Dermatological Procedures Practice Questions

Q: A child presents with erythematous, non-blanching, bosselated lesions on the left side of the face. What is the treatment of choice?

Flash light-pumped dye laser. ### Explanation **Correct Answer: C. Flash light-pumped dye laser (FPDL)** The clinical description—erythematous, non-blanching, bosselated (bumpy/lobulated) lesions—is characteristic of a **Port-Wine Stain (PWS)** or a **Capillary Malformation**. The **Flash light-pumped pulsed dye laser (FPDL)**, typically at a wavelength of **585 nm or 595 nm**, is the gold standard treatment for vascular lesions like PWS. It operates on the principle of **selective photothermolysis**. The laser energy is specifically absorbed by **oxyhemoglobin** (the chromophore) within the blood vessels, leading to thermal destruction of the vessel walls while sparing the surrounding skin. This minimizes scarring, making it ideal for pediatric facial lesions. **Analysis of Incorrect Options:** * **A. Erbium:YAG Laser (2940 nm):** This is an ablative laser used primarily for skin resurfacing and removing benign epidermal growths. It targets water, not hemoglobin. * **B. Nd:YAG Laser (1064 nm):** While used for deeper vascular malformations due to its high penetration depth, it carries a higher risk of scarring and is not the first-line "treatment of choice" for superficial PWS. * **D. Q-switched Ruby Laser (694 nm):** This is primarily used for pigmentary disorders (like Nevus of Ota) and black/blue tattoo removal. It targets melanin, not vascular structures. **Clinical Pearls for NEET-PG:** * **Chromophore for Vascular Lasers:** Oxyhemoglobin. * **Chromophore for Pigment/Tattoo Lasers:** Melanin/Exogenous ink. * **Port-Wine Stains:** Unlike strawberry hemangiomas, PWS do not involute spontaneously; they grow proportionately with the child and may become "bosselated" or hypertrophic over time. * **Sturge-Weber Syndrome:** Always rule this out if a PWS involves the V1/V2 distribution of the trigeminal nerve.

Q: Patch test is done to document which type of hypersensitivity?

Delayed type hypersensitivity. ### Explanation **Correct Answer: B. Delayed type hypersensitivity** The **Patch Test** is the gold standard diagnostic tool for **Allergic Contact Dermatitis (ACD)**. ACD is a classic example of **Type IV Hypersensitivity** (also known as Delayed-type Hypersensitivity). * **Mechanism:** This reaction is **T-cell mediated** (specifically Th1 cells). When an allergen is applied to the skin, it is processed by Langerhans cells and presented to memory T-cells. This process takes time, which is why the test results are typically read at **48 hours** (initial reading) and **72–96 hours** (delayed reading). **Why other options are incorrect:** * **Type I Hypersensitivity (Option A):** This is IgE-mediated (immediate). It is tested using the **Skin Prick Test** or RAST, used for conditions like urticaria or asthma. * **Autoimmune disease (Option C):** While some skin diseases are autoimmune (e.g., Pemphigus), they are diagnosed via biopsy and Direct Immunofluorescence (DIF), not patch testing. * **Immunocomplex deposition (Option D):** This refers to **Type III Hypersensitivity** (e.g., SLE or Vasculitis), which involves antigen-antibody complexes depositing in tissues. **High-Yield Clinical Pearls for NEET-PG:** * **Standard Series:** The most common series used globally is the **European Standard Series**. * **Common Allergens:** The most common allergen globally is **Nickel** (found in artificial jewelry). * **Reading Results:** * (+) = Erythema and edema. * (++) = Erythema, edema, and papulovesicles. * (+++) = Confluent vesicles or bullae. * **Open Patch Test:** Used for testing substances with potential irritancy (e.g., shampoos). * **Photopatch Test:** Used for Photoallergic Contact Dermatitis (e.g., reactions to NSAIDs or sunscreens).

Q: All of the following are used in cryosurgery except?

