Undifferentiated spondyloarthritis (USpA) is reportedly the most difficult disease to diagnose in the spondylitis family and consequently eludes a correct diagnosis in many patients who have it. USpA is the least well known of the group and is still unrecognized by some physicians. Sometimes a doctor may make an initial diagnosis of “spondyloarthritis” or “unclassified seronegative spondyloarthritis” if certain symptoms are present, but are not enough to make a specific diagnosis. Sadly, people with USpA may initially hear that they are “anxious and depressed” or receive a diagnosis of fibromyalgia, which is a chronic disorder associated with widespread muscle and soft tissue pain.
A person with USpA may have signs and symptoms of spondylitis that do not quite fit into a specific category. For example, someone may have (or have experienced) iritis and heel pain, as well as being HLA-B27 positive, but initially not have the SI joint or spinal involvement associated with ankylosing spondylitis.
A rheumatologist is commonly the type of physician who will diagnose USpA, since they are doctors who are specially trained in diagnosing and treating disorders that affect the joints, muscles, tendons, ligaments, connective tissue, and bones. A diagnosis of USpA normally comes after a physical exam, laboratory tests, and X-rays.
The differences in diagnostic criteria between ankylosing spondylitis and undifferentiated spondyloarthritis include:
The diagnostically helpful tissue type gene called HLA-B27, seen in the majority of people with ankylosing spondylitis, is commonly absent in undifferentiated spondyloarthritis. Approximately 20-25 percent of people with USpA test positive for HLA-B27.
While X-ray of the pelvic region (where the sacroiliac joint is located) is essential for diagnosis in AS, subtle erosions do not always show in X-rays of those with USpA.
Symptoms of inflammatory spinal pain are the first clues of AS, which is not necessarily the case in people with USpA. However, oftentimes women with any form of spondylitis feel primary pain in a different area of the body than the spine or lower back. Subsequently, a misdiagnosis of fibromyalgia is too often made in women with undifferentiated spondyloarthritis, who present with diffuse muscle aches and pains, without any measurable lab or X-ray abnormalities.
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