Post-Herpetic Neuralgia

Post-herpetic neuralgia is a painful condition usually affecting a limited area of the body. In its classic form it follows one ore more attacks of acute herpes zoster. In this form it most commonly presents as a burning pain in the region of the attack, which persists for more than 6 weeks after the rash has healed. The pain of post herpetic neuralgia is usually constant, but with periodic exacerbations which can be quite severe. The disease is associated with a poor prognosis so the major focus of treatment should be prevention.

 

The pain of post-herpetic neuralgia is neuropathic and so responds poorly to most common pain therapies such as anti-inflammatory agents and narcotics. Medical management with anti-epileptic agents such as gabapentin is more effective but usually limited by side effects, the most common of which is sedation. Ablative therapy (destroying or disabling a nerve with hear, cold or pulsed electrical energy) is often disappointing. While initially effective in up to 50% of cases long-term failures of therapy are common and it is not uncommon for patients to report a worsening of their pain associated with the numbness after an ablative procedure. Neuromodulation is the most successful form of treatment. It has the greatest potential for pain relief and the lowest incidence of side effects, but is still only effective in about 50% of patients.

 

Neuromodulation for post-herpetic neuralgia usually involves stimulation. In cases where the nerve is superficial TENS (transcutaneous electrical nerve stimulation) may be very effective, simple and inexpensive. In cases where TENS is ineffective or impractical, spinal cord stimulation or peripheral nerve stimulation can be tried. I usually run very short trials of SCS for conditions such as diabetic neuropathy or post-laminectomy syndromes, but will often run much longer trials (lasting up to two weeks) for post-herpetic neuralgia. As with ablative therapy initial success with stimulation is followed by long-term failure in a disturbing number of cases. Because it is a neuropathic pain post-herpetic neuralgia usually responds poorly to classical intrathecal pump therapy using narcotics and local anesthetics. Some success has been had using Prialt, but the data is conflicting and large studies have to this date not been done. If this type of therapy is considered a relatively long trial of intrathecal infusion will be necessary and the risks of infection born in mind.

 

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