What is postherpetic neuralgia?

What is Postherpetic Neuralgia?

Postherpetic neuralgia (PHN) is a chronic neuropathic pain condition characterized by severe pain that persists for 3 months or more after the herpes zoster (shingles) rash has resolved. 1, 2, 3

Pathophysiology and Mechanism

• PHN develops from reactivation of the varicella zoster virus, which remains dormant in the dorsal root ganglia or sensory ganglia of cranial nerves after primary varicella (chickenpox) infection 4
• When the virus reactivates, it travels along nerve pathways causing inflammation and direct damage to peripheral and central neurons, resulting in the characteristic painful rash with dermatomal distribution 4, 5
• The nerve damage leading to PHN may be a byproduct of the immune/inflammatory response accompanying varicella zoster virus reactivation 5
• The pathophysiology may differ distinctly between patients with either reduced or increased skin sensitivity 6

Clinical Presentation

• Patients experience multiple types of pain including:

  • Constant deep, aching, or burning pain (often described as "cold burning pain") 3, 4
  • Paroxysmal, lancinating (sharp, shooting) pain 3
  • Hyperalgesia (painful stimuli are more painful than expected) 7, 3
  • Allodynia (pain from typically non-painful stimuli like light touch or clothing) 7, 3

• The pain follows a dermatomal distribution corresponding to the original shingles rash location 4

• Pain can persist from months to years after the rash has completely healed 1, 2, 3

Epidemiology and Risk Factors

• PHN is the most common complication of herpes zoster, affecting approximately 1 million cases annually in the US 5
• At least half of shingles sufferers over age 65 develop PHN 2
• PHN accounts for 11-15% of all referrals to pain clinics 2
• The primary risk factors in order of importance are:
  • Increasing age (elderly are most frequently and seriously affected) 2, 8, 6
  • Severity of acute shingles pain 2
  • Trigeminal nerve distribution 2

Impact on Quality of Life

• PHN can have a severe impact on patients' quality of life and functional ability 8
• Patients report decreased quality of life and significant interference with activities of daily living 5
• The condition can be incapacitating, particularly in patients with advanced disease and immunocompromised states 4

Common Pitfalls

• Do not confuse acute herpes zoster pain with PHN - by definition, PHN only refers to pain persisting at least 3 months after the onset of the acute rash 2, 3
• PHN remains highly resistant to current treatments, requiring aggressive early management 8
• The condition is likely to increase in incidence due to greater longevity and increasing numbers of immunocompromised patients 6