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Postherpetic neuralgia

German: Post-Zoster-Neuralgie

1 Definition

Postherpetic neuralgia is neuropathic pain following an infection with Varizella zoster virus, most commonly after the Herpes zoster, thus limiting the symptoms to the affected dermatome.

2 Epidemiology

In about 10-15% of patients with Herpes zoster, postherpetic neuralgia can be observed. However, this numbers increase with age (up to around 35% in patients aged 60 and older) and if facial sensitive nerves are affected.

3 Etiology

Following nerve damage by herpes zoster, a sensitization of the nerves in the affected dermatome may persist, resulting in hyperalgesia. Sensitization is believed to take place both in the peripherous nervous system (spontaneous firing) as well as the central nervous system (increased nociceptor transmission, disinhibition). This can even result in symptoms such as allodynia, commonly known in conditions with deafferentations.

4 Clinical presentation

All pain occuring within three months after restitution of a herpes zoster eruption is considered as post-herpetic neuralgia. The pain level varies. It is often described as permanent numb or burning pain. Intermitting gnawing, stabbing attacks are also often described. Hyperalgesia, allodynia, and "dysesthesia" often add to the discomfort for patients.

5 Diagnostics

The diagnosis is determined by patient history and clinical presentation of the symptoms. In young patients, occurrence of post-herpetic neuralgia should lead to further investigations into causes of a possible immune-deficiency.

6 Differential diagnoses

In absence of efflorescences, depending on the localization, processes on the spinal level (e.g. spinal disc herniation) or e.g. trigeminal neuralgia can be possible alternate causes for the symptoms.

7 Therapy

For targeting post-herpetic neuralgia, the different levels of perception of pain can be addressed.

Possible substances used for treatment of neuropathic pain are antidepressants (e.g. TCAs, SSRIs, SSNRIs), or anticonvulsants (e.g. Gabapentin, a substance often used is Pregabalin).

Local application of local anesthetics such as lidocaine gel or even topic treatment with capsaicin can be beneficial.

Classical pain medication following WHO guidelines is mostly provided additionally (e.g. opioids).

In severe cases, methods such as acupuncture or TENS can be offered, too. As the final treatment, even operations such as chordotomy can be considered.

8 Prevention

Early treatment of the underlying herpes zoster with antiviral treatment is essential for successfully avoiding post-herpetic neuralgia.

9 Prognosis

In 50% of the patients, spontaneous remission within the first year can be observed, 25% of the patients with the described therapy reach remission. If symptoms persist for more than one year, the prognosis is more negative.

10 References

Gharibo et al. "Postherpetic Neuralgia: An Overview of the Pathophysiology, Presentation, and Management", http://www.painmedicinenews.com/download/PostNeuralgiaPMN0411_WM.pdf retrieved on 01 June 2016

Opstelten et al. "Herpes zoster and postherpetic neuralgia: incidence and risk indicators using a general practice research database", http://fampra.oxfordjournals.org/content/19/5/471.long retrieved on 01 June 2016

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