“What does "seronegative" mean?” “Can a patient's diagnosis change from undifferentiated spondyloarthritis to AS?” Read this Q & A with rheumy Dr. Jessica Walsh for anyone who may have missed it the first time. There are 5 other closely related conditions, in addition to AS, that belong to our messy family of diseases; sometimes it's difficult to distinguish one from another, and sometimes one can morph into another.















