• A Truini, F Galeotti, M Haanpaa, R Zucchi, A Albanesi, A Biasiotta, A Gatti, and G Cruccu.
• Department of Neurological Sciences, La Sapienza University, Viale Università 30, 00185 Rome, Italy. andrea.truini@uniroma1.it
• Pain. 2008 Dec 1;140(3):405-10.

AbstractPostherpetic neuralgia is an exceptionally drug-resistant neuropathic pain. To investigate the pathophysiological mechanisms underlying postherpetic neuralgia we clinically investigated sensory disturbances, pains and itching, with an 11-point numerical rating scale in 41 patients with ophthalmic postherpetic neuralgia. In all the patients we recorded the blink reflex, mediated by non-nociceptive myelinated Abeta-fibers, and trigeminal laser evoked potentials (LEPs) related to nociceptive myelinated Adelta- and unmyelinated C-fiber activation. We also sought possible correlations between clinical sensory disturbances and neurophysiological data. Neurophysiological testing yielded significantly abnormal responses on the affected side compared with the normal side (P<0.001). The blink reflex delay correlated with the intensity of paroxysmal pain, whereas the Adelta- and C-LEP amplitude reduction correlated with the intensity of constant pain (P<0.01). Allodynia correlated with none of the neurophysiological data. Our study shows that postherpetic neuralgia impairs all sensory fiber groups. The neurophysiological-clinical correlations suggest that constant pain arises from a marked loss of nociceptive afferents, whereas paroxysmal pain is related to Abeta-fiber demyelination. These findings might be useful for a better understanding of pain mechanisms in postherpetic neuralgia.

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