In Reply:—

We are gratified to learn that Arndt et al.  1and Handwerker et al.  2have observed independently the dramatic increase of pain caused by tourniquet inflation above a capsaicin injection site. Their description of the response is consistent with our findings and encourages further investigation to determine its clinical relevance. Drs. Holthusen and Arndt’s suggestion that pain is caused by the spread of capsaicin to the paravascular space does not explain the sudden onset of pain, which occurs within seconds of tourniquet inflation. We agree that capsaicin may spread from the site of injection to the area around some blood vessels (small vessels must be in the injection area), but we expect this entirely extravascular spread to be an ongoing process not increased by tourniquet inflation. Alternatively, capsaicin taken up into veins might diffuse out of the vein after venous occlusion, as shown in the article by Arndt et al. , 1but we would expect this to begin after minutes, not seconds.

1.
Arndt JO, Kindgen-Milles D, Klement W: Capsaicin did not evoke pain from human hand vein segments but did so after injections into the paravascular tissue. J Physiol 1993; 463: 491–9
2.
Handwerker HO, Ringkamp M, Schmelz M: Neurophysiological Basis for Chemogenic Pain and Itch, Touch, Temperature and Pain in Health and Disease: Mechanisms and Assessments, vol 3, Progress in Pain Research and Management. Edited by Boivie J, Hansson P, Lindblom U. Seattle, IASP Press, 1994, pp 195–206