Late sensory function after intraoperative capsaicin wound instillation.
BACKGROUND
Intense capsaicin-induced C-fiber stimulation results in reversible lysis of the nerve soma, thereby making capsaicin wound instillation of potential interest for the treatment of post-operative pain. Clinical histological and short-term sensory studies suggest that the C-fiber function is partly re-established after skin injection of capsaicin. However, no study has evaluated the long-term effects of wound instillation of purified capsaicin on sensory functions.


METHODS
Patients included in a double-blind placebo-controlled randomized study of the analgesic effect of capsaicin after groin hernia repair were examined by quantitative sensory testing before, 1 week and 2 years post-operatively. The primary endpoint was occurrence of hyperalgesia/allodynia. The secondary endpoints were acute and late sensory changes between the two patient groups. Patients were blinded to the allocated treatment.


RESULTS
Twenty (100%) capsaicin and 16 (76%) placebo-treated patients were seen at the 2 1/2 year follow-up. Hyperalgesia was seen in five capsaicin- vs. one placebo-treated patient (P=0.2). The mechanical detection threshold was significantly increased on the operated side in the capsaicin vs. placebo group at the 1-week follow-up (P<0.05), but was not different at the 2 1/2 year follow-up (P=0.3). There were no other significant differences in sensory function on the operated side between groups at the pre-operative, 1-week or 2 1/2 year post-operative follow-up (P>0.05). The sensory function on the contralateral side was comparable between groups throughout the study (P>0.1).


CONCLUSIONS
This small-volume study calls for further long-term safety studies of wound capsaicin instillation.
Aasvang
E K
EK
Section of Surgical Pathophysiology, Copenhagen University, Rigshospitalet, Copenhagen, Denmark. eskeaasvang@yahoo.dk
Hansen
J B
JB
Kehlet
H
H
D000293:Adolescent; D000328:Adult; D000368:Aged; D000700:Analgesics / Q000008:administration & dosage / Q000627:therapeutic use*; D002211:Capsaicin / Q000008:administration & dosage / Q000627:therapeutic use*; D004311:Double-Blind Method; D005500:Follow-Up Studies; D006552:Hernia, Inguinal / Q000601:surgery; D006801:Humans; D006930:Hyperalgesia / Q000209:etiology; D007322:Instillation, Drug; D007430:Intraoperative Care; D008297:Male; D008875:Middle Aged; D009412:Nerve Fibers / Q000187:drug effects; D010147:Pain Measurement; D017288:Pain Threshold / Q000187:drug effects; D010149:Postoperative Pain / Q000517:prevention & control*; D010919:Placebos; D011312:Pressure; D012677:Sensation / Q000187:drug effects; D018689:Sensory System Agents / Q000008:administration & dosage / Q000627:therapeutic use*; D012684:Sensory Thresholds / Q000187:drug effects; D013526:Surgical Mesh; D013697:Thermosensing / Q000187:drug effects; D014110:Touch / Q000187:drug effects; D016896:Treatment Outcome; D055815:Young Adult
D000700:Analgesics; D010919:Placebos; D018689:Sensory System Agents; D002211:Capsaicin