Dermatological Pharmacology — MCQs

Q: A patient developed fixed drug eruptions after taking certain medications. Which of the following drugs is known to cause these skin lesions?

All of the above. **Explanation:** **Fixed Drug Eruption (FDE)** is a unique type of cutaneous drug reaction characterized by the recurrence of a lesion (usually a dusky red or violaceous macule) at the **exact same anatomical site** every time the offending drug is ingested. This occurs due to the persistence of **CD8+ memory T-cells** in the basal keratinocytes at the site of the lesion. **Why Option D is correct:** All three drugs listed are classic and high-yield triggers for FDE: * **Phenolphthalein:** Historically the most common cause (found in older laxatives). * **Aspirin (NSAIDs):** A very frequent trigger in clinical practice. * **Dapsone (Sulfonamides):** Sulfonamides are among the most common drug classes associated with FDE. **Analysis of Options:** * **Phenolphthalein:** Often presents as "bullous" FDE. * **Aspirin:** Along with other NSAIDs (like Ibuprofen and Naproxen), it is a leading cause of multi-focal FDE. * **Dapsone:** As a sulfone, it shares cross-reactivity patterns and is a well-documented cause. **High-Yield Clinical Pearls for NEET-PG:** 1. **Most Common Site:** The **glans penis** is the most common site for FDE, followed by the lips and palms. 2. **Commonest Causes (Overall):** NSAIDs, Sulfonamides (Cotrimoxazole), Tetracyclines, and Anticonvulsants. 3. **Clinical Feature:** Lesions often leave behind **post-inflammatory hyperpigmentation (PIH)** after healing. 4. **Refractory Period:** After an eruption, there is a brief refractory period where the drug may not cause a reaction. 5. **Diagnosis:** Primarily clinical; however, a **Patch Test** performed at the site of the previous lesion (not on the back) can confirm the offending agent.

Q: Dapsone is used in which of the following conditions?

Dermatitis herpetiformis. **Explanation:** **Dapsone (Diaminodiphenyl sulfone)** is the drug of choice for **Dermatitis Herpetiformis (DH)**. DH is an autoimmune blistering disorder characterized by IgA deposits at the dermal papillae, leading to intense pruritus and neutrophilic infiltration. Dapsone works by inhibiting the enzyme myeloperoxidase and preventing the chemotaxis of neutrophils to the skin, providing rapid symptomatic relief (often within 24–48 hours). **Analysis of Options:** * **A. Dermatitis Herpetiformis:** Correct. It is the primary indication for Dapsone in dermatology. * **B. Pityriasis Rosea:** This is a self-limiting inflammatory condition (likely viral/HHV-6,7). Treatment is supportive (antihistamines, topical steroids); Dapsone has no role. * **C. Contact Dermatitis:** This is a Type IV hypersensitivity reaction. Management involves allergen avoidance and topical or systemic corticosteroids. * **D. Oculocutaneous Albinism:** This is a genetic disorder of melanin synthesis. There is no pharmacological "cure"; management focuses on photoprotection and monitoring for skin cancers. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism of Action:** Antifolate (inhibits dihydropteroate synthase) and anti-inflammatory (inhibits neutrophil recruitment). * **Other Indications:** Leprosy (part of MDT), Pemphigoid, Subcorneal Pustular Dermatosis (Sneddon-Wilkinson disease), and Brown Recluse spider bites. * **Mandatory Pre-screening:** Always check **G6PD levels** before starting Dapsone to prevent severe **hemolytic anemia**. * **Side Effects:** Dose-dependent hemolysis, methemoglobinemia (presents as cyanosis), and the "Dapsone Syndrome" (fever, malaise, exfoliative dermatitis, and hepatitis).

Q: Which of the following monoclonal antibodies is used in the treatment of atopic dermatitis?

Dupilumab. **Explanation:** **1. Why Dupilumab is Correct:** Dupilumab is a fully human monoclonal antibody that targets the **interleukin-4 receptor alpha (IL-4Rα) subunit**. By binding to this subunit, it inhibits the signaling of both **IL-4 and IL-13**. These cytokines are the key drivers of **Type 2 (Th2) inflammation**, which is the primary pathophysiological mechanism in atopic dermatitis. It is currently the first-line systemic biologic approved for moderate-to-severe atopic dermatitis unresponsive to topical therapies. **2. Why the Other Options are Incorrect:** * **Ipilimumab:** A checkpoint inhibitor that targets **CTLA-4**. It is used in the treatment of advanced melanoma and renal cell carcinoma. * **Durvalumab:** A checkpoint inhibitor that targets **PD-L1**. It is primarily used in the treatment of non-small cell lung cancer (NSCLC) and bladder cancer. * **Reslizumab:** An interleukin-5 (**IL-5**) antagonist. It is used as add-on maintenance treatment for severe eosinophilic asthma, not atopic dermatitis. **3. High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Dual inhibitor of IL-4 and IL-13. * **Common Side Effect:** The most characteristic side effect of Dupilumab is **allergic conjunctivitis** and blepharitis. * **Other Indications:** It is also FDA-approved for moderate-to-severe asthma (eosinophilic phenotype) and chronic rhinosinusitis with nasal polyposis. * **Memory Aid:** "Dupi" stops the "D"ermatitis by blocking the "4" and "13" (IL-4/13).

