There is no direct link between rheumatoid arthritis and fibromyalgia. Neither condition is known to cause the other. However, both are relatively common, so a person could have both conditions. In addition, some research studies have found an increased incidence of fibromyalgia among people with rheumatoid arthritis. This suggests that having rheumatoid arthritis may be a risk factor for fibromyalgia.

Rheumatoid arthritis causes chronic inflammation in multiple joints. The joints (especially of the hands and wrists) become swollen and warm, and have a limited range of motion. If this isn't treated, joint damage commonly develops over time. Rheumatoid arthritis can also affect the lungs, eyes and other organs. Treatment can protect the joints and prevent complications.

There is no inflammation in fibromyalgia. People with this condition have widespread pain in their muscles and joints, but the joints move normally and are not swollen. Instead, they have multiple sore areas (called tender points) that feel like bruises. These can be over the upper chest, back, arms and legs. Poor-quality sleep is common among people with fibromyalgia.

New cases of rheumatoid arthritis and fibromyalgia are most common among young and middle-aged women. Because these conditions are long lasting (chronic) and commonly begin early in adulthood, there are many people who will eventually have both. The cause of both conditions is unknown.