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People suffering from inflammation have lower pain thresholds and therefore experience pain quicker. This is concluded by scientists from the Radboudumc in the Netherlands. “Everybody will recognize this form everyday life. This relationship is proven for the first time in humans by using  a combination of unique models”, says Professor Peter Pickkers, researcher and Professor of Experimental Intensive Care Medicine at the Radboudumc.

Pain threshold
Systemic inflammation in the human body lower the pain threshold by 15 till 20 percent, the researchers (link 1) conclude. This explains why our body is more sensitive for pain during the flu or a cold compared to when healthly. Pickkers and his colleagues of the department of Anesthesia and Intensive Care combined two special models: an injection of endotoxin of E. coli bacteria and various types of pain threshold measurements. Pickkers: “So far, this combination of methods can only be implemented in the Radboudumc.”

For this study, 47 subjects got their pain thresholds tested twice with three tests.  "They were given a test were pressure was exerted on parts of the body where the bone is close to the skin, a test with electrodes and a test with ice water. Meanwhile, the subjects had to indicate when something began to feel sore. For them, that point is the pain threshold”, according to Pickkers.

Endotoxin injection
Subsequently, intravenous administration of E. coli endotoxin in 27 of the 47 healthy volunteers took place. Two hours later, when the inflammatory response was at his highest point, all 47 subjects underwent the pain thresholds tests again. “After this test, we clearly saw a decreased pain threshold in the endotoxin-treated subjects. In the control group, we saw no difference”, says Pickkers.

Isolating, purifying and injecting a part of the cell wall of a bacterium is an almost unique concept. Pickkers: “This method is operational in just a few centers worldwide. To get a hundred percent security, the logistics and other conditions must be very well organized.”

New focus for pain medication
Not only do Pickkers and his colleagues prove the existence of the relationship between the reduced pain threshold and inflammatory activity, they also see it as a starting point for research into another group of pain medication. “We know that pain during inflammation is difficult to reduce with medication such as morphine. Because we now know that humans experience pain faster during inflammation, it is important to focus research on medication defeating the inflammatory proteins that cause the pain rather than the pain itself. Eventually, pain management may become a lot more effective.”

Source:
de Goeij M, van Eijk LT, Vanelderen P, Wilder-Smith OH, Vissers KC, et al. (2013) Systemic Inflammation Decreases Pain Threshold in Humans In Vivo. PLoS ONE 8(12): e84159. doi: 10.1371/journal.pone.0084159