Q: All of the following statements are true regarding warfarin toxicity (skin necrosis) except?

Most common sites are buttocks and abdomen.. **Explanation:** Warfarin-induced skin necrosis (WISN) is a rare but severe complication occurring in approximately 0.01% to 0.1% of patients treated with vitamin K antagonists. **Why Option B is the correct answer (The False Statement):** While the buttocks and abdomen are common sites, the **most common sites** for warfarin necrosis are areas with **high subcutaneous fat content**, specifically the **breasts** (in females), followed by the thighs and buttocks. The statement in Option B is considered the "except" because it overlooks the breast as the primary site of predilection. **Analysis of Other Options:** * **Option A:** True. Necrosis typically occurs **3 to 10 days after initiation** of therapy, often due to a large loading dose. * **Option C:** True. Warfarin inhibits Vitamin K-dependent factors (II, VII, IX, X) and anticoagulant proteins (C and S). **Protein C has a shorter half-life** (6 hours) compared to clotting factors. This creates a transient "prothrombotic window" where natural anticoagulants are depleted while procoagulant factors are still active, leading to microvascular thrombosis. * **Option D:** True. Starting **Low Molecular Weight Heparin (LMWH)** as a "bridge" provides immediate anticoagulation, preventing the thrombotic complications during the initial drop in Protein C levels. **Clinical Pearls for NEET-PG:** * **Risk Factor:** Underlying **Protein C deficiency** is the most significant risk factor. * **Clinical Presentation:** Sudden onset of painful, erythematous, or purpuric lesions that rapidly progress to **hemorrhagic bullae and eschar**. * **Management:** Immediate discontinuation of Warfarin, administration of **Vitamin K**, and starting **Heparin** or Protein C concentrates.

Q: Lichenoid reactions are mainly due to:

Intake of certain drugs. **Explanation:** **Lichenoid drug eruptions** (LDE) are cutaneous reactions that clinically and histologically mimic Lichen Planus. The correct answer is **Intake of certain drugs** because LDE is a well-recognized T-cell mediated delayed hypersensitivity reaction triggered by systemic medications. These drugs act as haptens, altering the antigenicity of keratinocytes and leading to a lichenoid tissue reaction characterized by a "saw-tooth" appearance of rete ridges and a band-like lymphocytic infiltrate at the dermo-epidermal junction. **Analysis of Options:** * **A. Intake of certain drugs (Correct):** Common culprits include NSAIDs, Antihypertensives (Beta-blockers, ACE inhibitors, Thiazides), Antimalarials (Chloroquine), and Gold salts. * **B. Betel nut chewing:** This is primarily associated with **Oral Submucous Fibrosis (OSMF)** and squamous cell carcinoma, not lichenoid reactions. * **C. Cigarette smoking:** While smoking is a risk factor for various dermatoses and oral cancers, it is not a primary cause of lichenoid eruptions. Interestingly, smoking is sometimes noted to have a paradoxical (though not therapeutic) inverse relationship with oral lichen planus. * **D. Intake of alcohol:** Alcohol is a trigger for psoriasis and rosacea exacerbations but does not directly cause lichenoid reactions. **High-Yield Clinical Pearls for NEET-PG:** * **Distinguishing LDE from Lichen Planus (LP):** LDE typically lacks **Wickham’s striae**, involves the trunk more than the wrists, and often shows parakeratosis and eosinophils on histology (features usually absent in classic LP). * **Photo-distribution:** Lichenoid drug eruptions often occur in sun-exposed areas (e.g., due to Hydrochlorothiazide). * **Latent Period:** The time between drug intake and eruption can range from weeks to several months.

Q: Potassium iodide is contraindicated in all of the following conditions, EXCEPT:

