Differential effect of Incobotulinumtoxin A on pain, neurogenic flare and hyperalgesia in human surrogate models of neurogenic pain

Background The effectiveness of Botulinum‐neurotoxin A (BoNT/A) to treat pain in human pain models is very divergent. This study was conducted to clarify if the pain models or the route of BoNT/A application might be responsible for these divergent findings. Methods Sixteen healthy subjects (8 males, mean age 27 ± 5 years) were included in a first set of experiments consisting of three visits: (1) Visit: Quantitative sensory testing (QST) was performed before and after intradermal capsaicin injection (CAPS, 15 μg) on one thigh and electrical current stimulation (ES, 1 Hz) on the contralateral thigh. During stimulation pain and the neurogenic flare response (laser‐Doppler imaging) were assessed. (2) Four weeks later, BoNT/A (Xeomin®, 25 MU) was injected intracutaneously on both sides. (3) Seven days later, the area of BoNT/A application was determined by the iodine‐starch staining and the procedure of the (1) visit was exactly repeated. In consequence of these results, 8 healthy subjects (4 males, mean age 26 ± 3 years) were included into a second set of experiments. The experimental setting was exactly the same with the exception that stimulation frequency of ES was increased to 4 Hz and BoNT/A was injected subcutaneously into the thigh, which was stimulated by capsaicin. Results BoNT/A reduced the 1 Hz ES flare size (p