Post-herpetic neuralgia
Exam Tips
- In OSCE/viva, define PHN by timing: neuropathic dermatomal pain persisting >=3 months after shingles onset/healing.
- Map pain and sensory signs against a dermatome chart and compare with the opposite side; allodynia to light touch is a classic high-yield sign.
- Ask directly about prior shingles because some patients do not link old rash to current pain.
- Explain why paracetamol/opioids alone are often inadequate: PHN is primarily neuropathic, so adjuvant neuropathic agents are usually needed.
- For prescribing stations, state titration and safety: start low, go slow, early review, renal adjustment for gabapentinoids, and caution sedation/falls/polypharmacy in older adults.
- Revise with visual aids: use a standard dermatome map figure and a neuropathic pain pathway diagram (dorsal root ganglion and dorsal horn sensitization) from your core neurology/pain textbook.
Definition
Post-herpetic neuralgia is persistent neuropathic pain in a unilateral dermatomal distribution that continues for at least 3 months after the onset or healing of a herpes zoster (shingles) rash. It reflects chronic nerve injury after varicella-zoster virus reactivation and is typically described as burning, stabbing, or electric-shock-like pain with sensory disturbance in the same dermatome.
Pathophysiology
After latent varicella-zoster virus reactivates in dorsal root or trigeminal ganglia, acute neuritis damages peripheral sensory fibres and ganglion neurons. Ongoing ectopic discharges from injured A-delta and C fibres, plus deafferentation, drive peripheral sensitization and central sensitization in dorsal horn pathways (including reduced inhibitory interneuron function), which explains hyperalgesia and allodynia. Structural and functional changes can persist after the rash resolves, so pain becomes chronic and less responsive to simple analgesia.
Risk Factors
- Increasing age (risk rises markedly in older adults)
- Prodromal pain before acute shingles eruption
- Severe acute zoster pain
- Extensive rash, especially spread beyond a single dermatome
- Ophthalmic zoster involvement
- Diabetes mellitus
- Chronic respiratory disease
- Autoimmune disease
- Severe immunosuppression
Clinical Features
Symptoms
- Unilateral dermatomal pain persisting beyond rash healing (often >=3 months)
- Burning, aching, sharp, lancinating, or itching neuropathic pain
- Pain may be constant or intermittent
- Pain triggered by light touch or clothing (allodynia)
- Sleep disturbance, reduced activity, low mood, and anxiety due to chronic pain
Signs
- Sensory change in affected dermatome versus contralateral side
- Hyperalgesia to pinprick or pressure
- Allodynia on light tactile stimulation
- Reduced thermal, tactile, vibration, or pinprick sensation
- Patchy anaesthesia within or around the previous zoster dermatome
Investigations
Management
Lifestyle Modifications
- Explain chronic neuropathic nature of PHN and set realistic goals (pain reduction and function, not always complete pain abolition)
- Reduce mechanical irritation with soft cotton/silk clothing
- Protect hypersensitive skin (for example with a light dressing, compression garment, or plastic barrier if tolerated)
- Trial cool packs if tolerated (avoid if this worsens allodynia)
- Encourage pain diary, sleep hygiene, paced activity, and early review during dose titration
- Screen for depression/anxiety and consider CBT or pain-management programme when function is significantly affected
Pharmacological Treatment
Simple analgesia (adjunct for mild to moderate pain)
- Paracetamol 1 g orally every 4-6 hours when required (maximum 4 g/24 hours)
- Codeine phosphate 30-60 mg orally every 4 hours when required (maximum 240 mg/24 hours)
Often insufficient alone for neuropathic pain. Avoid codeine in severe respiratory depression; caution constipation, sedation, falls, and dependence risk in older adults.
First-line oral neuropathic pain agents
- Amitriptyline 10 mg at night, increase by 10-25 mg every 1-2 weeks according to response/tolerability (usual pain dose 25-75 mg nocte)
- Duloxetine 30 mg once daily for 1 week then 60 mg once daily (usual target 60 mg/day)
- Gabapentin 300 mg once daily on day 1, 300 mg twice daily on day 2, 300 mg three times daily on day 3; then titrate (usual 900-3600 mg/day in 3 divided doses)
- Pregabalin 75 mg twice daily, increase after 3-7 days to 150 mg twice daily; may increase further to maximum 300 mg twice daily
Choose based on comorbidity, interactions, and frailty. Renal dose adjustment is essential for gabapentin/pregabalin. Amitriptyline: caution anticholinergic effects, QT risk, glaucoma, urinary retention, and overdose toxicity. Duloxetine: avoid with severe hepatic impairment and uncontrolled hypertension; watch for serotonin syndrome and withdrawal. Gabapentinoids: dizziness, sedation, gait instability, misuse/dependence potential; counsel on driving impairment.
Topical therapy
- Lidocaine 5% medicated plaster: apply to painful area for up to 12 hours in any 24-hour period (up to 3 plasters daily)
Useful for focal pain and prominent allodynia, especially in older adults or when systemic adverse effects are a concern. Apply only to intact skin; avoid external heat over patch.
