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Author: Arcana Luo, Medical Student, University of Auckland, New Zealand; Chief Editor: Dr Amanda Oakley, Dermatologist, Hamilton, New Zealand, March 2014.
Post-herpetic neuralgia describes chronic skin pain in an area previously affected by herpes zoster (shingles).
Herpes zoster is a localised painful blistering rash caused by reactivation of herpes varicella-zoster virus sometime after the primary generalised infection with varicella (chickenpox).
Because post-herpetic neuralgia is defined as pain after and caused by, re-activation of the herpes zoster virus, evidence of herpes zoster infection is critical for diagnosis.
Usually, the diagnosis of herpes zoster is easily made when a painful blistering rash arises that has dermatomal distribution (ie, along the pathway of a cutaneous nerve).
However, not all patients with post-herpetic neuralgia have a history of rash or acute symptoms. In these cases, a rise in antibody levels on serial blood tests may confirm the previous infection by herpes zoster virus.
Post-herpetic neuralgia is often used to describe any pain that persists after herpes zoster blisters have cleared up. Some experts prefer to reserve the term only for pain that lasts for more than 28 days or more than 120 days. 'Acute' and 'sub-acute' herpetic neuralgia may be used to describe earlier pain associated with herpes zoster infection.
Features of post-herpetic neuralgia include:
Chronic pain can lead to insomnia, anxiety and depression.
The main risk factors for post-herpetic neuralgia are:
Some other possible risk factors include:
Acute herpes zoster pain is due to direct damage of peripheral nerves by the herpes zoster virus. Ongoing post-herpetic neuralgia is due to slow recovery and the involvement of the central nervous system.
Research has shown that the nerves or neurones affected by post-herpetic neuralgia are damaged. Microscopic changes include:
It has been suggested that these damaged nerves send fewer signals from the skin to central nervous structures, which leads to neuron hyperexcitability and the constant perception of pain. However, the exact pathways are unknown.
It is likely that acute and sub-acute pain, and sensory changes such as allodynia, arise from slightly different mechanisms.
Herpes zoster pain and post-herpetic neuralgia are common and very debilitating conditions. But they can be prevented to a large extent by vaccination of at-risk individuals and by prompt antiviral treatment during the acute phase of herpes zoster infection.
The following have not been shown to prevent post-herpetic neuralgia:
Multiple treatments are often required to control post-herpetic neuralgia.
The duration of post-herpetic neuralgia is variable.
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