Post-herpetic Neuralgia

Post-herpetic neuralgia (PHN) is a chronic neuropathic pain condition that occurs as a complication of herpes zoster (shingles).

• It results from damage to peripheral and central nerve fibers during a herpes zoster infection.

• Pain can persist weeks to months after the rash has healed, sometimes lasting years.

• PHN predominantly affects older adults and immunocompromised individuals, with severity often correlating with age and severity of the initial shingles outbreak.

• Pathophysiology involves nerve inflammation, demyelination, and sensitization of nociceptors, leading to persistent pain signals.

Signs & Symptoms

• Pain characteristics:

  • Burning

  • Stabbing or lancinating

  • Gnawing or deep aching

• Allodynia: Pain elicited by normally non-painful stimuli such as light touch or clothing contact

• Hyperalgesia: Exaggerated pain response to painful stimuli

• Sensory changes: Numbness, tingling, or itching in the affected dermatome

• Distribution: Follows dermatomal patterns corresponding to the site of the previous herpes zoster rash, commonly thoracic or cranial nerves

• Impact on daily life: Sleep disturbance, reduced mobility, and psychological distress (anxiety, depression)

Diagnostic Criteria

Diagnosis is primarily clinical, based on:

• History of recent shingles (herpes zoster)

• Persistent neuropathic pain in the same dermatome ≥ 90 days after rash onset

• Pain described as burning, stabbing, or gnawing, often with associated allodynia

• Absence of other causes of neuropathic pain in the same distribution

Note: Early recognition and treatment of herpes zoster may reduce the risk of PHN.

Investigation

• Laboratory tests: Usually not required for diagnosis

• Electrodiagnostic studies (nerve conduction studies): Rarely indicated, may help in atypical cases

• Imaging (MRI/CT): Only if other neurological causes of pain are suspected

Treatment

Management of PHN requires a multimodal approach, combining pharmacological therapy, non-pharmacological measures, and specialist referral when needed.

Non-Pharmacological Treatment

• Physical therapy: Gentle exercises and stretching to maintain mobility

• Transcutaneous electrical nerve stimulation (TENS): Can provide temporary relief in some patients

• Psychological support: Counseling or cognitive behavioral therapy to cope with chronic pain

• Topical therapies: Lidocaine 5% patches or capsaicin cream in localized pain areas

Note: Early initiation of pain management is crucial to prevent central sensitization and chronic pain.

Pharmacological Treatment

• First-line therapies:

  • Tricyclic antidepressants (TCAs):

    • Amitriptyline 25 mg PO at night, titrated up to 150 mg as tolerated

    • Mechanism: Modulates neuropathic pain by inhibiting reuptake of serotonin and norepinephrine

  • Anticonvulsants:

    • Gabapentin 300–900 mg daily in divided doses for at least two weeks, titrated as needed

    • Mechanism: Reduces excitability of damaged nerves and neuropathic pain transmission

• Adjunct therapy:

  • Topical analgesics: Lidocaine patches, capsaicin cream

  • Opioids: Reserved for refractory cases under specialist supervision

• Referral:

  • Immediate referral for herpes zoster ophthalmicus to an ophthalmologist for atropinization

  • Refer if severe pain is unresponsive to first-line therapy

Prevention

• Vaccination: Shingles (zoster) vaccine significantly reduces incidence of herpes zoster and subsequent PHN in older adults

• Early antiviral therapy: For acute shingles (acyclovir, valacyclovir) within 72 hours of rash onset to reduce risk of PHN

• Pain control during acute shingles: Early analgesics and topical therapy may prevent central sensitization

Complications

• Chronic neuropathic pain, sometimes lasting years

• Sleep disturbances and reduced quality of life

• Psychological distress: Anxiety, depression, social withdrawal

• Secondary complications from medications (e.g., sedation, constipation from opioids or TCAs)

Prognosis

• Pain often decreases over months but may persist in some individuals, particularly the elderly

• Early antiviral therapy and aggressive pain management improve outcomes