Pain
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Randomized Controlled Trial Clinical Trial
Effect of adrenergic receptor activation on post-herpetic neuralgia pain and sensory disturbances.
Patients with acute herpes zoster, and to a lesser extent post-herpetic neuralgia (PHN), have been reported to respond to local anesthetic blockade of the sympathetic nervous system. In animal models of nerve injury, local injection of adrenergic agonists after nerve injury, but not before, excites nociceptors. In some patients with chronic neuropathic pain, local application of norepinephrine evokes pain. ⋯ After injection of the adrenergic agonist into PHN skin, both overall PHN pain and allodynia severity were significantly greater than after saline injection, peaking at 10-15 min post-injection. Even when PHN has been present for years, adrenergic receptor stimulation in PHN skin increases pain, most likely through direct activation of C-nociceptors in the painful skin. Increased allodynia is most likely mediated centrally and driven by the increase in C-nociceptor input.