Ankylosing spondylitis (AS) is a rare type of arthritis that causes inflammation, pain, and stiffness in the joints of the spine. It is a lifelong condition that usually begins in early adulthood.
The symptoms start out as lower back pain but could spread to other parts of the body, including the neck, hips, ribs, shoulder joints, and sometimes the heels.
But many other common conditions can have the same type of symptoms. That could make it harder for a doctor to diagnose you with AS. Here are some of the conditions that your doctor may try to rule out before they know that you have AS.
Muscle pain. At some point, almost everybody will have aches in their lower back, neck, hips, or shoulders -- the same areas where AS symptoms can appear. Everyday muscle pain can happen for many reasons, including tension, overuse, and minor physical injuries. But muscle pain with prolonged morning stiffness that doesn’t get better after a few days or weeks could be a sign of a disorder like AS.
Spinal disk problems. Trouble with any of the rubbery cushions that sit between the bones in your spine could cause symptoms that match AS, especially lower back pain. A herniated disk, for example, happens when one of your spinal disks, usually in the lower back, pushes out and irritates a nearby nerve. Imaging tests like X-rays, CT scans, and MRI can help your doctor look for a spinal disk problem or for changes in bones and joints that point to AS.
Back injuries. You can injure your back from a whole host of physical activities. You might get a mild strain from playing sports or lifting heavy objects. A bad fall or a car accident could cause more severe injuries such as a fractured spine. But like AS, the lower back is the commonly affected area. The pain from the injury could eventually spread to other parts of the body and affect how well you can move. If you already have AS, back injuries could be more severe than they would be for someone without the condition.
Sciatica. Sciatic nerves are the long, thick nerves that run from your lower back and buttocks down each of your legs. When one of them gets compressed, irritated, or pinched by conditions like a herniated disk, you will have mild to severe pain, called sciatica. You might feel it in your low back. It can also cause muscle weakness, pain, and a tingling “pins and needles” feeling in one or both of your legs and feet. Conditions like AS, fracture in the spine, spinal disk problems, scar tissue, infection, and pregnancy are some of the causes of sciatica.
Osteoarthritis. It’s the most common form of arthritis. It happens as the cartilage within your joints starts to break down, making bones rub together. It usually begins very slowly and gets worse over time. OA mostly affects the hips, knees, lower back, and hands. It causes pain, swelling, and stiffness, which makes it hard for you to do everyday tasks. Unlike AS, OA affects more women than men and is more common as people get older, often showing up in your 50s.
Fibromyalgia. People with this condition have widespread pain all over their body. You may feel numbness and tingling in your hands and feet; pain in your low back, face, or jaw; or even digestive issues like bloating, constipation, belly pain, and irritable bowel syndrome. It is possible to have fibromyalgia and AS at the same time. Unlike AS, fibromyalgia will not cause physical signs or changes that show up on imaging exams like X-rays.