Dermatological Procedures — MCQs

Dermatological Procedures Indian Medical PG Practice Questions and MCQs

Question 11: Cryosurgery utilizes which of the following?

A. Nitrous oxide (Correct Answer)
B. Carbon dioxide
C. Liquid oxygen
D. Nitric dioxide

Explanation: **Explanation:** Cryosurgery is a dermatological procedure that involves the controlled destruction of tissue by applying extreme cold. The mechanism of action involves the formation of intracellular ice crystals, leading to cell membrane rupture and vascular stasis. **1. Why Nitrous Oxide (N₂O) is Correct:** Nitrous oxide is a commonly used cryogen in dermatology, particularly in closed-system cryoprobes. It has a boiling point of **-88.5°C**. It is preferred in clinical settings because it is relatively easy to store in pressurized cylinders and provides a temperature cold enough to treat benign lesions (like warts and seborrheic keratosis) and some premalignant conditions. **2. Analysis of Incorrect Options:** * **Carbon Dioxide (CO₂):** While CO₂ snow (dry ice) was historically used (boiling point **-78.5°C**), it is less commonly used today compared to N₂O and Liquid Nitrogen due to lower efficacy in treating deeper lesions. * **Liquid Oxygen:** This is **never** used in cryosurgery because it is highly flammable and poses a significant explosion risk in a clinical environment. * **Nitric Dioxide (NO₂):** This is a toxic gas and a common air pollutant; it has no therapeutic application in cryosurgery. **3. High-Yield Clinical Pearls for NEET-PG:** * **Liquid Nitrogen (LN₂):** This is the **"Gold Standard"** and most common cryogen used. It has the lowest boiling point (**-196°C**) and is the treatment of choice for malignant lesions. * **Mechanism of Cell Death:** The "Slow Thaw" phase is more lethal to cells than the "Fast Freeze" phase. * **Contraindications:** Avoid in patients with cold urticaria, cryoglobulinemia, or over areas with compromised circulation. * **Common Side Effect:** Permanent hypopigmentation (melanocytes are highly sensitive to cold).

Question 12: Patch test is done to document which type of hypersensitivity?

A. Type I hypersensitivity
B. Delayed type hypersensitivity (Correct Answer)
C. Autoimmune disease
D. Immunocomplex deposition

Explanation: ### 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).

Question 13: All of the following are used in cryosurgery except?

A. Liquid nitrogen
B. Argon
C. Helium (Correct Answer)
D. Carbon dioxide

Explanation: **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."

Question 14: Wood's light can be used for the evaluation of which of the following conditions?

A. Tinea capitis
B. Freckles
C. Vitiligo
D. All of the above (Correct Answer)

Explanation: **Explanation:** Wood’s light (UV light with a wavelength of **365 nm**) is a fundamental diagnostic tool in dermatology that utilizes fluorescence and pigmentary contrast to identify various skin conditions. * **Tinea Capitis:** Wood’s light is used to detect fungal infections of the hair. Specifically, **Microsporum** species produce a characteristic **bright blue-green fluorescence** due to pteridine. (Note: *Trichophyton tonsurans*, the most common cause, does not fluoresce). * **Vitiligo:** It is used to differentiate between **depigmented** (vitiligo) and **hypopigmented** (pityriasis alba) lesions. In vitiligo, the complete loss of melanin causes the light to be reflected back, resulting in a **stark, bright "chalky white"** appearance with sharp margins. * **Freckles (Lentigines/Pigmentation):** Wood’s light helps determine the depth of melanin. **Epidermal pigmentation** (like freckles) becomes more accentuated and darker under the light, whereas dermal pigmentation fades or becomes less apparent. **High-Yield Clinical Pearls for NEET-PG:** * **Erythrasma:** Shows a pathognomonic **Coral Red** fluorescence (due to Coproporphyrin III from *Corynebacterium minutissimum*). * **Pseudomonas:** Shows **Yellow-Green** fluorescence (due to Pyoverdin). * **Porphyria Cutanea Tarda:** Urine shows **Pink-Orange** fluorescence. * **Pityriasis Versicolor:** Shows **Yellowish-white/Copper-orange** fluorescence. * **Scabies:** While not for the mite itself, Wood's light can be used to track burrows if fluorescein dye is applied.

Question 15: What is the wavelength of light produced by a Wood's lamp?

A. 320 nm
B. 360 nm (Correct Answer)
C. 400 nm
D. 760-800 nm

Explanation: **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 16: What is the primary diagnostic procedure for basal cell carcinoma?

