PainSci summary of Kennedy 2010?This page is one of thousands in the PainScience.com bibliography. It is not a general article: it is focused on a single scientific paper, and it may provide only just enough context for the summary to make sense. Links to other papers and more general information are provided at the bottom of the page, as often as possible. ★★★☆☆3-star ratings are for typical studies with no more (or less) than the usual common problems. Ratings are a highly subjective opinion, and subject to revision at any time. If you think this paper has been incorrectly rated, please let me know.
Ever wish you could get rid of some nerve endings? It turns out that you can — just apply chili peppers! This experiment showed that nerve endings shrivel away from an application of capsaicin, the active ingredient in peppers. The effect was quite dramatic.
Healthy volunteers took one for the team: a single application of highly concentrated capsaicin on their thighs, for just one hour. The density of nerve endings and sensitivity to various stimuli was recorded before and after, and then checked again after 1 and 12 and 24 weeks. The results were amazing: nerve ending density was down 80% after a week, and pain sensitivity was also reduced (though much less). Touch sensitivity reduced slightly, and heat and cold sensation remained normal.
Over the next several weeks, the nerves regenerated and sensation returned to normal. Given this surprisingly potent effect on nerve endings, capsaicin may be an effective and safe way to treat some pain problems.
original abstract†Abstracts here may not perfectly match originals, for a variety of technical and practical reasons. Some abstacts are truncated for my purposes here, if they are particularly long-winded and unhelpful. I occasionally add clarifying notes. And I make some minor corrections.
Desensitization of nociceptive sensory nerve endings is the basis for the therapeutic use of capsaicin in neuropathic pain syndromes. This study evaluated the pharmacodynamic effects of a single 60-minute application of NGX-4010, a high-concentration (8% w/w) capsaicin patch, on both thighs of healthy volunteers.
Epidermal nerve fiber (ENF) density and quantitative sensory testing (QST) using thermal, tactile, and sharp mechanical-pain (pinprick) stimuli were evaluated 1, 12 and 24 weeks after capsaicin exposure. After 1 week, there was about an 80% reduction of ENF density compared to unexposed sites. In addition, there was about an 8% increase in tactile thresholds compared to baseline and the proportion of stimuli reported as sharp mechanical pain decreased by about 15 percentage points.
Twelve weeks after exposure to capsaicin, ENF regeneration was evident, but not complete, and sharp mechanical-pain sensation and tactile thresholds did not differ from unexposed sites. Nearly full (93%) ENF recovery was observed at 24 weeks. No statistically significant changes in heat- or cold-detection thresholds were observed at any time point. NGX-4010 was generally well tolerated. Transient, mild warming or burning sensations at the site of application were common adverse effects.
PERSPECTIVE: This article evaluates the effect of a single 60-minute NGX-4010 application on ENF density and QST in healthy volunteers followed for 24 weeks. The results help predict the long-term safety of NGX-4010 applications in patients.
- “Topical capsaicin (high concentration) for chronic neuropathic pain in adults,” Sheena Derry, Andrew Sven-Rice, Peter Cole, Toni Tan, and R Andrew Moore, Cochrane Database of Systematic Reviews, 2013.
These two articles on PainScience.com cite Kennedy 2010 as a source:
- PS Heat for Pain — A detailed guide to using heat as therapy for acute and chronic pain
- PS Frozen Shoulder Guide — An extremely detailed & readable guide to one of the strangest of all common musculoskeletal problems, for both patients and pros
This page is part of the PainScience BIBLIOGRAPHY, which contains plain language summaries of thousands of scientific papers & others sources. It’s like a highly specialized blog. A few highlights:
- A Bayesian model-averaged meta-analysis of the power pose effect with informed and default priors: the case of felt power. Gronau 2017 Comprehensive Results in Social Psychology.
- The neck and headaches. Bogduk 2014 Neurol Clin.
- Agreement of self-reported items and clinically assessed nerve root involvement (or sciatica) in a primary care setting. Konstantinou 2012 Eur Spine J.
- Effect of NSAIDs on Recovery From Acute Skeletal Muscle Injury: A Systematic Review and Meta-analysis. Morelli 2017 Am J Sports Med.
- Association of Spinal Manipulative Therapy With Clinical Benefit and Harm for Acute Low Back Pain: Systematic Review and Meta-analysis. Paige 2017 JAMA.