Most back pain isn’t caused by ankylosing spondylitis (AS). However, the symptoms, especially in the early stages, can be very similar to more common back problems. Because of this, many people put up with the pain for some time before seeking help. When you first see your doctor, there may be little to show whether the problem is ankylosing spondylitis or some other, more common, back problem. Unfortunately, ankylosing spondylitis may even be misdiagnosed at first. Ankylosing spondylitis is normally diagnosed by a rheumatologist.

Source: Diagnosis