As indicated above, the incidence of herpes zoster rises with age. Hope-Simpson has estimated that if a cohort of 1,000 people lived to 85 years of age, half would have had one attack of zoster and 10 would have had two attacks. The notion that one attack of zoster provides lifelong immunity is incorrect, although recurrent attacks are rare and most localized repeated herpetic eruptions are caused by HSV. The sexes are equally affected, as is each side of the body. Herpes zoster occurs in up to 10 percent of patients with lymphoma and 25 percent of patients with Hodgkin disease—particularly in those who have undergone splenectomy or received radiotherapy. Conversely, approximately 5 percent of patients who present with herpes zoster are found to have a concurrent malignancy (about twice the number that would be expected), and the proportion appears to be even higher if more than two adjacent dermatomes are involved.
The vesicular eruption is usually preceded for several days by itching, tingling, or burning sensations in the involved dermatome, and sometimes by malaise and fever. Or there is severe localized or radicular pain that may be mistaken for pleurisy, appendicitis, cholecystitis, muscle strain, or, quite often, ruptured intervertebral disc, until the diagnosis is clarified by the appearance of vesicles (nearly always within 72 to 96 h).
The rash consists of clusters of tense clear vesicles on an erythematous base, which become cloudy after a few days (as a result of accumulation of inflammatory cells), and dry, crusted, and scaly after 5 to 10 days. In a small number of patients, the vesicles are confluent and hemorrhagic, and healing is delayed for several weeks. In most cases, pain and dysesthesia last for 1 to 4 weeks; but in the others (7 to 33 percent in different series) the pain persists for months or, in different forms, for years, and presents a difficult problem in management. Impairment of superficial sensation in the affected dermatome(s) is common, and segmental weakness and atrophy are added in approximately 5 percent of patients. In the majority of patients, the rash and sensorimotor signs are limited to the territory of a single dermatome, but in some, particularly those with cranial or limb involvement, two or more contiguous dermatomes are involved.
Rarely (and usually in association with malignancy) the rash is generalized, like that of chickenpox, or it is altogether absent (zoster sine herpete) in which case, the pain is often attributed to another more mundane process such as sciatica.
In more than half of the cases, the CSF shows a mild increase in cells, mainly lymphocytes, and a modest increase in protein content (although lumbar puncture is not performed to establish the diagnosis). The herpetic nature of the eruption can be confirmed by direct immunofluorescence of a biopsied skin lesion, using antibody to VZV, or inferred by finding multinucleated giant cells in scrapings from the base of an early vesicle (Tzanck smear). The spinal fluid also contains antibodies to the virus or evidence of the organism by PCR testing in 35 percent of cases according to a prospective study by Haanpää and colleagues.
Virtually any dermatome may be involved in zoster, but some regions are far more frequent than others. The thoracic dermatomes, particularly T5 to T10, are the most common sites, accounting for more than two-thirds of all cases, followed by the craniocervical regions. In the latter cases the disease tends to be more severe, with greater pain, more frequent meningeal signs, and involvement of the mucous membranes. Another rare complication of zoster, taking the form of a subacute amyotrophy (zoster paresis) of a portion of a limb or trunk, is probably linked to a restricted form of VZV myelitis.