What is the definition of post‑herpetic neuralgia and how is it managed?

Definition and Management of Post-Herpetic Neuralgia

Post-herpetic neuralgia (PHN) is chronic neuropathic pain persisting for 3 months or more following resolution of herpes zoster skin lesions, and should be managed with gabapentin as first-line therapy, followed by pregabalin if inadequate response, with topical capsaicin 8% as a highly effective adjunct. 1

Definition

PHN is a complication of acute herpes zoster infection that is distinct from other peripheral neuropathies 1. The condition manifests as:

• Constant deep, aching, or burning pain
• Paroxysmal, lancinating (sharp shooting) pain
• Hyperalgesia (painful stimuli more painful than expected)
• Allodynia (pain from typically non-painful stimuli like light touch)
• Pain confined to one or more dermatomes where the original zoster eruption occurred 2

The diagnosis requires pain persisting beyond 3 months after healing of the herpetic rash 1, 2.

Management Algorithm

First-Line Pharmacological Treatment

Gabapentin is the recommended first-line oral agent (strong recommendation, moderate evidence) 1:

• Start with 100-200 mg/day in older adults or those with renal impairment 3
• Titrate to 2400 mg per day in divided doses for typical adults 1
• Effective dose range: 900-3600 mg/day in 2-3 divided doses 3
• Benefits include improved sleep scores; expect somnolence in up to 80% of patients 1
• Allow adequate time between dose escalations to monitor effects 3

Topical capsaicin 8% is strongly recommended as concurrent therapy (strong recommendation, high evidence) 1:

• Single 30-minute application of 8% dermal patch at pain site
• Provides pain relief for at least 12 weeks
• Pre-treat with 4% lidocaine for 60 minutes, then wipe off before capsaicin application to reduce application pain
• Common side effects: erythema and pain at application site 1

Second-Line Options (If Inadequate Response to Gabapentin)

Pregabalin (weak recommendation, moderate evidence) 1:

• Start with 25-50 mg/day
• Effective dose: 150-600 mg/day in two divided doses 3
• May be preferred over gabapentin due to easier titration and more predictable pharmacokinetics 3

Tricyclic antidepressants (weak recommendation, moderate evidence) 1:

• Nortriptyline preferred over amitriptyline due to fewer side effects 4
• Start 10-25 mg at bedtime
• Increase every 3-7 days to 25-100 mg at bedtime as tolerated
• Number needed to treat (NNT) = 2.64 1
• Common side effects: dry mouth, constipation, sedation 4
• Earlier initiation after zoster onset improves outcomes 4

Serotonin-norepinephrine reuptake inhibitors (SNRIs) (weak recommendation, moderate evidence) 1:

• Consider based on effectiveness in general neuropathic pain populations

Additional Topical Options

Lidocaine patches 5% 1:

• NNT = 2.0
• High safety profile due to low systemic absorption 3
• Particularly appropriate for older adults 3

Third-Line: Opioids (Use With Caution)

Opioids should NOT be first-line agents (strong recommendation, moderate evidence) 1:

• Reserve for patients with moderate to severe pain unresponsive to first-line therapies
• If used, combine short- and long-acting formulations
• Consider morphine plus gabapentin combination for possible additive effects at lower individual doses 1
• Effective opioids include: oxycodone, extended-release morphine, methadone (NNT = 2.67); tramadol (NNT = 4.76) 1

Non-Pharmacological Approaches

Cognitive behavioral therapy (strong recommendation, moderate evidence) 1:

• Promotes adaptive behaviors and addresses maladaptive pain responses

Physical and occupational therapy (strong recommendation, low evidence) 1

Hypnosis for neuropathic pain (strong recommendation, low evidence) 1

Critical Pitfalls to Avoid

1. Do not use lamotrigine - it is NOT effective for PHN and carries risk of serious rash 1

2. Start low, go slow - Older adults are particularly susceptible to side effects like somnolence, dizziness, and mental clouding from gabapentinoids 3

3. Adjust for renal function - Both gabapentin and pregabalin require dose adjustment in renal impairment 3

4. Pre-treat before capsaicin - Always apply lidocaine first to reduce the severe burning pain during capsaicin application 1

5. Avoid opioids as first-line - Risk of pronociception, cognitive impairment, respiratory depression, and addiction outweighs benefits when other options available 1

Evidence Quality Notes

The strongest evidence supports gabapentin and topical capsaicin 8% as first-line therapies 1. The systematic review showing analgesic efficacy (NNT <5.00) for multiple agents provides robust support for the treatment hierarchy 1. While tricyclic antidepressants have excellent NNT values (2.64), their side effect profile in older adults makes gabapentinoids preferable as initial therapy 3.