Shingles is caused by the varicella-zoster virus (VZV), which primarily affects the dorsal root ganglia (DRG) of the spinal nerves or trigeminal nerve. A single DRG is commonly affected, but a small number of adjacent DRGs may be affected, usually on the same side.
Acute herpetic neuralgia is defined as pain during the first 30 days after the eruption of the rash. If the pain resolves within the next 4 months, it is defined as subacute herpetic neuralgia. Pain persisting beyond this time frame is called postherpetic neuralgia (PHN). Although spontaneous resolution of herpes zoster may be expected in many patients, a significant number of patients develop chronic intractable pain of PHN.
Herpes zoster most frequently occurs in adults who previously have had chickenpox. The virus remains dormant in the DRG until, many years later, it is reactivated, producing herpes zoster because of decreased cell-mediated immunity. The decrease in immunity that permits the reactivation may be caused by infection or malignancy, or it may be iatrogenic. Persistent stress and untreated depression are thought to lower immunity, hence increasing the likelihood of shingles with severe pain, increasing the risk of chronic PHN.1,2
Although the DRGs of the spinal and cranial nerves are involved most commonly, any part of the central nervous system (CNS) can be affected. For example, the anterior motor horn may be involved, or the patient may have myelitis or encephalomyelitis. It has been suggested that T-cell recognition of VZV proteins is a likely mechanism involved in the control of reactivation of the virus from latency.3–5
The incidence of herpes zoster in the U.S. population indicates a steep increase in the general population over the past 30 years.6 The incidence of herpes zoster is low in immunocompetent children7 but is higher in immunosuppressed children.8 The disease is more common in elderly adults, and the risk increases proportionately with age. The best incidence data for PHN in older patients come from the placebo arm of a large randomized trial that evaluated vaccination against VZV.9 In 334 patients from 60 to 69 years of age who developed herpes zoster, PHN occurred in 6.9%. In contrast, among 308 patients age 70 years or older who developed herpes zoster, PHN occurred in 18.5%.
The virus may be recovered from early vesicles and has been recovered from blood, lung, liver, and cerebrospinal fluid (CSF) but only occasionally from the oropharynx. Scrapings also provide cellular material containing multinuclear giant cells. Acidophilic intranuclear inclusions can be seen in the Tzanck smear stained with hematoxylin and eosin, Giemsa, Papanicolaou, or Paragon multiple stain. A punch biopsy for electron microscopic examination provides even more reliable material; the more reliable material ...