Herpes Zoster Neuralgia

Herpes zoster neuralgia is the acute neuropathic pain of shingles that precedes the rash by 1 to 5 days (prodrome) and continues during the eruption and healing phase (up to 30 days). It is caused by reactivation of varicella zoster virus in a dorsal root or cranial nerve ganglion.

• Lifetime risk of shingles is about 25 to 30 percent, higher in older adults, HIV, malignancy and immunosuppression.
• Severe acute pain predicts postherpetic neuralgia.

Burning, stabbing or aching pain, itch and paraesthesia in one dermatome, then unilateral clustered vesicles on an erythematous base that crust over 7 to 10 days; allodynia is common.

• Zoster sine herpete: pain without a rash.
• Thoracic dermatomes are most commonly involved; ophthalmic division involvement threatens vision (Hutchinson sign: vesicles on the nasal tip).
• Differential diagnosis: herpes simplex, contact dermatitis, cellulitis, angina or pleurisy (prodrome), renal colic, cholecystitis, appendicitis, radiculopathy, impetigo, bullous disease, dermatitis herpetiformis.
• Complications: postherpetic neuralgia, secondary bacterial infection, scarring, zoster ophthalmicus (keratitis, uveitis, vision loss), Ramsay Hunt syndrome, motor neuropathy, meningoencephalitis, stroke, disseminated zoster in immunosuppression.

Clinical in typical cases.

• PCR of vesicle swab or fluid for varicella zoster virus (preferred), direct fluorescent antibody, culture.
• HIV test, glucose, full blood count; consider malignancy screening in severe or recurrent disease.
• Ophthalmology review (slit lamp) for ophthalmic division involvement.

Antiviral therapy within 72 hours, with a stepped analgesic plan.

• Supportive: cool compresses, loose clothing, keep lesions clean and dry, avoid contact with pregnant women, newborns and immunocompromised people until crusted, rest.
• Pharmacological: valaciclovir 1 g three times daily for 7 days, or famciclovir 500 mg three times daily for 7 days, or aciclovir 800 mg five times daily for 7 days. Analgesia: paracetamol 1 g four times daily, ibuprofen 400 mg three times daily, add tramadol 50 to 100 mg four times daily, then gabapentin 300 mg at night titrated to 900 to 1800 mg daily; amitriptyline 10 to 25 mg at night early reduces chronic pain risk. Topical lidocaine 5 percent plaster for localised pain after lesions have crusted. Prednisolone 40 to 60 mg daily for 7 days tapered over 2 weeks in severe pain in older healthy adults (with antivirals). Severe, disseminated or immunocompromised: aciclovir 10 mg/kg IV every 8 hours for 7 to 10 days. Secondary infection: flucloxacillin 500 mg four times daily for 7 days.
• Procedures: nerve block for severe pain; ophthalmic emergency management of zoster ophthalmicus.
• Special groups: pregnancy, aciclovir or valaciclovir acceptable; immunocompromised, IV therapy and admission; renal impairment, reduce antiviral dose; elderly, avoid high dose tricyclics and sedating drugs; children, aciclovir 20 mg/kg four times daily for 5 days (maximum 800 mg per dose).
• Red flags: eye involvement, facial paralysis, widespread vesicles, confusion or headache, fever, bacterial superinfection, immunosuppression.
• Follow-up: review at 1 week; reassess pain at 4 weeks and refer if persisting beyond 3 months; recombinant zoster vaccine after recovery for older and immunocompromised adults.