CORRELATION BETWEEN LOCAL VASCULAR AND SENSORY CHANGES FOLLOWING TISSUE INFLAMMATION-INDUCED BY REPETITIVE APPLICATION OF TOPICAL CAPSAICIN

The aim of the present study was to investigate local vascular and sen sory changes and their correlation in order to obtain a better underst anding of the mechanisms of allodynia, hyperalgesia and vascular chang es following tissue inflammation induced by repetitive application of capsaicin cream. This type of application was utilized as a controlled model of inflammation which was altered in intensity due to its repet itive applicability. Ten healthy volunteers participated in two experi ments separated by at least five days. Each experiment consisted of a baseline session followed by five additional sessions. Before these se ssions either 1.5 g capsaicin (1%) or placebo cream was applied to the volar site of the forearm for 15 min. The areas of stroking allodynia and pin-prick hyperalgesia were mapped and the intensity of spontaneo us pain (VAS) was assessed after each application of the cream. In add ition, the visible flare, temperature (IR-Thermography), and blood-flo w (Laser-Doppler) were measured. The first application of capsaicin wa s perceived as painful; it induced both secondary hyperalgesia and all odynia. Compared to placebo, the first application of capsaicin cream also resulted in an increased blood-flow, elevated temperature and vis ible flare. The highest values of these sensory and vascular parameter s were reached after the third application. A direct correlation betwe en visible flare, secondary mechanical hyperalgesia and allodynia foll owing repetitive application of capsaicin indicates that both common c entral and peripheral mechanisms were involved in these changes. (C) 1 998 Elsevier Science B.V.