AS is a progressive, inflammatory form of arthritis affecting the axial skeleton (spine) and nearby joints.

The chronic inflammation over time can cause the vertebrae in the spine to fuse together. As a result, the spine will be less flexible.

As the disease progresses, the spine loses its flexibility, and back pain may get worse. AS can also affect other areas of the body besides the joints, including the eyes, heart, and gastrointestinal (GI) system.

Understanding the possible complications of AS as it progresses can help you prepare for the future. Be sure to talk with your doctor if any new symptoms come up.

If left untreated, chronic inflammation can cause the vertebrae in your spine to fuse together. When this happens, your spine may become less flexible and more rigid.

You may have decreased range of motion when:

  • bending
  • twisting
  • turning

You may also have greater and more frequent neck and lower back pain.

When AS becomes very advanced, you may develop a stooped posture. If bones in the neck fuse together, you may have problems looking straight ahead or turning your head fully.

The inflammation isn’t limited to your spine and vertebrae. It can involve other nearby joints, including your:

  • hips
  • shoulders
  • ribs

Inflammation can also cause pain in your peripheral joints (the joints in your arms and legs). This may cause more pain and stiffness in your body.

The inflammation may also affect the tendons and ligaments that connect to your bones, which may make moving your joints increasingly difficult.

Iritis, also called anterior uveitis, is a type of eye inflammation that about 50% of people with AS experience.

If inflammation spreads to your eyes, you may develop:

  • eye pain
  • sensitivity to light
  • blurred vision

Iritis is typically treated with topical corticosteroid eye drops and needs immediate medical attention to prevent lasting damage.

Although the main area of inflammation with AS is the spine, pain and joint damage may also occur in the:

  • jaw
  • chest
  • neck
  • shoulders
  • hips
  • knees
  • ankles

According to the Spondylitis Association of America, about 15% of people with AS have jaw inflammation, which can affect chewing and swallowing.

A 2019 study of 120 participants with AS found that about 86% experienced fatigue. Brain fog and a general lack of energy are also common.

A number of factors can contribute to this, such as:

  • anemia
  • loss of sleep from pain or discomfort
  • muscle weakness forcing your body to work harder
  • depression or other mental health issues
  • certain drugs used to treat arthritis

Treating fatigue often requires a complex approach because it can have multiple causes. More than one treatment might be needed, and it may take time to find the right method that works for you.

Osteoporosis is a common complication for people with AS. It causes weakened bones. Up to half of all people with this condition will develop osteoporosis.

Damaged, weakened bones may break more easily. For people with AS, this is especially true in the spine’s vertebrae.

The risk of fractures in your spinal bones is due to a combination of a stiff spine and low bone density. Fractures in your spine may damage your spinal cord and the nerves connected to it.

If you have AS, it’s important you’re screened for bone loss early and often. Your doctor will use dual-energy X-ray absorptiometry (DEXA or DXA) scans to diagnose osteoporosis. Ideally, they’ll also use newer imaging techniques and systems.

AS has been associated with a number of cardiovascular diseases, including:

  • aortitis, or inflammation of the aorta, your body’s main artery
  • aortic valve disease
  • conduction disorders, or problems with your heart’s rhythm
  • cardiomyopathy, a disease affecting the heart muscles
  • ischemic heart disease, also called coronary artery disease

Inflammation can affect your heart and aorta. Over time, the aorta may become enlarged and distorted as a result of inflammation. A damaged aortic valve may impair your heart’s ability to function properly.

Talk with your doctor as soon as possible if you have any chest pain.

Up to 60% of people with AS experience inflammation of the GI tract, but not all show symptoms. Those who do develop symptoms may experience:

  • stomach pain
  • diarrhea
  • other digestive problems

Lasting GI symptoms may eventually lead to a diagnosis. AS has links to:

  • inflammatory bowel disease
  • ulcerative colitis
  • Crohn’s disease

Complications within the lungs are less common, but they do happen. They include:

  • stiffening (fibrosis) of the upper lobes of the lungs
  • interstitial lung diseases caused by scarring in the lungs
  • ventilatory impairment, or less efficient breathing
  • sleep apnea
  • collapsed lungs

If your posture is affected by AS, it may also make it harder to expand your chest to take deep breaths.

Cauda equina syndrome (CES) is a rare, debilitating neurological complication of AS that mostly occurs in people who’ve had AS for many years.

CES can disrupt motor and sensory function in the lower legs and bladder. It can even cause paralysis, or the loss of ability to move parts of the body.

People with AS who go on to develop CES may experience:

  • low back pain that radiates down the leg
  • numbness or reduced reflexes in the legs
  • loss of feeling in the groin and buttocks
  • sexual dysfunction
  • loss of control over the bladder or bowels

Amyloidosis is a rare complication of AS that occurs when a protein called amyloid builds up in your tissues and organs, such as the heart, liver, or kidneys. Amyloid isn’t naturally found in the body and can cause organ failure.

While rare, kidney amyloidosis is the most common kidney complication found in people with AS.

If amyloid builds up in the kidneys, you’re at a higher risk of developing kidney disease that requires dialysis.

One 2021 study found that people with AS were over six times more likely to develop amyloidosis than a control group.

Ideally, you and your doctor will discover and diagnose AS early. Starting treatment early on can help you reduce symptoms and lessen the chance of possible long-term complications.

However, not everyone will be diagnosed with the condition at an early stage. It’s important to see your doctor if you’re experiencing back pain and are unsure of the cause.

If you’re diagnosed with AS and start experiencing new symptoms, you should also check in with your doctor. These include:

  • worsening stiffness or pain
  • changes to your vision
  • chest pain
  • stomach issues
  • breathing problems
  • loss of feeling or control in your lower limbs

Be sure to keep up with regular screenings and visits with your doctor so you can identify any possible complications as early as possible.