title: Capsaicin-induced flare and vasodilatation in patients with post-herpetic neuralgia.
abstract: The aim of the present study was to investigate the role of primary afferent fibres with polymodal nociceptors in the various pain symptoms and signs associated with post-herpetic neuralgia (PHN). Forty-four patients with PHN affecting thoracic dermatomes were examined clinically for evidence of sensory disturbance to touch and pinprick and compared to 14 normal subjects and 9 subjects with evidence of past herpes zoster infection but no pain. The patients were then divided into 3 groups on the basis of their clinical symptoms and signs-those with steady burning discomfort only (n = 12), those with burning discomfort, allodynia and hyperalgesia to pinprick (n = 17), and those with burning discomfort, allodynia and hypalgesia to pinprick (n = 15). Indirect measurement of primary afferent fibre function was performed by measuring the neurogenic axon reflex flare to topical capsaicin using Doppler flowmetry in the 5 clinical groups. The 2 groups with allodynia had significantly decreased neurogenic flare responses compared to PHN subjects without allodynia and the 2 control groups. These results suggest that allodynia in patients with post-herpetic neuralgia may be a consequence of disrupted function of primary afferent fibres.
authors.affiliation: Geriatric Medicine, Prince Philip Hospital, Llanelli, Wales, UK National Ageing Research Institute, North West Hospital, Mount Royal Campus, Parkville, Victoria 3052 Australia.
authors.forename: Granville C
authors.initials: GC
authors.lastname: Morris
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Gibson
authors.forename: Robert D
authors.initials: RD
authors.lastname: Helme
mesh_terms: D000287:Administration, Topical; D000344:Afferent Pathways / Q000187:drug effects; D000368:Aged; D001369:Axons / Q000187:drug effects* / Q000502:physiology; D002211:Capsaicin / Q000494:pharmacology*; D016022:Case-Control Studies; D004487:Edema / Q000139:chemically induced; D005260:Female; D006562:Herpes Zoster / Q000150:complications* / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009412:Nerve Fibers / Q000187:drug effects* / Q000502:physiology; D009437:Neuralgia / Q000209:etiology* / Q000503:physiopathology; D009619:Nociceptors / Q000187:drug effects; D017288:Pain Threshold; D014665:Vasodilator Agents / Q000494:pharmacology*
chemical_list: D014665:Vasodilator Agents; D002211:Capsaicin