Postherpetic neuralgia (PHN) is the most common complication of herpes zoster (shingles). It produces chronic pain along cutaneous nerves and often some distortion of sensation. The pain can either persist after the acute episode of shingles or it can recur in an area previously affected by shingles.

There is a separate article on herpes zoster, entitled Shingles.

Epidemiology

• There are various definitions for postherpetic neuralgia with regards to time of onset and duration of pain. This makes estimates about its prevalence difficult.¹
• The incidence in UK primary care is thought to be about 28 per 100,000 person-years.²
• Approximately 20% of people will experience postherpetic neuralgia after the initial rash has cleared.³
• It is uncommon in children.

Risk factors

Factors that may predispose to postherpetic neuralgia (PHN) include:

• Older age (>50 years).⁴
• Female sex.⁴
• Presence of severe pain during the attack of shingles.⁴
• A more extensive and severe rash from shingles.^4,5
• The presence of a prodrome (48-72 hours of throbbing pain and paraesthesia in the region of the affected sensory nerve before the shingles rash develops).⁴
• Psychosocial factors may predispose to PHN.⁶
• The site of the herpes lesion:⁵
  • Risk of PHN is low in the jaw, neck, sacral, and lumbar regions.
  • Risk is moderate in the thoracic area.
  • The highest risk is in the trigeminal area, especially the ophthalmic division, and also the brachial plexus.

Research is currently underway looking at biomarkers that can help to identify those at risk of developing PHN.⁴

Presentation

• Herpes zoster presents initially with a painful vesicular eruption in a single dermatome.
• The eruption resolves but, in postherpetic neuralgia (PHN), pain continues. Some sources say that pain must continue for at least three months to fulfil the definition of PHN.⁵ Others say that PHN is pain persisting more than 30 days after lesions have healed.⁷ Another source says that PHN is pain persisting for more than four months after the rash has healed.⁴
• Pain is intense and may be described as burning, stabbing, shooting or throbbing.
• The affected area may be itchy.
• There may be allodynia. This is when pain is produced by stimuli that are not usually painful, e.g. a cold draught or heat, or light touch.
• Hyperalgesia may be present. This is where there is increased sensitivity to painful stimuli.
• Pain can be debilitating. It can interfere with sleep, activities of daily living, and can also be so severe that it leads to depression and social isolation.^4,8
• Symptoms may be present for a few months or even years.⁴

Examination

• The area affected by shingles may show some scarring.
• There may be either hypersensitivity or reduced sensation in affected areas.
• Allodynia may be demonstrated.

Investigations

The diagnosis is usually clinical and no specific investigations are indicated.

Management

General advice

• Explain the nature of the condition to the patient, including expected duration of symptoms and aims of treatment.
• Advise the patient to wear loose clothing and, next to the skin, cotton. This will cause less irritation.
• Cling film or a plastic wound dressing may help to protect sensitive areas.
• Cold packs may help to ease pain (unless there is associated allodynia made worse by cold).

Pharmacological

• Start with paracetamol or a paracetamol/codeine combination.
• If there is severe pain at the outset or if the above measures are not sufficient, add in either a tricyclic antidepressant (off-licence) or gabapentin (licensed) which have been shown to be effective in the treatment of postherpetic neuralgia (PHN).^9,10
  • Tricyclic antidepressants:
    • Amitriptyline (most widely used), imipramine, or nortriptyline may be used.
    • Care should be taken, especially in the elderly, due to the possibility of anticholinergic side-effects which can lead to acute confusion or cardiac arrhythmias.⁴
    • Initial dose is 25 mg at night (10 mg if elderly/frail).
    • Increase by weekly increments of 25 mg (10 mg if elderly/frail) until pain is controlled or side-effects occur.
    • Maximum dose is 75 mg at night (50 mg if elderly/frail).
  • Gabapentin:
    • Start with 300 mg once daily on day one, 300 mg twice daily on day two, and 300 mg three times daily on day three.⁹
    • Then increase the dose by 300 mg daily every two to three days according to the response.
    • Maximum dose is 3,600 mg. This dose should be achieved over a minimum period of three weeks. Slower titration may be needed for patients such as the elderly or frail.
• Capsaicin 0.075% cream can be used topically if other treatments are not appropriate, or at a patient's request.
• Topical lidocaine 5% patches may be considered if oral or other topical treatment is not suitable or is not tolerated. They are not recommended as first-line treatment. A Cochrane review found limited evidence for their effectiveness.¹¹

Acupuncture and transcutaneous electrical nerve stimulation (TENS) have been reviewed by the American Academy of Neurology and found to be ineffective in the management of PHN.¹²

When to refer to a specialist pain clinic

• The above treatment does not control pain after four to six weeks.
• There are adverse effects of medication that are affecting/limiting treatment.
• When considering the use of strong opioids or carbamazepine.

