Pearls for NEET-PG:** * **Most Common Trigger:** Herpes Simplex Virus (HSV-1 and HSV-2) is the most frequent cause of EM Minor. *Mycoplasma pneumoniae* is the most common bacterial cause (often associated with EM Major). * **EM Minor vs. Major:** EM Minor involves little to no mucosal involvement; EM Major involves at least two mucosal surfaces (oral, ocular, or genital). * **Differential Diagnosis:** Unlike Stevens-Johnson Syndrome (SJS), EM is usually triggered by infections rather than drugs and involves <10% body surface area. * **Histology:** Shows vacuolar degeneration of the basal layer and subepidermal bullae.

Q: Clutch claw and ball appearance is seen in which of the following conditions?

Lichen nitidus. **Explanation:** The **"Clutch Claw and Ball"** appearance is a classic histopathological hallmark of **Lichen Nitidus**. This appearance is created by a dense, well-circumscribed lymphohistiocytic infiltrate (the "ball") located within a single dermal papilla, which is closely embraced by elongated, downward-extending epidermal rete ridges (the "clutching claw"). **Why the other options are incorrect:** * **Pemphigus:** Characterized by intraepidermal blisters due to acantholysis (loss of intercellular connections). Histology shows a "row of tombstones" appearance on the basal layer. * **Lichen Planus:** Features a "saw-tooth" appearance of rete ridges and a band-like (lichenoid) infiltrate at the dermo-epidermal junction, but lacks the focal "ball" configuration. * **Psoriasis:** Notable for regular elongation of rete ridges (test-tube appearance), Munro’s microabscesses, and Kogoj’s pustules, but does not show the claw and ball pattern. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** Lichen Nitidus presents as multiple, tiny (1-2 mm), skin-colored, shiny, flat-topped papules. * **Koebner Phenomenon:** Like Lichen Planus and Psoriasis, Lichen Nitidus can exhibit the Koebner phenomenon (lesions appearing at sites of trauma). * **Key Histology Buzzword:** "Claw and Ball" or "Ball and Claw" is pathognomonic. * **Common Site:** Often involves the shaft of the penis, forearms, and dorsum of the hands.

Q: What is the classical presentation described?

Pityriasis Rosea. ***Pityriasis Rosea*** - Classical presentation includes a **herald patch** (initial large oval lesion) followed by smaller **salmon-colored oval lesions** distributed in a **Christmas tree pattern** on the trunk. - Lesions follow **Langer's lines** and typically appear on the **trunk and proximal extremities**, often with mild **pruritus**. *Pityriasis Alba* - Presents as **hypopigmented patches** with fine **scaling**, commonly on the **face and arms** of children. - Associated with **atopic dermatitis** and lacks the characteristic **herald patch** and Christmas tree distribution. *Pityriasis Rubra* - Also known as **pityriasis rubra pilaris**, characterized by **orange-red scaly plaques** with **islands of normal skin**. - Presents with **keratoderma** of palms and soles, and **follicular hyperkeratosis**, unlike the oval lesions of pityriasis rosea. *Pityriasis Versicolor* - Caused by **Malassezia furfur** fungus, presenting as **hypo- or hyperpigmented patches** with fine scaling. - Typically affects **seborrheic areas** like chest, back, and shoulders, with **positive KOH test** showing spaghetti and meatballs appearance.

Q: A 50-year-old woman develops pink macules and papules on her hands and forearms in association with a sore throat. The lesions are targetlike, with the centers a dusky violet. A diagnosis of erythema multiforme is made. What is the most important information to obtain from this patient's history?

