Herpes Zoster

An acute eruption caused by reactivation of latent varicella virus in the dorsal root ganglia.

Herpes zoster may occur at any age, but peak incidence is between ages 50 and 70. Herpes zoster usually affects otherwise healthy people, but immunosuppressed persons are at higher risk. The higher incidence among elderly persons may be explained partially by a decrease in cellular immunity--up to 30% of previously immune healthy persons > 60 have no detectable antibodies to varicella zoster. Other factors that predispose persons to a reactivation of varicella virus include use of immunosuppressants or corticosteroids, malignancy, local irradiation, trauma, and surgery. Herpes zoster recurs in about 6% of patients, usually at the same site as the initial episode.

Herpes zoster lesions are infectious until dry crusts appear. A person who has never had varicella may develop it after direct contact with the lesions or with moist contaminated dressings. Usually, only young children are susceptible, although pregnant women (because of risk of teratogenicity) and immunocompromised persons are also vulnerable.

Symptoms and Signs

Prodromal symptoms may include chills, fever, malaise, GI disturbance, and paresthesia or neuralgia along the affected dermatome. Rarely, prodromal symptoms persist for 5 to 7 days, leading to a variety of misdiagnoses, from herniated disk to acute abdomen.

Red papules usually appear along the affected dermatome within 3 days. The distribution of dermatomal herpes zoster infections is 50 to 60% thoracic, 10 to 20% trigeminal, 10 to 20% cervical, 5 to 10% lumbar, and < 5% sacral; 99% of cases are unilateral. These eruptions rapidly develop into grouped vesicles, which vary in size, may be hemorrhagic, and may be extremely painful. The pain, which is an acute neuralgia, may represent a persistence of prodromal neuralgia or arise de novo. After about 5 days, the vesicles begin to dry and crust; gradual healing occurs over the next 2 to 4 weeks. Persistent hyperpigmentation or true scarring may result, particularly in the elderly.

In about 50% of patients with uncomplicated herpes zoster, some vesicles appear outside the affected area. However, if widespread severe dissemination occurs, an underlying lymphoma or other cause of immunodeficiency should be suspected.

In geniculate neuralgia (Ramsay Hunt's syndrome), facial paralysis (usually temporary) occurs, pain develops in the ear on the affected side (with or without deafness, tinnitus, and vertigo), and taste is lost in the anterior two thirds of the tongue. Vesicles appear on the soft palate, fauces, and external auditory meatus on the affected side. Consultation with a neurologist is advisable.

Complications

The major difference between herpes zoster in the elderly and in young adults is the incidence of postherpetic neuralgia (variably defined as pain that persists > 30 days or that appears after the eruption has healed), which increases sharply with age to about 40% in persons >= 60. The duration and severity of postherpetic neuralgia increase even more markedly with age than does incidence. Other risk factors for postherpetic neuralgia include prodromal neuralgia, severe neuralgia during the acute phase, and ophthalmic herpes zoster. The pain in postherpetic neuralgia is of three types: constant, deep aching or burning pain; spontaneous intermittent lancinating pain; and dysesthetic pain provoked by trivial stimuli (eg, light touch or cold) and often persisting long after the stimulus is removed.

Rare complications of herpes zoster include encephalitis, corneal scarring (when the ophthalmic branch of the trigeminal nerve is involved), motor neuropathies, Guillain-Barré syndrome, and urinary retention (when sacral dermatomes are involved).

Ophthalmic herpes zoster results from involvement of the ophthalmic division of the trigeminal nerve. Lesions on the tip of the nose indicate involvement of the ophthalmic and nasociliary nerves. Conjunctivitis, iridocyclitis, and keratitis may occur. In such cases, an ophthalmologic consultation should be sought. The risk of postherpetic neuralgia is greater with ophthalmic involvement than with involvement of other dermatomes.

Diagnosis

The finding of multinucleate giant cells on a Tzanck smear or biopsy of a vesicle confirms a viral infection. Although not commonly needed, vesicle fluid culture or direct fluorescent antibody analysis can also identify the virus and distinguish it from herpes simplex.

Treatment

Trials of zoster vaccine are underway and offer hope of prevention in the future.

Topical treatment consists of soaking the affected area in Burow's solution (aluminum acetate 5%), diluted 1:20 to 1:40, to remove vesicle crusts, decrease oozing, and dry and soothe the skin. Gauze dressings are soaked in the solution, applied to the affected areas, and loosely bandaged. The dressings are changed every 2 to 3 hours. If impetigo develops, systemic antibiotics should be given.

Oral acyclovir is appropriate if an elderly patient is seen within 3 days of the onset of the eruption. This drug inhibits the development of new vesicles and decreases the duration of viral shedding and discomfort. The effect of acyclovir on the incidence and duration of postherpetic neuralgia is debated, although several controlled trials have demonstrated benefit in otherwise healthy elderly patients. The recommended oral dosage is 800 mg 5 times daily for 10 days. Severely immunocompromised patients should receive IV therapy, 10 mg/kg q 8 h for 7 days. Alternatively, valacyclovir 1 g po tid for 7 days, or famciclovir 500 mg po tid for 7 days, may enhance compliance. The dose of all three drugs must be reduced in patients with moderate to severe renal insufficiency.

A systemic corticosteroid (eg, prednisone 40 to 60 mg/day po), started within a few days to a week of the eruption as monotherapy or combined with acyclovir, appears to reduce the duration of acute neuralgia but may not lower the risk of postherpetic neuralgia more successfully than acyclovir alone. Corticosteroids combined with an antiviral drug are the treatment of choice in patients with geniculate neuralgia.

Analgesia is usually needed. Acetaminophen or aspirin given every 4 hours, or other nonsteroidal anti-inflammatory drugs (NSAIDs), may be sufficient, but some patients require opioids.

Postherpetic neuralgia, once established, is difficult to treat. In addition to simple analgesics, capsaicin cream or lotion may be tried or the anesthetic EMLA patch. Opioids may be tried but are potentially addictive and often insufficient. Drugs used for neuropathic pain (eg, tricyclic antidepressants) are often helpful. Newer drugs for neuropathic pain, such as gabapentin, are being studied. Nerve block may be considered in resistant cases.

Isolation: Because varicella virus is teratogenic during early fetal development, pregnant women should avoid contact with herpes zoster patients. Severely immunocompromised persons should also avoid exposure. Ordinarily, however, isolating herpes zoster patients from casual contact with other adults is not necessary.