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, as well as in any age group of immunocompromised patients. Treatment is generally with acyclovir. Many develop a painful condition termed postherpetic neuralgia.

Signs and symptoms

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.

As the blisters originate from one ganglion (see below), they only affect one area of the body and do not cross the midline.

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. 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.

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.

External links

• NIH Facts About Shingles
• NINDS Shingles Information Page
• eMedicine Health Shingles Page