Evaluation of allodynia and pain associated with postherpetic neuralgia using current perception threshold testing

Postherpetic neuralgia has various clinical features, and the implicated pathophysiologic mechanisms are controversial. This study was carried out to clarify the roles of peripheral sensory nerves in the production of allodynia and ongoing pain. Current perception threshold (CPT) testing was used to evaluate the sensory function.

The intensities of ongoing pain and dynamic allodynia were assessed using a numeric rating scale (0-10). Assessment of sensory nerve function was performed by a series of 2,000-, 250-, and 5-Hz stimuli using CPT testing. These measurements were made in ipsilateral and contralateral area.

CPTs at all frequencies in the ipsilateral area were significantly higher than those in the contralateral area. There were significant and inverse correlations between the intensity of allodynia and CPTs at all frequencies. No correlation was found between the intensity of ongoing pain and CPTs at any frequency. There was no correlation between the intensity of ongoing pain and the intensity of dynamic allodynia.

The intensity of dynamic allodynia in postherpetic neuralgia correlates with the preserved functions of Abeta, Adelta, and C fibers. In contrast, the intensity of ongoing pain does not correlate with either the preserved function of C fibers or the intensity of dynamic allodynia. Therefore, it is suggested that postherpetic neuralgia might be a pain syndrome including both peripheral and central mechanisms.