Herpes zoster
Description
- Reactivation of latent VZV from dorsal root/cranial nerve ganglia
- Dermatomal vesicular eruption; incidence and severity rise steeply with age due to declining cell-mediated immunity
Epidemiology
- ~1/3 lifetime risk, rising sharply >50yo
- Incidence and PHN risk both increase with age and immunosuppression
- Thoracic dermatomes commonest; ophthalmic division of CN V important subtype
Aetiopathogenesis
- Primary varicella -> latency in dorsal root ganglia -> reactivation with waning T-cell immunity (age, malignancy, chemo, high-dose steroids, biologics, HIV)
- Viral replication along sensory nerve -> dermatomal vesicular rash + neuritis
Diagnosis
- Clinical - dermatomal, unilateral vesicular rash, often with preceding neuralgic pain/paraesthesia
- PCR/viral swab if atypical or immunocompromised (disseminated, multi-dermatomal)
- Ophthalmic zoster (HZO) - Hutchinson's sign (tip of nose) predicts ocular involvement - urgent ophthalmology review
- Ramsay Hunt syndrome - facial nerve palsy + ear vesicles + auditory/vestibular symptoms
- Disseminated zoster (>3 dermatomes, or visceral) - think significant immunosuppression
Management
Antivirals - start within 72h of rash onset (or later if new vesicles/complicated/immunocompromised/HZO)
- Valaciclovir or famciclovir oral - reduces severity, duration, PHN risk
- IV aciclovir - disseminated disease, ophthalmic with ocular involvement, immunocompromised, CNS involvement
Analgesia
- Regular paracetamol +/- NSAID; neuropathic agents (amitriptyline, gabapentinoids) early if pain severe - caution with anticholinergic/sedative burden in the frail
Specific syndromes
- HZO - urgent ophthalmology, topical + systemic antivirals
- Ramsay Hunt - antivirals + corticosteroids (evidence extrapolated from Bell's palsy), ENT/neurology input
Prevention
- Recombinant zoster vaccine (Shingrix) - preferred over old live vaccine, effective even in immunocompromised (non-live)
- Funded on National Immunisation Program for defined age/risk groups - check current eligibility
- Infection control - isolate/cover lesions until crusted (varicella-non-immune contacts, immunocompromised at risk)
Associations
- Postherpetic neuralgia - strongest risk factor is age
- Underlying immunosuppression - screen if young/recurrent/disseminated/multidermatomal
- Stroke risk transiently elevated post-zoster (esp. ophthalmic)
Natural history & complications
- Rash resolves 2-4 weeks
- Postherpetic neuralgia - pain persisting >3 months, risk rises steeply with age (up to ~30-50% in >80s), can be debilitating and refractory
- Recurrence possible but uncommon in immunocompetent - recurrent/disseminated disease should prompt immunosuppression workup
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