Herpes zoster is a viral disease characterized by a painful skin rash with blisters in a limited area on one side of the body (left or right), often in a stripe.
The initial infection with varicella zoster virus (VZV) causes the acute, short-lived illness chickenpox, which generally occurs in children and young adults. Once an episode of chickenpox has resolved, the virus is not eliminated from the body and can go on to cause shingles—an illness with very different symptoms—often many years after the initial infection. Herpes zoster is not the same disease as herpes simplex, despite the name similarity; both the varicella zoster virus and herpes simplex virus belong to the same viral subfamily Alphaherpesvirinae.
After the initial episode of chickenpox resolves, the varicella zoster virus remains latent in the nerve cell bodies and, less frequently, the non-neuronal satellite cells of the dorsal root, cranial nerve or autonomic ganglia, without causing any symptoms. Years or decades after the initial infection, the virus may break out of nerve cell bodies and travel down nerve axons to cause viral infection of the skin in the region of the nerve. The virus may spread from one or more ganglia along nerves of an affected segment and infect the corresponding dermatome (an area of skin supplied by one spinal nerve) causing a painful rash. Although the rash usually heals within two to four weeks, some sufferers experience residual nerve pain for months or years, a condition called post–herpetic neuralgia. Exactly how the virus remains latent in the body, and subsequently re-activates, is not understood.
Throughout the world, the incidence rate of herpes zoster every year ranges from 1.2 to 3.4 cases per 1,000 healthy individuals, increasing to 3.9–11.8 per year per 1,000 individuals among those older than 65 years. Over a lifetime, a large fraction of people develop herpes zoster, though usually only once; a 1965 16-year British study proposed that, of those individuals living to age 85, 50% would likely have had at least one attack, and 1% had at least two attacks.
The shingles vaccine is considered the most effective way to reduce incidence of herpes zoster and post-herpetic neuralgia, and to reduce severity of any outbreak. Antiviral drug treatment is considered a second-line approach, but can reduce the severity and duration of herpes zoster if a seven- to ten-day course of these drugs is started within 72 hours of the appearance of the characteristic rash.
Signs and Symptoms
The earliest symptoms of herpes zoster, which include headache, fever, and malaise, are nonspecific, and may result in an incorrect diagnosis. These symptoms are commonly followed by sensations of burning pain, itching, hyperesthesia (oversensitivity), orparesthesia (pins and needles, tingling, pricking, or numbness). The pain may be mild to extreme in the affected dermatome, with sensations that are often described as stinging, tingling, aching, numbing or throbbing, and can be interspersed with quick stabs of agonizing pain.
Herpes zoster in children is often painless, but older people are more likely to get zoster as they age, and the disease tends to be more severe.
In most cases after one to two days, but sometimes as long as three weeks, the initial phase is followed by the appearance of the characteristic skin rash. The pain and rash most commonly occurs on the torso, but can appear on the face, eyes or other parts of the body. At first the rash appears similar to the first appearance of hives; however, unlike hives, herpes zoster causes skin changes limited to a dermatome, normally resulting in a stripe or belt-like pattern that is limited to one side of the body and does not cross the midline. Zoster sine herpete (“zoster without herpes”) describes a patient who has all of the symptoms of herpes zoster except this characteristic rash.
Later the rash becomes vesicular, forming small blisters filled with a serous exudate, as the fever and general malaise continue. The painful vesicles eventually become cloudy or darkened as they fill with blood, and crust over within seven to ten days; usually the crusts fall off and the skin heals, but sometimes, after severe blistering, scarring and discolored skin remain.