Chronic pain is the worst houseguest ever, sticking around long after it arrives and making it tough to carry on with your life and activities. The difference is you can send your houseguest home. Sending chronic pain packing isn’t as easy.

Most people view pain as having an underlying cause; treat the cause, and the pain should disappear. According to this theory, getting rheumatoid arthritis, RA, under control should get pain under control. And replacing a joint damaged by osteoarthritis, OA, should eliminate pain in that joint.

Often, these measures work. Taking disease-modifying drugs and having joints replaced can give people their lives back, eliminating or drastically reducing pain.

But as too many people with well-controlled RA and/or artificial joints know, pain often lingers. And because it’s not well understood why that happens, effective treatment can be elusive.

“Chronic pain is a very difficult problem for doctors to [help patients] with,” says David Borenstein, MD, clinical professor of medicine at The George Washington University Medical Center in Washington, D.C., and head of the Pain Management Task Force for the American College of Rheumatology. “If you have acute pain – a broken bone, say – you can diagnose and treat it. But if you’ve had the same pain for five years and nothing has worked, the pain has become ingrained in your psyche and physiology. Its home isn’t in the various [body parts] that may have been the pain’s initial starting point.”

That may be because chronic pain turns independent, essentially becoming its own disease. “If you have inflammation in RA that hurts over long periods, that pain message is always being sent to the brain,” says psychologist Afton L. Hassett, an associate research scientist at the Chronic Pain and Fatigue Research Center, University of Michigan Medical School in Ann Arbor. “Because of the plastic nature of the central nervous system [CNS], those very neurons that carry the message begin to change, and probably become more efficient messengers.”

The upshot? Your brain may begin to misread a small message of pain as a big one. Doctors call this “centralized pain.”

A Quest For Answers

Hassett and other researchers are trying to figure out which patients will have this kind of pain response and why, and OA is a good basis for study. “Cartilage doesn’t have [nerves], so a key area of damage – the cartilage – is not directly causing pain,” says Jacqueline Hochman, MD, assistant professor of rheumatology at the University of Toronto. In OA, damage to joints doesn’t always correlate with symptoms;

X-rays can show significant joint damage, but a person may feel little pain – or vice versa.