Prognosis

• Most patients with postherpetic neuralgia (PHN) will experience a slow improvement over a long period of time, particularly when medical management is used.
• There is a small group failing to show any improvement despite medical treatment.⁵

Prevention

• No treatment has been shown to prevent postherpetic neuralgia (PHN) completely.⁷
• Antiviral therapy started within 72 hours of onset of the shingles rash may reduce the incidence of PHN.^13,14
• A study showed that amitriptyline initiated within 48 hours of shingles rash onset may reduce pain prevalence at six months by up to 50%. Numbers needed to treat were five.¹⁵
• Studies have shown that giving older people (adults aged over 60) varicella zoster vaccine boosts their waning immunity and significantly reduces the morbidity due to herpes zoster and PHN.^16,17 A universal vaccination programme for 70-79 year-olds will be started when a vaccine becomes commercially available.¹⁸
• The introduction of a childhood varicella zoster vaccine (as in the USA) will reduce the risk of herpes zoster, and therefore PHN, when this cohort of children becomes elderly. However, there is concern that reducing the number of children with varicella zoster by introducing a vaccine could lead to a short-term increase in herpes zoster in those who are latently infected.⁴
• Oral steroids do not seem to prevent PHN.¹⁴
• Epidural steroids repeatedly administered, combined with a continuous infusion of anaesthetic for up to 21 days, have been shown to reduce the incidence of PHN but the risks and practicalities of this intervention need to be looked into further.¹⁹

Document references

1. Christo PJ, Hobelmann G, Maine DN; Post-herpetic neuralgia in older adults: evidence-based approaches to clinical management. Drugs Aging. 2007;24(1):1-19. [abstract]
2. Hall GC, Carroll D, McQuay HJ; Primary care incidence and treatment of four neuropathic pain conditions: a descriptive study, 2002-2005. BMC Fam Pract. 2008 May 6;9:26. [abstract]
3. Tyring SK; Management of herpes zoster and postherpetic neuralgia. J Am Acad Dermatol. 2007 Dec;57(6 Suppl):S136-42. [abstract]
4. Wareham DW, Breuer J; Herpes zoster. BMJ. 2007 Jun 9;334(7605):1211-5.
5. McElveen WA et al; Postherpetic Neuralgia, Medscape, Jul 2010
6. Katz J, McDermott MP, Cooper EM, et al; Psychosocial risk factors for postherpetic neuralgia: a prospective study of patients with herpes zoster.; J Pain. 2005 Dec;6(12):782-90. [abstract]
7. Mounsey AL, Matthew LG, Slawson DC; Herpes zoster and postherpetic neuralgia: prevention and management. Am Fam Physician. 2005 Sep 15;72(6):1075-80. [abstract]
8. Schmader K; Herpes zoster and postherpetic neuralgia in older adults. Clin Geriatr Med. 2007 Aug;23(3):615-32, vii-viii. [abstract]
9. Neuropathic pain - pharmacological management, NICE Clinical Guideline (March 2010); The pharmacological management of neuropathic pain in adults in non-specialist settings
10. Wiffen PJ, McQuay HJ, Edwards JE, et al; Gabapentin for acute and chronic pain. Cochrane Database Syst Rev. 2005 Jul 20;(3):CD005452. [abstract]
11. Khaliq W, Alam S, Puri N; Topical lidocaine for the treatment of postherpetic neuralgia. Cochrane Database Syst Rev. 2007 Apr 18;(2):CD004846. [abstract]
12. Dubinsky RM, Kabbani H, El-Chami Z, et al; Practice parameter: treatment of postherpetic neuralgia: an evidence-based report of the Quality Standards Subcommittee of the American Academy of Neurology. Neurology. 2004 Sep 28;63(6):959-65. [abstract]
13. Jackson JL, Gibbons R, Meyer G, et al; The effect of treating herpes zoster with oral acyclovir in preventing postherpetic neuralgia. A meta-analysis. Arch Intern Med. 1997 Apr 28;157(8):909-12. [abstract]
14. Alper BS, Lewis PR; Does treatment of acute herpes zoster prevent or shorten postherpetic neuralgia? J Fam Pract. 2000 Mar;49(3):255-64. [abstract]
15. Bowsher D; The effects of pre-emptive treatment of postherpetic neuralgia with amitriptyline: a randomized, double-blind, placebo-controlled trial. J Pain Symptom Manage. 1997 Jun;13(6):327-31. [abstract]
16. Oxman MN, Levin MJ; Vaccination against Herpes Zoster and Postherpetic Neuralgia. J Infect Dis. 2008 Mar 1;197 Suppl 2:S228-36. [abstract]
17. Tseng HF, Smith N, Harpaz R, et al; Herpes zoster vaccine in older adults and the risk of subsequent herpes zoster JAMA. 2011 Jan 12;305(2):160-6. [abstract]
18. Joint Committee on Vaccination and Immunisation (JCVI) statement on herpes zoster (shingles) vaccine, (January 2010)
19. Pasqualucci A, Pasqualucci V, Galla F, et al; Prevention of post-herpetic neuralgia: acyclovir and prednisolone versus epidural local anesthetic and methylprednisolone. Acta Anaesthesiol Scand. 2000 Sep;44(8):910-8. [abstract]

Acknowledgements