Dermatological Pharmacology Practice Questions

Q: A 50-year-old woman presents with a well-defined erythematous patch on her leg following the administration of an antibiotic. What is the most likely diagnosis?

Fixed drug eruption. ***Fixed drug eruption*** - This condition presents as a **solitary, well-demarcated erythematous patch** that recurs at the **same cutaneous site** upon re-exposure to an offending drug. - The history of antibiotic administration followed by a localized patch is highly characteristic of a **fixed drug eruption**. *Contact dermatitis* - This typically results from direct skin exposure to an allergen or irritant, causing an **itchy rash** that is usually not well-demarcated and may include vesicles or bullae. - It would not typically be related to systemic drug administration and does not recur at the same site with repeated systemic exposure. *Psoriasis* - Characterized by **silvery scales** on well-demarcated **erythematous plaques**, often on extensor surfaces like elbows and knees. - It is a chronic inflammatory condition and does not typically present as a single, acute lesion in response to medication. *Tinea corporis* - This is a **fungal infection** of the skin, presenting as a **ring-shaped lesion** with central clearing and raised, scaly borders. - It is not caused by drug administration and has specific morphological features (e.g., scaling, annular pattern) that differentiate it from the described lesion.

Q: The patient came with history of bullae involving >30% of body surface area along with erosions of the lips and other mucosae for the past 7 days. What is the most probable underlying etiology?

Drug reaction. ***Drug reaction*** - The formation of widespread bullae involving >30% of the body surface area, along with significant mucosal erosions (lips), points strongly towards **toxic epidermal necrolysis (TEN)**, a severe form of cutaneous adverse drug reaction. - TEN is characterized by **extensive epidermal detachment** resulting from a drug-induced immune response, commonly occurring within days to weeks of drug exposure. *Bacterial skin infection* - While certain bacterial infections can cause bullae (e.g., **bullous impetigo**), they rarely lead to such widespread involvement (>30% BSA) and extensive mucosal erosions within 7 days, as seen in TEN. - The rapid progression to severe, widespread blistering and mucosal involvement is more typical of drug-induced hypersensitivity rather than common bacterial skin infections. *Viral skin infection* - Viral infections like **herpes simplex virus** or **varicella-zoster virus** can cause bullae, but typically in localized patterns or with specific morphologies (e.g., vesicles on an erythematous base) and usually without such extensive body surface area involvement or severe mucosal erosion in an immunocompetent adult. - Widespread bullae and mucosal erosions over >30% BSA are not characteristic of typical viral skin infections. *Skin malignancy* - Skin malignancies, such as **cutaneous lymphomas** or other aggressive tumors, can present with various skin lesions, but they rarely manifest acutely with widespread bullae and erosions involving >30% of the body surface area within a 7-day timeframe. - Such a rapid and severe presentation is inconsistent with the typical indolent or slowly progressive nature of most primary skin cancers.

Q: Which drug is most commonly associated with causing fixed drug eruptions?

Sulfonamide. ***Sulfonamide*** - **Sulfonamides**, particularly **sulfamethoxazole-trimethoprim**, are frequently implicated in causing fixed drug eruptions. - A fixed drug eruption characteristically recurs at the **same cutaneous site** each time the offending drug is administered. *Aminoglycoside* - **Aminoglycosides** are broad-spectrum antibiotics known for potential **ototoxicity** and **nephrotoxicity**. - While they can cause various adverse reactions, fixed drug eruptions are **not a common association** with this drug class. *Erythromycin* - **Erythromycin** is a macrolide antibiotic primarily associated with **gastrointestinal side effects**, such as nausea and abdominal cramping. - Although drug eruptions can occur, fixed drug eruptions are **not typically linked** to erythromycin. *None of the options* - This option is incorrect because **sulfonamides** are well-documented causes of fixed drug eruptions. - Therefore, there is a specific drug class listed that is strongly associated with this condition.

Q: A 27-year-old sexually active male develops a vesiculobullous lesion on the glans shortly after taking a tablet of paracetamol for fever. The lesion healed with hyperpigmentation. What is the most likely diagnosis?

Fixed drug eruption. ***Fixed drug eruption*** - A **fixed drug eruption** is highly suggested by the development of a solitary **vesiculobullous lesion** on the glans shortly after taking **paracetamol**, which then heals with **hyperpigmentation**. The recurrence at the same site upon re-exposure to the drug is a hallmark. - The rapid appearance following drug intake and the consistent site of eruption with residual pigmentation are classic features. *Behcet's syndrome* - Behcet's syndrome is a **multisystemic inflammatory disorder** characterized by recurrent **oral** and **genital ulcers**, skin lesions, and ocular inflammation. - While it involves genital ulcers, its recurrent nature, systemic symptoms (like uveitis or neurological manifestations), and lack of a clear drug trigger differentiate it from this presentation. *Herpes genitalis* - Herpes genitalis presents with clusters of small, painful, itching **vesicles** often on an erythematous base, but it is caused by the **herpes simplex virus (HSV)** and is sexually transmitted, not drug-induced. - Lesions from herpes typically recur due to viral reactivation, but not in response to a specific medication, and typically resolve without significant hyperpigmentation unless secondary infection occurs. *Pemphigus vulgaris* - Pemphigus vulgaris is a rare, severe **autoimmune blistering disease** affecting the skin and mucous membranes, characterized by **flaccid bullae** that rupture easily, leading to erosions. - This condition presents with widespread blistering, not a solitary, drug-induced lesion, and typically does not heal with localized hyperpigmentation in this manner.

Question 1

A 50-year-old woman presents with a well-defined erythematous patch on her leg following the administration of an antibiotic. What is the most likely diagnosis?

Accepted Answer

Fixed drug eruption

Answer

Contact dermatitis

Answer

Psoriasis

Answer

Tinea corporis

Question 2

The patient came with history of bullae involving >30% of body surface area along with erosions of the lips and other mucosae for the past 7 days. What is the most probable underlying etiology?

Accepted Answer

Drug reaction

Answer

Bacterial skin infection

Answer

Viral skin infection

Answer

Skin malignancy

Question 3

Which drug is most commonly associated with causing fixed drug eruptions?

Accepted Answer

Sulfonamide

Answer

Aminoglycoside

Answer

Erythromycin

Answer

None of the options

Question 4

A 27-year-old sexually active male develops a vesiculobullous lesion on the glans shortly after taking a tablet of paracetamol for fever. The lesion healed with hyperpigmentation. What is the most likely diagnosis?

Accepted Answer

Fixed drug eruption

Answer

Behcet's syndrome

Answer

Herpes genitalis

Answer

Pemphigus vulgaris

Dermatological Pharmacology — MCQs

Dermatological Pharmacology — MCQs

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