Herpes Zoster and Postherpetic Neuralgia
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Direct answer
Herpes zoster is a painful, unilateral, dermatomal eruption caused by reactivation of latent varicella-zoster virus in a sensory ganglion. Grouped vesicles appear on an erythematous base in one nerve's territory, typically after burning or lancinating pain. Postherpetic neuralgia is pain that persists beyond about 90 days after the rash has healed, and early antiviral treatment within 72 hours of the rash is the main way to limit both.
What you must remember
- Mechanism: varicella-zoster virus reactivates from a dorsal root or cranial nerve ganglion and travels down the sensory nerve to the skin.
- Prodrome: burning or lancinating pain in the dermatome typically precedes the vesicles, sometimes by several days.
- Commonest site: the thoracic dermatomes are most often involved, forming a girdle-like band of vesicles on one side of the trunk.
- Hutchinson sign: vesicles on the tip, side or root of the nose signal involvement of the nasociliary branch and a high risk of eye disease.
- Ramsay Hunt syndrome: geniculate ganglion zoster causes ipsilateral facial palsy, severe ear pain and vesicles in the ear canal or pinna.
- Antiviral timing: valaciclovir, famciclovir or aciclovir started within 72 hours of the rash shortens the illness and reduces pain.
- Postherpetic neuralgia: pain persisting beyond about 90 days after healing, more likely with older age and severe prodromal pain.
- Zoster vaccine: the recombinant vaccine is given as two doses to adults aged 50 years and above, according to current guidance.
Variants of zoster by nerve involved
A zoster episode is named by the dermatome, and the nerve involved decides both the complications and how urgently the patient must be seen. The table groups the variants examiners test most often.
| Variant | Nerve or ganglion | Key feature |
|---|---|---|
| Thoracic zoster | Thoracic dorsal root ganglia | Unilateral girdle band of vesicles |
| Ophthalmic zoster | Trigeminal ophthalmic division | Forehead and nasal vesicles, with risk of keratitis and uveitis |
| Ramsay Hunt syndrome | Geniculate ganglion | Facial palsy, ear pain and vesicles in the ear |
| Disseminated zoster | Several dermatomes | Widespread vesicles, typically in immunocompromised patients |
| Zoster sine herpete | Any affected ganglion | Dermatomal pain and nerve signs without a visible rash, confirmed by PCR |
Ophthalmic zoster and Ramsay Hunt syndrome need the most urgent review, because the eye and the facial nerve can be permanently damaged. Disseminated zoster signals underlying immune compromise, so the patient needs a fuller work-up and often intravenous antiviral therapy. The rash can lag behind the pain, so the clinician should examine the face and ear carefully and document the dermatome, since that record guides later decisions.
Where the exam plants its traps
Stems on zoster test the nerve involved, the timing of antivirals and the definition of postherpetic neuralgia.
- Trap: managing ophthalmic zoster with antivirals alone and no eye review Correct: a vesicle on the nose with a Hutchinson sign requires urgent ophthalmology assessment alongside antivirals.
- Trap: starting antivirals ten days after the rash appeared Correct: the benefit depends on starting within 72 hours of rash onset.
- Trap: labelling pain present two weeks after the rash as postherpetic neuralgia Correct: postherpetic neuralgia is defined by pain persisting beyond about 90 days after the rash has healed.
Frequently asked questions
What is Ramsay Hunt syndrome?
Ramsay Hunt syndrome is herpes zoster of the geniculate ganglion, causing ipsilateral facial palsy, severe ear pain and vesicles in the ear canal or pinna. Hearing loss or vertigo can also occur, and early antiviral treatment is essential to limit lasting damage.
What is the Hutchinson sign in herpes zoster?
The Hutchinson sign is the presence of vesicles on the tip, side or root of the nose, which indicates involvement of the nasociliary branch of the ophthalmic division of the trigeminal nerve. It signals a high risk of ocular complications that need urgent ophthalmology review.
When must antiviral therapy be started for herpes zoster?
Antiviral therapy for herpes zoster should be started within 72 hours of rash onset, because the benefit depends on early treatment. Valaciclovir, famciclovir or aciclovir is used, and it shortens the illness and reduces the severity of pain.
What defines postherpetic neuralgia?
Postherpetic neuralgia is pain that persists beyond about 90 days after the zoster rash has healed, and it is more likely with older age and severe prodromal pain. Gabapentinoids, tricyclic antidepressants and topical agents are used in its management.
Who should receive the zoster vaccine?
The recombinant zoster vaccine is given as two doses to adults aged 50 years and above, according to current guidance, to reduce the risk of herpes zoster and postherpetic neuralgia. It is a non-live vaccine, which is why it can be given to many immunocompromised adults.