Herpes Zoster: Pathophysiology and Management

Etiology and Pathogenesis

Herpes zoster, commonly known as shingles, is caused by the reactivation of the varicella-zoster virus (VZV), the same virus that causes varicella (chickenpox). After a primary VZV infection, the virus remains dormant in sensory nerve ganglia. Reactivation typically occurs due to declining cell-mediated immunity, often associated with aging, immunosuppression, or stress. The reactivated virus travels along sensory nerves to the skin, causing inflammation and characteristic vesicular eruptions within a dermatomal distribution.

Clinical Presentation

The disease typically presents with prodromal symptoms such as pain, itching, or tingling in a specific dermatome, which can precede the rash by several days. The rash begins as erythematous macules and papules, which rapidly evolve into vesicles. These vesicles usually rupture and crust over within a week. The eruption is typically unilateral and confined to a single dermatome, most commonly the thoracic, lumbar, or trigeminal regions. Associated symptoms may include fever, headache, malaise, and regional lymphadenopathy.

Pharmacological Interventions

Antiviral Medications

Antiviral agents are the mainstay. These medications work by inhibiting viral replication and can reduce the severity and duration of the illness, as well as the risk of postherpetic neuralgia (PHN). Commonly prescribed antivirals include:

• Acyclovir: A nucleoside analog that inhibits viral DNA polymerase.
• Valacyclovir: A prodrug of acyclovir with improved oral bioavailability.
• Famciclovir: A prodrug of penciclovir, another nucleoside analog.

Treatment is most effective when initiated within 72 hours of rash onset.

Pain Management

Pain control is a critical aspect of care. Options include:

• Analgesics: Over-the-counter pain relievers such as acetaminophen or ibuprofen may be sufficient for mild pain. Opioid analgesics may be required for more severe pain.
• Anticonvulsants: Medications such as gabapentin and pregabalin are often used to manage neuropathic pain, particularly PHN.
• Tricyclic Antidepressants: Amitriptyline, nortriptyline, and desipramine can also be effective for neuropathic pain.
• Topical Agents: Lidocaine patches or capsaicin cream may provide localized pain relief.

Non-Pharmacological Interventions

• Cool Compresses: Application of cool, moist compresses can help relieve pain and itching.
• Calamine Lotion: May help to soothe irritated skin and reduce itching.
• Colloidal Oatmeal Baths: Can provide relief from itching and inflammation.
• Maintaining hygiene: Keeping the affected area clean and dry can prevent secondary bacterial infections.

Complications

Potential complications include:

• Postherpetic Neuralgia (PHN): Chronic pain that persists for months or years after the rash has resolved.
• Bacterial Superinfection: Secondary bacterial infections of the skin lesions.
• Ophthalmic Zoster: Involvement of the ophthalmic branch of the trigeminal nerve, which can lead to vision impairment.
• Disseminated Zoster: Spread of the virus to multiple dermatomes or internal organs, more common in immunocompromised individuals.

Prevention

Vaccination is the most effective strategy for preventing reactivation and subsequent complications. The recombinant zoster vaccine (RZV) is currently recommended for adults aged 50 years and older, regardless of prior history of varicella or zoster.