Osteoporosis and Ankylosing Spondylitis

Reviewed by: HU Medical Review Board | Last reviewed: February 2019 | Last updated: May 2019

Osteoporosis is a condition in which the bones are weakened and brittle and at an increased risk of fracture. The word "osteoporosis" means porous bone.1 People with ankylosing spondylitis (AS) are at an increased risk of developing osteoporosis.

How common is osteoporosis among people with AS?

One study found that 21% of people with AS over the age of 50 in their research study met the criteria for osteoporosis, and another 44% had osteopenia - a condition where there is bone loss but not to the degree of osteoporosis. Osteopenia may develop into osteoporosis, and people with osteopenia are at an increased risk of osteoporosis.2,3

Osteoporosis is common in the general population. The National Osteoporosis Foundation estimates that approximately 54 million Americans have osteoporosis and osteopenia.1

How does AS put a person at greater risk for osteoporosis?

AS causes chronic inflammation in the joints, particularly in the spine. Over time, this inflammation wears away at the bone tissue. Bone is a living tissue that normally undergoes a process of old bone tissue breaking down and new bone tissue forming. However, in people with AS there is increased bone loss due to the chronic inflammation, as well as abnormal bone growth, which can cover ligaments (syndesmophyte formation) and fuse joints. The increased bone loss can lead to osteoporosis. In addition, the abnormal bone formation and fused joints reduce flexibility and also make the bones more fragile and more likely to fracture.2

More risks

In addition to AS, several other conditions can increase a person's risk of developing osteoporosis, including rheumatoid arthritis, lupus, multiple sclerosis, inflammatory bowel disease, celiac disease, breast cancer, prostate cancer, blood cancers, diabetes, hyperthyroidism, menopause, and chronic obstructive pulmonary disease (COPD).1

Some medicines can cause bone loss and increase the risk of developing osteoporosis, including certain chemotherapy drugs, methotrexate, corticosteroids, proton pump inhibitors, and selective serotonin reuptake inhibitors (SSRIs). Patients should talk to their healthcare professional about all medications they take and understand the possible risks and side effects.1

Other factors that increase the risk of developing osteoporosis include smoking, an inactive lifestyle, high alcohol consumption, and a diet that does not contain enough calcium or vitamin D.4

What is GIOP (Glucocorticoid-induced osteoporosis)?

People who have AS may take corticosteroids in the lifetimes. These can help reduce inflammation and help with pain and other issues. Corticosteroids can reduce bone density, increase your risk for fractures, and put you at higher risk for osteoporosis. If you have ever taken corticosteroids, you may be at risk for GIOP. Talk with your healthcare provider.

How is osteoporosis diagnosed in people with AS?

Osteoporosis does not cause any symptoms by itself, although since it makes bones more brittle and susceptible to fractures, some people discover they have it when they have a broken bone. Because treatment can help protect bones and prevent fractures, early diagnosis is important. Osteoporosis is commonly diagnosed with a bone mineral density (BMD) test. A DXA (dual energy x-ray absorptiometry) test of the hip and spine, or in some people the forearm is generally recommended. It is a painless test much like an x-ray. Additional tests that may be used in diagnosis include blood tests, a medical history, and a physical exam.5

In people with advanced AS, the lumbar spine (low back) may pose difficulties for a BMD test, as the new bone formation or the presence of syndesmphytes caused by AS may create an inaccurate result.2,6 Older BMD scans of the lumbar spine had patients laying on their side, which caused difficulties accurately assessing the person for osteoporosis. Newer techniques allow the patient to lie face up, offering a more precise measurement.2 Another imaging test that may be used in people with AS is spine quantitative tomography (QCT).6

How is osteoporosis treated in people with AS?

The first line of treatment for osteoporosis (in both people with and those without AS) are medications called bisphosphonates. Bisphosphonates inhibit the activity of osteoclasts, the cells in the body which break down bone. While there have been limited studies of the effectiveness of bisphosphonates in people with AS, bisphosphonates have been proven to reduce the risk of fractures in people with osteoporosis.6

TNF inhibitors, a type of biologic medication used to treat AS that has not responded to non-steroidal anti-inflammatory drugs (NSAIDs), can also help reduce the effects of osteoporosis in people with AS. Treatment with TNF inhibitors in people with both AS and osteoporosis has demonstrated the ability to increase bone density, as measured in BMD tests.6

In addition to medication, lifestyle approaches that are critical in the treatment of osteoporosis include an adequate intake of calcium and vitamin D and exercise with weight-bearing activities.6

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