Pregnant women. **Explanation:** Potassium Iodide (SSKI) is a versatile drug in dermatology, primarily used for its anti-neutrophilic and fibrinolytic properties. However, its use is strictly governed by specific contraindications. **Why Option D is the Correct Answer:** The question asks for the condition where Potassium Iodide is **NOT** contraindicated (i.e., where it can be used, albeit with caution). While SSKI is generally avoided in pregnancy due to the risk of fetal goiter and hypothyroidism (Category D), it is **not an absolute contraindication** in life-threatening situations or specific thyroid emergencies. More importantly, in the context of this specific MCQ, the other three options represent **absolute contraindications** where the drug can cause severe disease exacerbation or fatal reactions. **Analysis of Incorrect Options:** * **A. Dermatitis Herpetiformis (DH):** Iodides are strictly contraindicated. Ingestion of potassium iodide can trigger or severely exacerbate the blistering skin lesions in DH patients due to increased neutrophilic chemotaxis. * **B. Iodine Hypersensitivity:** This is an absolute contraindication. Administration can lead to anaphylaxis or severe drug eruptions (iododerma). * **C. Hypocomplementemic Vasculitis:** Also known as Urticarial Vasculitis. Iodides are known to flare the vasculitic process and are avoided in these patients. **NEET-PG High-Yield Pearls:** * **Drug of Choice:** SSKI is the drug of choice for **Sporotrichosis** (cutaneous-lymphatic type). * **Mechanism:** It inhibits the "oxygen burst" in neutrophils and suppresses inflammation. * **Other Indications:** Erythema Nodosum, Sweet Syndrome, and Pyoderma Gangrenosum. * **Side Effects:** "Iodism" (metallic taste, burning mouth, sore teeth/gums, and coryza-like symptoms). * **Wolff-Chaikoff Effect:** High doses of iodide cause a temporary reduction in thyroid hormone synthesis.

Q: A male presents with an erythematous patch over the penis after taking an over-the-counter medication. What is the most likely causal drug?

Aceclofenac. **Explanation:** The clinical presentation of a solitary erythematous patch appearing at the same site (specifically the glans penis) following drug ingestion is a classic description of a **Fixed Drug Eruption (FDE)**. **1. Why Aceclofenac is correct:** NSAIDs are the most common cause of Fixed Drug Eruptions worldwide. Among them, the propionic acid derivatives and oxicams are frequent culprits, but in the Indian context, **NSAIDs (like Aceclofenac, Diclofenac, and Naproxen)** and Paracetamol are the leading causes of FDE. The glans penis is the most common site for FDE in males, often presenting as a well-demarcated, dusky red or violaceous macule that may evolve into a bulla and leaves behind post-inflammatory hyperpigmentation. **2. Analysis of Incorrect Options:** * **Azithromycin:** While macrolides can cause cutaneous reactions, they are a rare cause of FDE compared to NSAIDs. * **Ofloxacin:** Fluoroquinolones are known causes of FDE, but statistically, NSAIDs are more frequently implicated in OTC-related penile eruptions. * **Doxycycline:** Tetracyclines are a common cause of FDE; however, they are less likely to be taken as "over-the-counter" self-medication for minor pains compared to Aceclofenac. **3. High-Yield Clinical Pearls for NEET-PG:** * **Most common site for FDE:** Glans penis (Males), Labia (Females). * **Most common drugs causing FDE (Overall):** NSAIDs, Sulfonamides (Cotrimoxazole), Tetracyclines, and Carbamazepine. * **Pathogenesis:** Mediated by **CD8+ effector memory T cells** that remain resident in the skin lesion even after healing. * **Character:** The lesion recurs at the **exact same site** upon re-exposure to the offending drug.

Q: Recurrent erythematous plaques on the glans penis in a 19-year-old sexually active male, which heal with residual hyperpigmentation, are suggestive of?

Fixed Drug Eruption. **Explanation:** The clinical presentation of recurrent, well-circumscribed erythematous plaques that resolve leaving behind **residual hyperpigmentation** (post-inflammatory hyperpigmentation) is the hallmark of a **Fixed Drug Eruption (FDE)**. In males, the glans penis is a classic site of involvement. The term "fixed" refers to the fact that the lesion recurs at the exact same anatomical site upon re-exposure to the offending drug. Common triggers include NSAIDs (most common), sulfonamides, tetracyclines, and anticonvulsants. **Analysis of Incorrect Options:** * **Aphthous Balanitis:** Presents as painful, shallow ulcers rather than erythematous plaques, and typically does not leave significant hyperpigmentation upon healing. * **Herpes Gestationis (Pemphigoid Gestationis):** This is a pregnancy-associated autoimmune bullous disorder. It would not occur in a male patient. * **Chlamydial Infection:** Typically presents as urethritis (discharge and dysuria). While it can be associated with Circinate Balanitis (in Reactive Arthritis), those lesions are usually painless, geographic, and do not characteristically heal with the deep "slate-grey" hyperpigmentation seen in FDE. **High-Yield Clinical Pearls for NEET-PG:** * **Most common site:** Glans penis (males), Labia (females). * **Most common drug:** Cotrimoxazole (historically) and NSAIDs (specifically Paracetamol and Oxyphenbutazone). * **Pathogenesis:** Mediated by **CD8+ effector memory T cells** that remain resident in the skin site. * **Diagnosis:** Primarily clinical; a "Provocation Test" can be done but is often avoided in severe cases.

Q: Which of the following adverse effects is known to be caused by Paracetamol?

