Ankylosing spondylitis (AS) is a chronic, progressive type of arthritis that affects the spine and the joints in the pelvis and the lower extremities. It causes inflammation of the joints between the vertebrae in the spine, leading to the fusion of the bones and a decrease in the range of motion of the spine. Symptoms include pain and stiffness of the spine, low back pain, fatigue, and limited mobility. In some cases, AS can also affect other organs, such as the eyes, heart, lungs, and kidneys. Treatment for AS usually involves medications, such as non-steroidal anti-inflammatory drugs (NSAIDs), to reduce pain and inflammation, physical therapy to help maintain function and mobility, and exercise to strengthen the muscles surrounding the spine.