CAPSAICIN-INDUCED FLARE AND VASODILATATION IN PATIENTS WITH POSTHERPETIC NEURALGIA

The aim of the present study was to investigate the role of primary af ferent fibres with polymodal nociceptors in the various pain symptoms and signs associated with post-herpetic neuralgia (PHN). Forty-four pa tients with PHN affecting thoracic dermatomes were examined clinically for evidence of sensory disturbance to touch and pinprick and compare d to 14 normal subjects and 9 subjects with evidence of past herpes te ster infection but no pain. The patients were then divided into 3 grou ps on the basis of their clinical symptoms and signs - those with stea dy burning discomfort only (n = 12), those with burning discomfort, al lodynia and hyperalgesia to pinprick (n = 17), and those with burning discomfort, allodynia and hypalgesia to pinprick (n = 15). Indirect me asurement of primary afferent fibre function was performed by measurin g the neurogenic axon reflex flare to topical capsaicin using Doppler flowmetry in the 5 clinical groups. The 2 groups with allodynia had si gnificantly decreased neurogenic flare responses compared to PI-IN sub jects without allodynia and the 2 control groups. These results sugges t that allodynia in patients with post-herpetic neuralgia may be a con sequence of disrupted function of primary afferent fibres.