Phototoxicity. **Explanation:** **1. Why Phototoxicity is the Correct Answer:** Phototoxicity is a non-immunologic reaction that occurs when a drug (chromophore) absorbs UV radiation (usually UVA), leading to the formation of free radicals or reactive oxygen species. These cause direct tissue damage. **Paracetamol (Acetaminophen)** is a known, albeit less common, cause of phototoxicity. The mechanism involves the drug’s metabolites reacting under UV light to cause cellular damage in the skin. Unlike photoallergy, phototoxicity can occur on the first exposure and is dose-dependent. **2. Why the Other Options are Incorrect:** * **Photosensitivity:** This is a broad "umbrella term" that encompasses both phototoxicity and photoallergy. While technically correct in a general sense, **Phototoxicity** is the specific pathological mechanism attributed to Paracetamol, making it the more precise answer for a medical examination. * **Photoallergy:** This is a Type IV (delayed) hypersensitivity reaction. It requires prior sensitization and is not dose-dependent. Paracetamol does not typically trigger this cell-mediated immune response; its cutaneous reactions are primarily direct toxic effects. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Common Phototoxic Drugs:** Remember the mnemonic **"SAT for Photo"**: **S**ulfonamides/Sulfonylureas, **A**miodarone, **T**etracyclines (especially Demeclocycline), and **F**luoroquinolones (Lomefloxacin). Other common causes include NSAIDs (Naproxen) and Phenothiazines. * **Clinical Presentation:** Phototoxicity resembles an exaggerated sunburn (erythema, edema, blistering) limited to sun-exposed areas. Photoallergy, conversely, often presents as an eczematous dermatitis that can spread to non-exposed areas. * **Paracetamol & Skin:** While rare, Paracetamol is also a notorious trigger for **Stevens-Johnson Syndrome (SJS)** and **Toxic Epidermal Necrolysis (TEN)**, which are high-yield dermatological emergencies.

Q: All are drugs known to be associated with drug hypersensitivity syndrome, EXCEPT:

Tetracycline. **Explanation:** Drug Hypersensitivity Syndrome, commonly known as **DRESS (Drug Reaction with Eosinophilia and Systemic Symptoms)**, is a severe, idiosyncratic Type IVb hypersensitivity reaction. It is characterized by the clinical triad of fever, rash, and internal organ involvement (most commonly the liver), typically occurring 2 to 8 weeks after drug initiation. **Why Tetracycline is the correct answer:** While tetracyclines can cause various cutaneous side effects (like photosensitivity or fixed drug eruptions), they are **not** classically associated with DRESS syndrome. Minocycline is the only member of the tetracycline family frequently linked to DRESS; standard tetracycline is considered a rare or negligible cause. **Analysis of incorrect options:** * **Lamotrigine:** A well-known trigger among anticonvulsants. The "Aromatic Anticonvulsants" (Phenytoin, Carbamazepine, Phenobarbital) and Lamotrigine are the most common causes of DRESS. * **Allopurinol:** The most frequent cause of DRESS in many global cohorts, especially in patients with renal impairment or those carrying the **HLA-B*5801** allele. * **Nevirapine:** A Non-Nucleoside Reverse Transcriptase Inhibitor (NNRTI) strongly associated with DRESS and Stevens-Johnson Syndrome (SJS) in HIV patients. **High-Yield Clinical Pearls for NEET-PG:** * **Latent Period:** DRESS has a uniquely long onset (2–8 weeks), unlike SJS/TEN (1–3 weeks). * **Hallmark Lab Finding:** Peripheral blood **eosinophilia** (>1500/mm³) and atypical lymphocytosis. * **Organ Involvement:** The **liver** is the most common internal organ affected (hepatitis). * **Association:** Often linked to the reactivation of Human Herpesvirus 6 (**HHV-6**). * **Management:** Immediate withdrawal of the offending drug and systemic corticosteroids.

Dermatological Pharmacology Indian Medical PG Practice Questions and MCQs

Question 1: A patient developed fixed drug eruptions after taking certain medications. Which of the following drugs is known to cause these skin lesions?

