Introduction

Herpes zoster (known widely as shingles) is becoming increasingly common in elderly individuals, because of the overall aging of the population and the increasing number of immune-suppressed people. One estimate concludes that if someone is over 60 and has had varicella (chickenpox) as a child, they have a 50% chance of developing zoster by the time they are 85. For such individuals, the risk of herpes zoster is closely related to the loss of varicella-zoster virus (VZV) cell-mediated immune responses, which decline with aging or immune-suppression. Dr. Kenneth Schmader, an expert in this field from Duke University, has recently reviewed the epidemiology, clinical features, management and prevention of herpes zoster in the elderly.

Epidemiology

Herpes zoster is caused by the reactivation of VZV from a latent state where it resides in dorsal sensory and cranial ganglia. This reactivation is permitted by cellular immune dysfunction, such as can be found with hematological malignancies, AIDS and immunosuppressive therapy. Studies show a significant age-related reduction in the number and function of T-cell responses to VZV. For example, a low or absent stimulation response is seen in 33% of elderly healthy persons, compared with 0% in 20 - 40 year-olds.

After controlling for age, the presence of cancer, and other demographic factors, African Americans living in North Carolina, USA, were four times less likely than whites from the same area to have had zoster in their lifetime, and they were significantly less likely to develop zoster in a six-year follow-up period. Of course, these significant racial differences might be related to differences in the timing of the primary infection and re-exposure to VZV during adult life.

While malignancies such as Hodgkin's disease, non-Hodgkin's lymphomas, and leukemias carry a high risk for herpes zoster, solid tumors are less likely causes. Herpes zoster is not a risk factor for cancer, and the presence of zoster in an elderly patient should not, per se, initiate an intense search for an underlying cancer.

Clinical features

Pain or abnormal sensations in the affected dermatome is usually the first symptom, occurring days or even weeks before the rash appears. The differential diagnosis at this stage can be difficult, with many different conditions competing for consideration. The pain can be intense, and quite variable in nature. This prodromal phase is sometimes accompanied by flu-like symptoms - fever, muscle aches, etc.

The characteristic rash is erythematous, becoming macular, then papular, and finally vesicular, before crusting in about 7 days. Again, the pattern follows the affected dermatome, and is always unilateral.

Antiviral therapy must be started within 72 hours of the onset of rash if there is to be hope of a satisfactory outcome. However, delay in seeking medical advice, due to ageism, fear, cognitive impairment, or barriers to health care, can postpone initiating treatment, leading to greater suffering.

The vesicles contain cell-free virus, which can be transmitted to others by direct contact or by the airborne route. People with no history of chickenpox or who are known to be sero-negative should avoid close contact with the patient until the rash has crusted over; this is important in nursing home settings, where caregivers are often women of childbearing age. Fortunately, there is no risk of patients with herpes zoster causing zoster in sero-positive people, who constitute over 95% of the adult population.

Post-herpetic neuralgia (PHN) is a common complication. Pain occurring in the area of the affected dermatome 1 to 3 months after the rash is severe, long lasting and highly distressing. It can be a deep ache, punctuated by sharp pains and associated painful muscle contractions.

PHN is age-related, occurring in up to 68% of untreated zoster patients over 60 years, compared with only 10% of those under 40. Duration of PHN for more than one year is seen in up to 48% of persons over 70, compared with less than 5% of young persons. There is no obvious reason why elderly people are so susceptible to PHN (as opposed to their obvious vulnerability to zoster itself).

Other, much less frequent, complications in the elderly include: loss of vision (ophthalmic zoster), facial or limb paresis, encephalitis, hepatitis, and pneumonitis. Although rare, these complications can be devastating.

Management

Limitation of pain and disability are the main targets of treatment. Three antiviral agents have been shown to be effective in reducing acute pain and the duration of chronic pain, if started within 72 hours of the onset of rash. These are acyclovir (oral or intravenous), famciclovir and valacyclovir. Side effects include nausea, diarrhea, and headache, seen in roughly 10% of patients, but otherwise there are no serious side effects, apart from a risk of hemolytic-uremic syndrome in immune-suppressed patients given valcyclovir.

Corticosteroids have been used for many years to reduce the inflammation, and hence the pain, of zoster. However, they are not effective in reducing the incidence or duration of PHN, independent of whether acyclovir is given as well.

Infectivity in nursing home settings is a matter of importance. In the USA, the Centers for Disease Control and Prevention recommend a private room for immune-competent patients, to protect susceptible staff members and patients. For immune-incompetent patients, even stricter precautions (e.g. negative pressure ventilation) are required, to protect the patient from secondary infections. Such measures are more feasible in hospitals than in nursing homes.

Prevention

Doubtless, antiviral agents will be developed that have superior VZV activity, improved pharmacokinetics and/or a different mechanism of action. Better agents should also reduce the incidence of PHN.

Varicella vaccines are at present being studied in large-scale clinical trials in elderly patients in the USA. The vaccines significantly increase VZV responder-cell frequency, but it is not yet known whether they can prevent the occurrence of zoster or the frequency of PHN in those who have lost some of their specific cellular immune responses. It is hoped that a good vaccine will render this distressing and occasionally disastrous disease a thing of the past for elderly people.