The patient is taking phenytoin.. **Explanation:** The clinical presentation of targetoid lesions (dusky centers with concentric rings) on the extremities following a prodrome (sore throat) is classic for **Erythema Multiforme (EM)**. EM is a hypersensitivity reaction triggered primarily by infections or drugs. **Why Option B is Correct:** While **Herpes Simplex Virus (HSV)** is the most common trigger for EM Minor, **drugs** are a significant cause, especially in EM Major. **Phenytoin**, an antiepileptic, is a well-known culprit associated with severe cutaneous adverse reactions (SCARs), including EM, Stevens-Johnson Syndrome (SJS), and Toxic Epidermal Necrolysis (TEN). Identifying a drug trigger is the most critical step in management to prevent progression and recurrence. **Analysis of Incorrect Options:** * **Option A:** Tampon use is associated with **Toxic Shock Syndrome (TSS)**, which presents with high fever, hypotension, and a diffuse macular erythroderma (sunburn-like rash), not target lesions. * **Option C:** Measles presents with a cephalocaudal spread of a morbilliform rash and Koplik spots; it does not cause targetoid lesions. * **Option D:** While EM can follow a streptococcal sore throat, the priority in a 50-year-old is to rule out drug-induced triggers like phenytoin, which carry a higher risk of systemic complications. **NEET-PG High-Yield Pearls:** * **Target Lesion Anatomy:** Three zones—a central dusky/bullous area, a pale intermediate ring of edema, and an outer erythematous halo. * **Most Common Cause:** HSV (Type 1 > Type 2). * **Drug Triggers:** "SOAPS"—**S**ulfonamides, **O**thers (Phenytoin/Allopurinol), **A**nticonvulsants, **P**enicillins, **S**alicylates. * **EM Minor vs. Major:** EM Major involves at least one mucosal surface and systemic symptoms, whereas EM Minor involves only the skin.

Q: The Wood's lamp filter is made of?

Nickel oxide and silica. **Explanation:** The **Wood’s lamp** is a diagnostic tool that emits long-wave ultraviolet radiation (UVA). The core component of the lamp is its filter, known as the **Wood’s filter**. 1. **Why Option B is correct:** The filter is composed of **Barium silicate with 9% Nickel oxide**. This specific chemical composition allows the filter to be opaque to all visible light rays except for a narrow band between **320 nm and 400 nm** (peaking at 365 nm). The nickel oxide acts as the primary filtering agent that blocks visible light, while the silica (silicate) provides the structural glass base. 2. **Why other options are incorrect:** * **Option A & C:** While chromium, copper, and barium are used in various optical glass manufacturing, they do not possess the specific property of filtering out visible light while permitting UVA transmission required for Wood's lamp diagnostics. * **Option D:** Zinc oxide is commonly used in sunscreens as a physical blocker of UV rays, which is the opposite function of a Wood’s lamp filter. **Clinical Pearls for NEET-PG:** * **Principle:** It works on the principle of **fluorescence**, where the skin or hair absorbs low-wavelength UV light and emits longer-wavelength visible light. * **High-Yield Fluorescence Colors:** * **Tinea capitis (Microsporum):** Brilliant Green. * **Erythrasma (Corynebacterium minutissimum):** Coral Red (due to porphyrins). * **Pseudomonas infection:** Yellowish-green (due to pyoverdin). * **Porphyria Cutanea Tarda:** Pink-orange (urine fluorescence). * **Vitiligo:** "Milky white" (due to total loss of melanin, which normally absorbs UV light). * **Examination Tip:** The exam must be performed in a **dark room** to allow the faint fluorescence to be visible.

Q: A Tzanck smear is useful for the diagnosis of which of the following conditions?

