Herpetic Neuralgia

Overview – Herpetic Neuralgia

Herpetic neuralgia (commonly known as shingles) is a painful reactivation of the Varicella-Zoster Virus (VZV), typically occurring years after primary infection (chickenpox). The virus lies dormant in neural ganglia and re-emerges under triggers like stress, sunlight, or immunosuppression. It presents as burning pain and vesicular lesions in a dermatomal distribution and may lead to chronic neuropathic pain (postherpetic neuralgia), especially in older adults.

Definition

• Herpetic Neuralgia = Neuropathic pain associated with reactivated Herpes Zoster (VZV).
• Also known as shingles.
• Postherpetic neuralgia = persistent pain >3 months after the rash resolves.

Aetiology

• Reactivation of latent Herpes Zoster Virus (VZV)
• Triggers:
  • Immunosuppression
  • Stress
  • UV exposure
  • Advanced age

Pathogenesis

• VZV remains latent in dorsal root or cranial nerve ganglia.
• Triggered reactivation → viral replication → virus migrates down sensory axons
• → Painful inflammation and vesicular eruption in the affected dermatome
• Most commonly affects:
  • Thoracic dermatomes
  • Trigeminal nerve (especially ophthalmic division)

Morphology

• Erythematous, vesicular rash strictly confined to a unilateral dermatome
• No crossing of midline
• May show crusting and scabbing in later stages

Clinical Features

• Prodrome (1–3 days):
  • Burning, tingling, or hyperalgesia in the dermatome
• Acute Phase (2–4 weeks):
  • Painful, grouped vesicular lesions
  • Erythematous base in a dermatomal pattern
• Complications:
  • Postherpetic neuralgia (PHN)
  • Superinfection of lesions
  • Vision loss (if ophthalmic branch of CN V involved)
  • Ramsay Hunt syndrome (facial palsy + vesicles in ear)

Investigations

• Clinical diagnosis is typically sufficient
• Confirmatory:
  • PCR or direct fluorescent antibody test (DFA) on lesion sample
  • Tzanck smear (non-specific; shows multinucleated giant cells)

Management

Antivirals

• Famciclovir or Valaciclovir
  • Most effective if started within 72 hours of rash onset
  • Shorten duration and reduce risk of postherpetic neuralgia

Pain Control

• Neuropathic agents:
  • Tricyclic antidepressants (e.g. amitriptyline)
  • Anticonvulsants (e.g. gabapentin, pregabalin)
• Topical agents:
  • Lidocaine 5% patches
  • Capsaicin cream
• Others:
  • NSAIDs or opioids if pain is severe

Prevention

• Zoster Vaccine (e.g. Shingrix®):
  • Recommended for adults >50 years
  • Strongly reduces risk of shingles and postherpetic neuralgia

Summary – Herpetic Neuralgia

Herpetic neuralgia (shingles) is caused by reactivation of latent Herpes Zoster virus and manifests as painful vesicular rash in a dermatomal pattern. Prompt antiviral therapy and pain management are essential to reduce complications like postherpetic neuralgia. For a broader context, see our Nervous System Overview.