Rescue analgesia (short-term only)
- Tramadol 50-100 mg every 4-6 hours when required (maximum 400 mg/24 hours)
Use only for short acute rescue, not long-term without specialist input. Contraindications/cautions include epilepsy, serotonergic drug interactions (serotonin syndrome), dependence risk, confusion, and falls in elderly patients.
Complications
- Chronic sleep disturbance and fatigue
- Reduced mobility and impaired activities of daily living
- Social withdrawal and reduced quality of life
- Anxiety and depressive symptoms
- Persistent opioid/gabapentinoid adverse effects or dependence if poorly monitored
Prognosis
Course is variable: a substantial proportion continue to have pain for many months, and up to about half may have symptoms beyond one year. Meaningful pain control is often difficult, with complete relief uncommon, so follow-up should focus on functional improvement, mood, and tolerability of treatment.
Sources & References
💊BNF Drug References(2)
- Amantadine hydrochloride[management.pharmacological]
- Capsaicin[management.pharmacological]
✅NICE Guidelines(1)
- Post-herpetic neuralgia[overview]
📖Textbook References(19)
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1650)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 951, 952)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 952)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1649, 1650)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1650)[context]
- [Oxford Medical Handbooks] Ian Wilkinson, Tim Raine, Kate Wiles, Anna Goodhart, Catriona Ha - Oxford Handbook of Clinical Medicine (2017, Oxford University Press) - libgen.li.pdf(pp. 900)[context]
- [Oxford Medical Handbooks] Ian Wilkinson, Tim Raine, Kate Wiles, Anna Goodhart, Catriona Ha - Oxford Handbook of Clinical Medicine (2017, Oxford University Press) - libgen.li.pdf(pp. 453)[context]
- [Oxford Medical Handbooks] Ian Wilkinson, Tim Raine, Kate Wiles, Anna Goodhart, Catriona Ha - Oxford Handbook of Clinical Medicine (2017, Oxford University Press) - libgen.li.pdf(pp. 897, 898)[context]
- [Oxford Medical Handbooks] Ian Wilkinson, Tim Raine, Kate Wiles, Anna Goodhart, Catriona Ha - Oxford Handbook of Clinical Medicine (2017, Oxford University Press) - libgen.li.pdf(pp. 110)[context]
- [Oxford Medical Handbooks] Ian Wilkinson, Tim Raine, Kate Wiles, Anna Goodhart, Catriona Ha - Oxford Handbook of Clinical Medicine (2017, Oxford University Press) - libgen.li.pdf(pp. 418, 419)[context]
- [Oxford Medical Handbooks] Ian Wilkinson, Tim Raine, Kate Wiles, Anna Goodhart, Catriona Ha - Oxford Handbook of Clinical Medicine (2017, Oxford University Press) - libgen.li.pdf(pp. 898)[context]
- [Oxford Medical Handbooks] Ian Wilkinson, Tim Raine, Kate Wiles, Anna Goodhart, Catriona Ha - Oxford Handbook of Clinical Medicine (2017, Oxford University Press) - libgen.li.pdf(pp. 79, 80)[context]
- [Oxford Medical Handbooks] Ian Wilkinson, Tim Raine, Kate Wiles, Anna Goodhart, Catriona Ha - Oxford Handbook of Clinical Medicine (2017, Oxford University Press) - libgen.li.pdf(pp. 897, 898)[context]
- [Oxford Medical Handbooks] Ian Wilkinson, Tim Raine, Kate Wiles, Anna Goodhart, Catriona Ha - Oxford Handbook of Clinical Medicine (2017, Oxford University Press) - libgen.li.pdf(pp. 452, 453)[context]
- [Oxford Medical Handbooks] Ian Wilkinson, Tim Raine, Kate Wiles, Anna Goodhart, Catriona Ha - Oxford Handbook of Clinical Medicine (2017, Oxford University Press) - libgen.li.pdf(pp. 80)[context]
- [Oxford Medical Handbooks] Ian Wilkinson, Tim Raine, Kate Wiles, Anna Goodhart, Catriona Ha - Oxford Handbook of Clinical Medicine (2017, Oxford University Press) - libgen.li.pdf(pp. 419)[context]
- [Oxford Medical Handbooks] Ian Wilkinson, Tim Raine, Kate Wiles, Anna Goodhart, Catriona Ha - Oxford Handbook of Clinical Medicine (2017, Oxford University Press) - libgen.li.pdf(pp. 109, 110)[context]
- [Oxford Medical Handbooks] Ian Wilkinson, Tim Raine, Kate Wiles, Anna Goodhart, Catriona Ha - Oxford Handbook of Clinical Medicine (2017, Oxford University Press) - libgen.li.pdf(pp. 110)[context]
- [Oxford Medical Handbooks] Ian Wilkinson, Tim Raine, Kate Wiles, Anna Goodhart, Catriona Ha - Oxford Handbook of Clinical Medicine (2017, Oxford University Press) - libgen.li.pdf(pp. 899, 900)[context]