Herpes virus infection. **Explanation:** The **Tzanck smear** is a rapid bedside diagnostic test used primarily for the identification of **Herpes virus infections**, including Herpes Simplex Virus (HSV-1, HSV-2) and Varicella-Zoster Virus (VZV). **Why Option B is Correct:** The procedure involves scraping the base of a freshly opened vesicle and staining it (typically with Giemsa, Wright, or Leishman stain). The hallmark finding is the presence of **multinucleated giant cells** (formed by the fusion of infected keratinocytes) and **acantholytic cells**. It is important to note that while a Tzanck smear confirms a herpesvirus infection, it cannot distinguish between HSV and VZV. **Analysis of Incorrect Options:** * **A. Erythrasma:** Caused by *Corynebacterium minutissimum*. Diagnosis is made using **Wood’s lamp** (showing coral-red fluorescence) or KOH mount showing Gram-positive bacilli. * **C. Superficial Pseudomonas infection:** Often presents as "Green Nail Syndrome" or ecthyma gangrenosum. Diagnosis is clinical or via culture; Wood’s lamp may show apple-green fluorescence. * **D. Pneumocystis infection:** *Pneumocystis jirovecii* is diagnosed using induced sputum or bronchoalveolar lavage (BAL) stained with **Gomori Methenamine Silver (GMS)** or Toluidine blue. **High-Yield Clinical Pearls for NEET-PG:** * **Tzanck Smear Findings:** Look for "Multinucleated Giant Cells" and "Cowdry Type A" intranuclear inclusion bodies. * **Other uses of Tzanck:** It can also be used in **Pemphigus Vulgaris** (to see Tzanck/acantholytic cells) and **Molluscum Contagiosum** (to see Henderson-Patterson bodies). * **Gold Standard:** While Tzanck is fast, **Viral Culture** or **PCR** is the gold standard for herpes diagnosis.

Q: Nikolsky's sign is positive in each of the following conditions, EXCEPT:

Psoriasis. **Explanation:** **Nikolsky’s Sign** is a clinical dermatological sign where slight lateral pressure applied to the skin results in the separation of the superficial layer (epidermis) from the deeper layer, leading to an erosion. It indicates a loss of intercellular cohesion (**acantholysis**) or widespread epidermal necrosis. **Why Psoriasis is the Correct Answer:** Psoriasis is a chronic inflammatory condition characterized by epidermal hyperplasia (acanthosis) and hyperkeratosis, rather than the loss of cell-to-cell adhesion. The skin layers are tightly bound; therefore, Nikolsky’s sign is **negative**. In Psoriasis, the characteristic clinical sign is **Auspitz sign** (pinpoint bleeding upon removal of scales). **Analysis of Other Options:** * **Pemphigus:** This is the classic condition for a positive Nikolsky sign. Autoantibodies against desmogleins cause acantholysis within the epidermis. * **Toxic Epidermal Necrolysis (TEN):** A severe drug reaction causing extensive keratinocyte death and full-thickness epidermal necrosis, leading to a positive Nikolsky sign. * **Staphylococcal Scalded Skin Syndrome (SSSS):** Caused by exfoliative toxins from *S. aureus* that cleavage desmoglein-1 in the upper epidermis (stratum granulosum), resulting in a positive sign. **Clinical Pearls for NEET-PG:** * **Direct Nikolsky:** Elicited on involved/perilesional skin. * **Indirect/Marginal Nikolsky:** Extension of an existing blister by applying pressure to the roof. * **False Nikolsky (Shevelly Sign):** Seen in subepidermal blisters like Bullous Pemphigoid (where the sign is typically negative, but the blister can be moved laterally). * **Key Differentiator:** Nikolsky sign is **Positive** in Pemphigus Vulgaris (Intraepidermal) but **Negative** in Bullous Pemphigoid (Subepidermal).

Q: Tzank test is positive in the following conditions, except?

