by David Borenstein, MD
Although the term “arthritis” means “joint inflammation,” for most people the most common symptom of arthritis is pain. Whether arthritis is caused by cartilage breakdown (osteoarthritis, or OA) or a disordered immune system (rheumatoid arthritis, or RA), sooner or later it will cause pain. This article takes a look at the different types of pain that arthritis can cause and how various drugs are used to treat them.
Pain is defined as an unpleasant sensory and emotional experience that is brought on by damage — or the perception of damage — to the body’s tissues. But how does pain actually work in the body? The question has been asked for centuries. Today, our knowledge of the pain process is much more sophisticated than it was at the time of French philosopher René Descartes, who thought there was a single thread that attached a portion of each limb to the brain. This simplistic notion has been replaced by a model of complex nerve interconnections working together with chemicals produced by the nerves and surrounding tissues. These nerves and chemicals transmit pain signals from the site of tissue damage to the spinal cord and then the brain, where the signals are processed into physical sensations of pain. The communication chain by which pain signals are transmitted is known as a “pain pathway,” although, as we will see, there are different pathways for different types of pain.
The nervous system’s communications about pain don’t only travel one way — signals also travel back down the spinal cord, and some of these signals work to reduce pain. Pain-reducing signals travel along a “pain inhibitory pathway,” in which the nervous system produces pain-relieving chemicals. Endorphins, which block the transmission of pain signals to the brain, are among these chemicals. Increased activity in the pain inhibitory pathway decreases pain and promotes a feeling of well-being. For example, people with chronic pain experience less pain when they exercise regularly because exercise releases endorphins. The nerves in the pain inhibitory pathway also release the chemicals serotonin and norepinephrine in response to exercise. These chemicals, like endorphins, are thought to decrease pain, and medicines that increase levels of serotonin and norepinephrine have been shown to be effective in relieving pain.
There are many ways to describe the characteristics of pain. One can talk of the onset of pain (when and how it begins), its location (where it is), its duration (how long it lasts), and its quality (what it feels like). In this article, I will concentrate on the duration and the quality of pain. Pain of short duration — that is, pain that lasts only a short time — is called acute pain. Long-lasting pain is chronic pain. Understanding the difference between acute and chronic pain can help determine which drug or combination of drugs will work best for your arthritis.
Acute pain. Acute pain acts as a warning sign that you have an injury. When an injury occurs, the body releases a specific array of chemicals that signal tissue damage. These chemicals cause a part of your nervous system to recognize the injury immediately, which in turn causes the muscles to react in an attempt to limit the damage. This is the system that pulls your hand away when you touch a hot stove.
These acute events do not have a long-term effect on the nervous system. For example, you may have severe acute pain caused by an attack of gout. But once the attack is over, the pain goes away and the affected joint returns to feeling normal.
Chronic pain. In contrast, chronic pain does bring about changes to the nervous system that affect how you feel pain. Chronic pain was once thought to be acute pain that continued well beyond the period for normal healing. It was assumed the “acute” chemicals released in response to acute pain were simply being released over a longer period. However, research has shown that chronic pain involves a different set of chemicals and that chronic pain signals travel along a separate pathway to the brain. In addition, chronic pain can cause changes to structures within the nervous system, and these changes can increase sensitivity to painful stimuli. Because of these changes, chronic pain may persist even when there is no injury or after an initial injury has healed.
Another difference between acute pain and chronic pain is that chronic pain has effects on parts of the brain associated with emotions and mood. Chronic pain may therefore contribute to stress, anxiety, and depression.
For the purposes of discussing pain, the different forms of arthritis can be divided into two basic categories. In one category are the conditions that cause body-wide inflammation that includes the joints. RA is the prime example of this group; systemic lupus erythematosus is another well-known example. In the other category are conditions that involve a minimal amount of inflammation in the joints. OA is in this group.
Last Reviewed on June 15, 2011
David Borenstein is a rheumatologist and Clinical Professor of Medicine at The George Washington University Medical Center in Washington, DC. He is the chairman of the American College of Rheumatology’s Pain Management Task Force.
Get the latest arthritis news and the most useful self-management tips delivered to your inbox twice a month! Sign up for our free e-mail newsletter today.
Statements and opinions expressed on this Web site are those of the authors and not necessarily those of the publishers or advertisers. The information provided on this Web site should not be construed as medical instruction. Consult appropriate health-care professionals before taking action based on this information.