Undifferentiated spondyloarthritis (USpA) is a term used to describe symptoms and signs of spondylitis in someone who does not meet the criteria for a definitive diagnosis of AS or a related disease. Sometimes a doctor may make an initial diagnosis of “spondyloarthritis” or “unclassified spondyloarthritis” if certain spondylitis symptoms are present but are not distinctive enough to make a specific diagnosis.
For example, an adult may have iritis, heel pain (enthesitis), and knee swelling, WITHOUT back pain, psoriasis, a recent infection, or intestinal symptoms. This person’s combination of disease features suggests spondyloarthritis, but they don’t neatly fit into the categories of ankylosing spondylitis, psoriatic arthritis, reactive arthritis, juvenile spondyloarthritis, or enteropathic arthritis. Over time, some people with USpA will develop a more well-defined form of spondylitis such as ankylosing spondylitis.
Many people with USpA have been told over the years that they are simply “anxious and depressed” or received a diagnosis of fibromyalgia, a chronic disorder associated with widespread muscle and soft tissue pain.