Shingles, postherpetic neuralgia and why the pain can outlast the rash by years

After chickenpox, the varicella zoster virus does not leave. It persists in the dorsal root and cranial nerve ganglia, held in check by cell-mediated immunity. As that immunity declines — with age, illness, or immunosuppression — the virus can reactivate, travel down the sensory nerve, and produce shingles in the area of skin that nerve supplies.

Roughly one in three people develops shingles in their lifetime, with incidence rising steeply after fifty.

How it presents

Frequently the pain comes first. Two to three days of burning, stabbing or itching in a band on one side of the body, before any rash appears. This prodrome is a common source of misdiagnosis — chest wall pain investigated as cardiac, abdominal pain investigated as biliary, headache investigated as something else entirely.

Then the rash: grouped vesicles on a red base, in a dermatomal distribution, respecting the midline. The unilateral, band-like pattern is highly characteristic.

The vesicles crust over roughly seven to ten days and heal over two to four weeks, sometimes with scarring or pigmentary change.

Postherpetic neuralgia

This is the reason shingles matters. Pain persisting beyond the healing of the rash — conventionally defined as beyond 90 days from onset — occurs in a minority of cases overall but in a substantial proportion of older patients. Estimates commonly range from 10 to 18 per cent of all cases, rising markedly with age; in those over seventy it is considerably higher.

The pain is neuropathic and can be severe: constant burning, sudden shooting pains, and allodynia — pain from stimuli that should not hurt, such as clothing or a light breeze. It can persist for months or years, and it disrupts sleep, mood and function profoundly. Depression rates in people with postherpetic neuralgia are high.

Risk factors for developing it are older age, severe acute pain, extensive rash, and prodromal pain before the rash appeared.

Treating the neuralgia

Options are the standard neuropathic pain agents, all with age-relevant caveats.

Gabapentin and pregabalin have reasonable evidence. Both cause dizziness and sedation, increase falls risk, and require renal dose adjustment. Start low, titrate slowly.

Tricyclic antidepressants, particularly nortriptyline, are effective and anticholinergic. Amitriptyline is generally avoided in older adults for that reason.

Topical lidocaine 5% plasters are useful and, because systemic absorption is minimal, are often the most appropriate first choice in an older person on multiple medications.

Topical capsaicin, including the high-concentration patch applied in clinic, has evidence but causes considerable initial burning.

Response is often partial. A realistic aim is a meaningful reduction in pain and improvement in sleep rather than abolition.

The complications that are not skin

Herpes zoster ophthalmicus — reactivation in the ophthalmic division of the trigeminal nerve. Involvement of the tip of the nose, known as Hutchinson's sign, indicates nasociliary nerve involvement and a high likelihood of ocular disease. This needs same-day ophthalmology assessment; it can cause keratitis, uveitis and permanent vision loss.

Ramsay Hunt syndrome — reactivation in the geniculate ganglion, producing facial palsy with vesicles in the ear canal, sometimes with hearing loss and vertigo. Prompt antiviral and steroid treatment improves recovery.

Disseminated zoster in immunocompromised patients, which requires intravenous treatment.

Stroke risk is transiently elevated after shingles, particularly after ophthalmic zoster, an association demonstrated in several large studies.

Contagion, which is misunderstood

Shingles cannot be caught from someone with shingles. What can be transmitted, from the fluid in the vesicles, is varicella — chickenpox — to someone who has never had it or been vaccinated.

Transmission requires direct contact with the lesions, and the person is no longer infectious once everything has crusted. Covering the rash is sufficient precaution. Avoid contact with pregnant women who have not had chickenpox, newborns, and immunocompromised people.

Prevention

The recombinant zoster vaccine has efficacy above 90 per cent in trials, including in older age groups where the older live vaccine performed considerably less well, and it maintains protection for years. It is two doses, and the second frequently causes a day or two of feeling genuinely unwell — which is an immune response, not a complication.

It reduces both shingles and, importantly, postherpetic neuralgia. Prior shingles does not confer reliable immunity, so vaccination is recommended even after an episode.

Uptake lags well behind influenza in almost every country that offers it, and it is probably the most under-taken high-value vaccine available to older adults.