A 27 year old sexually active male develops a vesicobullous lesion on the glans soon after taking tab paracetamol for fever. The lesion healed with hyper pigmentation. The most likely diagnosis is:
**Core Concept**
The question tests the ability to identify a rare but well-known adverse reaction to a commonly used medication, specifically an idiosyncratic reaction involving the skin.
**Why the Correct Answer is Right**
The patient's symptoms, including the development of a vesicobullous lesion on the glans soon after taking paracetamol, are characteristic of a condition known as Steven-Johnson Syndrome (SJS) or Toxic Epidermal Necrolysis (TEN). These conditions are severe cutaneous adverse reactions (SCARs) that occur in response to medications, including non-steroidal anti-inflammatory drugs (NSAIDs) like paracetamol. The exact pathophysiology is not fully understood, but it is thought to involve an abnormal immune response, leading to the activation of cytotoxic T cells that target the skin, resulting in the formation of characteristic bullae and subsequent skin necrosis.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the scenario presented, as it does not describe a well-known adverse reaction to paracetamol.
* **Option B:** This option is incorrect because contact dermatitis is a type IV hypersensitivity reaction that typically occurs in response to allergens or irritants, not medications like paracetamol.
* **Option C:** This option is incorrect because erythema multiforme (EM) is a distinct entity that can be triggered by infections, medications, or other factors, but it does not typically present with the severe skin necrosis seen in SJS/TEN.
**Clinical Pearl / High-Yield Fact**
SJS/TEN are rare but life-threatening conditions that require prompt recognition and withdrawal of the offending medication. They are characterized by the presence of mucosal involvement, fever, and the development of skin lesions, which can progress to full-thickness skin necrosis.
**Correct Answer:** C.