A. Phenolphthalein
B. Aspirin
C. Dapsone
D. All of the above (Correct Answer)

Explanation: **Explanation:** **Fixed Drug Eruption (FDE)** is a unique type of cutaneous drug reaction characterized by the recurrence of a lesion (usually a dusky red or violaceous macule) at the **exact same anatomical site** every time the offending drug is ingested. This occurs due to the persistence of **CD8+ memory T-cells** in the basal keratinocytes at the site of the lesion. **Why Option D is correct:** All three drugs listed are classic and high-yield triggers for FDE: * **Phenolphthalein:** Historically the most common cause (found in older laxatives). * **Aspirin (NSAIDs):** A very frequent trigger in clinical practice. * **Dapsone (Sulfonamides):** Sulfonamides are among the most common drug classes associated with FDE. **Analysis of Options:** * **Phenolphthalein:** Often presents as "bullous" FDE. * **Aspirin:** Along with other NSAIDs (like Ibuprofen and Naproxen), it is a leading cause of multi-focal FDE. * **Dapsone:** As a sulfone, it shares cross-reactivity patterns and is a well-documented cause. **High-Yield Clinical Pearls for NEET-PG:** 1. **Most Common Site:** The **glans penis** is the most common site for FDE, followed by the lips and palms. 2. **Commonest Causes (Overall):** NSAIDs, Sulfonamides (Cotrimoxazole), Tetracyclines, and Anticonvulsants. 3. **Clinical Feature:** Lesions often leave behind **post-inflammatory hyperpigmentation (PIH)** after healing. 4. **Refractory Period:** After an eruption, there is a brief refractory period where the drug may not cause a reaction. 5. **Diagnosis:** Primarily clinical; however, a **Patch Test** performed at the site of the previous lesion (not on the back) can confirm the offending agent.

Question 2: Dapsone is used in which of the following conditions?

A. Dermatitis herpetiformis (Correct Answer)
B. Pityriasis rosacea
C. Contact dermatitis
D. Oculocutaneous albinism

Explanation: **Explanation:** **Dapsone (Diaminodiphenyl sulfone)** is the drug of choice for **Dermatitis Herpetiformis (DH)**. DH is an autoimmune blistering disorder characterized by IgA deposits at the dermal papillae, leading to intense pruritus and neutrophilic infiltration. Dapsone works by inhibiting the enzyme myeloperoxidase and preventing the chemotaxis of neutrophils to the skin, providing rapid symptomatic relief (often within 24–48 hours). **Analysis of Options:** * **A. Dermatitis Herpetiformis:** Correct. It is the primary indication for Dapsone in dermatology. * **B. Pityriasis Rosea:** This is a self-limiting inflammatory condition (likely viral/HHV-6,7). Treatment is supportive (antihistamines, topical steroids); Dapsone has no role. * **C. Contact Dermatitis:** This is a Type IV hypersensitivity reaction. Management involves allergen avoidance and topical or systemic corticosteroids. * **D. Oculocutaneous Albinism:** This is a genetic disorder of melanin synthesis. There is no pharmacological "cure"; management focuses on photoprotection and monitoring for skin cancers. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism of Action:** Antifolate (inhibits dihydropteroate synthase) and anti-inflammatory (inhibits neutrophil recruitment). * **Other Indications:** Leprosy (part of MDT), Pemphigoid, Subcorneal Pustular Dermatosis (Sneddon-Wilkinson disease), and Brown Recluse spider bites. * **Mandatory Pre-screening:** Always check **G6PD levels** before starting Dapsone to prevent severe **hemolytic anemia**. * **Side Effects:** Dose-dependent hemolysis, methemoglobinemia (presents as cyanosis), and the "Dapsone Syndrome" (fever, malaise, exfoliative dermatitis, and hepatitis).

Question 3: Which of the following monoclonal antibodies is used in the treatment of atopic dermatitis?

A. Ipilimumab
B. Dupilumab (Correct Answer)
C. Durvalumab
D. Reslizumab

Explanation: **Explanation:** **1. Why Dupilumab is Correct:** Dupilumab is a fully human monoclonal antibody that targets the **interleukin-4 receptor alpha (IL-4Rα) subunit**. By binding to this subunit, it inhibits the signaling of both **IL-4 and IL-13**. These cytokines are the key drivers of **Type 2 (Th2) inflammation**, which is the primary pathophysiological mechanism in atopic dermatitis. It is currently the first-line systemic biologic approved for moderate-to-severe atopic dermatitis unresponsive to topical therapies. **2. Why the Other Options are Incorrect:** * **Ipilimumab:** A checkpoint inhibitor that targets **CTLA-4**. It is used in the treatment of advanced melanoma and renal cell carcinoma. * **Durvalumab:** A checkpoint inhibitor that targets **PD-L1**. It is primarily used in the treatment of non-small cell lung cancer (NSCLC) and bladder cancer. * **Reslizumab:** An interleukin-5 (**IL-5**) antagonist. It is used as add-on maintenance treatment for severe eosinophilic asthma, not atopic dermatitis. **3. High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Dual inhibitor of IL-4 and IL-13. * **Common Side Effect:** The most characteristic side effect of Dupilumab is **allergic conjunctivitis** and blepharitis. * **Other Indications:** It is also FDA-approved for moderate-to-severe asthma (eosinophilic phenotype) and chronic rhinosinusitis with nasal polyposis. * **Memory Aid:** "Dupi" stops the "D"ermatitis by blocking the "4" and "13" (IL-4/13).

Question 4: All of the following statements are true regarding warfarin toxicity (skin necrosis) except?

