Postherpetic neuralgia (PHN) - Jaipur Block for Postherpetic neuralgia (PHN)

Postherpetic neuralgia (PHN) Jaipur Block for Postherpetic neuralgia (PHN)

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Varicella zoster

Definition of Postherpetic neuralgia (PHN)

Postherpetic neuralgia (PHN) is a localized dermatomal neuropathic pain experienced 1 month after herpes zoster.

Immunosuppression is the commonest risk factor for PHN.

Varicella-zoster virus (VZV) is the causative agent of varicella, or ” the chickenpox,” and herpes zoster, or “shingles.”

Acute herpes zoster typically presents with a rash that is painful but self-limited. Some patients may continue to experience pain for months to years after the resolution of the rash, a condition known as postherpetic neuralgia (PHN).

Risk factors for post herpetic neuralgia

age more than 60 years
severe pain during acute herpes zoster
severe or more rash with acute herpes zoster

How long does the pain of PHN lasts?

Generally pain of PHN lasts from few months to several. Most of them last for few months.

Is there sensory loss with PHN?

Yes, the same dermatomes involved with herpes and PHN may also have sensory loss like loss of thermal, tactile, inprick or vibration sensations.

Occasionally the sensory deficit may cross dermatome margins but the uninvolved contralateral dermatomes are normal or unimpaired.

herpes zoster

Does PHN cause allodynia?

Allodynia is a condition that causes pain from the stimuli that normally wouldnt cause pain suchas light touch, brushing, combing hair, wearing clothing etc.

And PHN may occasionally cause allodynia as well.

Pain in Postherpetic neuralgia (PHN)

Broadly type of pain in PHN is divided into two broad categories spontaneous and stimulus evoked.

Spontaneous pain can be either continuous (burning, aching, throbbing) or intermittent (stabbing, shooting, electric-shock-like pain). Stimulus-evoked pain can present as allodynia and hyperalgesia. Allodynia is the commonest type of pain reported in PHN.

Diagnosis of PHN

The diagnosis of PHN is made when localized neuropathic pain persists beyond three months in the same distribution as a preceding documented episode of acute herpes zoster.

Testing for varicella-zoster virus (VZV) antibodies in the blood or cerebrospinal fluid is available and may be useful in atypical cases to confirm past exposure to the virus; however, positive tests do not specify PHN as the source of pain

Differential diagnosis of PHN

Trigeminal neuropathy
Other forms of craniofacial pain
Acute radiculopathy
Diabetic amyotrophy and idiopathic lumbosacral radiculoplexus neuropathy
Recurrent acute herpes zoster

Treatment of Postherpetic neuralgia (PHN) with local anesthetics

Local anesthetics act by suppressing sodium channels and decreasing ectopic discharges, thus reducing membrane excitability.

Lignocaine has faster onset of action (2-3 min) of but the duration of action (2 h) in contrast bupivacaine though is slow to act but has a continued activity for longer time (4-8 h).

There is no consensus on the concentration of anesthetics required, though few studies have reported a dose-related effect.

Treatment of Postherpetic neuralgia (PHN)

Intradermal therapy leads to faster onset of action, and the reservoir effect leads to sustained action with less systemic absorption. A higher dose of local anesthetics may cause arrythmias

Steroids and Anesthetics for Postherpetic neuralgia (PHN)

A combination of dexamethasone and local anesthetics gives a good response in stimulus-induced postherpetic neuralgia

Treatment options for PHN

Following medications can be used for treatment of PHN:

Gabapentinoids like gabapentin or pregabalin
Tricyclic antidepressants TCAs like Amitriptyline, Nortriptyline, Desipramine
Capsaicin topical
Lidocaine patches
Antiseizure medications like valproic acid, carbamazepine, oxcarbazepine. lamotrigine
SNRI like duloxetine, venlafaxine
Botulinum toxin
Opioids
Glucocorticoid injections
Neuromodulation and nerve stimulation like TENS, Pulse radiofrequency, spinal cord stimulation
Cognitive behavior therapy