What Are Treatment Options for Post-Herpetic Neuralgia?

Blaine P. Carmichael, MPAS, PA-C

Disclosures

November 21, 2000

Question

An older patient with intractable post-herpetic neuralgia has tried many different avenues of treatment such as Lidoderm (lidocaine patch 5%), Neurontin (gabapentin capsules). He is now maintained on OxyContin (oxycodone hydrochloride controlled-release). Are there any other therapeutic options?

Linda Kulp, PA-C

Response from Blaine P. Carmichael, MPAS, PA-C

Based on evidence from randomized trials, tricyclic antidepressants (TCAs) seem to be the only agents of proven benefit for established post-herpetic neuralgia (PHN). PHN occurs as a complication of herpes zoster in 10% of patients overall, 50% of patients over 60 years, and 75% of patients over 70 years.[1] Sixty percent to 70% of patients with PHN respond well to treatment with amitriptyline introduced at a low dose with step-wise increases. The remainder are considered to be intractable (resistant to treatment). The tricyclic drugs (eg, amitriptyline and nortriptyline) have been studied for their analgesic properties in the treatment of PHN. TCAs work in patients with PHN as analgesics, not as antidepressants. The analgesic action of TCAs may or may not occur at lower doses than are normally required for the antidepressant effects. The median dose of amitriptyline for analgesia in PHN is 75 mg/day, and some patients may attain pain relief at a dose of 10-20 mg/day compared with 75-150 mg/day for antidepressant activity. The mechanism of action of this class of drugs in PHN is not clear. They block the re-uptake of the monoamine neurotransmitters and may act on the descending systems from the brainstem.

Amitriptyline, desipramine, nortriptyline, and maprotiline have been shown to be effective in PHN. Imipramine and doxepin seem to be less effective than amitriptyline. The selective serotoninergic drugs such as fluoxetine are also considered to be less effective or ineffective. Amitriptyline, which has both serotoninergic and noradrenergic actions, is considered to be more effective than the purely noradrenergic group, but some patients may respond only to a noradrenergic agent and not amitriptyline.[2]

The dose of tricyclic antidepressant agents should be adjusted for the individual patient and doses reduced in the elderly. For example, amitriptyline can be started at 25 mg nightly for patients under 65 years old (10 mg nightly in those over 65 years) and the dose increased step-wise by the same amount every 5-7 days until either pain relief is attained or the side effects are intolerable. The dose varies for the individual patient.

An approach in patients in whom tricyclic antidepressants are contraindicated or not effective is the novel yet not new application of topical aspirin and other NSAIDs combined with chloroform or diethyl ether. The solution is daubed onto the painful skin. As the solvent evaporates, the active drug is left behind to penetrate to cutaneous nerve endings. There have been a number of limited studies using topical NSAIDs but no long-term trial that I can find in the literature.

Many nonpharmaceutical therapies for PHN have been described, although scientific evidence of efficacy from double-blind and controlled studies is lacking. These include physical therapies such as Transcutaneous Nerve Stimulation (TENS), acupuncture, ultrasound, and laser treatment. Cold packs can also be useful for temporary relief of symptoms in patients with PHN but without cold allodynia. They must be applied frequently and with a protective layer such as a cotton towel between the pack and the skin. Creams may be helpful either because of the physical benefit of gentle massage or possibly because of inclusion of an ingredient such as capsaicin, a local anesthetic, or an NSAID. Plastic "artificial skin" sprays or light cotton clothing may reduce tactile allodynia from the rubbing of clothes.

If therapy with tricyclic antidepressants, social support, and hydrocodone or oxycodone is ineffective within 2-3 weeks, referral to a pain medicine physician is indicated. A number of therapeutic options are available, including peripheral nerve blockade and subcutaneous or intravenous injection of lidocaine. If IV lidocaine is effective, oral mexiletine may be useful. In persistent PHN, morphine or methadone is indicated for pain management. The dose of opioids in patients with neurogenic pain is less than the dose that causes psychological effects. Intrathecal and epidural opiates can be very useful.

Neurodestructive techniques such as Dorsal Root Entry Zone (DREZ) lesioning and cordotomy have been used to treat PHN in the past and are now considered inappropriate. Sympathetic nerve block seldom helps established PHN. Interpleural analgesia may be of use in some patients with thoracic PHN.

Psychological interventions such as counseling, cognitive-behavior modification, relaxation training, biofeedback, and hypnosis are very widely used in the treatment of PHN. These techniques are an integral component of state-of-the-art, multidisciplinary chronic pain treatment.[1]

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