A. Wedge biopsy (Correct Answer)
B. Shave biopsy
C. Incisional biopsy
D. Punch biopsy

Explanation: **Explanation:** The primary diagnostic procedure for **Basal Cell Carcinoma (BCC)** is a **Wedge Biopsy**. BCC is a locally invasive tumor that often presents with a "pearly" border and central ulceration (Rodent ulcer). To confirm the diagnosis and assess the depth and subtype (e.g., nodular vs. morpheaform), a full-thickness specimen is required. A wedge biopsy provides a cross-section of the tumor, including the epidermis, dermis, and subcutaneous fat, allowing the pathologist to evaluate the peripheral margins and the relationship of the tumor to the surrounding stroma. **Analysis of Options:** * **Wedge Biopsy (Correct):** It is the gold standard because it provides a representative sample of both the center and the margin of the lesion, ensuring high diagnostic accuracy. * **Shave Biopsy:** While commonly used in clinical practice for superficial lesions, it is often inadequate for BCC as it may miss the deeper invasive component, leading to an underestimation of the tumor's aggressiveness. * **Incisional Biopsy:** This involves removing only a portion of the lesion. While useful for very large tumors, a wedge biopsy is specifically preferred for BCC to capture the architecture of the advancing edge. * **Punch Biopsy:** This provides a cylindrical core of tissue. While useful for inflammatory conditions, it may sample only a small area of a heterogeneous tumor, potentially missing diagnostic features found at the periphery. **High-Yield Clinical Pearls for NEET-PG:** * **Most common site:** Upper 2/3rd of the face (above the line joining the tragus to the angle of the mouth). * **Characteristic Histology:** Peripheral palisading of nuclei and retraction artifacts (clefts between tumor nests and stroma). * **Treatment of Choice:** Mohs Micrographic Surgery (MMS) provides the highest cure rate and maximal tissue conservation. * **Inheritance:** Associated with **Gorlin Syndrome** (PTCH1 gene mutation).

Question 17: What is the first-line treatment for keloid?

A. Intralesional injection of corticosteroid (Correct Answer)
B. Topical corticosteroid
C. Radiotherapy
D. Wide surgical excision

Explanation: **Explanation:** **1. Why Intralesional Corticosteroid is Correct:** Intralesional injection of corticosteroids (specifically **Triamcinolone Acetonide**, 10–40 mg/mL) is the gold-standard, first-line treatment for keloids. Corticosteroids work by inhibiting fibroblast proliferation, reducing collagen synthesis, and increasing collagenase levels, which helps flatten the lesion and relieve symptoms like pruritus and pain. **2. Why Other Options are Incorrect:** * **Topical Corticosteroids:** These have poor penetration through the thick, keratinized epidermis of a keloid and are generally ineffective as a primary treatment. * **Radiotherapy:** While effective in inhibiting fibroblasts, it is reserved for recalcitrant cases or as an adjuvant therapy post-surgery due to the potential risk of long-term carcinogenesis. * **Wide Surgical Excision:** When used alone, surgical excision has an extremely high recurrence rate (50–100%), often resulting in a larger keloid than the original. It should only be performed in combination with adjuvant therapies like intralesional steroids or pressure therapy. **Clinical Pearls for NEET-PG:** * **Triamcinolone Acetonide** is the most commonly used agent; side effects include hypopigmentation and skin atrophy. * **Keloid vs. Hypertrophic Scar:** Keloids extend beyond the boundaries of the original wound and do not regress spontaneously, whereas hypertrophic scars stay within the wound margins and may regress over time. * **Common Sites:** Presternal area, deltoid, and earlobes are high-risk zones. * **Combination Therapy:** For better results, intralesional steroids are often combined with **Cryotherapy** (which softens the keloid for easier injection) or **5-Fluorouracil**.

Question 18: Which of the following is not an agent used in chemical peeling?

A. Glycolic acid
B. Kojic acid (Correct Answer)
C. Phenol
D. Salicylic acid

Explanation: In chemical peeling, specific chemical agents are applied to the skin to cause controlled destruction of a portion of the epidermis and/or dermis, leading to exfoliation and subsequent regeneration of new tissues. **Why Kojic Acid is the correct answer:** While **Kojic acid** is a common ingredient in dermatological practice, it is classified as a **skin-lightening (depigmenting) agent**, not a primary peeling agent. It works by inhibiting tyrosinase, the enzyme responsible for melanin synthesis. It is frequently used as an adjuvant in "pre-peel" priming creams or post-procedure maintenance to treat hyperpigmentation, but it does not possess the keratolytic or caustic properties required to induce a chemical peel on its own. **Analysis of incorrect options:** * **Glycolic acid (A):** An Alpha-hydroxy acid (AHA) derived from sugarcane. It is the most common agent used for **superficial peels**. * **Phenol (C):** A potent agent used for **deep peels**. It causes protein coagulation and can reach the reticular dermis; however, it requires cardiac monitoring due to potential systemic toxicity (arrhythmias). * **Salicylic acid (D):** A Beta-hydroxy acid (BHA). It is lipophilic, making it the agent of choice for **acne-prone skin** as it can penetrate the sebaceous unit. **High-Yield Clinical Pearls for NEET-PG:** * **Jessner’s Solution:** A popular combination peel containing Salicylic acid (14g), Lactic acid (14g), and Resorcinol (14g) in Ethanol. * **Trichloroacetic acid (TCA):** Used for medium-depth peels. The "frosting" seen during the procedure is due to protein denaturation. * **Priming:** Patients are often started on Tretinoin or Hydroquinone 2–4 weeks before a peel to ensure uniform penetration and prevent post-inflammatory hyperpigmentation (PIH).

