Herpes Zoster (Shingles) and Post-Herpetic Neuralgia (PHN)

What is Herpes Zoster?

Shingles (or herpes zoster) is a condition that causes an area of skin (frequently on the face) to become painful, and is later covered by a rash (papules and vesicles) which eventually crusts over.

The condition is secondary to a previous infection with varicella zoster virus (the virus that causes chicken pox) which is a virus that remains dormant in the nerve cells (the dorsal root ganglion). Shingles is caused by re-activation of that virus in an area of skin supplied by a single nerve (dermatome), this usually occurs due to old age or immunosuppression.

Shingles can sometimes be complicated by (amongst other conditions) post-herpetic neuralgia (PHN), a condition in which there is persistent pain in that area of skin.

Statistics on Herpes Zoster?

Shingles is a very common illness. The incidence of shingles is thought to be 100-225 per 100,000 general population per year, and it is thought that 20% of adults are affected by zoster at any one time.

People of any age can get shingles (provided they have been infected with the chicken pox virus in the past) but it is more common in people over 50 years of age.

Risk Factors for Herpes Zoster

Shingles occurs in people who have been infected with the chicken pox virus in the past.
Most cases occur for no particular reason, commonly in older people.
Some cases are due to an underlying illness.
Sometimes there is an underlying malignancy (cancer) - Leukaemia of lymphoma commonly;
Some patients have underactive immune systems - e.g. due to AIDS, malnutrition, diabetes, transplant recipients;
Some have a disturbance of the spine or spinal cord - e.g. tumour or radiotherapy.

Progression of Herpes Zoster

Prior to the rash developing, there is usually several days of pain in the area supplied by the nerve, with hyperaesthesa (even minor touch may be painful).
The papular/vesicular rash then develops.
Later there is crusting, with separation of the scabs after around 10-14 days. There may be depigmentation of the area affected after it resolves.

Various complications may occur:

Post-herpetic neuralgia occurs in 10% of patients overall, though it complicates shingles in older patients more commonly.
Eye complications (with inflammation of the cornea, eyelid, or the internal eye) may occur with involvement of the sensory nerve to the eye;
Rarely neurological complications such as meningoencephalitis (inflammation of the meninges and brain) or motor paralysis can occur.

How is Herpes Zoster Diagnosed?

Diagnosis is usually clinical. Swabs and culture of the chicken pox virus may help to confirm the diagnosis.

Investigations may be undertaken if an underlying immunosuppression is suspected:

Full blood count - specifically lymphocyte count which are important for fighting viral infections;
Differential lymphocyte count: CD4/CD8 lymphocytes.

Prognosis of Herpes Zoster

Shingles usually resolves within two weeks, but it may be followed by one of the complications above. PHN (Post-herpetic neuralgia) may occur in as many as 30-50% of patients over 70, though around 10% overall.

The neuralgia (persistent neurological pain due to PHN) resolves within a year in around 70-80% of patients, though in some it may persist for years. Post-herpetic neuralgia is the result of damaged nerve fibers caused by shingles/herpes zoster virus. The electrical signals normally sent between the brain and the skin are disturbed causing exaggerated pain in the area where the shingles occurred.

How is Herpes Zoster Treated?

Shingles is only mildly contagious.

Young children and infants should avoid contact with an affected individual if they have never had chicken pox since they may develop the condition.
Immunosuppressed individuals should also be kept away from affected individuals.
The painful rash itself may be soothed with tepid water compresses or menthol solution or calamine lotion - though overtreating the rash should be avoided as it may lead to secondary bacterial infection.

Medications include:

Simple analgesics - aspirin, paracetamol.
Antiviral agents - Aciclovir 800mg 5 times daily or Famciclovir 250mg three times daily or Valacyclovir 1000mg three times daily - all need to be taken for 7 days.

Treatment of post-herpatic neuralgia is difficult but may include:

Simple painkillers - aspirin, paracetamol, codeine, tramadol.
Anti-viral treatments
Anti-depressants or anti-epileptics may be useful due to the nature of the pain.

Herpes Zoster References

Hankey G, Wardlaw J. Clinical Neurology. Demos Medical Publishing, United Kingdom, 2002.
Kumar P, Clark M. Clinical Medicine. WB Saunders 2002.
Murtagh J. General Practice. Second Ed. McGraw-Hill, 1998.