**Question:** An 80-year-old female patient complains of a 3-day history of a painful rash extending over the right half of her forehead and down to her right eyelid. There are weeping vesicular lesions on physical examination. Which of the following is the most likely diagnosis?

A. Herpes Simplex Virus (HSV)
B. Herpes Zoster
C. Impetigo
D. Epidermolysis Bullosa

**Core Concept:**
The presented symptoms and examination findings are indicative of an infection or autoimmune disease affecting the skin or mucous membranes. The correct answer lies within the options involving viral infections.

**Why the Correct Answer is Right:**
The most likely diagnosis among the given options is **Herpes Zoster (HZ)**, also known as shingles. HZ is caused by the reactivation of the Varicella-Zoster virus (VZV), which is the same virus responsible for causing chickenpox in childhood. The rash distribution is characteristic, with vesicles localized to a single dermatome (nerve territory). In this case, the rash is confined to the right half of her forehead and right eyelid, suggesting a dermatomal distribution.

**Why Each Wrong Option is Incorrect:**

**A. Herpes Simplex Virus (HSV):** HSV type 1 and 2 cause oral or genital herpes, respectively. The rash distribution in HSV is not restricted to a single dermatome.

**B. Impetigo:** Impetigo is a bacterial skin infection, typically caused by Streptococcus pyogenes and Staphylococcus aureus. The rash distribution in impetigo is diffused, not confined to a single dermatome.

**C. Epidermolysis Bullosa:** This group of disorders involves blistering of the skin and mucous membranes, but it is not caused by a viral infection. The rash distribution in EB is non-specific and can be found on any part of the body.

**D. Herpes Zoster (HZ):** As explained above, HZ is caused by the reactivation of the VZV and presents with a dermatomal distribution. The correct answer is HZ, not HSV or Impetigo.

**Core Concept:**
Herpes Zoster typically presents as vesicular lesions in a dermatomal pattern, which is the key feature differentiating it from the other options.

**Why Each Wrong Option is Incorrect:**

**A. Herpes Simplex Virus (HSV):** HSV presents with vesicular lesions in a diffuse pattern involving multiple dermatomes, which is different from the dermatomal distribution seen in HZ.

**B. Impetigo:** Impetigo is a bacterial infection, typically involving the skin and mucous membranes, presenting with diffuse, often bullous lesions. This is different from HZ, which presents with vesicular lesions in a dermatomal pattern.

**C. Epidermolysis Bullosa:** EB presents with blistering of the skin and mucous membranes, which is different from the vesicular lesions seen in HZ.