Helium. **Explanation:** Cryosurgery involves the controlled destruction of unwanted tissue by the application of extreme cold. The efficacy of a cryogen depends on its boiling point; the lower the boiling point, the more effective it is at causing rapid tissue necrosis. **Why Helium is the correct answer:** Helium is **not** used as a cryogen in clinical dermatology. While liquid helium has an extremely low boiling point (-268.9°C), it is technically difficult to store, prohibitively expensive, and lacks the practical delivery systems required for cutaneous surgery. In medical contexts, helium is more commonly used in "Heliox" mixtures for respiratory distress or as a coolant for MRI magnets, but not for cryosurgery. **Analysis of other options:** * **Liquid Nitrogen (A):** The "Gold Standard" in cryosurgery. It has a boiling point of **-195.8°C**. It is the most commonly used agent due to its high efficacy in treating both benign and malignant lesions. * **Argon (B):** Used primarily in **cryoablation probes** (often for internal tumors like prostate or renal cell carcinoma) via the Joule-Thomson effect. * **Carbon Dioxide (D):** Used as "CO2 snow" or via specialized probes. It has a temperature of **-78.5°C**. While less potent than liquid nitrogen, it was historically popular for treating acne and hemangiomas. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism of Damage:** Cryosurgery causes cell death via ice crystal formation (intracellular), vascular stasis, and protein denaturation. * **Temperature Thresholds:** Benign lesions require -20°C to -30°C; Malignant lesions require -40°C to -50°C. * **Melanocyte Sensitivity:** Melanocytes are highly sensitive to cold (-4°C to -7°C), which is why **permanent hypopigmentation** is a common side effect of cryotherapy. * **Nitrous Oxide (-89.5°C):** Another common cryogen used in portable "cryo-pens."

Q: What is the wavelength of light produced by a Wood's lamp?

360 nm. **Explanation:** A **Wood’s lamp** is a diagnostic tool that emits long-wave ultraviolet radiation (UVA). It utilizes a high-pressure mercury arc light source filtered through a **Wood’s filter** (composed of barium silicate with 9% nickel oxide). This filter is opaque to all light rays except for a specific band, peaking at **360 nm** (range 320–400 nm). When this light hits certain structures (fluorophores), they emit visible light of a longer wavelength, resulting in characteristic fluorescence. **Analysis of Options:** * **B (360 nm):** This is the peak wavelength emitted by the Wood's lamp. It falls within the UVA spectrum and is the standard value tested in medical examinations. * **A (320 nm):** This represents the lower limit of the UVA spectrum and the cutoff for the Wood's filter, but it is not the peak emission wavelength. * **C (400 nm):** This is the upper limit of the UV spectrum where it transitions into visible violet light. * **D (760-800 nm):** This range corresponds to **Infrared light**, which is used in heat therapy, not diagnostic fluorescence. **High-Yield Clinical Pearls for NEET-PG:** * **Tinea Capitis:** *Microsporum* species show **Bright Green** fluorescence (due to Pteridine). Note: *Trichophyton tonsurans* (common cause of endothrix) does **not** fluoresce. * **Erythrasma:** Caused by *Corynebacterium minutissimum*; shows **Coral Red** fluorescence (due to Coproporphyrin III). * **Porphyria Cutanea Tarda:** Urine shows **Pink-Orange** fluorescence. * **Pseudomonas:** Shows **Yellow-Green** fluorescence (due to Pyoverdin). * **Vitiligo:** Shows **Milky White** fluorescence (due to total loss of melanin, which normally absorbs UV light).

Question 1

Which of the following is NOT true regarding patch testing?

Accepted Answer

False negative results can occur in patients with angry back syndrome

Answer

Used to diagnose allergic contact dermatitis

Answer

Readings are typically taken after 48 hours

Answer

The T.R.U.E. test is a type of patch test

Question 2

A child presents with erythematous, non-blanching, bosselated lesions on the left side of the face. What is the treatment of choice?

Accepted Answer

Flash light-pumped dye laser

Answer

Erbium laser

Answer

Nd-YAG laser

Answer

Q-switched ruby laser

Question 3

Patch test is done to document which type of hypersensitivity?

Accepted Answer

Delayed type hypersensitivity

Answer

Type I hypersensitivity

Answer

Autoimmune disease

Answer

Immunocomplex deposition

Question 4

All of the following are used in cryosurgery except?

Accepted Answer

Helium

Answer

Liquid nitrogen

Answer

Argon

Answer

Carbon dioxide

Question 5

What is the wavelength of light produced by a Wood's lamp?

Accepted Answer

360 nm

Answer

320 nm

Answer

400 nm

Answer

760-800 nm

Dermatological Procedures — MCQs

Dermatological Procedures — MCQs

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