A 65-year-old male presents with a painful rash on his chest, as shown in the image. The rash appeared suddenly and is associated with a burning sensation. Which of the following is the most likely diagnosis?

Explanation

## Image Findings * **Grouped vesicles and bullae** on an **erythematous base**. * **Unilateral distribution** of lesions. * Lesions follow a **dermatomal pattern** on the chest/trunk. * Some lesions appear to be **crusted** or in various stages of healing, indicating evolution of the rash. ## Diagnosis **Key Point:** The classic presentation of grouped vesicles on an erythematous base, distributed unilaterally in a dermatomal pattern, is pathognomonic for **Herpes Zoster**. The image clearly demonstrates **vesicular lesions** clustered together on a reddened skin background, consistent with a viral eruption. The most striking feature is the **unilateral distribution** strictly confined to a **dermatome** on the chest, which is the hallmark of **Herpes Zoster**, also known as **shingles**. This condition results from the reactivation of the **varicella-zoster virus (VZV)**, which lies dormant in the dorsal root ganglia after a primary chickenpox infection. The patient's age (65-year-old) and symptoms (painful, burning sensation) further support this diagnosis, as the incidence and severity of post-herpetic neuralgia increase with age. ## Differential Diagnosis | Feature | Herpes Zoster | Contact Dermatitis | Erysipelas | Bullous Pemphigoid | | :------------------ | :--------------------------------------------- | :----------------------------------------------- | :------------------------------------------------- | :------------------------------------------------ | | **Lesion Morphology** | Grouped vesicles/bullae on erythematous base | Erythematous papules, vesicles, bullae, crusts | Well-demarcated, raised, erythematous plaque | Large, tense bullae on erythematous or normal skin | | **Distribution** | Unilateral, strictly dermatomal | Localized to contact area, often linear/geometric | Often on face or lower extremities, spreading | Generalized or localized, often flexural | | **Symptoms** | Painful, burning, paresthesia | Pruritic, burning, stinging | Painful, warm, tender, fever, malaise | Intensely pruritic | | **Etiology** | Reactivation of Varicella-Zoster Virus (VZV) | Hypersensitivity reaction to allergen/irritant | Superficial bacterial infection (Streptococcus) | Autoimmune (antibodies against hemidesmosomes) | | **Age Group** | More common in older adults, immunocompromised | Any age | Any age, more common in infants, elderly, diabetics | Typically elderly (>60 years) | ## Clinical Relevance **Clinical Pearl:** Early initiation of antiviral therapy (within 72 hours of rash onset) is crucial in Herpes Zoster to reduce the severity and duration of the rash, pain, and the risk of **post-herpetic neuralgia (PHN)**, especially in older adults. ## High-Yield for NEET PG **High-Yield:** The most common complication of Herpes Zoster is **post-herpetic neuralgia (PHN)**, characterized by persistent pain in the affected dermatome for more than 3 months after the rash has healed. **Key Point:** Herpes Zoster Ophthalmicus (involving the trigeminal nerve, V1 division) can lead to severe ocular complications, including vision loss, and requires urgent ophthalmological consultation. **Hutchinson's sign** (lesions on the tip of the nose) indicates nasociliary nerve involvement and a high risk of ocular disease. ## Common Traps **Warning:** Do not confuse the dermatomal distribution of Herpes Zoster with other localized rashes. While **Herpes Simplex Virus (HSV)** can cause grouped vesicles, it typically recurs in the same localized area (e.g., lips, genitals) and does not follow a strict dermatomal pattern across the trunk. ## Reference [cite:Harrison's Principles of Internal Medicine, 21st Edition, Chapter 200: Varicella-Zoster Virus Infections; Robbins Basic Pathology, 11th Edition, Chapter 25: Skin]