A. Skin necrosis occurs during initiation of therapy.
B. Most common sites are buttocks and abdomen. (Correct Answer)
C. Decreased quantity of protein C.
D. Decreased incidence of adverse effects if therapy with LMWH is started.

Explanation: **Explanation:** Warfarin-induced skin necrosis (WISN) is a rare but severe complication occurring in approximately 0.01% to 0.1% of patients treated with vitamin K antagonists. **Why Option B is the correct answer (The False Statement):** While the buttocks and abdomen are common sites, the **most common sites** for warfarin necrosis are areas with **high subcutaneous fat content**, specifically the **breasts** (in females), followed by the thighs and buttocks. The statement in Option B is considered the "except" because it overlooks the breast as the primary site of predilection. **Analysis of Other Options:** * **Option A:** True. Necrosis typically occurs **3 to 10 days after initiation** of therapy, often due to a large loading dose. * **Option C:** True. Warfarin inhibits Vitamin K-dependent factors (II, VII, IX, X) and anticoagulant proteins (C and S). **Protein C has a shorter half-life** (6 hours) compared to clotting factors. This creates a transient "prothrombotic window" where natural anticoagulants are depleted while procoagulant factors are still active, leading to microvascular thrombosis. * **Option D:** True. Starting **Low Molecular Weight Heparin (LMWH)** as a "bridge" provides immediate anticoagulation, preventing the thrombotic complications during the initial drop in Protein C levels. **Clinical Pearls for NEET-PG:** * **Risk Factor:** Underlying **Protein C deficiency** is the most significant risk factor. * **Clinical Presentation:** Sudden onset of painful, erythematous, or purpuric lesions that rapidly progress to **hemorrhagic bullae and eschar**. * **Management:** Immediate discontinuation of Warfarin, administration of **Vitamin K**, and starting **Heparin** or Protein C concentrates.

Question 5: Lichenoid reactions are mainly due to:

A. Intake of certain drugs (Correct Answer)
B. Betel nut chewing
C. Cigarette smoking
D. Intake of alcohol

Explanation: **Explanation:** **Lichenoid drug eruptions** (LDE) are cutaneous reactions that clinically and histologically mimic Lichen Planus. The correct answer is **Intake of certain drugs** because LDE is a well-recognized T-cell mediated delayed hypersensitivity reaction triggered by systemic medications. These drugs act as haptens, altering the antigenicity of keratinocytes and leading to a lichenoid tissue reaction characterized by a "saw-tooth" appearance of rete ridges and a band-like lymphocytic infiltrate at the dermo-epidermal junction. **Analysis of Options:** * **A. Intake of certain drugs (Correct):** Common culprits include NSAIDs, Antihypertensives (Beta-blockers, ACE inhibitors, Thiazides), Antimalarials (Chloroquine), and Gold salts. * **B. Betel nut chewing:** This is primarily associated with **Oral Submucous Fibrosis (OSMF)** and squamous cell carcinoma, not lichenoid reactions. * **C. Cigarette smoking:** While smoking is a risk factor for various dermatoses and oral cancers, it is not a primary cause of lichenoid eruptions. Interestingly, smoking is sometimes noted to have a paradoxical (though not therapeutic) inverse relationship with oral lichen planus. * **D. Intake of alcohol:** Alcohol is a trigger for psoriasis and rosacea exacerbations but does not directly cause lichenoid reactions. **High-Yield Clinical Pearls for NEET-PG:** * **Distinguishing LDE from Lichen Planus (LP):** LDE typically lacks **Wickham’s striae**, involves the trunk more than the wrists, and often shows parakeratosis and eosinophils on histology (features usually absent in classic LP). * **Photo-distribution:** Lichenoid drug eruptions often occur in sun-exposed areas (e.g., due to Hydrochlorothiazide). * **Latent Period:** The time between drug intake and eruption can range from weeks to several months.

Question 6: Potassium iodide is contraindicated in all of the following conditions, EXCEPT:

A. Dermatitis herpetiformis
B. Iodine hypersensitivity
C. Hypocomplementemic vasculitis
D. Pregnant women (Correct Answer)

