Postherpetic neuralgia is a pain syndrome that occurs after resolution of Herpes zoster. Herpes zoster (HZ) is a viral infection that usually presents as a childhood infection of varicella (ie, chicken pox). Following the acute phase, the virus enters the sensory nervous system, where it is harbored in the geniculate, trigeminal, or dorsal root ganglia and remains dormant for many years. With advancing age or immunocompromised states, the virus reactivates and an eruption (ie, shingles) occurs. Even after the acute rash subsides, pain can persist or recur in shingles-affected areas. This condition is known as postherpetic neuralgia.
Incidence is 0.4 to 1.6 cases per 1000 in people aged less than 20 years and it is around 4.5 to 11 cases per 1000 among those 80 years or older. People who are in immunocompromised status because of either cancer or HIV status are more prone to get an attack.
It is more common in elderly age group more than 60 years of age. However, the recent trends show increase in incidence in younger age group. The reason could be mutation in the virus matrix, immunocompromised status secondary to HIV, chemotherapy-induced immunomodulation and some unexplained factors.
Postherpetic neuralgia patients may experience significant pain for a prolonged period of time.
No predilection for developing post herpetic neuralgia is known.
Pathophysiology of Postherpetic Neuralgia
Herpes zoster most often attacks thoracic, cervical and ophthalmic nerve roots. The attack often preceds by days or weeks of constant burning pain, aching sensation, hyperaesthesia in one or two adjacent dermatomes. It erupts as erythematous patch and soon small groups of vesicles will be seen in that area. Over course of 7 to 10 days the vesicles postulate and crust formation can be seen.
Some patients with postherpetic neuralgia have abnormal function of unmyelinated pain receptors and minimal sensory loss. Hypersensitivity of pain and touch receptors occurs to light mechanical stimulation, leading to severe pain (allodynia).
Allodynia may be related to formation of new connections involving central pain transmission neurons.
Other patients do not have allodynia but severe, spontaneous pain, possibly secondary to increased spontaneous activity in deafferented central neurons or reorganization of central connections.
Risk Factors for Post Herpetic Neuralgia
- Increased age
- Site of Herpes zoster
- Lower risk – Jaw, neck, sacral, and lumbar
- Moderate risk – Thoracic
- Highest risk – Trigeminal (especially ophthalmic division), brachial plexus
- Severe prodromal pain when Herpes zoster occurred
- Severe rash
Clinical Presentation of Postherpetic Neuralgia
This pain is of more neuropathic in nature and typically follows nerve distribution. Apart from the pain, patient may complain of touch hypersensitivity.
The site of pain in the distribution of the shingles and the scarring is often visible to confirm the diagnosis, if this is in doubt.
Pain could be described as burning, deep aching, crawling or stabbing in nature.
If visceral nerve is also involved, symptoms like constipation, indigestion, frequency or dysuria may occur depending on the affected nerve.
Physical examination may reveal scarring of the skin from prior herpes zoster except in small percentage of cases of subclinical herpes zoster where rash is not present. Decreased sensation or increased sensation may be present in the involved areas.
Allodynia could also be a finding.
Changes in autonomic function such as increased sweating over the involved area may be seen.
- Cavernous Sinus Syndromes
- Chronic Paroxysmal Hemicrania
- Cluster Headache
- Head Injury
- Hemifacial Spasm
- Migraine Headache
- Migraine Variants
- Persistent Idiopathic Facial Pain
- Tolosa-Hunt Syndrome
- Traumatic Peripheral Nerve Lesions
- Trigeminal Neuralgia
No lqb work is required for diagnosis of postherpetic neuralgia. CSF examination shows abnormality in 61% cases. Pleocytosis is observed in 46%, elevated protein in 26%, and varicella zoster virus DNA in 22%.
But these findings have no bearing on the clinical course or predictive value and are not generally required.
In cases where subclinical herpes zoster is suspected, antibodies to herpes zoster can be measured. A 4-fold increase has been used to support the diagnosis of subclinical herpes zoster.
Imaging studies are not necessary
Treatment of Postherpetic Neuralgia
The medical treatment is by use of tricyclic antidepressants, anticonvulsants, anesthetics, analgesics, corticosteroids, and antiviral agents. Recent vaccination is also effective for preventing herpes zoster outbreaks and postherpetic neuralgia.
- Tricyclic antidepressants
- Amitryptyline and nortryptaline
- Capsaicin topical
- Capsaicin 8% transdermal patch
- Antiviral agents
- Lidocaine anesthetic
- Zoster vaccine live- Reported decrease decreased 51.3% for herpes zoster and postherpetic neuralgia d 66.5%
Dorsal root entry zone lesioning is a type of surgery for nerve pain that is used when conservative treatments fail.
Epidural steroids and nerve blocks can also be used.
Postherpetic neuralgia shows slow resolution over the time. Response to tricyclic antidepressants is good. Pregabalin is said to be very effective.
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