A 27 year old sexually active male develops a vesiculobullous lesion on the glans soon after taking tablet paracetamol for fever. The lesion healed with hyperpigmentation. The most likely diagnosis is –
First, I need to recall vesiculobullous conditions affecting the genital area. The fact that it's on the glans is important. Vesiculobullous lesions can be caused by various things like infections (HSV), allergic reactions, or autoimmune conditions. But the timing after taking paracetamol suggests a possible drug reaction. However, paracetamol isn't known to cause such lesions typically. Wait, maybe it's a drug-induced hypersensitivity reaction?
Wait, another angle: the lesion healed with hyperpigmentation. That makes me think of fixed drug eruptions. Fixed drug eruptions (FDE) are characterized by recurrent, well-demarcated lesions that occur at the same site upon re-exposure to the offending drug. The healing with hyperpigmentation is a classic feature. Common drugs causing FDE include NSAIDs, sulfonamides, and sometimes anticonvulsants. Paracetamol is a known culprit here. The patient took paracetamol for fever, and the lesion appeared soon after. Since it's on the glans, which is a common site for FDE, this fits.
Now, considering the other options. Let's say the options were something like Herpes Simplex, Behçet's disease, Contact dermatitis, or something else. Herpes would present with clusters of vesicles, often with pain, and may have ulceration. The healing with hyperpigmentation is not typical of HSV. Behçet's can have oral and genital ulcers, but they are usually painless and not vesiculobullous. Contact dermatitis is an allergic reaction but usually presents with eczematous lesions, not vesiculobullous. Also, contact dermatitis would be due to topical allergens, not oral drugs. So FDE is the most likely diagnosis here.
The clinical pearl here is to remember that fixed drug eruptions present with well-defined lesions that recur at the same site upon drug re-exposure and leave hyperpigmented patches after healing. Paracetamol is a common cause, so avoiding it is crucial once diagnosed.
**Core Concept**
This question tests the recognition of **fixed drug eruption (FDE)**, a hypersensitivity reaction to medications characterized by recurrent, well-demarcated skin lesions that resolve with hyperpigmentation. Key features include a history of drug exposure and recurrence at the same site upon rechallenge.
**Why the Correct Answer is Right**
Fixed drug eruptions are caused by immune-mediated hypersensitivity to drugs like **paracetamol, NSAIDs, or sulfonamides**. The glans is a common site due to its high vascularity and frequent drug-induced immune reactivity. Lesions typically present as **vesiculobullous plaques**, heal with **hyperpigmentation**, and recur at the same location upon re-exposure to the offending drug. The temporal association with paracetamol intake and hyperpigmented healing strongly supports this diagnosis.
**Why Each Wrong Option is Incorrect**
**Option A:** *Herpes simplex virus (HSV