Herpes Zoster
Reactivation of the chickenpox virus causing a painful, blistering skin rash confined to one side of the body in a specific nerve distribution (dermatome).
Emergency Management: Disseminated zoster in an immunocompromised host or Herpes Zoster Ophthalmicus with visual changes requiring immediate IV Acyclovir and emergent ophthalmology consult.
Herpes zoster, commonly known as shingles, is a localized, intensely painful, blistering rash caused by the reactivation of the latent varicella-zoster virus (VZV) from the dorsal root or cranial nerve ganglia.
Detailed Overview
Following a primary infection with VZV (chickenpox), the virus travels retrogradely along sensory nerves to the dorsal root ganglia where it lies dormant for decades. As cellular immunity to VZV wanes with advancing age, immunosuppression, or severe stress, the virus reactivates. It replicates in the ganglion and travels anterogradely down the sensory nerve to the skin, causing severe neuropathic pain and a unilateral vesicular eruption strictly limited to a single dermatome. The most feared complication is postherpetic neuralgia (PHN), which can cause debilitating, treatment-resistant nerve pain persisting for months to years after the rash resolves. Prompt antiviral therapy is critical to reduce the duration of the rash and the severity of PHN.
Epidemiology & Demographics
Incidence: ~4 cases per 1,000 person-years in the general population, rising to >10 per 1,000 in those over 60. Lifetime risk: 1 in 3 adults will develop shingles. Age distribution: Drastic increase in incidence after age 50.
Etiological Mechanism
Reactivation of endogenous Varicella-Zoster Virus (Human Herpesvirus 3).
Primary Causes
Primary: Reactivation of latent VZV
Secondary (Triggers): Age-related immunosenescence, immunosuppressive drugs, HIV/AIDS, malignancy, extreme psychological stress
During childhood chickenpox, VZV infects the mucocutaneous tissues, then enters sensory nerve endings, traveling via retrograde axonal transport to the dorsal root, cranial nerve, or autonomic ganglia. Here, VZV establishes latency. The virus produces latency-associated transcripts but no infectious virions. The latency is maintained by VZV-specific memory T-cells. When this cell-mediated immunity drops below a critical threshold (due to age or immunosuppression), the virus begins replicating within the ganglion. This causes intense neuronal inflammation and necrosis, translating to severe pre-eruptive neuropathic pain. The newly formed virions then travel anterogradely down the sensory axon to the epidermal cells of the corresponding dermatome. Viral replication in the epidermis causes ballooning degeneration of keratinocytes, fluid accumulation, and the formation of characteristic grouped vesicles on an erythematous base.
Diagnostic Criteria & Guidelines
Diagnosis is almost always clinical based on the characteristic unilateral dermatomal rash with associated neuropathic pain. If the presentation is atypical (e.g., in immunocompromised patients), diagnosis is confirmed via PCR testing of vesicle fluid.
Antiviral therapy (must be started within 72 hours of rash onset to be maximally effective): Valacyclovir 1000 mg PO TID for 7 days OR Famciclovir 500 mg PO TID for 7 days OR Acyclovir 800 mg PO 5 times daily for 7 days. Provide adequate analgesia (NSAIDs, Acetaminophen, or short-course opioids if pain is severe).
Second-Line & Adjunctive Therapy
For Postherpetic Neuralgia (PHN): Gabapentin 300 mg PO TID titrated up to 3600 mg/day, Pregabalin 75 mg PO BID, or Tricyclic Antidepressants (Amitriptyline 10-25 mg PO QHS). Topical lidocaine 5% patches.
Surgical & Procedural Management
None.
Patient Counseling & Advice
Explain that shingles is a reactivation of their own childhood chickenpox virus. Emphasize taking the antiviral medication exactly as prescribed to prevent nerve damage. Clarify that while they cannot give someone else shingles, the fluid in the blisters contains active chickenpox virus and can give chickenpox to someone who is not immune.
Follow-Up & Monitoring Schedule
Outpatient follow-up in 2-4 weeks to assess for resolution of rash and presence of PHN. Immediate referral to ophthalmology is mandatory if Hutchinson's sign is present or if the eye is red/painful.
Preventive Strategies
Recombinant Zoster Vaccine (Shingrix): 2 doses given IM, 2-6 months apart. Highly effective (>90%) at preventing shingles and PHN. Recommended for all adults >= 50 years old, and immunocompromised adults >= 19 years old.
The rash usually heals in 2 to 4 weeks with no scarring. Prognosis is generally good, but older adults have a significantly higher risk of prolonged, quality-of-life limiting PHN.