Epstein-Barr Virus (EBV) infection. The **Tzanck smear** is a rapid bedside diagnostic test used primarily to identify **multinucleated giant cells**, which are characteristic of certain viral infections and autoimmune blistering diseases. ### **Why EBV is the Correct Answer** While the **Epstein-Barr Virus (EBV)** belongs to the *Herpesviridae* family, it primarily infects B-lymphocytes and epithelial cells of the oropharynx. It typically presents as Infectious Mononucleosis or Oral Hairy Leukoplakia. Unlike other herpes viruses, EBV does not cause the formation of intraepidermal vesicles or the specific cytopathic changes (like multinucleation and acantholysis) that a Tzanck smear detects. Therefore, the Tzanck test is **negative** in EBV infections. ### **Analysis of Other Options** * **Herpes Simplex (HSV-1 & 2):** Causes "dew drops on rose petals" vesicles. Tzanck smear shows characteristic multinucleated giant cells with **molding, margination of chromatin, and multinucleation** (the 3 M’s). * **Varicella (Chickenpox):** Caused by the Varicella-Zoster Virus (VZV). It produces intraepidermal vesicles where Tzanck cells are abundant. * **Herpes Zoster (Shingles):** Also caused by VZV (reactivation). Like Varicella and HSV, it shows positive Tzanck smears because these viruses are **epidermotropic**. ### **NEET-PG High-Yield Pearls** * **Tzanck Smear Findings:** Look for **multinucleated giant cells** (Tzanck cells). * **Other Positive Conditions:** Apart from HSV/VZV, the Tzanck test is positive in **Pemphigus Vulgaris** (shows acantholytic cells) and **Cytomegalovirus (CMV)** (rarely, but can show "owl’s eye" inclusions). * **Stains Used:** Giemsa, Wright’s, or Leishman stain. * **Limitation:** The Tzanck test can confirm a Herpes group infection but **cannot differentiate** between HSV-1, HSV-2, and VZV. For differentiation, Viral Culture or PCR is required.

Question 1

Which pigment, when yellow, brown, or black, shows fluorescence under UV light?

Accepted Answer

Tetracycline

Answer

Internal resorption

Answer

Fluorosis

Answer

None of the above

Question 2

Which one of the following is not a lichenoid reaction?

Accepted Answer

Pemphigus

Answer

Lichenoid contact reaction

Answer

Lichenoid drug eruption

Answer

Lichenoid reaction of graft versus host disease

Question 3

Regarding Erythema multiforme, all are true except?

Accepted Answer

Absence of vesicles

Answer

Presence of target lesions

Answer

Involvement of face and neck regions

Answer

Sign of internal malignancy

Question 4

Clutch claw and ball appearance is seen in which of the following conditions?

Accepted Answer

Lichen nitidus

Answer

Pemphigus

Answer

Lichen planus

Answer

Psoriasis

Question 5

What is the classical presentation described?

Accepted Answer

Pityriasis Rosea

Answer

Pityriasis Alba

Answer

Pityriasis Rubra

Answer

Pityriasis Versicolor

Question 6

A 50-year-old woman develops pink macules and papules on her hands and forearms in association with a sore throat. The lesions are targetlike, with the centers a dusky violet. A diagnosis of erythema multiforme is made. What is the most important information to obtain from this patient's history?

Accepted Answer

The patient is taking phenytoin.

Answer

The patient has been using tampons.

Answer

The patient has never had measles.

Answer

No other family members have a sore throat.

Question 7

The Wood's lamp filter is made of?

Accepted Answer

Nickel oxide and silica

Answer

Tin and chromium oxide

Answer

Copper oxide and Barium oxide

Answer

Zinc oxide

Question 8

A Tzanck smear is useful for the diagnosis of which of the following conditions?

Accepted Answer

Herpes virus infection

Answer

Erythrasma

Answer

Superficial Pseudomonas infection

Answer

Pneumocystis infection

Question 9

Nikolsky's sign is positive in each of the following conditions, EXCEPT:

Accepted Answer

Psoriasis

Answer

Pemphigus

Answer

Toxic epidermal necrolysis

Answer

Staphylococcal scalded skin syndrome

Question 10

Tzank test is positive in the following conditions, except?

Accepted Answer

Epstein-Barr Virus (EBV) infection

Answer

Herpes Zoster

Answer

Herpes Simplex

Answer

Varicella

Basic Dermatology — MCQs

Basic Dermatology — MCQs

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