Ankylosing spondylitis (AS) is a type of arthritis that causes inflammation in the joints of your lower back. Over time, it can damage all the joints and bones of your spine.

Pain and stiffness in your lower back and buttocks are the main symptoms of AS. This disease can also cause long-term problems in other parts of your body, including your eyes and heart.

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Illustration by Jason Hoffman

Your body tries to heal damage from AS by making new bone. These new segments of bone grow in between the vertebrae of your spine. Over time, the bones of your spine can fuse into one unit.

The joints between your spinal bones give you a full range of motion, allowing you to bend and turn. Ankylosing, or fusion, makes the bones stiff and hard to move. This creates what’s known as bamboo spine.

The extra bone can limit movement in the lower part of your spine as well as the movement of the mid and upper spine.

New bone formations that are caused by AS are weak and can easily fracture. The longer you’ve had AS, the more likely it is you might fracture a bone in your spine.

Osteoporosis is very common in people with AS. More than half of people with AS have osteoporosis, according to a 2016 study.

Your doctor can help you strengthen your bones and prevent fractures by prescribing bisphosphonates or other medications, and discuss lifestyle management options.

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Although your eyes are nowhere near your spine, inflammation from AS can affect them, too. The eye condition uveitis (also called iritis) affects between 20 and 30 percent of people with AS. Uveitis causes swelling of the uvea, the layer of tissue lying beneath the sclera (white part) and cornea of your eye.

Uveitis also causes redness, pain, distorted vision, and sensitivity to light, usually in one eye. If left untreated, it can lead to:

  • glaucoma
  • cataracts
  • permanent vision loss

Your eye doctor will prescribe steroid eye drops to decrease eye inflammation. Steroid pills and injections are also options if the drops do not work.

Also, if your doctor prescribes a biologic drug to treat your AS, it can be used to treat and possibly prevent future episodes of uveitis too.

Like other forms of arthritis, AS causes swelling in joints such as the hips and knees. Over time, damage can make these joints stiff and painful.

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Every time you breathe, your ribs expand to give your lungs enough room inside your chest. When the bones of your spine fuse, your ribs also become more rigid and are unable to expand as much. As a result, there’s less space in your chest for your lungs to inflate.

Some people also develop scarring in the lungs that limits their breathing. Damage to the lungs can make it harder to recover if you get a lung infection.

If you have AS, protect your lungs by not smoking. Also ask your doctor about getting vaccinated against lung infections such as pneumococcal pneumonia, the flu, and COVID-19.

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Inflammation can also affect your heart.

Anywhere from 2 to 10 percent of people with AS have some type of heart condition. According to research from 2019, living with AS makes you 1.44 times as likely to have a heart attack and 1.37 times as likely to have a stroke.

Sometimes heart problems start before AS is diagnosed:

Cardiovascular disease (CVD)

People with AS are at increased risk of cardiovascular disease (CVD). If you have CVD, you’re more likely to have a heart attack or stroke.

Aortitis and aortic valve disease

AS can cause inflammation in the aorta, the main artery that sends blood from your heart to the rest of your body. This inflammation and swelling is called aortitis.

Inflammation in the aorta can prevent the artery from carrying enough blood to the body. It can also damage the aortic valve — the channel that keeps blood flowing in the right direction through the heart. Eventually, the aortic valve may narrow, leak, or fail to work properly.

Medications can help address inflammation in the aorta. Doctors can treat a damaged aortic valve with surgery.

Irregular heartbeat

People with AS are more likely to have a fast or slow heartbeat. These irregular heart rhythms prevent the heart from pumping blood as well as it should. Medications and other treatments can bring the heart back to its normal rhythm.

Here are some ways you can protect your heart if you have AS:

  • Manage the conditions that can damage your heart. These include diabetes, high blood pressure, high triglycerides, and high cholesterol. A balanced diet, regular exercise, and medication, if you need it, can help manage these conditions.
  • Avoid smoking. The chemicals in tobacco smoke damage the lining of your arteries and contribute to the plaque buildup that can lead to a heart attack or stroke.
  • Lose weight if your doctor recommends it. People with overweight or obesity have more heart disease risks, such as high blood pressure and high cholesterol. The extra weight also puts more strain on your heart.
  • Exercise. Your heart is a muscle. Working out strengthens your heart in much the same way that it strengthens your biceps or calves. Try to get at least 150 minutes of moderate-intensity aerobic exercise each week.
  • Ask your doctor whether you should take tumor necrosis factor (TNF) inhibitors. These drugs treat AS, but they also may increase cholesterol levels, which contribute to heart disease.
  • See your doctor regularly. Have your blood sugar, blood pressure, cholesterol, and other numbers checked. Ask if you need an echocardiogram or other diagnostic tests to look for problems with your heart.

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This rare complication happens when there’s pressure on the cauda equina, a bundle of nerves at the bottom of your spinal cord. Damage to these nerves causes symptoms such as:

  • pain and numbness in your lower back and buttocks
  • weakness in your legs
  • loss of control over urination or bowel movements
  • sexual problems

See your doctor as soon as possible if you have symptoms such as these. Early treatment may help prevent permanent damage.

Amyloidosis is another rare complication of AS. It occurs when the protein amyloid builds up in tissues and organs such as the kidneys and heart.

Amyloidosis can cause a range of signs and symptoms, depending on which tissues and organs are involved. They include:

  • proteinuria, or protein in the urine
  • an irregular heartbeat
  • unintended weight loss
  • diarrhea
  • fatigue
  • carpal tunnel syndrome

Medications such as steroids and immunosuppressants can be used to help you manage your symptoms.

In some cases, AS can increase your risk of cancer.

A 2016 research review concluded that the cancer risk for people with AS was 14 percent higher than the cancer risk for people without AS. In particular, people with AS had higher rates of cancers affecting the digestive system, multiple myelomas, and lymphomas.

A 2017 study found that men with AS were more likely to develop prostate or bone cancer than men without AS. Women with AS were more likely to develop colon cancer than women without AS.

The researchers recommended that all people with AS receive cancer screenings within 3 years of their initial AS diagnosis. This is especially important if you’re under 35 years old and have certain severe comorbidities, as measured by the Charlson comorbidity index (CCI).

Eating a balanced diet and exercising regularly are just two of the steps you can take to help lower your cancer risk.

The best way to avoid these complications is to get treated for your AS.

Medications such as TNF inhibitors and nonsteroidal anti-inflammatory drugs (NSAIDs) can bring down inflammation in your body. They can help prevent damage to your bones, eyes, and other parts of your body before it can cause long-term problems.