FRCA Notes

Post-Herpetic Neuralgia

Resources

  • Herpes zoster ('shingles') is caused by reactivation of the varicella zoster virus
  • After causing the primary infection, VZV lies dormant in sensory ganglia
  • If conditions allow, it may re-emerge to give rise to herpes zoster

  • The most common cause of reactivation is immunosuppression, e.g. due to:
    • Malignancy or its treatment e.g. chemotherapy, radiotherapy
    • HIV or other acquired immunodeficiencies e.g. lymphoma
    • Immunosuppressive drugs e.g. steroids, methotrexate, mycophenolate etc.

  • Post-herpetic neuralgia describes ongoing pain following herpes zoster
  • Intense, severe pain
    • Neuropathic in nature; throbbing or burning
    • Worse as the day progresses and maximal at night, leading to sleep disturbance
    • May form a prodrome prior to the emergence of blisters
    • Most commonly in the thoracic dermatomes, but may also affect the ophthalmic branch of the trigeminal nerve
    • Typically lasts <30 days, but may last up to 120 days

  • Characteristic blistering rash limited to the dermatomal distribution of the dorsal root ganglion in which the VZV lies

  • Fatigue, difficulty in concentrating and depression may follow from sleep disturbance

  • Some patients may experience pain which lasts after the herpes zoster skin lesions have healed
  • Once >3 months, this is termed post-herpetic neuralgia
  • It can last years, with significant debilitation due to severe pain

Risk factors

  • Increasing age (>60yrs)
    • Incidence only 3/100,000 overall but 20/100,000 beyond 60yrs
  • Female gender
  • Presence of a prodromal dermatomal pain
  • More severe pain or intense rash in the acute phase
  • Fever >38°C
  • Psychosocial factors including greater anxiety

Pain

  • Continuous or intermittent pain
  • Throbbing or burning in nature
  • Associated allodynia - unable to wear clothing over the affected region

Neurological

  • Sensory loss
  • Itching
  • Motor weakness
  • Autonomic disturbances with abnormal skin temperature, colour or sweating

Psychological

  • Isolation
  • Depression/anxiety
  • Sleep disturbance
  • Chronic fatigue
  • Weight loss

Prevention

  • Anti-viral drugs shorten the period of viral replication
  • Their use reduces the incidence of PHN at 6 months
  • Examples include:
    • Varicella zoster virus vaccination/booster
    • Acyclovir
    • Valaciclovir
    • Famciclovir

Non-pharmacological

  • Patient education
  • Support and counselling; CBT may be of benefit

Pharmacological

  • First line agents
    • Gabapentinoids
    • Tricyclic antidepressants

  • Topical agents
    • Topical capsaicin may be beneficial but can be painful to apply
    • Lidocaine patches may be used but are not robustly evidence-based

  • Other agents
    • Paracetamol
    • Tramadol
    • Highly selective, peripherally restricted, AT2-receptor antagonist (EMA401)