BERLIN - June 11, 2004 - Understanding the mechanisms involved in chronic pain and treating it as effectively as possible is and will continue to be a crucial component to the management of rheumatoid arthritis and other inflammatory diseases, according to several experts who presented here June 9^th at the annual meeting of the European Congress of Rheumatology.

"We now recognize pain to be such an important issue with these diseases that this meeting is devoting an entire session across conditions to the issue," said Gerold Stuchi, MD, a rheumatologist who practices in Munich, Germany. Dr. Stuchi was a co-chair of the session.

A variety of biochemical substances in the peripheral tissues can excite the sensory neurons and elicit pain. Therefore, medical therapy that addresses these multiple substances is an important part of chronic pain management, said Christoph Stein, MD, a consultant in the department of anesthesia at Charite Campus Benjamin Franklin in Berlin. These substances include substance P, calcitonin gene-related peptide (CGRP), bradykinin, prostaglandins, cyclo-oxygenase-2 (COX-2), and histamine.

"The sensory nerve terminals are very different in the inflamed state compared to the non-inflamed state," said Dr. Stein. "The sodium and potassium channels increase in an inflamed state, as do the bradykinin and prostaglandin receptors." Fortunately, the number of opioid receptors also increases and therefore inhibits neuronal excitability and therefore tempers the perception of pain.

The standard medical therapies that are used to address pain in inflammatory diseases include the COX-2 inhibitors, conventional nonsteroidal anti-inflammatory drugs (NSAIDs), acetaminophen, opioids, and topical capsaicin. He noted that one study found acetaminophen comparable only to placebo in its ability to address inflammatory pain (Am Pn Soc, 2002), and that two studies had shown that systemic opioids such as oxycodone and codeine only have a pain reduction benefit of approximately 16 percent to 17 percent.

However, intra-articular injections of opioids may be as effective as steroid injections in reducing pain. Interestingly, some studies have shown that opioid injections cause a reduction in the number of inflammatory cells in the synovial fluid, Dr. Stein said. "Today's pain therapies are able to reduce excitatory nerve conduction and therefore address pain," he said. Because certain drug classes such as COX-2 inhibitors and NSAIDs are associated with different toxicity issues, the development of effective pain management with better tolerability is crucial, he said.

In other presentations in the session, experts addressed the brain mechanisms involved in chronic pain and the issue of widespread use of complementary therapies among people who live with chronic pain. Daniel Jeanmonod, MD, a rheumatologist at the University Hospital Zurich in Zurich, Switzerland, pointed to electroencelograph (EEG) studies that show that the thalamocortical network is involved in several chronic pain conditions, and that whether pain is neurogenic or somatogenic, a thalamocortical dysrhythmia is evident on the EEGs of people with chronic pain.

Edzard Ernst, MD, of the Peninsula Medical School of Exeter and Plymouth, United Kingdom, stressed that physicians who treat patients with chronic pain need to be aware and ask patients about their use of complementary therapies. "Approximately 80 percent of your patients are using these therapies and not telling you," he said. The most common types of complementary therapies used in chronic pain conditions include acupuncture, chiropractic treatments, herbal treatments, and homeopathy.