Explanation: **Explanation:** Potassium Iodide (SSKI) is a versatile drug in dermatology, primarily used for its anti-neutrophilic and fibrinolytic properties. However, its use is strictly governed by specific contraindications. **Why Option D is the Correct Answer:** The question asks for the condition where Potassium Iodide is **NOT** contraindicated (i.e., where it can be used, albeit with caution). While SSKI is generally avoided in pregnancy due to the risk of fetal goiter and hypothyroidism (Category D), it is **not an absolute contraindication** in life-threatening situations or specific thyroid emergencies. More importantly, in the context of this specific MCQ, the other three options represent **absolute contraindications** where the drug can cause severe disease exacerbation or fatal reactions. **Analysis of Incorrect Options:** * **A. Dermatitis Herpetiformis (DH):** Iodides are strictly contraindicated. Ingestion of potassium iodide can trigger or severely exacerbate the blistering skin lesions in DH patients due to increased neutrophilic chemotaxis. * **B. Iodine Hypersensitivity:** This is an absolute contraindication. Administration can lead to anaphylaxis or severe drug eruptions (iododerma). * **C. Hypocomplementemic Vasculitis:** Also known as Urticarial Vasculitis. Iodides are known to flare the vasculitic process and are avoided in these patients. **NEET-PG High-Yield Pearls:** * **Drug of Choice:** SSKI is the drug of choice for **Sporotrichosis** (cutaneous-lymphatic type). * **Mechanism:** It inhibits the "oxygen burst" in neutrophils and suppresses inflammation. * **Other Indications:** Erythema Nodosum, Sweet Syndrome, and Pyoderma Gangrenosum. * **Side Effects:** "Iodism" (metallic taste, burning mouth, sore teeth/gums, and coryza-like symptoms). * **Wolff-Chaikoff Effect:** High doses of iodide cause a temporary reduction in thyroid hormone synthesis.

Question 7: A male presents with an erythematous patch over the penis after taking an over-the-counter medication. What is the most likely causal drug?

A. Azithromycin
B. Ofloxacin
C. Doxycycline
D. Aceclofenac (Correct Answer)

Explanation: **Explanation:** The clinical presentation of a solitary erythematous patch appearing at the same site (specifically the glans penis) following drug ingestion is a classic description of a **Fixed Drug Eruption (FDE)**. **1. Why Aceclofenac is correct:** NSAIDs are the most common cause of Fixed Drug Eruptions worldwide. Among them, the propionic acid derivatives and oxicams are frequent culprits, but in the Indian context, **NSAIDs (like Aceclofenac, Diclofenac, and Naproxen)** and Paracetamol are the leading causes of FDE. The glans penis is the most common site for FDE in males, often presenting as a well-demarcated, dusky red or violaceous macule that may evolve into a bulla and leaves behind post-inflammatory hyperpigmentation. **2. Analysis of Incorrect Options:** * **Azithromycin:** While macrolides can cause cutaneous reactions, they are a rare cause of FDE compared to NSAIDs. * **Ofloxacin:** Fluoroquinolones are known causes of FDE, but statistically, NSAIDs are more frequently implicated in OTC-related penile eruptions. * **Doxycycline:** Tetracyclines are a common cause of FDE; however, they are less likely to be taken as "over-the-counter" self-medication for minor pains compared to Aceclofenac. **3. High-Yield Clinical Pearls for NEET-PG:** * **Most common site for FDE:** Glans penis (Males), Labia (Females). * **Most common drugs causing FDE (Overall):** NSAIDs, Sulfonamides (Cotrimoxazole), Tetracyclines, and Carbamazepine. * **Pathogenesis:** Mediated by **CD8+ effector memory T cells** that remain resident in the skin lesion even after healing. * **Character:** The lesion recurs at the **exact same site** upon re-exposure to the offending drug.

Question 8: Recurrent erythematous plaques on the glans penis in a 19-year-old sexually active male, which heal with residual hyperpigmentation, are suggestive of?

A. Aphthous Balanitis
B. Fixed Drug Eruption (Correct Answer)
C. Herpes Gestationis
D. Chlamydial infection

Explanation: **Explanation:** The clinical presentation of recurrent, well-circumscribed erythematous plaques that resolve leaving behind **residual hyperpigmentation** (post-inflammatory hyperpigmentation) is the hallmark of a **Fixed Drug Eruption (FDE)**. In males, the glans penis is a classic site of involvement. The term "fixed" refers to the fact that the lesion recurs at the exact same anatomical site upon re-exposure to the offending drug. Common triggers include NSAIDs (most common), sulfonamides, tetracyclines, and anticonvulsants. **Analysis of Incorrect Options:** * **Aphthous Balanitis:** Presents as painful, shallow ulcers rather than erythematous plaques, and typically does not leave significant hyperpigmentation upon healing. * **Herpes Gestationis (Pemphigoid Gestationis):** This is a pregnancy-associated autoimmune bullous disorder. It would not occur in a male patient. * **Chlamydial Infection:** Typically presents as urethritis (discharge and dysuria). While it can be associated with Circinate Balanitis (in Reactive Arthritis), those lesions are usually painless, geographic, and do not characteristically heal with the deep "slate-grey" hyperpigmentation seen in FDE. **High-Yield Clinical Pearls for NEET-PG:** * **Most common site:** Glans penis (males), Labia (females). * **Most common drug:** Cotrimoxazole (historically) and NSAIDs (specifically Paracetamol and Oxyphenbutazone). * **Pathogenesis:** Mediated by **CD8+ effector memory T cells** that remain resident in the skin site. * **Diagnosis:** Primarily clinical; a "Provocation Test" can be done but is often avoided in severe cases.

