The most common symptom of ankylosing spondylitis (AS) is low back pain and stiffness due to inflammation. This usually begins around the sacroiliac joints, where the lower spine joins the pelvis. It may take days or weeks to develop.

Inactivity tends to make symptoms worse, and many patients experience back pain in the middle of the night and may feel stiff in the morning. Movement and exercise tend to reduce symptoms.

As the disease progresses, it may cause inflammation in the upper spine, chest and neck. As the inflammation associated with AS persists, new bone forms during the healing process, causing the vertebrae to grow together. This results in the formation of bony outgrowths (syndesmophytes) that cause the spine to become stiff and inflexible. This process can also occur in the rib cage, restricting lung capacity and function.

Other joints that may become inflamed include the hips, shoulder, knees or ankles. In some cases, the heels are affected and the patient may find it uncomfortable to stand or walk on hard surfaces. In other cases, inflammation can reach the heart, increasing the risk of heart problems. The severity of symptoms and level of disability triggered by AS vary from person to person.

Symptoms associated with more advanced cases of AS include:

• Restricted expansion of the chest and chest pain
• Chronic stooping
• Stiff, inflexible spine
• Loss of lateral flexion (bending sideways)
• Tenderness over the sacroiliac joint
• Fatigue
• Loss of appetite
• Unexplained weight loss
• Bowel inflammation
• Inflammation of the iris (iritis) and eye pain

Patients may have other symptoms if the heart or lungs are involved.