Pain Mechanisms

So much for the storied Las Vegas nightlife. PAINWeek 2010 attendees apparently retired early Tuesday evening, judging by the standing-room only attendance at “Pain Mechanisms,” one of the five concurrent sessions to open PAINWeek 2010 Wednesday morning. The speaker, David M. Glick, DC, DAAPM, CPE, set the stage for the show through an overview session that he called “Pain management-lite.”

You have to lay the groundwork to set the stage for what happens later,” said Glick. “If we have the fundamental story, we can follow everything else. I’m going to lay the foundation. Even if you know the material, it might help you find an area you have greater interest in as you look at the other sessions.”

Glick then proceeded to give a 30,000-foot overview presentation that was ideal for the primary care physician who treats patients in pain and most likely prescribes many medications that they don’t fully understand. “Pain mechanisms can be very complicated,” Glick said. “We could have a meeting called Pain Mechanisms Week, and we wouldn’t even scratch the surface. That’s daunting.”

The picture Glick painted of the pathways and receptors of pain revealed exactly why pain management is such a difficult and complicated field. In short, it’s because of the nature of good and pain. “Some pain is good; it’s purposeful—it’s a warning sign,” Glick said. “If I have a heart attack, I want pain to let me know there’s a problem. Pain can be good.”

Nociceptive pain is pain with a purpose, pain of perception. If you touch something hot, you have to remove yourself from it. “I’m always looking for the pain generator. I’m proverbially looking for the spear in the foot. I’m going to have trouble managing that pain if the spear is there. If you can remove the cause, alleviating the pain becomes a lot easier.”

Bad pain is pain that doesn’t have a purpose—often, pain linked to disorder, illness, or damage. “It’s like a car that’s out of tune,” said Glick. “There’s an error somewhere in the system.”

Within the category of “bad pain,” Glick further identified two types: Neuropathic pain, and functional pain. The latter, according to Glick, is the most recent area of discovery and includes pain conditions that don’t fall into the inflammatory category, such as fibromyalgia and irritable bowel syndrome. “The majority of the advances and change in pain management is going to come in these last two categories,” he said.

Glick then went into some detail on the transduction, conduction, transmission, and perception of pain. Transduction is simply the conversion of one signal to another, like a pain stimulus. Conduction takes the signal to the spine, like a conductor taking a passenger from one place to another. Transmission takes the signal from the nerves to the brain. Once in the brain, perception occurs.

“People perceive pain different ways,” Glick remarked. “There’s an emotional component involved in it. You can have a patient with a paper cut and ask him to rate his pain on a scale from 1 to 10, and they’ll tell you it’s a 15. Another patient with a knife to the abdomen might describe his pain as a 2, because it could be a lot worse.”

Perhaps the most interesting aspect of Glick’s talk was the role that evolution (or intelligent design, Glick was careful to mention) plays in the difficulty of treating pain. For example, he walked through the number of different ways that nociceptors transmit signals to the spine. This intentional redundancy has a powerful purpose in sustaining human life—responding to good pain, if you will. But it creates many challenges to treating pain at its source, because the many signals a medication would need to block are so numerous and varied. “Nociceptors are mediated by many things,” Glick said. “There is a lot going on under the skin.”

Glick said that the difficulty associated with blocking pain from all of those mediators means a multimodal approach is needed—what he calls “rational polypharmacy.”

Why is pain management so complicated? “There are lots of overlapping things happening at the same time, each of which react in their own way,” he said. “Many of the current treatments focus on modulation. We’ve decided we can control this pain better than the body can. If that was true, would we be here? No, because we’d have the solution. We’re just making a dent in it.”