Herpes zoster and post-herpetic neuralgia

Definition. Herpes zoster (shingles) is reactivation of latent varicella-zoster virus (VZV) from the dorsal root ganglion, where it lies dormant after childhood chickenpox. Reactivation occurs because of immunosenescence. Post-herpetic neuralgia (PHN) is severe shooting, burning or stabbing pain persisting beyond 3 months after the rash.

Epidemiology and risk. Incidence rises considerably after age 50, with a 50% lifetime risk by 85 years. Incidence is 11.8 per 1000 per year in those over 60 versus 1.2–3.4 per 1000 per year at all ages. Increasing age is the strongest risk factor for PHN; others are severe rash, severe acute pain and prodromal pain.

Clinical features. A prodrome of neuropathic pain — intense burning or aching in the dermatome — precedes the rash. Then a unilateral, dermatomal cluster of vesicles on an erythematous base, which crusts over in 7–10 days, after which the patient is no longer contagious.

Important clinical variants. Herpes zoster ophthalmicus (V1 division; Hutchinson's sign = vesicles on the nose tip indicating nasociliary involvement — urgent ophthalmology referral); Ramsay Hunt syndrome (facial palsy with vesicles in the ear canal); disseminated zoster in the immunosuppressed.

Complications. PHN is the commonest. Also zoster encephalitis — most common in advanced age, immunosuppression and disseminated cutaneous zoster; contralateral hemiplegia occurring weeks after zoster ophthalmicus (VZV granulomatous arteritis) accounts for up to one-third of CNS zoster; post-herpetic itch; secondary bacterial infection; myelitis; ocular complications.

Diagnosis. Usually clinical. VZV DNA PCR from vesicle fluid confirms. In suspected CNS disease, CSF shows lymphocytic pleocytosis with raised protein (also seen in up to 40% of zoster patients without CNS involvement); CSF VZV PCR specificity >95%, sensitivity 80–95%; viral culture is rarely helpful.

Antiviral therapy. Start ideally within 72 hours of symptom onset for maximum effect. Aciclovir 800 mg five times daily, or valaciclovir 1 g three times daily, or famciclovir — for 7 days. Early therapy prevents new vesicles and reduces pain intensity and duration, viral shedding and PHN incidence. Reduce dose for renal impairment — GFR falls ~30% with normal ageing. IV aciclovir 30 mg/kg/day in divided doses for CNS disease.

Acute pain management. Paracetamol and, where safe, an NSAID; moderate-to-severe pain may require opioids. Corticosteroids or gabapentin may be added if pain persists — but corticosteroids have NOT been shown to reduce the incidence of PHN in the elderly.

Treatment of established PHN. Approved options: topical 5% lidocaine patch, gabapentin and pregabalin. Nortriptyline and opioids are also of benefit; combination therapy is often necessary. Avoid amitriptyline in older adults — strongly anticholinergic (dry mouth, retention, constipation, delirium, tachycardia, blurred vision, falls). Gabapentinoids need renal dose reduction and cause sedation and ataxia.

Prevention (textbook position). Zostavax, a live attenuated vaccine, is recommended for immunocompetent adults ≥60 years (permitted from 50). It reduces the incidence of herpes zoster by 51% and of PHN by 66%, and also reduces ophthalmic zoster and zoster hospitalisations.

Recombinant zoster vaccine (RZV, Shingrix) has replaced the live vaccine. Two IM doses 2–6 months apart, efficacy >90%, now the preferred vaccine from age 50 and — because it is non-live — the only zoster vaccine usable in the immunocompromised. Live Zostavax was discontinued in the USA (2020) and many other countries.

Zoster vaccination and dementia risk. Nature 2025 (Eyting et al., Wales natural experiment) found roughly a 20% relative reduction in dementia over 7 years after zoster vaccination; Nature Medicine 2024 (Taquet et al.) showed RZV was associated with lower dementia risk than the live vaccine — 17% more diagnosis-free time (≈164 extra days). Large cohort data (Kaiser Permanente, Medicare) are concordant. This is now a strong additional argument for offering RZV to all older adults.