Postherpetic neuralgia (PHN) is a painful condition that can sometimes occur after the rash of shingles has gone away. Shingles is a rash caused by a re-activation of the same virus that causes chicken pox.
Definition of Postherpetic Neuralgia
There are several types:- Acute herpetic neuralgia - Pain that accompanies the rash and persists for up to 30 days after the start of the rash.
- Subacute herpetic neuralgia - Pain that persists for one to four months after the start of the rash.
- Postherpetic neuralgia - Pain that persists beyond four months after the start of the rash.
Risk Factors for Postherpetic Neuralgia
The biggest risk factor for developing postherpetic neuralgia is older age. In people 60 to 69 years old who developed shingles, 6.9% developed PHN, and in people over 70 years old who developed shingles, 18.5% developed PHN, according to research. The major risk factors for PHN are:- Older age
- More pain with the shingles rash
- Greater shingles rash severity
Cause of Postherpetic Neuralgia
We currently do not know what causes postherpetic neuralgia. One possible contributing factor is inflammation in the skin and nerves caused by the movement of the viral particles to the skin. Another possible cause is damage to the nerves sensitizing them to milder stimuli.Symptoms of Postherpetic Neuralgia
Both shingles and postherpetic neuralgia can cause severe pain that interferes with most aspects of life. Specific symptoms include:- A burning sensation in the area where the rash has healed
- Pain in the area that is brought on by normally non-painful stimuli such as light touch
- Areas of numbness and difficulty sensing temperature, vibration, and pinprick
- As in shingles, these symptoms occur in a dermatomal distribution and the other side of the body is not affected
Treatment of Postherpetic Neuralgia
The treatment of postherpetic neuralgia is complex and often requires multiple medications. The American Academy of Neurology has published the following treatment options that have been shown to improve the symptoms of postherpetic neuralgia:- Tricyclic antidepressants such as amitriptyline, nortriptyline, and desipramine at bedtime
- Gabapentin - 300mg daily and increased over a 4-week period to 1,200mg three times a day
- Pregabalin - 75mg twice a day and increased over 7 days to 150mg twice a day
- Long-acting, controlled release pain medications such as morphine sustained-release or fentanyl patches
- Lidocaine patches applied to the painful area every 12 hours - should only be applied to healed, intact skin
Prevention of Postherpetic Neuralgia
Some recommendations for preventing postherpetic neuralgia include:- Effective, early treatment of shingles
- Using the shingles vaccine to decrease the incidence of shingles and postherpetic neuralgia
- Some studies show that tricyclic antidepressants such as amitriptyline and nortriptyline started within 48 hours of the onset of the shingles rash may reduce the risk of developing postherpetic neuralgia by half.
Sources:
Bowsher, D. "Pathophysiology of postherpetic neuralgia: towards a rational treatment." Neurology 45(1995):S56.
Bowsher, D. "The effects of pre-emptive treatment of postherpetic neuralgia with amitriptyline: a randomized, double-blind, placebo-controlled trial." Journal of Pain Symptom Management 13(1997):327.
Dubinsky, R.M., et al. "Practice Parameter: Treatment of Posterpetic Neuralgia." Neurology 63(2004): 959-65.
Dworkin, RH, and RK Portenoy. "Pain and its persistence in herpes zoster." Pain 67(1996): 241-51.
Gnann, John, and Richard Whitley. "Herpes Zoster." The New England Journal of Medicine 347(2002): 340-6.
Jung, Beth, et al. "Risk Factors for Postherpetic Neuralgia in Patients with Herpes Zoster." Neurology 62(2004): 1545-51.
Oxman, M.N., et al. "A Vaccine to Prevent Herpes Zoster and Postherpetic Neuralgia in Older Adults." The New England Journal of Medicine 352(2005): 2271-84.
