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

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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.

Who gets 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.

Predisposing Factors

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

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.

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