The names that are given to different kinds of arthritis can be very confusing, and I want to explain a little more about undifferentiated arthritis. It is considered undifferentiated because the arthritis is at such an early stage that it hasn’t turned into full-blown rheumatoid arthritis, psoriatic arthritis, or autoimmune arthritis such as Sjögren’s or lupus. Therefore, no diagnosis can be made other than that you have some form of arthritis that appears to be inflammatory. “Undifferentiated arthritis” is used to describe people who have had arthritis for six to twelve weeks but still don’t meet the criteria for any other knee arthritis diagnosis. This is an important category because 30 percent of people who go to their doctor with early arthritis will initially be diagnosed with UA. Of those, about 30 percent will end up with RA. The other 70 percent will end up with an assortment of diagnoses, including OA and autoimmune diseases.
Arthritis is a symptom that people often have as part of another autoimmune disease, especially systemic lupus erythematosus, Sjögren’s syndrome, and systemic sclerosis (scleroderma). These are called systemic autoimmune diseases because the affected tissues are spread throughout the body instead of being restricted to one particular organ, like we see in an autoimmune disease such as Hashimoto’s thyroiditis, for example, which is called an organ-specific autoimmune disease. In contrast to rheumatoid arthritis, these disorders have other systemic features, such as rashes, dry mouth and eyes, muscle pain, and kidney involvement. And so, while the joints may be involved, it is just one of many symptoms. People with RA usually test positive for inflammation, whereas in this group of autoimmune diseases, these tests are often normal or only mildly elevated. Additionally, the typical findings of morning stiffness, symmetric arthritis, and deformities that we usually see in rheumatoid arthritis are not present. The bottom line is that if you have arthritis, it is important to see your doctor to determine if your primary problem is a systemic autoimmune disease or inflammatory arthritis.