Untreated Lyme disease, which is caused by a bacterium, may progress to infectious arthritis, causing joint pain and swelling. Even at this stage, Lyme disease can be treated. However, no one knows for sure what causes the majority of cases of arthritis. Research already has greatly improved the understanding of arthritis and has provided many useful treatments. People of all ages, including children and young adults, can develop arthritis.
Some people seem to inherit a tendency to develop certain kinds of arthritis.
Research indicates that there may be a subtle defect in their immune systems. Perhaps arthritis is more easily triggered by something, such as a virus, in these people. Proper treatment depends on which disease is present. Different types of arthritis can be hard to tell apart and can affect people differently. No matter which type of arthritis is present, treatment works best when it is begun early in the disease.