Ankylosing spondylitis (AS) is a type of arthritis in which there is a long-term inflammation of the joints of the spine. Typically the joints where the spine joins the pelvis are also affected. Occasionally other joints such as the shoulders or hips are involved. Eye and bowel problems may also occur. Back pain is a characteristic symptom of AS, and it often comes and goes. Stiffness of the affected joints generally worsens over time.Although the cause of ankylosing spondylitis is unknown, it is believed to involve a combination of genetic and environmental factors. More than 85% of those affected in the UK have a specific human leukocyte antigen known as the HLA-B27 antigen. The underlying mechanism is believed to be autoimmune or autoinflammatory. Diagnosis is typically based on the symptoms with support from medical imaging and blood tests. AS is a type of seronegative spondyloarthropathy, meaning that tests show no presence of rheumatoid factor (RF) antibodies. It is also within a broader category known as axial spondyloarthritis.There is no cure for ankylosing spondylitis. Treatments may improve symptoms and prevent worsening. This may include medication, exercise, physical therapy, and surgery in rare cases. Medications used include NSAIDs, steroids, DMARDs such as sulfasalazine, and biologic agents such as TNF inhibitors.Between 0.1% and 0.8% of people are affected. Onset is typically in young adults. Males and females are equally affected. It used to be thought that three times as many men as women had the disease. This was based on a diagnosis of the disease using X-ray. Men are more likely than women to experience changes to the bones and fusion, and thus they were being picked up using X-ray. Over time MRIs were developed which could identify inflammation. Women are more likely than men to experience inflammation rather than fusion.The condition was first fully described in the late 1600s by Bernard Connor, but skeletons with ankylosing spondylitis are found in Egyptian mummies. The word is from Greek ankylos meaning crooked, curved or rounded, spondylos meaning vertebra, and -itis meaning inflammation.