A Human Experimental Model for Neuropathic Pain Using Combined Application of Capsaicin and Local Anesthetics

Main of the present study was to develop a model of concomitant C-fibre block and sensitization eliciting spontaneous pain as well applying topical capsaicin and local anesthetics (LA) to examine the sensory alterations after combined C-fiber block and sensitization in both different application orders (sensitization of blocked C-fibers and block of sensitized C-fibers), compared to each of both mechanisms alone. Thereby, we expect stronger sensory changes during the combined substance application than during the monoapplication. We expect also contralateral sensory alterations mirroring the changes on the intervention site after the combined capsaicin and LA application, being stronger than after sensitization alone absent after C-fiber block alone.

Inclusion Criteria:

• healthy subject, older than 18 years, provided written informed consent

Exclusion Criteria:

• insufficient comprehension of the German language, history of severe internal, neurological or dermatological diseases, substance abuse, manifest psychiatric diseases, chronic and acute pain, any medication intake (except contraceptives in females) regularly or on demand during the last 14 days before study inclusion and during the study period, hypersensitivity to lidocaine or other amide-type anesthetics, hereditary or acquired methemoglobinemia, pregnancy, nursing, abnormal sensory profile in the quantitative sensory testing (QST) with side-to-side differences beyond the normal range at baseline and participation in clinical trials during the last month.