Oh, the Pain! 3 new studies from the Journal of Pain

The latest Journal of Pain was a potpourri of pain science pleasers. Today I present moist summaries of three dry scientific papers about:

• why injuries go bad
• how to temporarily destroy your nerve endings with chili pepper (and why this is a good thing)
• the pain of being a drama queen

“Bio-psychosocial determinants of persistent pain 6 months after non-life-threatening acute orthopaedic trauma”

Clay et al. Journal of Pain. Volume 11, Number 5, p420-30. May 2010.

How often does injury lead to chronic pain? Why do some injured people develop chronic pain and others do not? Researchers kept tabs on 168 patients who suffered non-life-threatening orthopaedic injuries.

54% reported persistent pain six months after the injury and 87% reported that this pain interfered with their normal work activities.

Long-term pain was more likely to the extent that pain was acute at the beginning (independently of injury severity), if patients felt responsible for the injury, and if they were pessimistic or emotionally traumatized. “Psychosocial factors strongly predicted persistent pain, pain-related work disability, and pain severity,” the researchers concluded, and noted that “many of these factors are potentially modifiable and should alert the clinician about the need for interventions in order to prevent the development of pain chronicity.”

“A Randomized, Controlled, Open-Label Study of the Long-Term Effects of NGX-4010, a High-Concentration Capsaicin Patch, on Epidermal Nerve Fiber Density and Sensory Function in Healthy Volunteers”

Kennedy et al. Journal of Pain. Volume 11, Number 6, p579-587. Jun 2010.

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.

“Emotional Regulation and Acute Pain Perception in Women”

Ruiz-Aranda et al. Journal of Pain. Volume 11, Number 6, p564-569. Jun 2010.

This experiment presents clear evidence that “pain is an opinion”: an experience modified by mental and emotional factors.

I don’t think anyone will be surprised to learn that being a drama queen actually hurts. (“Drama queens,” of course, is exaggeration for comedic effect — please don’t actually call anyone in pain a drama queen unless you want to get smacked around.)

Two groups of women were tested for pain tolerance with the traditional, unpleasant method: immersion of the hands in ice water. One group was rated with better emotional coping skills, and (predictably) they were more tolerant of pain than women with poorer coping skills.

Although the results seem unsurprising, the authors say that “currently there are no experimental investigations of the relation between emotional regulation and pain.” Based on this study, it can be assumed that emotional state and skills are relevant to pain management.