Herpes zoster
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Herpes zoster, colloquially known as shingles, is the reactivation of varicella zoster virus, leading to a crop of painful blisters over the area of a dermatome. It occurs very rarely in children and adults, but its incidence is high in the elderly (over 60), as well as in any age group of immunocompromised patients. It strikes 500,000 people per year in the United States. Treatment is generally with acyclovir. Many develop a painful condition termed postherpetic neuralgia.
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Signs and symptoms
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Often, the pain is the first symptom. Then 2-3 crops of red lesions develop, which gradually turn into small blisters filled with serous fluid. A general feeling of unwellness often occurs.
As long as the blisters have not dried out, HZ patients may transmit the virus to others. This could lead to chickenpox in people (mainly young children) who are not yet immune for this virus.
Shingles blisters are unusual in that they only appear on one side of the body. That is because the chickenpox virus can remain dormant for decades, and does so inside the spinal column or a nerve fiber. If it reactivates as shingles, it affects only a single nerve fiber, or ganglion, which can radiate to only one side of the body. The blisters therefore only affect one area of the body and do not cross the midline. They are most common on the torso, but can also appear on the face (where they are potentially hazardous to vision) or other parts of the body.
Diagnosis
The diagnosis is visual - very few other diseases mimic herpes zoster. In case of doubt, fluid from a blister may be analysed in a medical laboratory.
Pathophysiology
The causative agent for herpes zoster is varicella zoster virus (VZV). Most people are infected with this virus as a child, as it causes chickenpox. The body eliminates the virus from the system, but it remains dormant in the ganglia adjacent to the spinal cord or the ganglion semilunare (ganglion Gasseri) in the cranial base.
Generally, the immune system suppresses reactivation of the virus. In the elderly, whose immune response generally tends to deteriorate, as well as in those patients whose immune system is being suppressed, this process fails. (Some researchers speculate that sunburn and other, unrelated stresses that can affect the immune system may also lead to viral reactivation.) The virus starts replicating in the nerve cells, and newly formed viruses are caried down the axons to the area of skin served by that ganglion (a dermatome). Here, the virus causes local inflammation in the skin, with the formation of blisters.
The pain characteristic of herpes zoster is thought to be due to irritation of the sensory nerve fibers in which the virus reproduces.
Therapy
Aciclovir (an antiviral drug) inhibits replication of the viral DNA, and is used both as prophylaxis (e.g. in patients with AIDS) and as therapy for herpes zoster. Other antiviral are valaciclovir and famciclovir. Steroids are often given in severe cases.
The long term complication postherpetic neuralgia may cause persistent pain that lasts for years. Pain management is difficult as conventional analgesics may be ineffective. Alternative agents are often used, including tricyclic antidepressants, anticonvulsants, and/or topical agents.
A vaccine called live attenuated Oka/Merck VZV has been developed by Merck & Co. has proven successful in preventing half the cases of herpes zoster in a study of 38,000 people who received the vaccine. The vaccine also reduced by two-thirds the number of cases of postherpetic neuralgia. (Oxman, et al., 2005)
Prognosis
The rash and pain usually subside within 3 to 5 weeks. Sometimes serious effects including partial facial paralysis (usually temporary), ear damage, or encephalitis may occur. Shingles on the upper half of the face (the first branch of the trigeminal nerve) may result in eye damage and require urgent ophthalmological assessment.
Since shingles is a reactivation of a virus contracted previously—often decades earlier—it cannot be induced by exposure to another person with shingles or chickenpox. However, those with active blisters can spread chickenpox to others who have never had that condition or who have not been vaccinated against it.
References
External links
- NIH Facts About Shingles (http://www.niaid.nih.gov/factsheets/shinglesFS.htm)
- NINDS Shingles Information Page (http://www.ninds.nih.gov/health_and_medical/disorders/shingles_doc.htm)
- eMedicine Health Shingles Page (http://www.emedicinehealth.com/articles/17511-1.asp)
- NHS Direct Online Health Encyclopaedia: Shingles (http://www.nhsdirect.nhs.uk/en.asp?TopicID=414)da:Helvedesild
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