Question 19: What is the initial treatment of a keloid?

A. Topical steroid
B. Intralesional steroid (Correct Answer)
C. Excision
D. Radiotherapy

Explanation: **Explanation:** The primary goal in treating a keloid is to reduce fibroblast proliferation and collagen synthesis. **Intralesional steroid injection** (specifically Triamcinolone Acetonide, 10–40 mg/mL) is the **first-line treatment** for keloids. Corticosteroids inhibit the expression of transforming growth factor-beta (TGF-β) and increase collagenase activity, which helps flatten the lesion and relieve symptoms like itching and pain. **Analysis of Options:** * **Topical Steroids (A):** These are ineffective for keloids because the thick, fibrous collagen bundle acts as a barrier, preventing the drug from reaching the deep dermis where the pathology lies. * **Excision (C):** Surgical excision alone has an extremely high recurrence rate (45–100%), often resulting in a new keloid larger than the original. It is never the initial monotherapy; it is reserved for refractory cases and must be combined with adjuvant therapies (like pressure or radiation). * **Radiotherapy (D):** This is a secondary or adjuvant treatment. It is typically used immediately post-excision to prevent recurrence by inhibiting myofibroblast activity. It is not used as an initial standalone treatment due to the risk of long-term side effects. **High-Yield Clinical Pearls for NEET-PG:** * **Keloid vs. Hypertrophic Scar:** Keloids extend beyond the boundaries of the original wound and rarely regress, whereas hypertrophic scars stay within the wound margins and may regress over time. * **Common Site:** Pre-sternal area, earlobes, and deltoid region. * **Combination Therapy:** The most effective approach for resistant keloids is often a combination of **Cryotherapy** (to soften the tissue) followed by **Intralesional Triamcinolone**. * **Side Effects:** Watch for skin atrophy, telangiectasia, and hypopigmentation at the injection site.

Question 20: Mohs micrographic excision for basal cell carcinoma is used for all of the following indications except:

A. Recurrent tumor
B. Tumor less than 2 cm in diameter (Correct Answer)
C. Tumors with aggressive histology
D. Tumors with perineural invasion

Explanation: **Explanation:** Mohs Micrographic Surgery (MMS) is a specialized surgical technique designed to provide the highest possible cure rate while maximizing tissue conservation. The core principle of MMS is the **100% evaluation of peripheral and deep surgical margins** through horizontal sectioning while the patient waits. **Why Option B is the correct answer:** Size alone is not an absolute indication for Mohs surgery. In fact, **tumors larger than 2 cm** (especially in the "M" or "H" zones of the face) are considered high-risk and are primary indications for MMS. A small tumor (<2 cm) with non-aggressive histology in a low-risk area (like the trunk or extremities) is typically treated with standard wide local excision, as Mohs would be unnecessarily resource-intensive. **Analysis of Incorrect Options:** * **A. Recurrent tumor:** Recurrent BCCs often have unpredictable "finger-like" extensions and subclinical spread, making Mohs the gold standard to ensure complete removal. * **C. Aggressive histology:** Subtypes like morpheaform, infiltrative, or micronodular BCC have higher rates of local recurrence and require the precise margin control offered by Mohs. * **D. Perineural invasion:** This indicates a high risk of tracking along nerve sheaths far beyond the visible tumor border, necessitating microscopic mapping. **High-Yield Clinical Pearls for NEET-PG:** * **Indications for Mohs (The "H" Zone):** High-risk areas include the "Mask area" of the face (eyelids, nose, lips, ears, temples). * **Tissue Sparing:** It is the treatment of choice for areas where cosmesis and function are critical (e.g., digits, genitalia). * **Cure Rate:** MMS offers a 99% cure rate for primary BCC and 94-96% for recurrent BCC. * **Key Difference:** Unlike standard pathology (vertical "bread-loafing" which examines <1% of margins), Mohs examines **100% of the margin.**

Practice by Chapter

Skin Biopsy Techniques

Practice Questions

Cryotherapy

Practice Questions

Electrosurgery

Practice Questions

Curettage and Electrodessication

Practice Questions

Excisional Surgery

Practice Questions

Mohs Micrographic Surgery

Practice Questions

Chemical Peels

Practice Questions

Dermabrasion and Microdermabrasion

Practice Questions

Laser Therapy Basics

Practice Questions

Injectable Fillers and Botulinum Toxin

Practice Questions

Photodynamic Therapy

Practice Questions

Wound Care and Dressings

Practice Questions

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