Herpes zoster results from reactivation of latent varicella-zoster virus (VZV) in dorsal root or cranial nerve ganglia, with annual incidence 3-5/1000 rising to 10/1000 after age 60. Pathophysiology involves age-related decline in cell-mediated immunity, immunosuppression, or stress-induced reactivation, with virus traveling along sensory nerves to skin/mucosa. Lifetime risk is 30%; recurrence is uncommon (5-6%) except in immunocompromised. Cardinal clinical feature is unilateral painful vesicular rash in 1-3 contiguous dermatomes (most often thoracic, then cervical, lumbar, trigeminal V1).
Complications include post-herpetic neuralgia (PHN, persistent pain >90 days, 10-20% overall, 50% in age >60), herpes zoster ophthalmicus (HZO, V1 trigeminal involvement, 10-20% of cases, complications include keratitis, uveitis, retinitis, ARN/PORN, optic neuritis, glaucoma, sight loss; Hutchinson sign = vesicles on nose tip indicates nasociliary involvement and high ocular risk), Ramsay Hunt syndrome (geniculate ganglion zoster with facial palsy, otalgia, ear canal vesicles, hearing loss, vertigo, dysgeusia), disseminated zoster (>20 vesicles outside primary dermatome, immunocompromised, visceral involvement risk), motor neuropathy, CNS complications (meningoencephalitis, myelitis, ventriculitis, vasculopathy/stroke especially after HZO), bacterial superinfection, and post-herpetic itch.
Diagnosis is clinical (characteristic rash) confirmed by PCR (most sensitive), DFA, or culture if needed. Management includes early antiviral therapy within 72 hours of rash onset (acyclovir 800 mg 5x/day, valacyclovir 1 g TID, or famciclovir 500 mg TID for 7 days; IV acyclovir 10 mg/kg q8h for severe disease, immunocompromise, ophthalmicus, encephalitis), pain control (acetaminophen, NSAIDs, gabapentin/pregabalin, tricyclics, opioids if severe), and topical care (calamine, cool compresses). HZO requires ophthalmology consult, topical/systemic antivirals, possible topical steroids per ophthalmology, and dilated exam. Ramsay Hunt: prompt antivirals + corticosteroids may improve outcomes. PHN treatment: gabapentin/pregabalin, tricyclics (amitriptyline, nortriptyline), topical lidocaine 5% patch, capsaicin 8% patch, opioids (last line). Prevention: recombinant zoster vaccine (Shingrix, RZV) is preferred for adults ≥50, two doses 2-6 months apart, 90% efficacy against shingles and PHN, recommended even after prior zoster episode.