Question 9: Which of the following adverse effects is known to be caused by Paracetamol?

A. Photosensitivity
B. Photoallergy
C. Phototoxicity (Correct Answer)
D. None of the above

Explanation: **Explanation:** **1. Why Phototoxicity is the Correct Answer:** Phototoxicity is a non-immunologic reaction that occurs when a drug (chromophore) absorbs UV radiation (usually UVA), leading to the formation of free radicals or reactive oxygen species. These cause direct tissue damage. **Paracetamol (Acetaminophen)** is a known, albeit less common, cause of phototoxicity. The mechanism involves the drug’s metabolites reacting under UV light to cause cellular damage in the skin. Unlike photoallergy, phototoxicity can occur on the first exposure and is dose-dependent. **2. Why the Other Options are Incorrect:** * **Photosensitivity:** This is a broad "umbrella term" that encompasses both phototoxicity and photoallergy. While technically correct in a general sense, **Phototoxicity** is the specific pathological mechanism attributed to Paracetamol, making it the more precise answer for a medical examination. * **Photoallergy:** This is a Type IV (delayed) hypersensitivity reaction. It requires prior sensitization and is not dose-dependent. Paracetamol does not typically trigger this cell-mediated immune response; its cutaneous reactions are primarily direct toxic effects. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Common Phototoxic Drugs:** Remember the mnemonic **"SAT for Photo"**: **S**ulfonamides/Sulfonylureas, **A**miodarone, **T**etracyclines (especially Demeclocycline), and **F**luoroquinolones (Lomefloxacin). Other common causes include NSAIDs (Naproxen) and Phenothiazines. * **Clinical Presentation:** Phototoxicity resembles an exaggerated sunburn (erythema, edema, blistering) limited to sun-exposed areas. Photoallergy, conversely, often presents as an eczematous dermatitis that can spread to non-exposed areas. * **Paracetamol & Skin:** While rare, Paracetamol is also a notorious trigger for **Stevens-Johnson Syndrome (SJS)** and **Toxic Epidermal Necrolysis (TEN)**, which are high-yield dermatological emergencies.

Question 10: All are drugs known to be associated with drug hypersensitivity syndrome, EXCEPT:

A. Lamotrigine
B. Allopurinol
C. Nevirapine
D. Tetracycline (Correct Answer)

Explanation: **Explanation:** Drug Hypersensitivity Syndrome, commonly known as **DRESS (Drug Reaction with Eosinophilia and Systemic Symptoms)**, is a severe, idiosyncratic Type IVb hypersensitivity reaction. It is characterized by the clinical triad of fever, rash, and internal organ involvement (most commonly the liver), typically occurring 2 to 8 weeks after drug initiation. **Why Tetracycline is the correct answer:** While tetracyclines can cause various cutaneous side effects (like photosensitivity or fixed drug eruptions), they are **not** classically associated with DRESS syndrome. Minocycline is the only member of the tetracycline family frequently linked to DRESS; standard tetracycline is considered a rare or negligible cause. **Analysis of incorrect options:** * **Lamotrigine:** A well-known trigger among anticonvulsants. The "Aromatic Anticonvulsants" (Phenytoin, Carbamazepine, Phenobarbital) and Lamotrigine are the most common causes of DRESS. * **Allopurinol:** The most frequent cause of DRESS in many global cohorts, especially in patients with renal impairment or those carrying the **HLA-B*5801** allele. * **Nevirapine:** A Non-Nucleoside Reverse Transcriptase Inhibitor (NNRTI) strongly associated with DRESS and Stevens-Johnson Syndrome (SJS) in HIV patients. **High-Yield Clinical Pearls for NEET-PG:** * **Latent Period:** DRESS has a uniquely long onset (2–8 weeks), unlike SJS/TEN (1–3 weeks). * **Hallmark Lab Finding:** Peripheral blood **eosinophilia** (>1500/mm³) and atypical lymphocytosis. * **Organ Involvement:** The **liver** is the most common internal organ affected (hepatitis). * **Association:** Often linked to the reactivation of Human Herpesvirus 6 (**HHV-6**). * **Management:** Immediate withdrawal of the offending drug and systemic corticosteroids.

Practice by Chapter

Topical Corticosteroids

Practice Questions

Topical Antibiotics

Practice Questions

Topical Antifungals

Practice Questions

Topical Antivirals

Practice Questions

Topical Retinoids

Practice Questions

Systemic Retinoids

Practice Questions

Immunosuppressive Agents

Practice Questions

Antihistamines in Dermatology

Practice Questions

Biological Agents in Dermatology

Practice Questions

Dermatological Vehicles and Delivery Systems

Practice Questions

Phototherapeutic Agents

Practice Questions

Adverse Cutaneous Drug Reactions

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free