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Herpes Zoster and Postherpetic Neuralgia
Elizabeth K. Stanford, MD
Zoster usually presents as a painful unilateral dermatomal eruption. Zoster results from reactivation of varicella-zoster ( chickenpox) virus which has been dormant in the dorsal root ganglia.
Clinical Evaluation
Zoster is usually heralded by dermatomal pain, sometimes accompanied by fever. Within a few days, the skin overlying the dermatome reddens and blisters. A few vesicles are usually grouped on one erythematous base, in contrast to the scattered, single vesicles of chickenpox. Several days later the vesicles become pustular and develop crusts, followed by scabs.
Zoster may occur in any dermatome, but the thoracic dermatomes are most often affected. In 90% of patients, pain eventually disappears completely.
The frequency of zoster increases markedly after age 55, but people of any age can be affected. Less than 5% of immunocompetent patients who have one episode of herpes zoster will have another, and the episodes are usually separated by years. HIV-infected patients are more likely to have recurrent herpes zoster infections.
Laboratory evaluation
The diagnosis of herpes zoster can be made on clinical grounds without the need for laboratory tests. Viral isolation and culture assays are not useful for varicella-zoster.
An isolated case of zoster in an apparently healthy young or middle-aged adult is probably not an indicator of an underlying immunodeficiency. HIV testing is considered when a patient who engages in high-risk behavior (sexual activities, drug use) develops zoster. Testing for HIV is also indicated when herpes zoster is protracted, recurrent, or involves multiple dermatomes.
Complications of herpes zoster
15% of patients with zoster have involvement of the ophthalmic branch of the trigeminal nerve. Hutchinson's sign, a lesion on the tip of the nose, indicates corneal involvement; however, ophthalmic involvement. Treatment with IV acyclovir and topical agents is required to prevent blindness.
Disseminated herpes zoster is present when 20 or more lesions occur outside of the primary contiguous dermatomes. These patients are at risk for visceral dissemination.
Therapy for zoster
Wet dressings or compresses with Burow's solution (Domeboro) will protect sensitive areas. Acetaminophen, nonsteroidal anti-inflammatory drugs, or analgesics with codeine (Vicodin) may be needed.
Antiviral therapy for zoster
An antiviral can hasten the resolution of the rash by several days. Relief of acute pain occurs two to three days after an antiviral is initiated. The duration of pain is reduced by about half. Antiviral therapy is more likely to be of benefit if initiated within 24 hours of rash onset.
Acyclovir ( Zovirax)
800 mg q4h while awake (5 times a day) for 7 days. [400, 800 mg tab].
Oral acyclovir does not have significant adverse effects; nausea, headaches, diarrhea, and constipation may sometimes occur.
IV acyclovir is reserved for the severely immunosuppressed (bone marrow transplant patients), disseminated infection, or ophthalmic zoster.
The IV dose for zoster is 10 mg/kg, administered over a one-hour, q8h. Nephrotoxicity can usually be avoided if the patient remains well-hydrated. The dosage should be reduced in renal failure.
Famciclovir (Famvir) is equally effective as acyclovir; it has a more convenient dosing interval; one 500-mg tablet tid for 7 days.
Valacyclovir (Valtrex), may be slightly more effective than acyclovir; 1,000 mg tid x 7 days [500 mg].
Foscarnet (Foscavir) is useful for acyclovir-resistant herpes infections.
Ophthalmic distribution zoster is a medical emergency which requires IV acyclovir and topical antivirals.
Postherpetic neuralgia
PNH is the most common complication of herpes zoster. It is defined as chronic pain persisting for at least one month after the skin lesions have healed.
The incidence of PHN after an episode of herpes zoster is 5-50%. Those aged 60 and older have a 50% chance of developing PHN. PHN resolves within two months in about half of those affected.
Antivirals, aspirin, and acetaminophen are usually not effective for PHN.
Topical preparations
Capsaicin cream OTC ( Zostrix, Zostrix-HP) 0.025% tid-qid reduces the pain. Ben-Gay, Flex-all 454 or Aspercreme may offer similar relief.
EMLA topical cream (lidocaine and prilocaine) qid may be useful.
Amitriptyline (Elavil) is often effective; 10-25 mg qhs, increasing in weekly increments of 25 mg as needed.
Gabapentin (Neurontin), 300 mg qd-tid, may be effective. Carbamazepine (Tegretol), 200 mg bid, has also been used.
Transcutaneous electrical nerve stimulation (TENS), lidocaine injections, nerve block injections, permanent nerve blocks with alcohol, and nerve resectioning have been used for recalcitrant cases.