September 27, 2011

The pathogenesis (cause) of shingles sounds like science fiction—a virus that causes a common childhood illness lies dormant for 50 or 60 years and then produces a different illness that can lead to severe, lifelong pain. Shingles, or herpes zoster, is caused by a relapse of the varicella-zoster virus (VZV); acute infection with this virus causes chicken pox. Varicella-zoster virus is a member of the herpesvirus family, which also includes herpes simplex I and II, and Epstein-Barr virus, which causes mononucleosis. Infection due to this family of viruses is characterized by an acute illness followed by lifelong infection, which is usually clinically silent, although chronic infection, mild relapses, and severe relapse due to immunosuppres-sion can occur. In the case of varicella-zoster virus, following acute infection (chicken pox), the virus remains dormant in the dorsal root ganglia in the spinal cord. Immune system surveillance keeps the virus dormant but the virus “hides” in the genome of the host cell and the immune system cannot eliminate it. Triggered by stress, immunosuppression (decreased functioning of the immune system), or decreased immune surveillance due to the prolonged elapsed time from the primary infection, the virus escapes the immune system and produces a local skin infection. The infection occurs in the area of the sensory nerve (the “dermatome”) from which it emanated (i.e., “hiding in the ganglia”). As a result, the skin lesions occur unilaterally (on one side of the body) in patterns predicted by the known distribution of sensory nerves.

The clinical presentation is distinct and a clinical diagnosis can be reliably made when the characteristic vesicular (bubble-like) rash is present. Pain and paraesthesias (altered sensory perception) can precede the rash, and on occasion the pain can be confused with other pathology depending on the location (e.g., pain in abdominal dermatomes may mimic an acute abdomen). The skin lesions may appear initially as small areas of erythema (localized redness of the skin), but evolve into small vesicular lesions developing along the dermatome (nerve distribution area on the skin). The most commonly affected areas are the thoracic (chest) and lumbar (back) dermatomes. The skin lesions are infectious, and nonimmune individuals can contract chicken pox from exposure to the skin lesions of an individual with shingles.

The acute illness lasts 1-2 weeks. The most common complications are pain and superinfection due to bacterial infection (staphylococcus and group A streptococcus). Other complications depend on the location of the infection. Cranial nerve shingles can lead to eye involvement and cranial neuropathies. Ramsay-Hunt syndrome results from shingles of the sensory branch of the trigeminal nerve and is characterized by skin lesions around the ear, hypersensitive hearing (hyperacusis), and paralysis of facial nerves (Bell’s palsy). Therapy with acyclovir or other antivirals has been shown in clinical trials to shorten the duration and severity of the acute illness when the therapy is begun within 48 hours of the appearance of the skin lesions. The role of antiviral medications in preventing chronic pain from shingles is discussed below. Management otherwise consists of pain control and monitoring for complications.

Shingles has a lifetime prevalence of 30% and is strongly associated with aging. Less than 5% of individuals 65 and under have a history of shingles; 10% of 75-year-olds and 30% of 85-year-olds have had shingles. About 30% of patients will experience a second episode of shingles in their lifetime, and about 5-10% will have a third episode. Shingles can occur in younger individuals in the absence of immunosuppression, but also may be associated with steroid therapy and immuno-suppressing illnesses. Shingles in young adults may be associated with immunosuppression from HIV, and should prompt consideration for HIV testing. With the notable exception of HIV, younger patients with shingles rarely have a related immunosuppressing illness, and the presence of shingles should not generally lead to a search for an underlying problem that is not evident on a routine history and physical examination.

While the acute illness may lead to some morbidity (illness) and may rarely lead to complications, acute shingles is largely self-limited. The most dreaded complication is severe, chronic nerve pain at the site of the infection. Pain due to shingles that persists for more than 30 days is termed postherpetic neuralgia (PHN). Pain due to postherpetic neuralgia can be disabling and may require complicated pain management in order for the patient to have sustained symptomatic relief. Therapy with antiviral medications during the acute infection can decrease the severity of postherpetic neuralgia. This benefit from antiviral therapy provides a strong indication for their use. There is ongoing research as to whether the use of vaccine to boost immunity in older individuals can prevent shingles.

See Also: Acquired immunodeficiency syndrome, Herpes simplex virus

Suggested Reading

  • Gnann, J. W., Jr., & Whitley, R. J. (2002). Herpes zoster. New England Journal of Medicine, 347, 340—346.
  • Whitley, R. J. (2000). Varicella-zoster virus. In G. L. Mandell, J. E. Bennett, & R. Dolin (Eds.), Principles and practices of infectious diseases (5th ed., pp. 1580-1585). New York: Churchill Livingstone.

Tags: , , ,

Category: S